JPH10107319A - Nitride compound semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase light-emitting intensity by providing gallium group-III nitride compound semiconductor, wherein indium is doped in the active layer with an atomic concentration within a specific range, distributed in one direction of the film thickness. SOLUTION: The atomic concentration profile in the depth direction shows on increase of indium concentration in an active layer 104 toward an interface, which is in a junction layer making a junction to the active layer 104 with a high lattice nonconformity. The concentration profile increases indium source supply to a growing reaction system in response to the increase of the thickness of the active layer. The range of indium-doping concentration change is within a range of 8×10<17> cm<-3> or grealy to 4×10<20> cm<-3> or smaller. Thus, in the vicinity of the interface between the active layer, an area wherein a carrier is enclosed or locally exists is formed. Therefore, the light-emitting intensity is increased for the light-emitting elements, and carrier mobility is increased for an electronic function devices.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention Gallium nitride (GaN) provided with an active layer composed of a lattice-mismatched nitride compound semiconductor layer
More particularly, the present invention relates to a nitride compound semiconductor light emitting device having an active layer (light emitting layer) capable of increasing light emission intensity.

[0002]

2. Description of the Related Art Light-emitting diodes (LEDs) and laser diodes (L) for short-wavelength light such as blue, blue-green or green light.
D) and other nitride compound semiconductor light emitting devices have the general formula Al _{x
Ga y In 1-xy N (} x + y = 1,0 ≦ x ≦ 1,0 ≦
y ≦ 1). For example, a ternary or quaternary group III nitride compound semiconductor mixed crystal containing boron (B) as a group III element can also be an active layer. In a light emitting element such as an LED or an LD, the active layer is a light emitting layer. In addition, for example, gallium arsenide nitride (GaAsN) or the like, or a nitride compound semiconductor containing a plurality of Group III elements and a plurality of Group V elements other than nitrogen (N) and a Group V element other than nitrogen as constituent elements Is also a material that can be an active layer.

FIG. 1 shows gallium indium nitride (Ga _x
In _1-x N: x ≠ 1, 0 ≦ x <1) The structure of a blue LED having a mixed crystal as a light-emitting layer will be exemplified. A conventional blue LED includes a sapphire substrate (101), an aluminum gallium nitride (Al _x Ga ₁ -xN: 0 ≦ x ≦ 1) buffer layer (102),
A lower cladding layer (10) made of an n-type gallium nitride (GaN) layer of silicon (Si) or undoped (doped).
3) The indium composition ratio (x) is about 0.05 to 0.06
N-type gallium indium nitride (Ga _1-x In
_xN ; 0 <x ≦ 1) an active layer (104) composed of a mixed crystal layer;
Upper cladding layer made of p-type aluminum-gallium nitride (Al _y Ga _1-y N; 0 <y <1) mixed crystal in which magnesium doped at the time of film formation is electrically activated by annealing (heat treatment). (105) and a contact layer (106) made of p-type gallium nitride (GaN). In the above laminated structure, the n-type gallium-indium nitride mixed crystal is used as a light emitting layer that emits blue light. The light emitting layer is also doped with an acceptor impurity such as zinc (Zn) and a donor impurity such as silicon at the same time, though the mechanism of the light emission and its influence on the principle have not been elucidated yet. This is always the case (see JP-A-6-260680). A gallium nitride-indium mixed crystal layer, which needs to contain a large amount of indium in gallium nitride to form a mixed crystal, is intentionally adopted as a light emitting layer because light emission that is considered to involve zinc impurities due to this mixed crystal is considered. This is because it is possible to shift to a blue light emission band in a wavelength band having high visibility (see Japanese Patent Publication No. 55-3834).

[0004] In addition to the blue LED, recently, a green LED having a light emission center wavelength of about 510 nanometers (nm) composed of the nitride compound semiconductor laminate shown in FIG. 2 has been put to practical use (S. Nakamura). Other, Jp
n. J. Appl. Phys. , Vol. 34, Par
t. 2, No. 10B (1995), L1332-L1
335. ). A green light-emitting LED composed of a nitride compound semiconductor laminate is a quasi-indirect transition type homojunction gallium phosphide (GaP) LED that includes conventional nitrogen as an isoelectric (trap) trap (Toshiji Fukami) When compared with the supervision, "Semiconductor Engineering" (published by Tokyo Denki University Press, March 20, 1993, 7th edition), p. 195), a remarkable improvement of the light emission luminance of about 60 times was achieved. Green LE that emits unprecedented high-intensity green light
The gallium nitride / indium mixed crystal (Ga _{1 -x} In _x N: 0 <x ≦) is also used as the light emitting layer of D.
1). In addition, it is a gallium nitride-indium mixed crystal whose indium mixed crystal ratio (x) is increased to about 0.20 as compared with the case of the blue LED. For this reason, the above blue color,
Not only green LEDs, but also short-wavelength LEDs such as blue-green or yellow LEDs and short-wavelength LDs such as blue or green are used in gallium nitride-indium mixed crystals (Ga _1-x In _x N: 0 <x ≦
1) has been used as a light emitting layer that provides a high light output.

However, it is well known that forming a gallium-indium nitride mixed crystal layer involves a great technical difficulty in crystal growth. In the case of a metal organic pyrolysis vapor deposition method generally used for growing a gallium indium / indium mixed crystal layer (generally abbreviated as MOCVD, MOVPE, OMCVD method or the like), the crystallinity is excellent. The range of the growth temperature at which a gallium-indium nitride mixed crystal layer is assumed to be stably obtained is limited to a very narrow range of about 750 ° C. to about 800 ° C. In addition, the incorporation rate of indium is extremely low, and the indium composition ratio does not change uniformly according to the concentration of the indium raw material added to the growth reaction system. In the MOCVD growth method, the incorporation rate is a ratio of the indium gas source to the total amount of the group III gas source generally added to the growth reaction system (usually represented by the number of moles (mol)). Molar ratio of indium raw material)
And the indium composition ratio in the gallium nitride-indium mixed crystal. This is the so-called ratio of the indium solid phase ratio (= indium composition ratio) to the indium gas phase composition ratio. The higher the rate of incorporation, the more efficiently indium is incorporated from the gas phase into the solid phase (mixed crystal). Means that. For example, when the growth temperature is 800 ° C., the incorporation rate of indium starts to increase sharply when the molar ratio of the raw material is about 0.9 or more (Appl. Phys. Lett.,
59 (18) (1991), 2251. ). Further, the instability in the mixed crystal growth is enhanced by the fact that the incorporation rate of indium into the layer fluctuates extremely due to a slight change in the growth temperature of about ± 10 ° C. What further hinders stable growth is that an appropriate indium composition ratio necessarily decreases with an increase in growth temperature. Suitability of a light-emitting element as an active layer (light-emitting layer) is usually determined by the intensity of photoluminescence (PL) light emission. The “appropriate” indium composition ratio referred to here is a composition ratio that causes photoluminescence emission. The “proper” indium composition ratio is a value that is almost uniquely determined with respect to the growth temperature, and even if the value is less than or greater than this value, no photoluminescence emission is obtained or the light is attenuated. In summary, there has been a problem in mixed crystal growth that extremely precise control of the indium composition ratio is required to obtain an appropriate indium composition ratio uniquely determined for a set growth temperature.

In the MOCVD method which is known as a general method for growing a gallium-indium mixed crystal, this mixed crystal uses trimethyl indium ((CH ₃ ) ₃ In: TMI) or the like as an indium source. It is customary to grow using ammonia as the nitrogen source. However, trialkylindium compounds such as TMI exhibit Lewis acidity (GEC).
OATES, J.A. Chem. Soc. , [ 1951 ]
(1951), 2003. ), And one ammonia is a Lewis basic substance similar to the hydride of another group V element such as arsine (AsH ₃ ). Thus, one of the starting compounds has the property of supplying outer electrons to other molecules (electron donating property).
Has the property of accepting the other electron (electron accepting property)
In the raw material constitution system composed of the combination of the raw material compounds described above, the molecules of the raw material compounds are easily combined due to their strong attraction to each other. As a result, the polymer (pol
ymer) -like substances are formed (J. Steenstr)
a, et al., Surf. Sci. , 279 (1992), 27
2. Etc.). It is known that such a polymerization reaction in the gas phase occurs particularly remarkably in MOCVD growth of an indium-based compound using a trialkyl compound and a hydride of Group V (R. DIDCHENKO et al., J. In.
org. Nucl. Chem. , Vol. 14 (196
0), 35-37. And Electron Lett. ,
Vol. 16 , no. 6 (1980), 228. Such). If the indium raw material supplied into the growth reaction system is consumed to form such a composite in order to obtain a mixed crystal having a certain indium composition ratio, naturally, the indium-based mixed material having the desired indium composition ratio is consumed. This causes a problem that crystals cannot be obtained. In conducting such an indium-based mixed crystal growth, the complicated gas-phase reaction between the raw materials also makes it more difficult to solve the above-mentioned problems associated with the prior art, particularly the instability of the indium mixed crystal ratio.

Group III elements other than the constituent elements such as indium have an atomic concentration of 1 × 10 ¹⁷ cm ^-3 to 7 × 10 ²² c.
A method of growing a nitride compound semiconductor layer doped over a wide concentration range of m ^-3 has also been disclosed (Japanese Patent Laid-Open No. 5-2 / 5-2).
43614). As described above, for example, gallium indium nitride (Ga _1-x In _x ) provided as a light emitting layer in a conventional nitride compound semiconductor laminate for a light emitting device is used.
N; 0 <x ≦ 1) The mixed crystal has a composition ratio (x) of indium of about 0.05 to about 0.15 (JP-A-6-2).
09121, etc.). For example, the concentration (atomic concentration) of indium atoms in an In _0.15 Ga _0.85 N mixed crystal having an indium composition ratio of 0.15 is calculated to be 6.6 × 10 ²¹ cm ⁻³ . This calculated value is calculated according to the above conventional example (Japanese Patent Laid-Open No.
No. 3614) is within the doping concentration range of indium atoms and the like. That is, the doping concentration of indium in the range shown in the conventional example is sufficient for forming an indium-containing nitride mixed crystal. For example, assuming that the gallium nitride layer is doped with the highest concentration of indium of 7 × 10 ²² cm ⁻³ , the amount calculated is not sufficient to form a gallium nitride-indium mixed crystal, It is an amount sufficient to be converted into indium (InN). Accompanying the high doping of indium, which can form a mixed crystal containing indium, is a problem in the growth technique which also causes instability of the indium composition ratio as described above. Even if high-concentration doping of indium is applied, the problem that the indium remains at interstitial positions and does not form a mixed crystal remains similar, and the vapor phase of the trialkylindium raw material and the nitrogen hydride raw material is similar. It is the instability of the indium solid solution concentration based on the complexation reaction. The prior art (see Japanese Patent Application Laid-Open No. 5-243614) does not disclose a method for solving these problems associated with high-concentration doping of indium.

[0008] By bypassing the difficulty of crystal growth of the indium-based nitride compound semiconductor mixed crystal layer, even when performing low-concentration indium doping, light emission that stably increases the light emission intensity in the light emitting device. The doping concentration range and the doping concentration distribution of indium effective for forming the layer have not been elucidated yet. Conventionally, the optimum doping concentration range of indium is defined only from the viewpoint of electrical characteristics based on a decrease in the free electron concentration in the growth layer or, conversely, on an increase in the acceptor concentration (Japanese Patent Laid-Open No. Hei. No. 243614). There, the free electron concentration in the indium is added in a concentration of ^{1 × 10 21 cm -3 1 ×} 10 16 cm -3
Is said to be the lowest. On the other hand, indium still has 1
It is said that the maximum acceptor concentration is obtained when added to a concentration of × 10 ²¹ cm ^-3 (see JP-A-5-24 / 1990).
No. 3614). Thus, 1 × 1 indium
It is only suggested that doping to an atomic concentration of 0 ²¹ cm ^-3 is most effective.

Further, the gallium / indium nitride mixed crystal light emitting layer which has been conventionally employed is doped with a plurality of impurities composed of a combination of zinc, silicon and the like (Japanese Patent Application Laid-Open Nos. 6-260680 and 6-260680). 260
No. 681). Recently, Group II elements and
There is also disclosed a nitride compound semiconductor light emitting device including, as a light emitting layer, a nitride compound semiconductor layer doped with a group VI element at the same time (see JP-A-7-249796).
This is because of the known phenomenon that the intensity of blue photoluminescence emission related to zinc impurities doped in the gallium nitride layer increases in the coexistence of silicon (Si) (Solid State Commun.
57 (6) (1991), 405-409. ) Is simply applied to a gallium nitride layer containing indium. This phenomenon of increase in light emission intensity is caused by the fact that a gallium nitride layer doped with zinc and silicon is used as a light emitting layer.
It has already been applied to an IS (metal-insulator-semiconductor) structure type LED (for example, Japanese Patent Application Laid-Open No.
-10666, JP-A-3-10667). In other words, in view of the distribution of the doping concentration of indium atoms to be provided to increase the light emission, the distribution of these doped impurity elements is optimized again in relation to the distribution of the indium atomic concentration. There is a need.

[0010] The magnitude of the light emission intensity strongly depends on the crystallinity of the light emitting layer. The blue or green LED uses sapphire as a substrate (see FIGS. 1 and 2). Gallium indium / indium mixed crystal (In _x Ga _1-x N; 0 <
x ≦ 1) does not lattice match with sapphire in the first place. The problems that arise when constructing a light emitting layer from a nitride compound semiconductor material that does not lattice match with sapphire, which is a practical substrate material, are dislocations and defects caused by lattice mismatch with the substrate material. To the light emitting layer. The propagation of such crystal defects lowers the crystal quality of the gallium-indium nitride mixed crystal used as the light emitting layer. As described above, the light emitting layer of the conventional light emitting element having the double hetero (DH) junction structure or the light emitting portion having the single quantum well structure does not lattice match with the sapphire substrate. That is, the structure is not sufficient to sufficiently suppress the propagation of crystal defects to the light emitting layer based on the lattice mismatch. A structure that is insufficient to suppress a decrease in the crystallinity of the nitride compound semiconductor layer that forms the light-emitting layer naturally impairs the improvement of the light-emitting characteristics and the like.

If the crystal defect caused by the lattice mismatch causes the deterioration of the crystal quality of the light emitting layer, the use of a material lattice-matched with the light emitting layer as the substrate prevents the deterioration of the crystal quality of the light emitting layer. One possible way is conceived. Examples of this configuration, aluminum nitride, gallium indium mixed crystal _{(Al x Ga y In z N} (x + y + z = 1,0 ≦
x, y, z ≦ 1), the manganese oxide (Mn) that lattice-matches the substrate crystal with the material of the light emitting layer when forming the light emitting layer from
O), zinc oxide (ZnO) and calcium oxide (CaO)
(See Japanese Patent Publication No. 6-14564). However, these oxide-based substrate materials are sublimated and thermally decomposed at high temperatures generally exceeding about 600 ° C. For this reason, although there are some differences in the film formation temperature depending on the film formation method, a substrate for growing a nitride compound semiconductor layer requiring a high film formation temperature of about 700 to 1150 ° C. is not suitable for its thermal instability. Not enough for practical use. In particular, in a metal organic chemical vapor deposition (MOCVD) method which is generally used as a film forming method of a nitride compound semiconductor of aluminum-gallium nitride (Al _x Ga _1-x N; 0 <x ≦ 1) mixed crystal, The film forming temperature is generally about 1000 ° C. to 1150 ° C. At such a high temperature, the practicality as the above-mentioned substrate material is further lost. This is evidenced by the fact that sapphire (α-Al ₂ O ₃ single crystal) is used, despite the disclosure of the substrate material that causes the lattice mismatch configuration as described above. is there. That is, although the emission characteristics such as an increase in emission intensity are expected to be improved by using a nitride compound semiconductor layer lattice-matched to the substrate as the light-emitting layer, it is necessary to obtain a lattice-matched stacked structure. However, in reality, the improvement of the light emission characteristics has not yet been stably realized due to restrictions on the heat resistance and the like of the substrate material selected.

In practice, as an alternative to using a substrate material having a problem with thermal resistance to form a laminate from a nitride compound semiconductor layer lattice-matched to the substrate, a certain portion of the laminate, for example, a light emitting portion Is constructed from a lattice matching system.
In order to alleviate the propagation of crystal defects such as dislocations due to lattice mismatch to the light emitting layer, Al _x Ga _{y
In z N (x + y +} z = 1,0 ≦ x, y, z ≦ 1) has a light-emitting layer and the composition ratio of lattice matching, and prohibited from emitting layer band width (band gap) is large Al _x Ga _y In _z N
(X + y + z = 1, 0 ≦ x, y, z ≦ 1) An example in which the mixed crystal layer is formed as a double heterojunction as an upper clad layer and a lower clad layer to form a light-emitting portion (see the above-mentioned Japanese Patent Publication No. Hei 6-106)
145564). However, the formation of the lattice-matched light emitting section is based on the premise that it is formed on a thermally denatured oxide-based substrate such as the above-described zinc oxide, and is not practical. .

There is also a configuration example in which a light emitting layer is bonded on a nitride compound semiconductor layer lattice-matched with the light emitting layer. This example shows a MIS containing a gallium nitride homo junction.
It can be seen in an LED with a (metal-insulator-semiconductor) structure. In addition, gallium indium nitride (In _x Ga
_1-x N; 0 ≦ x ≦ 1) In _x Ga _1-x N (0 ≦ x
.Ltoreq.1) An LED having a homojunction structure for depositing a layer has also been proposed (see JP-A-3-203388). In this configuration, gallium indium nitride (In _x
Ga _1-x N; 0 ≦ x ≦ 1) If the indium composition ratio (x) of both layers is the same, the light emitting layer has a homojunction configuration formed on a nitride compound semiconductor layer lattice-matched to the light emitting layer. be able to. However, it is a well-known fact that the homojunction mode is in principle disadvantageous in comparison with the hetero junction mode when obtaining an LED having excellent emission intensity. In order to obtain a light emitting element such as an LED having a high light emission intensity, it is essential to employ a hetero junction structure.

It is well known that a light-emitting portion of a double hetero-junction type is advantageous for obtaining a light-emitting element having a high light emission intensity. In addition to improving the crystallinity of the nitride compound semiconductor layer constituting the light emitting layer, the semiconductor layer forming the junction with the light emitting layer has excellent crystallinity if the semiconductor layer is a layer with excellent crystallinity. It is effective in obtaining a light emitting layer. In the double heterojunction structure, the light-emitting portion including the light-emitting layer and the bonding layer that is bonded to the light-emitting layer is formed of a nitride compound layer having excellent crystallinity, which is useful for providing a light-emitting element with high light-emission intensity. . The above-mentioned prior art (see JP-A-5-243614), in which a group III element other than a constituent element having an atomic radius larger than that of a constituent element is added to achieve an improvement in crystallinity, includes, for example, indium. It is described that the crystallinity can be improved by containing the gallium nitride-based layer. There is an example in which a gallium indium / indium mixed crystal layer is actually arranged in a part of a laminate for a light emitting device (Jp.
n. J. Appl. Phys. , Vol. 35 , Par
t2, No. 1B (January 15, 1996), L74-
L76. ). Specifically, this light-emitting element has a gallium indium nitride (Ga
_{A 0.8} In _0.2 N mixed crystal is used as a well layer, and a gallium nitride / indium mixed crystal (Ga _0.95 In _0.05 N) having an indium composition ratio of 0.05 is used as a barrier layer (barrier layer). ) Is a laser diode provided with a light emitting portion having a heterojunction multiple quantum well structure (abbreviated as MQW). In this case, a gallium nitride-indium mixed crystal (Ga _0.9 In _0.1 N) having an indium composition ratio of 0.1 is disposed between the n-type gallium nitride layer and the MQW light emitting portion having the double hetero junction. (Jpn. J. Appl. Phys., Vo, supra).
l. 35 , Part 2, no. 1B (1996), L
74 to L76. ). This gallium-indium nitride mixed crystal layer (Ga _0.9 In _0.1 N) is arranged for the purpose of improving the crystallinity of a nitride compound semiconductor laminated body deposited above the same layer (NIKKIELEE).
CTRONICS 1996.1.15. no. 65
3. Issued on January 15, 1996, published by Nikkei BP, 13-
15 pages). However, a gallium-indium nitride (Ga _0.9 In _0.1 N) mixed crystal layer, which is believed to bring about the improvement of the crystallinity, is arranged as a bonding layer to be bonded to the light emitting layer in the light emitting portion composed of a double hetero junction. It is not. Between the Ga _0.9 In _0.1 N mixed crystal layer and the light emitting portion, an aluminum gallium nitride mixed crystal layer (Al _0.15 Ga _0.85 N) having an aluminum composition ratio of 0.15 and an n-type gallium nitride layer are inserted. Have been. These inserted nitride compound semiconductor layers have no lattice matching with the underlying gallium nitride-indium mixed crystal (Ga _0.9 In _0.1 N) layer and the gallium nitride-indium layer constituting the MQW of the light emitting portion. . Therefore, Ga _0.9 In _0.1 N
By laying the mixed crystal layer, the crystallinity of the nitride compound semiconductor layer deposited on the mixed crystal layer is improved.
_{If the 0.9} In _0.1 N mixed crystal layer and the deposited layer are in a lattice mismatching relationship, the dislocation generated thereby propagates to the light emitting portion in reality. As described above, in the conventional laminate for a light-emitting element using a lattice-mismatched system, the indium-containing mixed crystal layer in which the crystallinity is improved by containing indium is used as a light-emitting layer composed of a double heterojunction. It is not used as a bonding layer with the light emitting layer in some parts. That is, such an arrangement of the indium-added layer found in the conventional example has a junction structure that directly affects the crystallinity of the nitride compound semiconductor layer constituting the light emitting layer or the double hetero junction light emitting portion. Has not been reached.

[0015]

The active layer is responsible for the function and characteristics of the semiconductor device. For example, an effective means for obtaining a light-emitting element having excellent light-emitting intensity is to employ a structure of a light-emitting layer or a light-emitting portion that directly increases light-emitting intensity. As described above, the conventional measures for improving the emission intensity have common points. It uses a nitride compound semiconductor mixed crystal to which indium is added as a light emitting layer,
Alternatively, it is used as an intermediate insertion layer for improving the crystallinity of the layer constituting the laminate.

A conventional indium-containing gallium nitride layer used as a blue light emitting layer is generally a mixed crystal layer having an indium composition ratio of about 10%. As described above, there is a problem in crystal growth in forming a gallium-indium nitride mixed crystal layer having excellent quality. In order to obtain emission in a green band having a longer wavelength than in a blue band, it is necessary to further increase the indium composition ratio. It is necessary to lower the growth temperature from the relation of the incorporation rate of indium so as to form a mixed crystal layer having a high indium composition ratio. There is a problem that the crystallinity of the In _x Ga ₁ -xN mixed crystal is impaired as the crystal is grown at a lower temperature (JSPS 125th Committee, 148th Meeting, Study Group, May 1994
27), pages 1-6).

In turn, the situation is the same when a crystal growth method of a nitride compound semiconductor layer which improves the crystallinity by adding indium (see JP-A-5-243614) is the same, and an indium-containing mixed crystal is formed. As long as it is intended to form a semiconductor layer to which enough indium is added, low reproducibility of the indium composition ratio of the obtained mixed crystal is a problem. Within the range of the amount of indium allowed in the conventional example (see Japanese Patent Application Laid-Open No. 5-243614), it is generally assumed that there is no need to change the growth temperature.
It is clear from the results of the inventor's diligent study that the inventor of the present invention did not noticeably increase the emission intensity when indium was doped at a low atomic concentration of about 0 ¹⁷ cm ^-3 to 10 ¹⁹ cm ^-3. Has become. This is a method of growing an indium-doped nitride compound semiconductor layer, as disclosed in the prior art (see Japanese Patent Application Laid-Open No. 5-243614), which improves the characteristics of a light emitting element such as an increase in light emission intensity. This is because an optimal method of doping indium having an effect on the above is not proposed.

LE made of gallium nitride based semiconductor material
As for D, as described above, it is customary to dope the light emitting layer with an impurity such as Group II, Group IV, or Group VI. However, inadequate control of the quantitative balance of the donor or acceptor impurity is accompanied by instability which cannot necessarily achieve an increase in light emission from the nitride compound semiconductor layer (Japanese Patent Application Laid-Open No. 4-10666 and Japanese Patent Application Laid-Open No. H10-6666). See JP-A-4-10667). In particular, a so-called electron-rich n ^{+ -type} light-emitting layer with a high carrier concentration doped with a donor impurity far exceeding the concentration of an acceptor impurity only causes weak light emission. In order to form a light-emitting layer with excellent crystallinity by indium doping, optimization of the optimum indium doping concentration range and concentration distribution that can contribute to an increase in light emission intensity, taking into account the quantitative balance of donor and acceptor impurities is required. Further, in addition to optimizing the indium doping, a bonding system between the indium-doped nitride compound semiconductor layer and the light-emitting portion for preventing a decrease in crystallinity of the light-emitting layer due to lattice mismatch is provided. Is also a problem to be solved by the present invention.

[0019]

That is, the present invention provides an active layer made of a gallium (Ga) group III nitride compound semiconductor on a crystal substrate and a first nitride semiconductor layer of a first conductivity type. And a second nitride compound semiconductor layer having a second conductivity type, the active layer has an atomic concentration of 8 × 10 ¹⁷ cm ⁻³ or more. A nitride compound semiconductor element having a gallium (Ga) -based group III nitride compound semiconductor doped with indium (In) with a concentration distribution in one direction in a layer thickness of not more than × 10 ²⁰ cm ^−3. Is provided. Especially,
A gallium-based group III nitride compound having a concentration distribution in which the indium atomic concentration is increased toward a bonding interface with the first or second nitride compound semiconductor having a smaller lattice constant as the active layer. In the active layer doped with both the semiconductor layer and the donor or acceptor impurity, one of the impurity of the donor and the acceptor is doped at a substantially constant atomic concentration in the layer thickness direction, and the other impurity of the indium is doped with indium. Gallium-based, doped in the thickness direction with a concentration distribution approximately inversely proportional to the atomic concentration
An object of the present invention is to provide a nitride compound semiconductor device having a group III nitride compound semiconductor layer. In addition, from the viewpoint of the junction mode, one of the first and second nitride compound semiconductor layers that joins the active layer and the active layer is made of the same nitride compound semiconductor material as the active layer doped with indium. It is intended to provide a nitride compound semiconductor device characterized by the above. Further, the first or second nitride compound semiconductor layer doped with indium substantially uniformly is bonded to the nitride compound semiconductor layer doped with indium. An element is provided.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, although there is no lattice matching with the nitride compound semiconductor constituting the active layer,
Conventionally, sapphire (α-Al ₂ O ₃ single crystal) having excellent heat resistance can be used as the substrate crystal. Silicon carbide (Si
Hexagonal and cubic crystalline materials such as C) and silicon (Si) can also be used conventionally. There are no particular restrictions on the specifications such as the plane orientation, off angle, and substrate thickness of these substrate crystals. In the present invention, the degree of lattice mismatch is represented by the ratio of the difference between the lattice constant of the crystalline layer forming the deposited layer and the lattice constant of the crystalline layer forming the layer to be deposited. For example, if the lattice constants of the substrate (reference crystal) and the crystal material (comparative crystal) constituting the active layer such as the light emitting layer and the electron channel layer are a ₀ and a, respectively, the lattice constant of the reference crystal (a ₀ ) Represents the degree of lattice mismatch (δ; unit%) occupied by the absolute value of the difference in lattice constant between the reference crystal and the comparison target crystal, and is given by the following equation (1). δ (%) = ｛| a−a ₀ | / a ₀ } × 100 (1) This δ is calculated using the lattice constant of the basic axis of the crystal such as the a-axis. The lattice spacing determined in consideration of the orientation relationship (orientation) between the substrate and the active layer is not used for calculating δ. The lattice constant used for the calculation of δ is the original lattice constant of those materials that have been published, for example, in a distorted state that has undergone some mechanical deformation at the junction interface of a lattice-mismatched system. It is not the lattice constant when it is below. In the present invention, δ between the substrate crystal and the active layer is approximately 0.2%
The case where the number exceeds the threshold value is defined as a lattice-mismatched active layer. For example, a laminate made of a nitride compound semiconductor that has a lattice mismatch with the sapphire substrate shown in FIG. 1 is a typical laminate composed of a lattice mismatch active layer in the present invention.

In the above description, the deposited layer forming the active layer and the like
In the present invention, it refers to a gallium-based nitride compound semiconductor layer. The gallium-based nitride compound semiconductor refers to a nitride compound semiconductor containing a group III element other than indium such as gallium and aluminum as a constituent element. For example, gallium nitride (GaN), aluminum nitride (AlN), aluminum-gallium nitride (Al _x Ga ₁ -xN; 0 <x ≦ 1) mixed crystal, and the like are applicable. Further, the kind of nitride compound semiconductor doped with indium is not limited to gallium nitride-based or aluminum nitride-based semiconductor. Gallium arsenide nitride (GaNAs), aluminum arsenide nitride (AlNA)
s) and nitride compound semiconductor materials containing Group V elements other than nitrogen, such as gallium phosphide nitride (GaNP),
The effect of indium doping according to the present invention becomes apparent. Therefore, the nitride compound semiconductor device according to the present invention is composed of a stacked body including, for example, indium-doped gallium nitride, aluminum nitride, gallium arsenide nitride, aluminum-gallium nitride mixed crystal, or the like as an active layer. The conduction type of the indium-doped nitride compound semiconductor layer forming the active layer is preferably an n-type or an insulation type. Here, in a single or multiple quantum well structure, a well layer, that is, a well layer is regarded as an active layer.

The present invention relates to a gas having a lattice mismatch with the substrate.
Even in a lithium-based group III nitride compound semiconductor layer,
Doping of indium with a high concentration can cause mixed crystal
That the emission intensity from the same layer can be increased without forming
It was used. As an example, FIG.
In doped zinc-doped gallium nitride (GaN) layers
Of photoluminescence (PL) intensity
Shows the dependence on the concentration Indium doping source
Is a source of nitrogen for growing the gallium nitride layer.
Lewis salt that can avoid complexation reaction with ammonia gas
Cyclopentadiyl having monovalent valency showing basic properties
Enilindium (C_Five H_Five In) available (J.o
f Cryst. Growth. ,106(1990),
260. And Japanese Patent Publication No. 8-17160). Dopi
As a method for determining the atomic concentration of
Various physical components such as electron electron spectroscopy (AES)
The indium concentration of the doped
Since the concentration is in the low concentration range, the
EPMA to analyzeEelectronProbe
Mmicro-Aanalysis methods such as
In this case, the second order is superior due to its ability to detect low concentration of atoms.
It is quantified by ion mass spectrometry (abbreviated SIMS).
As shown in FIG. 3, a light emitting helicopter with a wavelength of 325 nm
Excitation by laser beam of um (He) -cadmium (Cd)
Induced waves associated with zinc impurities from gallium nitride layers
Blue (blue-violet) emission with a length of about 430 nm
The luminescence intensity is strong against the indium doping concentration.
It depends heavily. Of doped indium
Atomic concentration is approximately 5 × 10¹⁷cm^-3In the vicinity, Injiu
The effect of increasing the emission intensity due to
is there. In other words, due to indium doping,
Luminescence intensity does not always increase
No. Indium doping concentration of 8 × 10¹⁷cm^-3To
Upon reaching a steady increase in luminescence intensity
Can be For example, about 6 × 10¹⁹cm^-3To the concentration of
Blue color associated with zinc impurities from doped gallium nitride layer
The emission intensity of (blue purple) is about 5 × 10¹⁸c
m^-3Doping to a concentration of about 60 times. one
On the other hand, disilane (Si_Two H₆ ) Use gas
Doping with silicon (Si) using
When a light emitting layer coexisting with
At most about five times. That is,
Gallium nitride layer with indium doping in positive concentration range
The effect on the increase in luminescence intensity from
Doping of both donor and acceptor impurities
Compared to the position, it is orders of magnitude larger. But Injiu
Overdoping the system will reverse the luminescence intensity
Decrease (see FIG. 3). Luminescence intensity is indium
4 × 10²⁰cm^-3Suddenly after
To decline. Therefore, when the emission intensity is intended to be increased,
Optimum indium doping concentration range is 8 × 10¹⁷c
m^-34 × 10 or more²⁰cm^-3The range is as follows. This optimal
The concentration range is extremely limited compared to the conventional range.
It is enclosed. Indium is a Group III element and II
Group I nitride compound semiconductors
Indium acts as an isoelectronic trap
Could be possible. Low indium doping concentration
If the concentration is too high, the improvement in crystallinity will be noticeable.
May be considered undoped
However, the density of electron traps, etc.
It is estimated that it is small. On the other hand, indium dopi
Rather, the upper limit of the toning concentration is due to indium doping.
It is assumed that there is a close relationship with the decrease in electron concentration in the layer.
You. By increasing the indium doping amount,
Although the density of the trap increases, the conventional example (Japanese Unexamined Patent Publication No.
Conversely, as seen in US Pat.
The child concentration decreases. That is, the indium doping concentration
The upper limit of the residual power is rather than from the viewpoint of improving the crystallinity.
It is considered to be determined based on the concentration of the proton.

In the atomic concentration range (doping concentration range) of indium disclosed in the present invention, the emission wavelength at the band edge inherent in the nitride compound semiconductor (corresponding to the band gap (energy gap) inherent to the semiconductor material) is not satisfied. No change. For example, the wavelength (approximately 365 nm) at which band edge emission of the indium-doped gallium nitride layer according to the present invention appears coincides with that from the indium-doped gallium nitride layer. As the alloy becomes more mixed, that is, when a large amount of indium is added, a spectrum peculiar to the near ultraviolet region of about 380 to about 390 nm appears (the 43rd Spring Applied Physics Related Conference, 1996, lecture number) 28a-ZB-1
o. 1, 292) and Lecture No. 28a-ZB-2 (Presentation No. 1, 293 pages). This near-ultraviolet spectrum hardly appears when an acceptor impurity such as zinc is added, and tends to appear when a donor such as silicon is added or when the carrier concentration is relatively high even when undoped. is there. However, even in the high carrier concentration n ^{+ -type} gallium nitride layer doped with indium according to the present invention, no luminescence in the near ultraviolet region was observed. Further, in gallium indium nitride containing a high concentration of donor impurities such as silicon, it is clearly observed that the emission wavelength of this near-ultraviolet spectrum shifts to a longer wavelength side as the indium content increases. However, in the gallium nitride layer to which indium is added at various concentrations within the concentration range of the present invention, since the near-ultraviolet spectrum does not appear, the shift to the longer wavelength side of the near-ultraviolet spectrum depending on the indium concentration cannot be observed. Was. That is, since the band gap does not change even by doping with indium in the concentration range described in the present invention, it is hard to recognize that gallium nitride has changed to gallium nitride-indium mixed crystal. From this, it is reasonable to consider that doping of indium at a concentration defined in the present invention does not cause a mixed crystal with indium in the layer to be doped. In other words, the present invention provides a technique for avoiding the problem of forming an indium-based mixed crystal accompanied by difficulties in crystal growth as described above, and furthermore, easily achieving an increase in emission intensity. This is one of the advantages of the present invention.

In the present invention, the gallium-based nitride compound semiconductor layer doped with indium uniformly in the thickness direction within the above concentration range is not used as the active layer. A gallium-based nitride compound semiconductor layer having a specific indium concentration distribution while limiting the indium concentration range that increases the emission intensity is used as the active layer. By imparting non-uniformity to the indium doping concentration distribution, a distribution is created in the electronic properties and the like inside the active layer. In particular, indium is present in the gallium-based nitride compound semiconductor layer that forms a junction with the active layer, and increases the doping concentration of indium toward the interface with the nitride compound semiconductor layer that makes the lattice constant smaller. Increasing the indium doping concentration in the layer thickness direction can be achieved by increasing the amount of the indium source supplied to the growth reaction system when forming the active layer with respect to the film formation time. Various concentration profiles can be created depending on how the indium source supply changes with respect to the film formation time. FIG. 4 illustrates an indium doping concentration distribution according to the present invention. The atomic concentration profile (111) in the depth direction indicates that the active layer (10
4) In the bonding layers ((108) and (109)) for bonding the indium concentration to the active layer (104), the interface (11) with the bonding layer (109) having a larger degree of lattice mismatch.
An example of a distribution monotonically increasing toward 0) is shown. Such a concentration profile can be obtained by monotonically increasing the supply amount of the indium source supplied to the growth reaction system as the thickness of the active layer increases. The atomic concentration profile (112) shows the concentration distribution of another indium atom, and shows the bonding layer (1).
The indium doping concentration is gradually increased toward the interface (110) with the active layer (09) from the start of the growth of the active layer (104). Further, the atomic concentration profile (113) indicates the doping amount of indium in the active layer (10).
4) The distribution of the atomic concentration of indium obtained by keeping the concentration constant in the middle and then increasing the doping amount stepwise is shown. If the indium doping amount is monotonically increased rather than stepwise, a profile (114) in which the atomic concentration of indium increases smoothly toward the interface (110) is obtained. In any case, in order to obtain a light emitting layer having excellent light emission intensity, the atomic concentration of indium is gradually increased toward the interface with the bonding layer having a smaller lattice constant in the bonding layer bonded to the light emitting layer. That is no different. The reason why the distribution is given to the doping concentration is to introduce a large amount of strain into the lattice strain region existing near the interface with the bonding layer, which increases the degree of lattice mismatch (the above δ (%)). is there. Further, in the as-grown state, the region near the interface is set as a region having a lower electron concentration.

The change range of the indium doping concentration is in the range of 8 × 10 ¹⁷ cm ^{−3 to} 4 × 10 ²⁰ cm ⁻³ . The rate of change of the doping concentration of indium within this range is appropriately determined in consideration of a desired emission wavelength and the thickness of the active layer. The rate of change is represented by the ratio (Δ) of the final indium concentration (N; unit cm ⁻³ ) to the initial doping concentration of indium (N ₀ ; unit cm ⁻³ ) by the following equation (2). Δ = N / N ₀ Equation (2) Explaining specifically with reference to FIG. 5, the active layers ((108) and (109)) which are bonded to the active layer (104) And a bonding layer (10
The atomic concentration of the doped indium at the interface (124) with 8) is the initial concentration (N ₀ ). On the other hand,
The bonding layer (10) having a larger lattice mismatch with the active layer
The concentration at the interface (110) with 9) is N. In the present invention, the doping concentration of indium is adjusted at both interfaces ((11
0) and (124)), the relationship is always N> N _{0 because} the value is increased toward the interface (110), and accordingly, Δ takes a positive value. When the thickness of the active layer is constant, the rate of change is relatively small in order to obtain emission of a short wavelength such as blue. If light emission on the long wavelength side such as green is intended, the rate of change is large. Conversely, if the rate of change is constant, green,
The thickness of the light-emitting layer is reduced to such an extent that yellow light and long-wavelength light are intended. That is, by narrowing the region where the doping concentration of indium is changed, the degree of change in the atomic concentration of indium with respect to the change in the layer thickness is increased. For example, the initial doping concentration (N ₀ ) of indium is 1 × 10 ¹⁸ c
Consider a case where m ⁻³ and the final concentration (N) are 4 × 10 ²⁰ cm ⁻³ and the rate of change (Δ) is 400. In this case, to obtain blue light emission having a wavelength of 430 nm to 450 nm, the thickness of the light emitting layer is generally set to 40 to 70 nm, and the wavelength is set to about 50 to
If a green band light emission of 0 to 550 nm is intended, the thickness of the light emitting layer is at least about 10 nm or less, preferably 5 n
m.

One advantage brought about by giving a distribution to the doping concentration of indium in the active layer is that the structure of the light emitting section can be simplified. For example, omitting the structure of a conventional green LED, the light emitting portion has a single quantum well structure. The well layer serving as the light emitting layer is a gallium nitride-indium mixed crystal layer ((104) in FIG. 2) having an indium composition ratio of 0.20. A gallium-indium nitride mixed crystal layer ((107) in FIG. 2) having an indium composition ratio of 0.05 is disposed as a base layer under the gallium nitride-indium mixed crystal light-emitting layer ((104) in FIG. 2). Have been. In other words, the light emitting portion has a multilayer structure of gallium nitride / indium mixed crystal layers having different indium composition ratios. Indium doping according to the present invention, that is, a gallium-based group III nitride semiconductor layer having a layer thickness suitable for green light emission and doped to increase the indium atom concentration sequentially in the layer thickness direction is used as the only light emitting layer. That's enough. As described above, in the nitride layer in which the indium doping concentration is varied, only one region having a relatively low indium concentration is formed in the conventional gallium nitride / indium underlayer, and the indium atom concentration is relatively low. The high region can carry each of the conventional gallium-indium nitride light-emitting layers. Therefore, the same increase in light emission intensity can be easily achieved without intentionally disposing a gallium-indium nitride mixed crystal, in which crystal growth is difficult, on the light-emitting layer. That is, as a barrier layer of the quantum well structure, or when a gallium indium / indium mixed crystal light emitting layer and an n-type gallium nitride layer are directly bonded, generation at a bonding interface is expected.
It is no longer necessary to provide a gallium-indium nitride underlayer as a lattice strain relaxation layer for reducing extreme carrier accumulation due to formation of quantum levels.

According to the present invention, the active layer is doped with either a donor or an acceptor at a substantially constant atomic concentration in the layer thickness direction, and the other impurity has a concentration distribution substantially inversely proportional to the indium atomic concentration. It is assumed that it is doped in the direction. This is a gallium nitride in which an acceptor impurity such as zinc is doped as an active layer with a substantially uniform atomic concentration in a layer thickness direction, and a donor impurity such as silicon is doped with a concentration almost inversely proportional to an indium atomic concentration. This means that a compound semiconductor layer is used. That is, in the present invention in which the atomic concentration of indium is gradually increased in the thickness direction of the active layer,
Conversely, the atomic concentration of donor impurities such as sulfur (S), selenium (Se), and tellurium (Te) of Group IV elements or Group VI elements such as silicon, germanium (Ge), and tin (Sn) may have a different layer thickness. Decrease in increasing direction. Such an inconsistent atomic concentration distribution is provided by a carrier (carr) in the active layer.
ie: carrier), that is, to create a concentration distribution of electrons or holes.
However, the concentrations that are kept in a substantially inverse proportion to each other are the atomic concentrations of the dopant, not the carrier concentrations such as the electron concentration. When the atomic concentration of the donor impurity gradually decreases in the layer thickness direction of the active layer, the electron concentration increases in the direction of increasing the layer thickness. In particular, the distribution may be opposite to the distribution of the donor impurity that rapidly increases at the interface with the lattice mismatched bonding layer bonded to the active layer. Contrary to the increase in the atomic concentration of indium accompanying the increase in the thickness of the active layer, the decrease in the atomic concentration of the donor impurity to be doped is due to the fact that the lattice strain near the interface with the bonding layer deposited on the active layer is completely reduced. This is because the purpose is to increase the carrier density of electrons and the like accumulated in the region that has not been removed. as-grown
In some cases, an increase in carrier density is already observed near the interface, and when a piezoelectric crystal such as aluminum nitride / gallium mixed crystal is bonded to the active layer, carrier accumulation near the interface is more remarkable. May be manifested. In this way, the intention is to form a so-called carrier-localized region in which carriers are confined in the vicinity of the interface with the active layer. The device achieves an increase in carrier mobility.

According to the present invention, the joint structure of the light emitting section is invented. The light emitting portion refers to a portion composed of a light emitting layer and a clad layer in a heterojunction configuration including a clad layer. In the quantum well structure, it refers to a portion including a multiple structure including a well layer and a barrier layer, and a cladding layer bonded to the multiple structure. Referring to the light emitting element only, in the present invention, the light emitting portion is further formed by joining the indium-doped gallium nitride compound semiconductor layer light emitting layer to the indium doped gallium nitride compound semiconductor layer. Form. Other elements such as a heat-resistant hole (Hal) may of course be used for a structure composed of junctions between nitride compound semiconductor layers doped with indium.
l) It can be used as an active region such as a device, a Schottky junction type field effect transistor (MESFET for short), a light receiving device in an ultraviolet region or a blue band region, or the like. The reason why the indium-doped nitride compound semiconductor bonding layer is bonded to the active layer is that the bonding is performed as an underlayer (deposited layer) that improves the crystallinity of the gallium-based nitride compound semiconductor layer that forms the active layer. This is because an active layer with significantly improved crystallinity can be obtained. The degree of improvement in the crystallinity of the active layer and the quality are as follows.
FWHM and photoluminescence (P
L) It can be determined from an examination of the emission intensity at the band edge of the spectrum. In the present invention, indium is not doped at such a high concentration as to achieve the mixed crystal of the material to be doped. Does not occur, the intensity of the band-edge emission and the half-value width can be directly used as an index for determining the quality of the crystal quality. FIG. 6 shows, as an example, a room-temperature photoluminescence spectrum (115) of a gallium nitride layer deposited on an n-type gallium nitride (GaN) junction layer doped with indium at an atomic concentration of about 8 × 10 ¹⁵ cm ^−3. . On the other hand, a spectrum (116) shows a room temperature spectrum from the gallium nitride layer deposited on the undoped n-type gallium nitride layer not doped with indium. As is clear from the comparison of the two spectra, the band-edge emission from the gallium nitride layer on the indium-doped gallium nitride junction layer (symbol B in FIG. 6)
D) is clearly increased as compared with the case where no indium is added. As described above, the crystallinity of the nitride compound semiconductor layer joined to the nitride compound semiconductor layer doped with indium is remarkably improved.

In the gallium-based group III nitride compound semiconductor layer to be bonded to the active layer, the optimum indium doping concentration range is 8 × 10 ¹⁷ cm ^-3 or more and 4 × 10 ²⁰ c
m ⁻³ or less. The atomic concentration of indium is about 8 × 10 ¹⁷
If it is less than cm ^-3 , no increase is observed in the room-temperature photoluminescence intensity at the band edge of the layer to be doped. When the concentration of doped indium atoms is around 8 × 10 ¹⁷ cm ⁻³ , an increase in band edge emission intensity may sometimes be observed, but the effect is unstable. In order to stably obtain a gallium-based group III nitride compound semiconductor layer having excellent crystallinity, the indium doping concentration is set to 8 × 10 ¹⁷ c
m ^-3 or more. Conversely, if the atomic concentration is 4 × 10
^If indium doping over ²⁰ cm ^-3 is caused by a hardening effect,
The probability that cracks occur in the nitride compound semiconductor film increases. The generation of the cracks causes deterioration of the surface state of the film, and also impairs the continuity of the film. Factors affecting the emission intensity also include the continuity of the nitride compound semiconductor film,
In a light-emitting element, a film lacking continuity causes an increase in interelectrode resistance in addition to a decrease in a light-emitting area, which is inconvenient for obtaining a compound semiconductor light-emitting element having excellent emission intensity. Therefore, in the present invention, the upper limit of the atomic concentration of indium in the bonding layer bonded to the active layer is set to 4 × 10 ²⁰ cm ⁻³ .

The concentration distribution of the doped indium atoms is not particularly limited. This is because the indium-doped nitride semiconductor layer bonded to the active layer is not used as a light emitting layer. Therefore, it is not necessary to provide the distribution of the indium atom concentration for increasing the emission intensity as described above. Indium may be uniformly doped. Further, the doping may be performed with a concentration gradient in the thickness direction of the bonding layer.
However, the atomic concentration at the interface between the bonding layer and the active layer is
As described above, the initial concentration of indium atoms in the active layer (N
Preferably, it is doped so as to be substantially equivalent to ₀ ). This is in order to suppress the occurrence of distortion, crystal defects, and the like due to the difference in atomic concentration of indium near the bonding interface between the active layer and the bonding layer.

In a double hetero junction type gallium nitride blue LED, a configuration is adopted in which the bonding layer on the sapphire substrate side to be bonded to the active layer is n-type, and a p-type layer is disposed above the active layer. I have. Even in a green LED having a single quantum well structure, the junction configuration is the same as viewed from the conduction type. On the other hand, when a material exhibiting p-type conductivity is used as the substrate instead of using an insulating crystal such as sapphire as the substrate, the semiconductor layer disposed on the substrate side to be bonded to the active layer is a p-type layer. Is a reasonable configuration. Therefore, the conduction type of the indium-doped nitride semiconductor layer to be joined to the active layer may be either n-type or p-type. It is essentially important that the nitride compound semiconductor layer is doped with indium in the atomic concentration range defined in the present invention and has improved crystallinity. However, when a gallium-based nitride semiconductor active layer in which indium is doped with a gradient in atomic concentration is arranged on the indium-doped n-type gallium-based nitride semiconductor layer, in the vicinity of the interface between the active layer and the n-type junction layer, In order to make the density of accumulated carriers smaller than that at the junction interface between the opposing active layer and the p-type junction layer, the concentration of indium atoms at the interface between the active layer and the n-type junction layer is substantially reduced. It is important to make them equal.

The number of bonding surfaces between the indium-doped nitride compound semiconductor bonding layer and the active layer may be either a single surface (one surface) or two surfaces. In other words, the bonding layer according to the present invention allows to be disposed immediately below, immediately above, or both directly above and immediately below the active layer.
If a nitride compound semiconductor bonding layer whose crystallinity has been improved by indium doping is arranged on the lattice mismatching substrate side immediately below the active layer, based on the lattice mismatch with the substrate,
The effect of suppressing permeation of crystal defects such as dislocations propagating to the bonding layer side into the active layer can be obtained. A nitride compound semiconductor light emitting device composed of a laminate having such a junction structure is composed of a laminate composed of constituent layers in which no measures are taken to reduce the introduction of crystal defects based on lattice mismatch. The light emission characteristics are remarkably improved as compared with the conventional LED. In the description of the embodiments described below, the characteristics will be specifically compared with a comparative example.

When the number of bonding surfaces is 2, it means that indium-doped nitride compound semiconductor layers are bonded on both sides of the active layer. Examples of the configuration of the double heterojunction between the indium-doped nitride compound semiconductor layer and the active layer according to the present invention include an n-type or p-type indium-doped gallium nitride layer / n-type, p-type or insulating (high resistance). ) gallium indium nitride (Ga _z an In
_1-z ; 0 ≦ z ≦ 1) Active layer / p-type or n-type indium-doped aluminum-gallium nitride layer junction structure. The main reason for disposing the indium-doped nitride compound semiconductor bonding layer also directly above the active layer is that it occurs due to lattice mismatch between the active layer and the bonding layer disposed directly above the active layer, Most of the crystal defects that propagate to the bonding layer are included in the bonding layer. Thus, the effect of suppressing propagation of crystal defects to the current diffusion layer and the contact layer disposed on the bonding layer above the active layer can be obtained. This is because a crystal layer having a small number of crystal defects has an advantage of enabling stable operation of the element, such as rarely causing current concentration around the crystal defect and occurrence of local leakage current.

The active layer is made of the same material as the active layer.
Indium on the indium-doped nitride compound semiconductor junction layer
If the doped active layer is configured to be joined,
Crystallinity is improved. The bonding layer and the active layer are made of the same
Tricks), the lattice of the bonding layer and the active layer
Crystallinity of active layer on bonding layer is further improved by matching
I do. Examples of such a configuration include those defined in the present invention.
N-type and p-type doped with indium in a certain concentration range
Alternatively, an insulated gallium nitride bonding layer
N-type, p-type or insulated nitride doped with uranium
There is a configuration in which an active layer made of gallium is formed. Mentioned earlier
As described above, the indium doping of the present invention is gallium nitride.
The change in the original bandgap does not come. Therefore, on
In the configuration example described above, the gallium nitride bonding layer and the active layer are:
Gallium indium nitride (Ga _1-x In_x N; x ≠
0, 0 <x ≦ 1) It does not lead to a mixed crystal. For this reason,
The bonding layer and the active layer are made of the same material, that is, gallium nitride.
It is composed of So, for example, safa
When the bonding system having the above configuration is provided on the ear substrate,
Although the active layer has a lattice mismatch, the active layer and the bonding layer
Are in a lattice matching relationship. Another example is indium
N-type, p-type or insulated aluminum nitride
Gallium (AlGaN) mixed crystal layer / Indium doped n
, P-type or insulated aluminum nitride-gallium mixed crystal
Junction structure consisting of active layer, indium-doped arsenide
Gallium (GaNAs) layer / Indium-doped arsenic nitride
An example is a junction configuration including a gallium arsenide active layer.

In a light-emitting element, a laminated structure having a band structure for further improving the emission intensity is provided in a bonding system between the bonding layer for improving the crystallinity of the active layer and the active layer for which the crystallinity is improved. Can also be provided. For example, a nitride compound semiconductor mixed crystal layer containing aluminum (Al) doped with indium is joined to one of the active layers. On the other hand, an indium-doped nitride compound semiconductor layer made of the same material as the active layer doped with indium is joined to obtain an asymmetric heterojunction structure. When a nitride compound semiconductor layer containing aluminum having a large band gap is bonded to the active layer, a "light emission confinement effect" that contributes to an increase in light emission intensity can be obtained. Therefore, a compound semiconductor light emitting device having excellent emission intensity is provided from the laminate having such a bonding structure.

Further, the present invention provides a nitride compound semiconductor device comprising a laminate including a junction structure between an indium-doped nitride compound semiconductor layer and a junction with an active layer. The layers constituting the laminate include a low-temperature buffer layer, a buffer layer, a lower clad layer, an active layer, an upper clad layer, a current diffusion layer, a contact layer, and the like in the case of a nitride compound semiconductor light emitting device. In the present invention, when the indium-doped nitride compound semiconductor forming a junction with the active layer is a lower cladding layer, the lower cladding layer is bonded to a nitride compound semiconductor layer forming a buffer layer doped with indium. is there. This is because this bonding method can more reliably prevent the propagation of crystal defects caused by the lattice mismatch between the substrate and the layer constituting the laminate to the nitride compound semiconductor layer that forms a bond with the active layer. Thereby, a ripple effect of further improving the crystallinity of the nitride compound semiconductor active layer bonded to the bonding layer is brought about.

The low-temperature buffer layer immediately above the substrate crystal is not necessarily required to be an indium-doped layer. However, a buffer layer, a lower cladding layer, an active A stacked structure in which the layers, the upper cladding layer, and the contact layer are layers doped with indium is also conceivable. According to this configuration, the effect of improving the crystallinity brought about by the doping of indium can be spread over the whole of the stacked constituent layers. Specifically, there can be mentioned a laminate for a light emitting element in which the following nitride compound semiconductor layers are sequentially deposited on a sapphire substrate. (1) Al _x Ga _1-x N (0 ≦ x ≦ 1) low temperature buffer layer. (2) A buffer layer or lower cladding layer made of an n-type gallium nitride layer doped with indium. (3) An n-type gallium nitride active layer to which a group II element and a group IV element, or an indium, a group II element, and a group VI element are added in addition to indium. For example, an n-type gallium nitride active layer to which indium, zinc and germanium are added. (4) p-type aluminum nitride doped with indium
Upper cladding layer made of gallium mixed crystal layer. (5) A p-type gallium nitride contact layer doped with indium. The light emitting element is formed through a process of forming an n-type electrode (negative electrode) on the layer (2) and a p-type electrode (positive electrode) on the layer (5).
This laminated structure has a junction between the active layer and the nitride compound semiconductor layer doped with indium, an indium-doped nitride compound semiconductor active layer composed of the same material (matrix) as the junction layer, and a low-temperature buffer. This is an example of a stacked structure in which all of the stacked constituent layers on the layers are nitride compound semiconductor layers doped with indium.

Another example of the nitride compound semiconductor device according to the present invention has a hexagonal or cubic crystal structure such as conductive or insulating silicon carbide (SiC) or zinc oxide (ZnO). A light-emitting element including a stacked body having a structure in which the following layers are sequentially stacked on a crystal substrate is given. (1) Aluminum-gallium nitride (Al _x Ga _1-x N; 0 ≦ x ≦ 1) low-temperature buffer layer having a thickness of 2 to 50 nm. (2) Indium doped carrier concentration is 1
0 ¹⁶ cm ^-3 or more and 10 ¹⁹ cm ^-3 or less and a layer thickness of about 0.01
A lower cladding layer made of an n-type or p-type aluminum-gallium nitride mixed crystal (Al _x Ga ₁ -xN; 0 <x ≦ 1) having a thickness of ５5 μm; (3) Indium, cadmium (Cd), and silicon (Si) are co-doped with a film thickness of 2 to 10 nm, and the carrier concentration is approximately 10 ¹⁵ cm ⁻³ or more and 5 × ¹⁸ cm ^−3.
An n-type or p-type aluminum gallium nitride (Al _x Ga ₁ -xN; 0 ≦ x ≦ 1) active layer to be described below. (4) Indium doped carrier concentration is 1
0 ¹⁶ cm ^-3 or more and 10 ¹⁹ cm ^-3 or less, and a layer thickness of about 0.0
N-type or n-type or p-type aluminum nitride-gallium mixed crystal (Al _x Ga _1-x N; 0 <x
≦ 1) an upper cladding layer. (5) An n-type or p-type aluminum gallium nitride (A) having a carrier concentration doped with indium of about 10 ¹⁶ cm ^-3 or more and a layer thickness of about 0.01 μm or more.
1 _x Ga _1-x N; 0 ≦ x ≦ 1) Contact layer. (6) Transparent conductive film or translucent thin film electrode. The low-temperature buffer layer, which is a constituent layer of the laminated structure for use in the light-emitting device according to the present invention as exemplified, may be doped with indium. If a low-temperature buffer layer doped with indium is adopted, a laminated body composed entirely of a nitride compound semiconductor doped with indium is formed on a substrate.

Examples of other nitride compound semiconductor devices according to the present invention include gallium phosphide (GaP), gallium arsenide (GaAs), boron nitride (BN), and boron arsenide (BA).
s), III-V group compound semiconductors such as boron phosphide (BP), or group IV element semiconductors such as silicon (Si) and germanium (Ge). There are light emitting elements. (1) Aluminum nitride, gallium, indium (Al
_{x Ga y In 1-xy N} ; x + y = 1,0 ≦ x ≦ 1,0 ≦
y ≦ 1) A low-temperature buffer layer composed of a single layer or a multilayer thereof. (2) Group IV elements or the group VI element or n-type both of which were added _{Al x Ga y In 1-xy} N (x + y = 1,
0 ≦ x ≦ 1, 0 ≦ y ≦ 1) A buffer layer composed of a single layer or a multilayer thereof. (3) n-type or p-type Al _x Ga doped with In
_1-x N _y P _1-y (0 ≦ x ≦ 1, 0 ≦ y <1) or n-type or p-type Al _x Ga _1-x N _y As _1-y (0 ≦ x ≦
A nitride containing a Group V element other than nitrogen, such as 1, 0 ≦ y <1), having a carrier concentration of about 10 ¹⁶ cm ^{−3 to} about 10 ¹⁹ cm ⁻³ and a layer thickness of about 0.01 to 5 μm. object compound lower cladding layer made of a semiconductor (4) Al indium and zinc and the germanium is doped simultaneously _{x Ga 1 -x N y P 1} -y (0 ≦ x ≦ 1,
0 ≦ y ≦ 1) or Al _x Ga _1−x N _y As _1−y (0 ≦ _y
x ≦ 1, 0 ≦ y <1) or other group V element other than nitrogen, having a carrier concentration of about 10 ¹⁵ cm ^{−3 to} 10 ¹⁸ cm ⁻³ and a layer thickness of about 0.01 to 2 μm. Light emitting layer. (5) Al _x G having a different conductivity type from the lower cladding layer
a _y In _1-xy N (x + y = 1, 0 ≦ x ≦ 1, 0 ≦ y
≦ 1) or Al _x Ga ₁ -xN (0
≦ x ≦ 1) or containing a group V element other than nitrogen and having a carrier concentration of about 10 ¹⁶ cm ^{−3 to} about 10 ¹⁹ cm ⁻³ ,
An upper cladding layer made of a nitride compound semiconductor having a layer thickness of about 0.01 to 5 μm. (6) Al _x G having the same conductivity type as the upper cladding layer
a _y In _1-xy N (x + y = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦
1) Al _x Ga _{1 -x} N to which In is added (0 ≦
x ≦ 1) or a nitride compound semiconductor containing a Group V element other than nitrogen, having a carrier concentration of about 10 ¹⁶ cm ⁻³ or more and a layer thickness of about 0.05 μm to about 3 μm. (7) A light-transmitting thin-film electrode layer or a transparent conductive film layer made of a metal nitride or a metal material.

Each of the above laminates is an example in which a nitride compound semiconductor layer doped with indium is provided as an active layer (light emitting layer), and a gallium indium nitride (GaInN) mixture having a high indium composition ratio as in the prior art. The crystal is not used as the active layer. That is, when the indium-doped nitride compound semiconductor layer according to the present invention is used as the active layer, it is not necessary to change the growth temperature for the purpose of growing the active layer. For example, in obtaining a laminate having the above structure, a light-emitting layer made of an indium-doped nitride compound semiconductor layer is grown while maintaining the same growth temperature as the lower clad layer, and then the upper layer is further grown at the same growth temperature. Can be grown. This is because in the present invention, indium is not added at a high concentration so that an indium-based mixed crystal is created.

The constituent layers of the above-mentioned laminated structure are formed by a metalorganic pyrolysis vapor deposition method (referred to as MOCVD method or MOVPE method), a molecular beam epitaxial growth method (MB).
E), and can be grown by a vapor phase growth method such as a chemical beam evaporation method (CBE method). In the MOCVD method, a normal pressure or a reduced pressure method may be used. That is, the pressure at the time of film formation does not matter. A nitride compound semiconductor layer containing no aluminum may be grown by a halogen or hydride vapor phase epitaxy method, and a nitride semiconductor layer containing aluminum may be obtained by using another growth method. A physical deposition method such as a high frequency sputtering method can also be used as one film forming method. The growth raw material is not particularly limited. For example, the gallium source may be a conventional metal gallium or trimethylgallium ((CH
₃ ) ₃ Ga), triethylgallium ((C ₂ H ₅ ) ₃ G
Organic gallium compounds such as a) and their halogen adducts can be used. Aluminum source is aluminum metal,
Trimethylaluminum _{((CH 3) 3 Al)} , triethylaluminum _{((C 2 H 5) 3} Al) and tri-isobutyl aluminum _{((i-C 4 H 9} ) 3 Al) the trialkyl aluminum compounds or aluminum and nitrogen atoms, such as And the like can be used. The indium-doped nitride compound semiconductor includes an organic indium compound having an aliphatic hydrocarbon group such as metal indium and a trialkyl In compound, and an alicyclic indium compound such as cyclopentadienyl I n (C ₅ H ₅ In). It can be obtained by adding indium to the nitride semiconductor layer as an addition source. No special raw materials are required to obtain the laminated constituent layers according to the present invention. As a method of adding indium, there is a method of injecting indium ions into the nitride compound semiconductor layer.

[0042]

The gallium-based group III nitride compound semiconductor active layer according to the present invention is doped with indium, and the indium-doped gallium-based group III nitride compound semiconductor bonding layer is bonded to a light emitting device. To increase the emission intensity.

[0043]

【Example】

(Embodiment 1) A nitride compound semiconductor device according to the present invention will be described in detail with reference to the drawings using a blue LED as an example. FIG. 7 is a schematic plan view of an LED according to this embodiment. FIG. 8 is a schematic sectional view taken along a broken line AA ′ in FIG. In this embodiment, a sapphire substrate was cut (sliced) from an ingot grown by the CZ (Czochralski) method, and the front and rear surfaces of the ingot were mirror-polished by a chemical mechanical polishing method. The sapphire substrate was circular with a diameter of 50 mm, the periphery of the substrate was chamfered, and the finished thickness was about 100 μm. The plane orientation was (0001), and the substrate surface was a so-called C plane. Immediately before loading this substrate into an atmospheric pressure metal-organic pyrolysis vapor deposition reactor (MOCVD reactor) for forming the constituent layers of the laminate shown in FIG. , And washed with ultrapure water having a specific resistance of about 18 megaohms (MΩ). Thereafter, the surface of the substrate was treated with a commercially available aqueous solution of ammonium fluoride, and the surface was again washed with ultrapure water. Then, the water was evaporated using an infrared lamp and dried.

A sufficiently dried substrate (101) is taken into the MOCVD reactor using an interlock-type substrate transfer system equipped with an extremely general vacuum exhaust mechanism without allowing outside air to enter the MOCVD reactor. The substrate was transported onto the surface of a cylindrical support (susceptor) made of high-purity graphite while maintaining the inside of the substrate transport system at a degree of vacuum of about 10 ⁻³ Torr (Torr). Next, the roughness of the inner surface is set to Rmax.
Compound electrolytic polishing was performed precisely so as to be less than 5 μm,
High-purity argon (Ar) gas was introduced as a purge gas into the reactor via a JIS 316L stainless steel pipe having an outer diameter of 1/4 inch. Argon gas is purified by a molecular sieve (molecular sieve) adsorption method with a dew point of about −90 ° C. The flow rate of the purge gas is an electronic mass flowmeter (abbreviated as MF).
In C), the volume was adjusted to 5 liters per minute and controlled. After continuing the flow of the argon purge gas into the reaction furnace for 20 minutes, the gas flowing through the reaction furnace was converted from argon gas to high-purity hydrogen (H ₂ ) gas having a flow rate of 8 liters per minute.

Next, while flowing hydrogen at the above-mentioned flow rate as a carrier (material feed) gas into the reaction furnace, the outer periphery serving also as a mounting table for the susceptor made of high-purity graphite was made of a molybdenum (Mo) material. Power was supplied to the cylindrical semi-closed resistance heating type heater, and the temperature of the sapphire substrate was raised to 450 ° C. for growing a low-temperature buffer layer over 15 minutes from room temperature. The temperature of the sapphire substrate is the center of the resistance heater, that is, a so-called ceramic heater using a carbon material as a heating element (element) deposited on a circular boron nitride (BN) substrate by chemical deposition (abbreviated CVD). The temperature was measured using a thermocouple that penetrated through the center of the element and reached a cut-out portion of a molybdenum disk constituting the upper surface of the heater. Thermocouple is platinum / platinum
A rhodium alloy-based thermocouple (JIS: R thermocouple) was used, and the distance between the welded tip of the thermocouple and the upper surface of the heater was 1 mm in the vertical direction. The sapphire substrate is placed at the center of a graphite circular susceptor having a thickness of 2 mm and a diameter of 120 mm. Further, the susceptor is disposed on a molybdenum disk constituting the upper surface of the heater. Accordingly, the distance between the sapphire substrate and the thermocouple is approximately 3 mm, and the existence of this distance naturally causes a difference between the temperature measured by the thermocouple and the actual temperature of the sapphire substrate, especially the surface of the substrate. For example, 600 ° C
Within the temperature range of ~ 700 ° C, the thermoelectromotive force of the thermocouple is 686.
The temperature measured as the substrate surface temperature from the JIS-R thermocouple in contact with the surface of the sapphire substrate when the temperature indicated value was given was 660 ° C., and a difference of approximately 26 ° C. was recognized. . As described above, although there is actually a difference between the temperature indicated by the thermocouple arranged in the heater and the surface temperature of the sapphire substrate heated mainly by heat transfer via the susceptor, the present embodiment For convenience, the temperature measured by a thermocouple disposed in the heater is referred to as a growth temperature.

After the temperature of the sapphire substrate reaches 450 ° C., the temperature indication value obtained by converting the thermoelectromotive force signal of the JIS: R thermocouple is monitored, and the transient response (overshoot) state of the substrate temperature due to the heating is monitored. It was canceled and waited for a while until the temperature reading became stable. After elapse of about 10 hours while maintaining the sapphire substrate at the same temperature, a seal material in a gas contact portion (a portion that comes into contact with gas) or the like is replaced with a Teflon resin o-trade name such as Kalrez. Electronic mass flow meter (MF) dedicated to ammonia (NH ₃ ) gas converted to a ring etc.
Ammonia gas whose flow rate was precisely controlled to 1 liter per minute by C) was mixed with the hydrogen carrier before reaching the reactor. The hydrogen carrier gas accompanying the ammonia gas was introduced into the reaction furnace from above the sapphire substrate surface almost vertically above the precision-polished stainless steel pipe.
Ammonia gas was supplied by decompressing and vaporizing liquefied ammonia contained in a pressure-resistant cylinder of approximately 10 liters made of an aluminum (Al) alloy whose inner surface was mirror-polished. Exactly 5 minutes after the start of the addition of the ammonia gas to the hydrogen carrier gas, a liquid of trimethylgallium ((CH ₃ ) ₃ Ga) as a gallium (Ga) material source is bubbled (foamed) to produce trimethylgallium. Hydrogen gas accompanying steam was mixed with a hydrogen carrier gas immediately before the reactor and supplied to the surface of the sapphire substrate in the reactor. Trimethylgallium is JI whose inner surface is mirror-polished
S: A bubbler (foaming container) made of 304 and 316L stainless steel having an inner volume of about 150 milliliters (ml) was initially filled with about 50 grams (g), and the temperature of the vessel, that is, trimethyl The gallium temperature was maintained at 0 ° C. in an electronic thermostat using the Peltier effect. Trimethylgallium is a liquid at a temperature of 0 ° C., and a high-purity hydrogen gas having a flow rate of 5 ml / min by an electronic mass flow meter (MFC) was passed through the liquid as a bubbling gas. Addition of a hydrogen bubbling gas accompanied by trimethylgallium into the growth furnace was used to start the growth of a low-temperature buffer (buffer) layer (102) made of gallium nitride (GaN), and the above flow rate was used as a nitrogen (N) supply source. The supply of the hydrogen bubbling gas accompanying the ammonia gas and the vapor of trimethylgallium into the reactor was continued for exactly 15 minutes. Thus, an undoped gallium nitride low-temperature buffer layer (102) having a layer thickness of about 7 nanometers (nm) was formed. After exactly 15 minutes had elapsed, the mixing of the hydrogen bubbling gas accompanying the vapor of trimethylgallium into the hydrogen carrier gas was instantaneously stopped by opening and closing a valve provided in the piping system of the raw material supply system.

At the same time, the gas type constituting the carrier gas is first switched instantaneously from hydrogen to argon gas at the same flow rate in order to suppress fluctuations in the pressure in the reactor by opening and closing a valve provided in the piping system. Was. Thereafter, the flow rate of argon gas was measured at 8 minutes per minute by an electronic mass flow meter (MFC) for about 2 minutes.
It was slowly reduced from 5 liters to 5 liters per minute. The ammonia gas flow rate was 1 liter per minute and was not changed. After changing the carrier gas to argon and adjusting its flow rate, the amount of electric power supplied to the above-mentioned resistance heating type heater is controlled through a thyristor-type electric circuit to raise the temperature of the sapphire substrate to gallium nitride. The temperature was increased to 1100 ° C., the growth temperature of the layer.
After reaching 1100 ° C., 5 minutes after it is judged from the temperature reading that the temperature transient has attenuated, the flow rate of the argon gas is reduced from 5 liters per minute to 3 liters per minute, and at the same time, hydrogen gas is removed. It was again fed into the reactor at a flow rate of 3 liters per minute. That is, the carrier gas was composed of hydrogen and argon having the same flow rate. At the same time, the flow rate of ammonia gas was increased from 1 liter per minute to 4 liters per minute. The changes in the flow rates of these gases were all completed concurrently within about 2 minutes. In the time zone where these flow rates were changed, disilane (Si ₂ H ₆ ) gas diluted to a volume concentration of about 1.2 ppm with high-purity hydrogen gas was supplied at a flow rate of 5 ml / min. Before supplying the gallium source described above, it was previously supplied into the reactor as a doping gas (doping source) of silicon (Si). After a lapse of exactly 3 minutes from the change in the flow rate, the carrier gas having the above composition is mixed with a hydrogen bubbling gas accompanied by trimethylgallium and trimethylaluminum vapor to form aluminum nitride.
Gallium growth layer growth was started. At this time, the temperature of the stainless steel bubbler container containing trimethylgallium was set at 13 ° C. by using the commercially available ethylene glycol as a heat transfer (cooling) medium by the electronic constant temperature layer. Also,
The flow rate of hydrogen for bubbling liquid trimethylgallium was 5 ml / min. The temperature of the stainless steel bubbler container containing trimethylaluminum, whose inner surface is mirror-polished, is controlled by an electronic constant temperature layer similar to that described above, using commercially available ethylene glycol as a heat transfer (cooling) medium.
0 ° C. The flow rate of hydrogen for bubbling the liquefied trimethylaluminum was 5 ml / min. While maintaining the flow rate conditions of these various gases, mixing of the hydrogen bubbling gas accompanied by the vapor of trimethylgallium into the carrier gas having the above composition is continued for 90 minutes to form a silicon layer having a layer thickness of about 3.5 μm. A Si) -doped n-type aluminum-gallium nitride mixed crystal layer (117) was grown. Precisely after 90 minutes, addition of hydrogen bubbling gas accompanied by trimethylgallium and trimethylaluminum vapor and disilane gas, which is a silicon doping gas, to the hydrogen / argon mixed carrier gas is stopped to prevent silicon-doped n-type aluminum nitride. -Gallium layer growth is completed. The carrier concentration of the silicon-doped n-type aluminum-gallium nitride mixed crystal layer deposited on the gallium nitride buffer layer grown under the same conditions as above was not substantially constant in the layer thickness direction. According to a usual stepping hole (Hall) measurement method, the carrier concentration in a region from the vicinity of the interface with the gallium nitride buffer layer to a thickness of about 1 μm is about 3 × 10 ¹⁸ cm ⁻³ , The carrier concentration tends to decrease slightly as the layer thickness increases from substantially the center toward the surface, and the carrier concentration at the surface is about 9 × 10 ¹⁷ cm.
^-3 and decreased from the layer depth (substrate side).

While the flow rate of the ammonia gas was kept as it was, the supply of the hydrogen gas constituting the carrier gas to the growth reaction system was cut off, and two types of gas, argon and ammonia, were introduced into the growth reaction system. This gas switching was performed within about 2 minutes after the supply of the above-mentioned trimethylgallium and hydrogen bubbling gas accompanying the vapor of trimethylaluminum to the growth reaction system was cut off. Thereafter, the substrate temperature was lowered from 1100 ° C. to 850 ° C. at a rate of 25 ° C./min. After the temperature hunting is eliminated in about 3 minutes after the temperature is reduced to 850 ° C., the supply of the hydrogen bubbling gas accompanied with the vapor of trimethylgallium and the doping source of indium (In) and zinc (Zn) is started. An active layer (118) consisting of a gallium nitride (GaN) layer doped with indium and zinc was formed. The above stainless steel bubbler container containing trimethylgallium was maintained at 0 ° C. by an electronic thermostat. The flow rate of high-purity hydrogen gas for bubbling liquid trimethylgallium is measured by an electronic mass flow meter (MFC).
To 5 milliliters per minute. As an indium source, cyclopentadienyl indium having a monovalent valence is used in order to avoid a complexation reaction with an electron-donating ammonia gas.
ium: C ₅ H ₅ In) was used (JP-A-1-9461
3 and J.I. Crystal Growth, 107 (1
991), pages 360-364). This indium source was housed in a cylindrical bottle made of 316L-stainless steel or the like whose inner surface was mirror-polished, and the bottle was kept at 60 ° C. in the same electronic thermostat as above. Initially, a high-purity hydrogen gas for entraining the sublimated indium source into the growth reaction system was passed through an electronic mass flow meter (MFC) inside the stainless steel bottle containing the indium source.
It circulated at a flow rate of 20 milliliters per minute. Zinc is about 1% by volume of diethyl zinc ((C ₂ H ₅ ) ₂ Zn).
Doping was performed by adding high-purity hydrogen gas containing 00 ppm to the growth reaction system. The supply amount of the diethyl zinc / high-purity hydrogen mixed gas to the growth reaction system was set at 40 ml / min by an electronic mass flow meter and kept constant until the growth of the indium and zinc-doped gallium nitride layers was completed. On the other hand, the supply amount of the high-purity hydrogen gas accompanying the sublimated indium source to the growth reaction system is 2 at the start of growth of the same layer.
The volume was set to 0 milliliter, and gradually increased linearly as the growth time elapses, that is, as the layer thickness of the layer increased, and was set to 220 milliliter at the end of the layer. Since it took 5 minutes to grow the indium and zinc doped gallium nitride layers,
The time increase of the supply amount of the indium source was 40 ml / min. Further, since the layer thickness of the indium and zinc-doped gallium nitride layer obtained by the growth for 5 minutes was 60 nm, the increase in the supply amount of the indium source per unit layer thickness (1 nm) was about 3.3 ml. became. The supply of the vapor of the gallium source and the hydrogen gas and the diethyl zinc / high-purity hydrogen gas accompanying the sublimated indium source to the growth reaction system were stopped to terminate the growth of the indium and zinc doped gallium nitride layers. At the same time as the supply of the raw material gas and the doping gas is stopped, the supply amount of the argon carrier gas is reduced from 3 liters per minute to 1 liter per minute, and the flow ratio of the argon gas to the ammonia gas (4 liters per minute) / Argon flow ratio) was relatively reduced.

In this state, the temperature of the substrate is changed from 850 ° C. to 11
The temperature was raised to 50 ° C. at a rate of 60 ° C./min for 5 minutes. The ammonia flow rate was increased from 4 liters per minute to 6 liters per minute while reaching 1150 ° C. 1150
Five minutes after the temperature reached, the flow rate of the argon gas was immediately increased from 1 liter per minute to 3 liters per minute, and the supply of hydrogen gas was restarted. The flow rate of hydrogen constituting the carrier gas together with argon was adjusted to 3 liters per minute by an electronic mass flow meter (MFC). After exactly one minute by adjusting the flow rate, a hydrogen bubbling gas accompanied by trimethylgallium vapor and a hydrogen bubbling gas accompanied by trimethylaluminum ((CH ₃ ) ₃ Al) vapor were added to the argon / hydrogen mixed carrier gas. . The doping gas of zinc and magnesium (Mg) was added at the same time as the addition of the group III raw material gas to the growth reaction system. As a result, an aluminum-gallium nitride mixed crystal (Al _x Ga ₁ -xN; x is an Al composition ratio with a layer thickness of 120 nm, doped with zinc and magnesium, which are group II acceptor impurities, is represented by: 0 <x <1) and the upper cladding layer (1
19) was grown. The doping source of magnesium is bismethylcyclopentadienyl magnesium (bis-me
thylcyclopentadienylmagnesium: (CH ₃ C ₅ H ₅ )
₂ Mg) was used. The magnesium source was maintained at 50 ° C., and the sublimated magnesium source was accompanied by a high-purity hydrogen gas to the growth reaction system in the same manner as the indium source described above. During the deposition of the aluminum nitride-gallium mixed crystal for 10 minutes, while the thickness of the layer reaches about 60 nm (about 5 minutes in growth time), the supply rate of the magnesium source is 40 minutes per minute.
It was kept constant at milliliters. In the latter half of the growth of the same layer (in the growth time from the start of growth of the same layer to about 5 minutes to 10 minutes), the supply amount of the magnesium source was increased from 40 ml / min to 20 ml / min. Gradually reduced. On the other hand, the supply amount of the diethyl zinc / hydrogen mixed gas into the growth chamber maintained a constant flow rate of 40 ml / min with respect to the growth time.

Thereafter, the supply of the aluminum source to the reaction system is cut off, and the contact layer (106) made of gallium nitride doped with zinc and magnesium together.
The process was shifted to film formation. The supply amount of the magnesium source was 20 ml / min at the beginning of growth, but was gradually increased linearly to 40 ml / min as the layer thickness increased. The growth of the zinc- and magnesium-doped gallium nitride contact layer intended to have a layer thickness of 10 nm was completed over 5 minutes. FIG. 9 shows the change in the substrate temperature in the process of obtaining the laminated body described in the present embodiment. FIGS. 10 to 12 show the flow rates of argon, hydrogen carrier gas, and ammonia used as a nitrogen source, which follow the change in the substrate temperature. Summarize the changes. FIG.
3 and 14 show changes in the flow rate of the group III raw material system corresponding to the change in the substrate temperature. In some cases, the temperature of the supply source of the group III raw material is changed for each growth process (FIG. 13).
And the temperature in parentheses in 14 is the holding temperature of the raw material. ). Therefore, what is shown in FIGS. 13 and 14 is a change in the flow rate in each growth process, and does not indicate the absolute value of the molecular concentration (molar concentration). The flow rate to the molar concentration can be converted by the vapor pressure or sublimation pressure value of the group III element raw material at the holding temperature. Incidentally, the vapor pressures of trimethylgallium at 0 ° C. and 13 ° C. are respectively
64.4 Torr (Torr) and 128.2 Torr. The sublimation pressure of cyclopentadienyl indium at 65 ° C. is 1.8 Torr. The vapor pressure of trimethylaluminum at a holding temperature of 25 ° C. is 11.9 Torr.
r. The pressure of the hydrogen gas circulated in the container containing these group III raw materials is accurately adjusted to 1 atm by gauge pressure by a low pressure reducing valve for semiconductor industry in which the gas contact portion is mirror-polished.

When the growth of the gallium nitride layer doped with both zinc and magnesium is completed, all the II
Supply of group I element materials to the growth reaction system was stopped. Immediately after the supply of the group III element raw material was stopped, the power supply to the resistance heater was stopped to start cooling the substrate. In particular, no measures were taken to forcibly cool the substrate, but it was observed that the substrate temperature dropped at a rate of about 30 ° C./min from 1150 ° C. to a temperature near 750 ° C. 450 from around 750 ° C
Cooling at a rate of about 20 ° C./minute to about 25 ° C. per minute to a temperature near ° C. was observed. When the substrate temperature dropped to around 450 ° C., the supply of ammonia gas to the growth reaction system was stopped. Approximately 4 to decrease from around 450 ° C to room temperature
It took 0 minutes.

The supply of hydrogen gas to the reactor was stopped, and argon was supplied instead. After a while, the supply of argon to the reaction furnace was continued, and then the supply of argon was stopped, and the inside of the reaction furnace was moved to about 2 × 1 with a normal rotary vane pump.
Evacuation was performed until the pressure reached 0 ^-3 Torr. Vacuum degassing in the furnace and purging with argon gas were repeated several times, and finally the pressure in the reactor was returned to almost atmospheric pressure by purging with argon gas. Then, after the wafer is taken out of the reactor from the furnace, two tungsten probes (probes) are brought into contact with the surface of the wafer at this time at an interval of about 1 mm, and the presence or absence of conduction between the probes is checked. Inspection revealed no conductivity. Next, the wafer was placed on a metal susceptor in an implantation station of an ion implantation apparatus with a maximum acceleration voltage of 200 kilovolts (KV). After performing the evacuation operation before the start of ion implantation, the acceleration voltage was set to 180 KV, and the dose was set to 7 × 10 ¹² cm ^−2.
And magnesium ions having a mass number of 24 were injected by a solid source method. Magnesium ions are perpendicularly incident on the (0001) plane used as the substrate, and are particularly subjected to plane channeling in ion implantation into a face-centered cubic crystal.
Eling) and axial channeling were not particularly noted. The plane orientation processing accuracy of the substrate used in the present embodiment is in the range of about (0001) ± 0.5 °.
The deviation of the incident angle of the incident ion beam from the sapphire C plane (with respect to the c-axis direction of the hexagonal crystal) is at most ± 0.5 °. An organic solvent such as isopropyl alcohol,
After surface treatment with high-purity hydrochloric acid (HCl), it was washed with ultrapure water and dried. Thereafter, the wafer was subjected to lamp heating by a halogen lamp in a nitrogen atmosphere. The temperature of the wafer is raised from room temperature to 1050 ° C. in about 30 seconds.
And then cooled to room temperature in about 20 minutes using both forced cooling by water cooling and natural cooling. After cooling, two probes were brought into contact with the surface at an interval of 1 mm, and the conductivity was measured. As a result, a tendency was found that the current increased linearly substantially in proportion to the voltage applied between the probes. As an example, if the imprint voltage between the probes is 10
The current flowing at volts (V) reached about 300 milliamps (mA). It is simply a current-voltage characteristic between probes, and an accurate resistivity or the like cannot be immediately obtained from these values due to diffusion of an electric field around the probe, but an example of preliminary evaluation data of electrical characteristics FIG. 16 compares current-voltage characteristics as a curve (120) immediately after wafer growth and a curve (121) after annealing after ion implantation.

Observation of the surface of the wafer with a general differential interference microscope revealed that there was an extremely gentle "undulation" of the surface under a low magnification of about 50 times. Magnification 5 × 1
Scanning electron microscope with a magnification of 0 ³ or 10 ⁴ (English abbreviation S
In the surface observation by EM), the observation target is limited to a small area due to high magnification, so that the macro-like “undulation” is no longer clearly observed, and the aperture is made substantially hexagonal. Pits (pores) were hardly observed in the region other than the peripheral portion of the wafer. Wafer periphery, especially diameter 2
An annular zone of about 3 to 6 mm inward from the edge of the inch substrate toward the center of the wafer has a side length of 1 mm.
The pores of approximately regular hexagons having a size of less than μm have a density of 5 × 10
There were as many as ³ cm ^-2 . For this reason, the central part of the wafer was recognized as being transparent to natural light, but the annular zone around the periphery did not need to be illuminated with high-intensity white light, and was turbid due to light scattering by pores. It became something to do.

Cesium (Cs) or oxygen ion
FIG. 17 shows the concentration distributions of constituent elements and dopants in the depth direction from the surface of the wafer, as analyzed by secondary ion mass spectrometry (SIMS) using a secondary ion beam (incident ion beam). First, when the laminated structure of the wafer is identified from the concentration distributions of the constituent elements and the dopants, a contact layer (106) made of gallium nitride doped with zinc and magnesium at the outermost surface and ion-implanted with magnesium after the growth is completed. From there on, if the layered structure is traced sequentially in the depth direction, zinc and magnesium are doped at the time of film formation, and after the growth is completed, magnesium ions are implanted. Upper cladding layer (119), a gallium nitride light emitting layer (118) doped with indium and zinc and having a thickness of about 60 nm, and an aluminum-gallium nitride lower cladding layer (11) doped with silicon.
7). However, the existence of the interface between the silicon-doped aluminum gallium nitride layer and the low-temperature buffer layer made of gallium nitride was not clearly recognized from the elemental profile by SIMS analysis. The concentrations of gallium and nitrogen are rapidly increasing near the outermost surface, and it appears as if these constituent elements had accumulated on the surface. This is due to chemical interference in SIMS analysis and the like. It was speculated. The intended thickness of the outermost gallium nitride contact layer (106) is 100 nm, whereas the thickness of the gallium nitride layer determined by SIMS from a depth-profile is about 97 nm. . The aluminum composition ratio (x) calculated from the atomic concentration ratio of aluminum and gallium constituting the upper cladding layer (105) made of the mixed crystal of aluminum nitride and gallium was approximately 0.12.

Similarly, the analysis results by SIMS showed that the concentration and distribution of the dopant in each layer were as follows. The outermost gallium nitride contact layer (1
06) near the surface side of the matrix
x) As in the case of the element, a mode is shown in which doping impurities of zinc and magnesium accumulate, but this was also presumed to be caused by the above-mentioned chemical interference. If the data in the region near the surface where the surface condition subtly affects the detection sensitivity of secondary ions is omitted, the concentration distribution of zinc in the gallium nitride contact layer (106) is substantially constant at 9 × 10 ¹⁸ c ^{Was -3} . on the other hand,
The concentration of magnesium atoms in the same layer (106) is as high as about 8 × 10 ¹⁸ cm ^{−3 in the} vicinity of the surface, and once the atomic concentration is reduced to 6 × 10 ¹⁸ cm ⁻³ in the depth direction, the ion implantation is performed again during ion implantation. The distribution of implanted atoms in the layer was distributed in a general normal distribution curve, and increased to 2 × 10 ¹⁹ cm ⁻³ near the interface between the same layer (106) and the lower layer (119). An active layer (11) made of an aluminum nitride-gallium mixed crystal (Al _0.12 Ga _0.88 N) having an aluminum composition ratio (x) of 12%
Within 8), the atomic concentration of magnesium also increases in the form of a normal distribution curve in the depth direction from the gallium nitride contact layer (106) side, and abruptly increases by about 5 × in a region deeper than about half of the layer thickness. The concentration had increased to 10 ¹⁹ cm ^-3 . In particular, the increase in the atomic concentration of magnesium near the interface with the active layer (118) is due to the increase or decrease in the amount of the magnesium source added to the growth reaction system during the growth of the upper clad layer (119). Was determined to be. That is, in the implantation of magnesium ions, the concentration distribution of the implanted atoms becomes a normal distribution (Gaussian distribution) curve in principle, and the concentration of the implanted atoms cannot be changed steeply particularly at the interface side deeper than the surface side. In addition, a region in which magnesium is doped at the time of growth (a region of about 60 nm from the interface with the active layer (118) in this embodiment) is previously arranged in a region near the interface, which indicates that the projection range is higher.
It was interpreted to be effective in avoiding a decrease in the concentration of magnesium atoms in a deeper region beyond e).
Here, zinc was distributed almost uniformly in the depth direction, and its concentration was 8 × 10 ¹⁸ cm ⁻³ .

In the indium-doped gallium nitride active layer (118) immediately below the upper cladding layer (119) made of aluminum nitride / gallium mixed crystal, the SI
The MS analysis results show that the concentration of indium atoms is the same (118)
From the interface (lower interface) with the silicon-doped aluminum-gallium nitride lower cladding layer (117), which is the lower layer, from the interface (upper interface) with the aluminum-gallium nitride mixed crystal layer of the upper cladding layer (119). It was shown that it increased steadily linearly with the increase in source supply. The concentration of indium atoms was 9 × 1 at the lower interface.
0 ¹⁷ cm ^-3 and 3 × 10 ²⁰ cm ^-3 at the upper interface. On the other hand, the concentration of zinc atoms in the active layer (118) is substantially constant at 8 × 10 ¹⁸ c corresponding to the fact that the flow rate of the diethyl zinc / high-purity hydrogen mixed gas supplied during film formation is kept constant.
m ^-3 . Elements other than indium and zinc were not intentionally added to the indium-doped gallium nitride active layer (118), but silicon (Si) was added to about 4 × 10
It was detected at a concentration of ¹⁷ cm ^-3 . It has been determined that the atomic concentration of silicon is sufficient to increase the intensity of luminescence emission from zinc (Solid St).
ate Commun. 57 (6) (1991), 4
FIG. 5 on page 408 with reference to pages 05-409. reference).

Another sample in which the surface layer of the gallium nitride layer doped with indium and zinc was exposed by performing etching from the surface of the wafer using a general ion sputtering method was manufactured. In surface observation by SEM at a high magnification of about 10 ⁴ times, macroscopic morphology was not clearly observed because the field of view became narrower at a higher magnification, but a differential interference optical microscope at a low magnification of about 50 times. In the surface observation by the method described above, substantially circular or elliptical protrusions were observed on the surface of the indium and zinc-doped gallium nitride layer. PL at room temperature using a helium (He) -cadmium (Cd) laser beam having a wavelength of 325 nm as an incident beam
In the measurement, a spectrum in the near-ultraviolet band having a wavelength of about 380 nm, which is assumed to appear when a gallium nitride-indium mixed crystal is formed, is not recognized, and the wavelength is simply 365 nm.
Only band edge emission of gallium nitride was observed before and after. That is, in the doping of indium in this example, no result was proved that gallium nitride / indium mixed crystal was formed.

The lower layer of the gallium nitride active layer (118) doped with zinc and indium is a lower cladding layer made of aluminum nitride / gallium mixed crystal having an aluminum mixed crystal ratio (x) of 0.01 based on the result of SIMS analysis. (117) was determined. The atomic concentration of silicon in the lower cladding layer (117) was determined to be 4 × 10 ¹⁸ cm ^{−3 by} SIMS analysis. Therefore, the gallium nitride layer (118) doped with both indium and zinc, which becomes the active layer (light emitting layer), has x = 0.12 on the upper surface.
Al _0.12 Ga _0.88 N mixed crystal layers are joined, and x = 0.
01 n-type Al _0.01 Ga _0.99 N mixed crystal layer was formed. Assuming the magnitude of the lattice constant of both aluminum nitride and gallium mixed crystals, the lattice constant of aluminum nitride is 3.111 Å (A) and the lattice constant of gallium nitride is 3.180 (A). Lattice constants, edited by Isamu Akasaki, “III-V Group Compound Semiconductors”
(Baifukan Co., Ltd., issued on May 20, 1994), 148
Table 7.1. Depends on ). Vegard
Assuming that the rule is satisfied (FIG. 1 in JP-A-59-228776, and page 8 of JP-A-4-192585, lines 8 to 3 from the lower left column in the upper column) When the lattice constants of both mixed crystals are calculated, the lattice constant of the Al _0.12 Ga _0.88 N mixed crystal is calculated to be 3.172 (A), and the lattice constant of the Al _0.01 Ga _0.99 N mixed crystal layer is calculated to be 3.179 (A). Based on the gallium nitride indium and zinc constituting-doped light-emitting layer, if indicated a mismatch of lattice between the layer of bonding to the light-emitting layer and the light-emitting layer in [delta] (see text), Al _0.12 G
a _0.88 % for N mixed crystal is 0.264%, Al _0.01 G
δ of the a _0.99 N mixed crystal layer is 2.2 × 10 ⁻² %. Looking at the correspondence between the degree of lattice mismatch (δ) with the light emitting layer and the above-mentioned indium atom concentration in the active layer, as shown in FIG. 17, the degree of lattice mismatch (δ) between indium atoms and the light emitting layer is shown. _Are distributed in such a manner that the atomic concentration increases toward the junction interface with the Al _0.12 Ga _0.88 N mixed crystal layer in which the ratio is larger. EBIC that confirm the presence or absence of the occurrence of the current induced by the electron beam irradiation can confirm the presence of the pn junction (E lectron B e
The evaluation by am I nduced C urrent) method, the pn junction is present in the vicinity of the interface between the Al _0.12 Ga _0.88 N mixed crystal layer and the light emitting layer was confirmed. Therefore, it can be said that indium in the light emitting layer is distributed so as to increase the degree of lattice mismatch (δ) and increase the atomic concentration toward the interface with the p-type bonding layer. That is, in the wafer of this embodiment, indium is doped with distribution in the layer thickness direction, and indium is doped with distribution such that the concentration of indium increases toward the junction interface with the active layer having a higher degree of lattice matching. The active (light emitting) layer was provided.

(Embodiment 2) In this embodiment, the present invention will be described by taking as an example a wafer in which gallium nitride having a donor impurity concentration distribution corresponding to the indium atom concentration distribution in the layer is used as a light emitting layer. The substrate used was (0001) (c-plane) sapphire having the same mechanical specifications as in the first embodiment. The sapphire used in this example had been previously surface-treated at a temperature of about 1200 ° C. in a hydrogen stream, but the gallium nitride buffer layer described in Example 1 and the gallium nitride layer doped only with silicon were used. Example 1
Before forming under the same conditions as described in (1), a heat treatment intended to clean the substrate surface at 1100 ° C. for 40 minutes in a MOCVD reactor with approximately 8 liters of high-purity hydrogen flowing per minute was performed. gave.

After the heat treatment of the sapphire substrate was completed, the gas species and flow rate flowing in the MOCVD furnace were instantaneously reset to those used when growing the gallium nitride buffer layer described in Example 1. After the change in the gas flow rate caused by the switching was corrected, a gallium nitride low-temperature buffer layer and a silicon-doped gallium nitride layer were sequentially deposited on the sapphire substrate under exactly the same conditions as in Example 1.

On the above-mentioned silicon-doped gallium nitride layer having the same layer thickness as in Example 1 and having a slightly reduced carrier concentration toward the surface side, basically the same layer thickness as in Example 1 is applied. A gallium nitride layer doped with indium and zinc was deposited as a light emitting layer. The conditions were gradually changed with the elapse of the growth time of the light emitting layer, with the intention that indium had a distribution increasing in the direction of increasing the thickness of the light emitting layer as in Example 1. That is, in the first embodiment, the distribution of the atomic concentration was created by linearly increasing the flow rate of the hydrogen gas accompanying the vapor of cyclopentadienylindium as the indium source with the growth time. In the example, the atomic concentration of indium was distributed by changing the substrate temperature with time from the start to the end of the growth of the light emitting layer. Substrate temperature from 850 ° C to 7
The temperature was reduced at a rate of 16 ° C./min for 5 minutes up to 70 ° C. The initial temperature at which to start lowering the substrate temperature is 850 ° C
The reason why the temperature attained by the drop was 770 ° C. is that when the supply rate of the high-purity hydrogen gas accompanying the sublimated indium source was set to 20 ml / min, the gallium nitride layer was doped at these substrate temperatures. The atomic concentration of indium is about 9 to 10 × 10 ¹⁷ cm ⁻³ and about 2 to 3 × 10 ²⁰
cm ^-3 is because it was previously known from experiments by the present inventors. The amount of change (decrease) in the substrate temperature with respect to the growth time was precisely controlled by a PID type programmable temperature controller. Further, the difference from the first embodiment is that silicon (Si) as a donor impurity is intentionally doped into the light emitting layer. This silicon doping is performed by using a high-purity hydrogen gas containing 1.2 ppm (parts per million) of disilane (Si ₂ H ₆ ) in volume concentration, and polishing the inner volume of which the inner surface is polished.
This was accomplished by feeding from a 10 liter manganese (Mn) steel high pressure cylinder. The addition amount (flow rate) of the disilane / high-purity hydrogen mixed gas into the growth reaction system was 8 ml / min at the start of the growth of the light-emitting layer, and was accurately 5 ml / min.
After one minute, it was reduced linearly to 1 milliliter per minute.
That is, the flow rate of the indium atom concentration was reduced at a rate of 1.4 ml / min for the purpose of providing the distribution of the silicon element in the layer thickness direction. On the other hand, the supply flow rate of the diethyl zinc (volume concentration: 100 ppm) / high-purity hydrogen mixed gas into the growth reaction system is kept constant, and the concentration distribution of zinc atoms in the light emitting layer is made almost constant as in Example 1. Intended. 18 to 20 schematically show changes over time in the substrate temperature, the raw material system, and the flow rate of the doping gas during the growth of the light emitting layer. FIG. 19 and FIG. 20 show the change in the flow rate, not the change in the absolute value of the actual molecular concentration (molar concentration). The molar concentration of the dopant supplied to the growth reaction system depends on the volume concentration of the dopant in the above mixed gas and the mole (mol) at the temperature of the supply system of the doping gas.
It can be calculated from the volume.

According to the method described in Example 1, an aluminum gallium nitride mixed crystal layer having an aluminum composition ratio of 0.12 and a gallium nitride layer were sequentially deposited on the light emitting layer. Both layers were doped with zinc and magnesium during growth as described in Example 1. Further, both layers were subjected to magnesium ion implantation according to the conditions of Example 1 after the growth. After performing such ion implantation, the flow rate is reduced to 2 per minute.
The so-called ion implantation annealing was carried out at 1050 ° C. for 40 minutes in an ammonia / argon mixed gas flow composed of ammonia gas at 1 liter and argon gas at 2 liters per minute. In the probe method in which the presence or absence of conductivity is easily evaluated based on the degree of current flow between tungsten (W) probes (probes), the conductivity was first confirmed after annealing after the ion implantation. . As-grown after wafer growth
In this state, no clear conductivity was obtained between the probes, and the current-
It was determined from the voltage characteristics that the resistance was rather high.

[0063] cesium ions (Cs ⁺⁾ or oxygen ions (O ₂ ⁺⁾ flight type to the primary beam (T ime o f
F light (TOF) SIMS was used to measure the concentration distribution of indium, silicon, and zinc, particularly in the light emitting layer.
FIG. 21 shows the concentration distribution of these dopants in the light emitting layer portion in the thickness direction of the light emitting layer. The thickness of the light-emitting layer was 57 nm when determined from the depth profile of the dopant. The lower cladding layer (1) made of an n-type aluminum nitride-gallium mixed crystal (Al _0.01 Ga _0.99 N) having an aluminum composition ratio (x) of 1% in the lower layer (substrate side) of the active layer (118) is indium atom concentration.
At the interface with (17), it was 1 × 10 ¹⁸ cm ⁻³ . on the other hand,
P-type Al _0.12 Ga bonded above the active layer (118)
_At the interface with the upper cladding layer (119) made of _0.88 N mixed crystal, it monotonically increased to 2 × 10 ²⁰ cm ⁻³ . Thus, the distribution of the indium atomic concentration in the light emitting layer in the increasing direction of the layer thickness is not limited to the means for changing the supply amount (flow rate) of the indium source described in the first embodiment. It has been found that this can also be achieved by means that change over time. However, the distribution of the atomic concentration of indium resulting from the means for changing the growth temperature of the substrate over time is as follows:
Although the atomic concentration of indium tends to increase monotonically in the direction of increasing the layer thickness, the distribution of the concentration of indium atoms depends on the means for increasing the supply flow rate of the indium source over time as in the first embodiment. In comparison, it can be seen that the distribution increases as a distribution curve (profile) slightly convex downward (see FIGS. 17 and 21). It is unclear at this time whether this is a unique distribution caused by the means for changing the substrate temperature over time, or whether it depends on mechanical factors such as the structure of the MOCVD furnace.

The silicon inside the active layer (118) exhibited a tendency opposite to that of indium atoms, as evident from the concentration distribution (profile) of the atoms. That is, the active layer (1)
18) a concentration of 1 × 1 at the interface with the lower cladding layer (117) made of n-type Al _0.01 Ga _0.99 N) joined below
0 ¹⁸ cm ^-3 , p-type Al on top of active layer (118)
Upper cladding layer made of _0.12 Ga _0.88 N mixed crystal (119)
It monotonically decreased to 1 × 10 ¹⁸ cm ⁻³ toward the interface with the substrate (see FIG. 21). On the other hand, zinc was distributed almost uniformly in the thickness direction of the light emitting layer at a concentration of 8 × 10 ¹⁸ cm ⁻³ irrespective of the mode of atomic concentration distribution of indium and silicon.

In a sputtering method using argon (Ar) having an etching effect similar to the ion sputtering method in SIMS analysis, zinc and magnesium are doped together at the time of film formation above the light emitting layer. the ion implantation gallium nitride layer of p-type formed by subjected and the p-type Al _0.12 Ga _0.88 N mixed crystal layer is removed by etching to expose indium, the surface of the silicon and zinc-doped gallium nitride light emitting layer. The surface of the exposed light-emitting layer was very slightly, but slightly yellowish. Furthermore, when the surface was polarized and observed with a low-power differential interference optical microscope, circular or elliptical hill-like projections (undulations) were observed. In photoluminescence (PL) measurement at room temperature, only a band edge of gallium nitride near 365 nm and a spectrum near 430 nm estimated to be caused by a level related to zinc were observed. PL in the near-ultraviolet region around 380-390 nm, which is peculiar to gallium-indium nitride mixed crystals, which is likely to appear when silicon is intentionally doped.
No luminescence was observed.

In summary, in this embodiment, indium was doped at a concentration that did not achieve the formation of the gallium nitride-indium mixed crystal, and the concentration distribution of indium atoms was given by means different from that of the first embodiment. Thus, a wafer having a gallium nitride layer as a light emitting layer was formed.

(Embodiment 3) In this embodiment, while having the same substrate, light emitting layer, and layer structure above the light emitting layer as described in Embodiment 1, indium is doped as a layer to be bonded below the light emitting layer. 2 shows a configuration example of a wafer provided with a gallium nitride layer. First, a buffer layer made of gallium nitride was deposited on the sapphire substrate described in Example 1 under the conditions of Example 1. After performing the growth of the buffer layer for exactly 15 minutes, II
By opening and closing a valve installed in the piping system of the Group I raw material supply system, mixing of the hydrogen bubbling gas accompanying the vapor of trimethylgallium with the hydrogen carrier gas was instantaneously stopped.

Next, in order to suppress the fluctuation of the pressure in the reactor, the gas type constituting the carrier gas is instantaneously switched from hydrogen to argon gas at the same flow rate by opening and closing a valve provided in the piping system. Was. Thereafter, the flow rate of argon gas was measured at about 8 minutes per minute by an electronic mass flow meter (MFC) in about 2 minutes.
It was slowly reduced from 5 liters to 5 liters per minute. The ammonia gas flow rate was 1 liter per minute and was not changed. After changing the carrier gas to argon and adjusting its flow rate, the amount of electric power supplied to the above-mentioned resistance heating type heater is controlled through a thyristor-type electric circuit to control the temperature of the sapphire substrate to silicon-doped gallium nitride. The temperature was raised to 1100 ° C., which is the growth temperature of the growth layer. After reaching 1100 ° C., it is judged from the temperature indication value that the transient of the temperature has attenuated. After about 5 minutes, the flow rate of the argon gas is reduced from 5 liters per minute to 3 liters per minute, and at the same time, the hydrogen gas is reduced. It was again fed into the reactor at a flow rate of 3 liters per minute. That is, the carrier gas was composed of hydrogen and argon having the same flow rate. At the same time, the flow rate of ammonia gas was increased from 1 liter per minute to 4 liters per minute. The changes in the flow rates of these gases were all completed in parallel within about two minutes. Also,
In the time zone where these flow rates were changed, disilane (Si ₂ H ₆ ) gas diluted to a volume concentration of about 1.2 ppm with high-purity hydrogen gas at a flow rate of 5 ml / min and the next gallium Before supplying the source, silicon (S
The doping gas (doping source) of i) was previously supplied into the reactor. Exactly three minutes after the change of the flow rate, the growth of the gallium nitride growth layer was started by mixing trimethylgallium and a hydrogen bubbling gas accompanied by trimethylaluminum vapor with the carrier gas having the above composition. At this time, the temperature of the stainless steel bubbler container containing trimethylgallium was 13 ° C. using commercially available ethylene glycol as a heat transfer (cooling) medium by the electronic constant temperature layer. The flow rate of hydrogen for bubbling liquid trimethylgallium was 5 ml / min. The temperature of the stainless steel bubbler container containing trimethylaluminum, whose inner surface is mirror-polished, is set at 25 ° C. using commercially available ethylene glycol as a heat transfer (cooling) medium by the same electronic thermostat as described above.
And The flow rate of hydrogen for bubbling the liquefied trimethylaluminum was 5 ml / min. While maintaining the flow rate conditions of these various gases, the mixing of the hydrogen bubbling gas accompanied by the vapor of trimethylgallium into the carrier gas having the above composition is continued for 90 minutes to obtain a silicon gas having a layer thickness of about 3.5 μm. A (Si) -doped n-type aluminum nitride-gallium mixed crystal layer was grown. After exactly 90 minutes, the addition of hydrogen bubbling gas accompanied by vapors of trimethylgallium and trimethylaluminum and disilane gas, which is a doping gas for silicon, to the hydrogen / argon mixed carrier gas is stopped, and silicon-doped n-type aluminum nitride is removed. -Gallium layer growth is completed. Under the same conditions, the carrier concentration of the silicon-doped n-type aluminum-gallium nitride mixed crystal layer deposited on the above-mentioned gallium nitride buffer layer was constant at about 3 × 10 ¹⁸ cm ⁻³ . .

While the flow rate of the ammonia gas was kept as it was, the supply of the hydrogen gas constituting the carrier gas to the growth reaction system was cut off, and two kinds of gas, argon and ammonia, were introduced into the growth reaction system. The switching of the gas was performed within about 2 minutes after the supply of the hydrogen bubbling gas accompanied by the vapor of trimethylgallium to the growth reaction system was cut off. After that, the substrate temperature is reduced from 1100 ° C. to 8
The temperature was lowered to 50 ° C. at a rate of 20 ° C./min. After the temperature dropped to 850 ° C., the hunting of the temperature was eliminated in about 3 minutes and the substrate temperature was stabilized. After that, the supply of hydrogen bubbling gas accompanied by the vapor of trimethylgallium, the indium source and the silicon doping source were started to supply indium and indium. A gallium nitride layer doped with silicon was formed. On this occasion,
The above stainless steel bubbler container containing trimethylgallium was maintained at 0 ° C. by an electronic thermostat. The flow rate of the high-purity hydrogen gas for bubbling the liquid trimethylgallium was 3.2 ml / min by an electronic mass flow meter (MFC). As the indium source, cyclopentadienyl indium, which hardly causes a gas phase reaction with electron-donating ammonia, was used. The indium source is housed in a stainless steel bottle whose inner surface is mirror-polished as in the case of the first and second embodiments. The bottle was kept at 60 ° C. by an electronically controlled thermostat. A high-purity hydrogen gas was supplied at a flow rate of 20 per minute to supply the sublimated indium source to the growth reaction system in the bottle containing the indium source. The n-type gallium nitride layer doped with indium and silicon was grown for 60 minutes. The silicon doping conditions were the same as those for the growth of the silicon-doped n-type gallium nitride. Thus, an n-type gallium nitride layer doped with both indium and silicon was deposited on the silicon-doped n-type gallium nitride layer as a bonding layer to be bonded below the light emitting layer (substrate side).

Thereafter, the conditions such as the flow rate of the carrier gas and the substrate temperature described in Example 1 are directly followed, and the gallium nitride light emitting layer doped with indium, silicon and zinc, and the aluminum nitride doped with zinc and magnesium are used. A gallium mixed crystal layer and a gallium nitride layer doped with zinc and magnesium were sequentially formed on the above-mentioned gallium nitride bonding layer doped with indium and silicon. As for the aluminum-gallium nitride mixed crystal layer and the gallium nitride layer doped with zinc and magnesium, magnesium ions having a mass number of 24 were implanted under the same conditions as in Example 1. The wafer on which the ion implantation was completed was subjected to ion implantation annealing under the conditions described in Example 1.

After the ion implantation annealing, the concentration distribution of the constituent elements and the dopant in the depth direction from the surface of the wafer to the deep portion on the substrate side was measured by SIMS. The lamination structure determined by SIMS analysis was as follows. That is, first, a gallium nitride layer having a layer thickness of about 100 nm, an aluminum nitride-gallium mixed crystal layer having an aluminum composition ratio of 0.12, indium, silicon, and zinc are formed from the front side of the wafer. The structure was composed of a gallium nitride layer having a doped layer thickness of about 60 nm, a gallium nitride layer having a layer thickness of about 200 nm doped with indium and silicon, and a gallium nitride layer doped only with silicon. The presence of the gallium nitride low temperature buffer layer was not clearly observed from SIMS analysis. On the other hand, no difference was observed between the dopant and the distribution form described in Example 1. In particular, it was recognized that the distributions of indium, silicon, and zinc in the gallium nitride layer doped with indium, zinc, and silicon grown in the light emitting layer were almost the same in the increasing direction of the layer thickness. The indium and silicon atoms in the indium and silicon-doped gallium nitride layer junction, which is disposed below the light emitting layer and is in contact with the light emitting layer, are substantially in the layer due to their distribution in the depth direction (concentration profile). Uniform distribution was observed. The atomic concentration of indium in the bonding layer is about 6 ×
It was measured to be 10 ¹⁹ cm ^-3 . In the bonding layer, silicon has a substantially uniform concentration (about 6 × 10 ^{19) in} the thickness direction of the same layer.
cm ^-3 ). The atomic concentration of silicon in the bonding layer is determined by the concentration of silicon atoms (about 3 × 10 ¹⁹ cm ⁻³ ) in the silicon-doped n-type gallium nitride layer disposed below the bonding layer.
The carrier concentration of the bonding layer is larger than that of the silicon-doped n-type gallium nitride layer disposed below the bonding layer (9 × 10 ¹⁷ cm ⁻³ ).
It was measured at a low concentration of about 5%. In this comparison, a silicon-doped n-type gallium nitride layer and a gallium nitride layer doped with indium and silicon were separately formed on the above gallium nitride buffer layer separately under the conditions described in this example. However, each was measured under a zero (0) bias by a general electrolytic CV method, that is, a comparison on a donor concentration.

Separately manufactured under the above conditions and having the same layered structure and almost the same dopant distribution as SIM
The wafer confirmed by the S analysis was replaced with argon ions (A
r ⁺ ) The surface layer was etched by a sputtering method. One sample was etched by sputter etching until the surface of the gallium nitride light emitting layer doped with indium, silicon and zinc was exposed. In other samples, the etching was further advanced to expose the surface of the indium and silicon-doped gallium nitride layer bonded to the lower portion of the light emitting layer. A wavelength of 325 was applied to the sample where the surface of the light emitting layer was exposed.
The PL spectrum was observed by irradiating He-Cd laser light having a wavelength of nm. The PL spectrum at room temperature has a wavelength of about 36.
Band edge emission of gallium nitride crystal at 5nm and about 430n
Light emission presumed to be caused by zinc was observed near m. The wavelength position of band edge emission obtained from another undoped gallium nitride crystal was also about 365 nm. The intensity of blue emission near a wavelength of about 430 nm observed in an n-type gallium nitride layer doped only with zinc and silicon having substantially the same thickness as that of the light emitting layer is about 1/50 of that of the present embodiment. It was about. From this, it was interpreted that the effect of indium doping is to obtain high-intensity blue luminescence in the 430 nm wavelength band as described in this example. On the other hand, even at room temperature PL from the indium-doped junction layer disposed below the light-emitting layer, the band of the gallium nitride crystal having a wavelength of about 365 nm is slightly weaker in emission intensity than that of the light-emitting layer. Only edge emission appeared. As in the PL spectrum from the surface of the light-emitting layer, no light was observed in the near-ultraviolet band near the wavelength of about 380 to 390 nm, which tends to appear due to silicon doping. In addition, since this bonding layer is not doped with zinc, the wavelength 430
Blue luminescence emission in the vicinity of nm did not appear.
Therefore, although the gallium nitride light-emitting layer and the gallium nitride layer bonded to the light-emitting layer are both doped with indium, the position (wavelength) at which band edge emission appears coincides with that of the gallium nitride crystal. It was determined that it was not gallium indium nitride converted but gallium nitride doped with indium without doubt. In addition, the coincidence of the wavelengths at which the band edge emission appears in both layers means that both layers have the same band gap (forbidden band width). That is, from the viewpoint of the junction structure, there are a total of two nitride compound semiconductor layers that form a junction with the light emitting layer, and one of the nitride semiconductor layers is made of the same material as the light emitting layer, that is, gallium nitride. Was formed.

A part of the wafer obtained in this example was cut in the vertical direction to produce a strip-shaped thin piece. After preparing the flake, a part of the cross section of the flake is further thinned by argon (Ar) ion etching, and the TEM (transmission electron microscope) is used.
It was subjected to observation. The presence of the gallium nitride buffer layer, which was unclear by the SIMS method as the elemental analysis, was clearly determined by the cross-sectional TEM method. The thickness of the gallium nitride buffer layer obtained by measuring the length from the captured bright field image is about 6.5 nm.
Met. In a region corresponding to the gallium nitride buffer layer imaged by the bright field method, at least one dark line image (contrast image) supposed to be caused by the presence of dislocations has a simple area of at least one in a width of 100 Å (A). It was present in a large amount at a density of about 10 ¹² cm ^-2 . However, observation under a high magnification such that a lattice image of the interface between the sapphire c-plane substrate and the gallium nitride buffer layer can be confirmed shows that at least several lattice images are arranged on the sapphire substrate surface. Was done. A dark line that linearly penetrates upward through the gallium nitride buffer layer, that is, the dislocation is substantially at the center of the aluminum nitride-gallium mixed crystal layer having a thickness of 3.5 μm on the gallium nitride buffer layer, and is vertical due to stacking faults and the like. There were signs that propagation upwards was suppressed. The dislocation propagating to the indium-doped gallium nitride junction layer and the light-emitting layer, which is almost halfway up the thickness of the aluminum-gallium nitride mixed crystal layer, clearly reduced its density. In addition, almost no new occurrence of dark contrast attributable to misfit dislocations was observed at the interface between the indium-doped gallium nitride junction layer and the indium-doped light-emitting layer. For this reason, in the bright-field cross-sectional TEM image of the indium-doped light emitting layer, it was confirmed that the region where no dark line image was observed was enlarged. This was interpreted to be because the light emitting layer and the bonding layer had a lattice matching relationship, and the density of dislocations and crystal defects generated at the bonding portion between the two layers was suppressed. When the observation area width reached about 1 μm in total, dark lines were observed concentrated in one or two extremely limited areas inside the light emitting layer and the bonding layer. The dark contrast was due to threading dislocations originating at or near the interface with the gallium nitride buffer layer. In some regions, these threading dislocations reached the surface of the above-described aluminum-gallium nitride mixed crystal and the outermost gallium nitride layer above the light-emitting layer. Pits were present on the surface of the gallium nitride layer corresponding to positions where threading dislocations penetrated.

(Embodiment 4) In this embodiment, in addition to the above-described first bonding layer for bonding to the light emitting layer, a second bonding layer for bonding to the first bonding layer is further doped with indium.
An example composed of a group I nitride semiconductor will be described. In short, the indium-doped gallium nitride bonding layer (first bonding layer) described in Example 3 above was provided on the indium-doped gallium nitride layer (second bonding layer) as well. An example of a wafer having the above configuration will be described.

On the gallium nitride buffer layer described in Example 3, an n-type aluminum-gallium nitride mixed crystal layer doped with both indium and silicon was grown. The mixed crystal layer was grown at 1100 ° C. in a mixed gas flow (carrier gas) composed of argon gas and hydrogen gas set at a flow rate of 3 liters per minute and ammonia gas set at a flow rate of 4 liters per minute. did. Before the start of mixed crystal growth, a volume concentration of about 1.
Disilane (Si ₂ H ₆ ) gas diluted to 2 ppm was added at a flow rate of 5 ml / min. Next, the growth of the gallium nitride growth layer was started by mixing the carrier gas of the above composition with a hydrogen bubbling gas accompanied by trimethylgallium and trimethylaluminum vapor. At this time, the temperature of the stainless steel bubbler container containing trimethylgallium was set at 13 ° C. by using the commercially available ethylene glycol as a heat transfer (cooling) medium by the electronic constant temperature layer. The flow rate of hydrogen for bubbling liquid trimethylgallium was 5 ml / min. The temperature of the stainless steel bubbler container containing trimethylaluminum and having an inner surface mirror-polished was set at 25 ° C. using commercially available ethylene glycol as a heat transfer (cooling) medium by the same electronic thermostat as described above. The flow rate of hydrogen for bubbling the liquefied trimethylaluminum was 5 ml / min.

In this embodiment, the addition of the hydrogen bubbling gas accompanying trimethylgallium and trimethylaluminum to the carrier gas was started, and at the same time, the addition of the high-purity hydrogen gas accompanying the indium source was started. This is for obtaining an aluminum-gallium nitride mixed crystal layer doped with indium. As the indium source, Lewis acidic cyclopentadienyl indium, which hardly causes a gas phase reaction with Lewis basic ammonia, was used. The indium source was housed in a stainless steel bottle whose inner surface was mirror-polished as in Examples 1 to 3. The bottle was kept at 60 ° C. by an electronically controlled thermostat. A high-purity hydrogen gas was supplied at a flow rate of 20 ml / min for supplying the sublimated indium source to the growth reaction system together with the sublimated indium source in the bottle containing the indium source. The growth of the n-type gallium nitride layer doped with indium and silicon was continued for 90 minutes, with a time intended for a layer thickness of about 3.5 μm. Silicon is disilane (Si ₂ H
₆ ) High purity hydrogen containing about 1.2 ppm by volume of
Doping was performed by adding a mixed gas of disilane (Si ₂ H ₆ ) at a flow rate of 5 ml / min into the above carrier gas. Thus, an n-type gallium nitride layer doped with both indium and silicon was deposited as a second bonding layer on the gallium nitride buffer layer.

On the second bonding layer, an n-type gallium nitride layer serving as a first bonding layer doped with indium and silicon according to the conditions described in Embodiment 3, and indium, silicon and zinc are doped. A gallium nitride layer serving as a light emitting layer, an aluminum / gallium nitride mixed crystal layer doped with zinc and magnesium (upper cladding layer), and a gallium nitride layer doped with zinc and magnesium (contact layer) were sequentially deposited. On the aluminum-gallium nitride layer and the gallium nitride layer doped with zinc and magnesium, magnesium ions were implanted under the implantation conditions described in Example 3. Accordingly, a light emitting layer, a first bonding layer bonded to the light emitting layer, and a second bonding layer bonded to the first bonding layer are each provided with a bonding structure in which a gallium nitride based semiconductor layer doped with indium is used. A wafer was prepared.

The obtained wafer was subjected to ion thinning (ion).
Thinning was performed by the thinning method. Next, the cross section TE
Based on the bright field image picked up by the M method, observation was made mainly on the state of occurrence of dislocation near the interface between the first and second bonding layers and the interface between the first bonding layer and the light emitting layer. The number of dark contrast lines in the aluminum gallium nitride layer was reduced by about 15% as compared with the case of the third embodiment. In addition, although a very rare occurrence of dislocations was found near the interface between the first and second bonding layers, the occurrence of dislocations was observed at the bonding interface between the first bonding layer and the light emitting layer. The number was clearly lower than in the case of No. 3. The dislocation density of the light emitting layer is generally 5 to 10 ×
It was estimated to be 10 ⁴ cm ^-2 . In summary, although there are still dislocations penetrating the light emitting layer from the gallium nitride buffer layer almost linearly to reach the surface of the outermost gallium nitride contact layer, both the first and second bonding layers are indium doped layers. Was found to be effective in reducing the dislocation density of the light emitting layer.

Comparative Example 1 The same indium source as described in Example 1 was placed on an aluminum nitride / gallium mixed crystal layer (Al _0.01 Ga _0.99 N) having the same aluminum composition ratio as in Example 1 as 0.01. A gallium nitride layer doped with indium, silicon and zinc was stacked as a light emitting layer using a silicon source and a zinc source. However, in the light emitting layer in this comparative example, the distribution of the atomic concentrations of silicon and zinc was the same as in Example 1, but the distribution of the atomic concentration of indium was given in the thickness direction of the light emitting layer. And constant. That is, the light emitting layer in this comparative example is composed of gallium nitride as in Example 1, but differs from Example 1 in the atomic concentration distribution of indium.

During the growth of the light emitting layer, in order to give a substantially constant concentration distribution of indium atoms in the increasing direction of the thickness of the light emitting layer,
The supply amount of the indium source (cyclopentadienyl indium (I)) (the flow rate of the hydrogen gas accompanying the sublimated indium source) into the growth reaction system was kept constant at 20 ml / min. The holding temperature of the stainless steel storage container storing the indium source was a constant temperature of 60 ° C. An aluminum nitride-gallium mixed crystal layer and a gallium nitride layer were formed on the light-emitting layer having a substantially constant concentration distribution of indium atoms in the thickness direction under exactly the same conditions and operations as described in Example 1, and And

Comparative Example 2 As in Comparative Example 1, a gallium nitride layer in which the distribution of indium atom concentration was almost constant was used as the light emitting layer. In Comparative Example 2, the doping was performed so that the concentration distribution of indium atoms in the gallium nitride light emitting layer was substantially constant, and the atomic concentration of silicon (Si) was also constant in the increasing direction of the layer thickness in the light emitting layer. did.

In order to make the concentration of indium in the gallium nitride light emitting layer substantially constant in the thickness direction of the light emitting layer, the supply amount of the indium source into the growth system was kept constant without changing over time. As an indium source, cyclopentadienyl indium (C ₅ H ₅ In) having a monovalent valence is used consistently.
Was used. In growing a gallium nitride layer doped with indium, silicon, and zinc as a light emitting layer on an aluminum nitride-gallium mixed crystal layer having an aluminum composition ratio of 0.01, hydrogen gas accompanying the sublimated indium source was used. The supply rate to the growth reaction system was fixed at 20 ml / min. Exactly 5 minutes later, the addition of hydrogen gas accompanying the indium source into the growth reaction system was stopped. The zinc doping was performed according to the method and conditions described in Example 1.
On this light emitting layer, an upper clad layer composed of an aluminum nitride / gallium mixed crystal and a gallium nitride contact layer similar to those described in Example 1 were laminated.

The concentration distribution of the dopant in the layer thickness direction in the light emitting layer was analyzed by the SIMS method, and compared with the concentration distribution in Comparative Example 1. As a result, indium in Comparative Example 2 was distributed in the thickness direction of the light emitting layer almost similarly to that in Comparative Example 1. The gallium nitride light emitting layer doped with indium or the like and the aluminum composition ratio of the lower layer are set to 0.1.
The indium atom concentration at the bonding interface with the aluminum nitride-gallium mixed crystal layer, which was 01, was about 9 × 10 ¹⁷ cm ⁻³ . On the other hand, the indium concentration at the joint interface with the aluminum nitride-gallium mixed crystal (upper cladding layer) having an aluminum composition ratio of 0.12 was also about 1 × 10 ¹⁸ cm ⁻³ . That is, the indium atom concentration was almost constant as in Comparative Example 1. The atomic concentrations of silicon and zinc were also substantially constant in the thickness direction of the light emitting layer. The thickness of the light emitting layer determined from the concentration profile obtained by SIMS analysis is about 56 nm.
Met. In summary, the gallium nitride light emitting layer obtained in Comparative Example 2 was doped with dopants of indium, silicon, and zinc so as to be substantially constant in the increasing direction of the layer thickness. In the gallium nitride light emitting layer of Comparative Example 2, neither the donor impurity (silicon) nor the zinc (acceptor impurity) was distributed so as to be substantially in inverse proportion to the concentration distribution of indium atoms. The concentration distribution was almost the same as that of atoms.

Comparative Example 3 The structure was the same as that of Example 1 except for the gallium nitride light emitting layer. That is, an aluminum nitride / gallium mixed crystal layer having an aluminum composition ratio of 0.01 is provided below the gallium nitride light emitting layer on the substrate side, and an aluminum monium / gallium mixed crystal having an aluminum composition ratio of 0.12 is provided above the light emitting layer. The layers were joined. Therefore,
Comparing the aluminum nitride-gallium mixed crystal layer bonded to the gallium nitride light-emitting layer with the degree of lattice mismatch (defined by δ in the text) of the gallium nitride constituting the light-emitting layer, the gallium nitride light-emitting layer and the lattice mismatch The smaller the degree of matching (δ) is the aluminum-gallium nitride bonding layer having an aluminum composition ratio of 0.01.

Comparative Example In Comparative Example 3, a gallium nitride layer having an atomic concentration distribution different from that of Examples 1 to 4 and Comparative Examples 1 and 2 with respect to indium was used as the light emitting layer. The gallium nitride light-emitting layer of Comparative Example 3 is a gallium nitride-based bonding layer that bonds the atomic concentration of indium to the light-emitting layer, and is bonded to a bonding layer having a smaller degree of lattice mismatch, that is, a lower portion of the light-emitting layer. It is distributed largely in the direction of the interface with the aluminum nitride-gallium mixed crystal layer where the aluminum composition ratio is 0.12. The doping condition of silicon was the same as that of Example 2, and the doping condition of zinc was according to the method described in Example 1. Therefore, the gallium nitride light emitting layer of Comparative Example 3 is one in which the indium atom concentration is gradually reduced in the thickness direction of the light emitting layer, and silicon and zinc are doped so as to have a substantially constant atomic concentration.

The distribution of the atomic concentration of indium was adjusted by changing the growth temperature over time during the growth of the gallium nitride light emitting layer. That is, after growing an aluminum-gallium nitride mixed crystal layer (Al _0.01 Ga _0.99 N) doped with silicon at 1100 ° C., the substrate temperature is immediately increased to 770 ° C.
° C. After the substrate temperature was stabilized, the amount (flow rate) of cyclopentadienyl indium (I) (C ₅ H ₅ In (I)) supplied to the growth reaction system as an indium source during the growth of the light-emitting layer was changed every time. The growth of the light emitting layer was started in a state of being fixed at a constant value of 220 ml. From the start of the growth, the growth temperature was linearly increased to the growth temperature with the elapse of the growth time. The growth temperature was changed to 850 ° C. when the growth of the light emitting layer was completed exactly 5 minutes later. Therefore, the growth temperature change rate per unit time was 16 ° C./min.
After the growth of the light emitting layer doped with indium, silicon, and zinc is completed, the growth temperature is instantaneously increased to 1100 ° C. again, and the aluminum composition ratio is adjusted to 0.12 according to the growth method and conditions described in Example 1. An aluminum nitride-gallium mixed crystal (upper cladding layer) and a gallium nitride contact layer were sequentially laminated.

FIG. 22 shows the atomic concentration distributions of the indium, silicon, and zinc dopants in the gallium nitride light emitting layer obtained by the SISM analysis. The concentration of indium atoms (indicated by the symbol (In) in FIG. 22) is determined from the vicinity of the junction surface with the Al _0.01 Ga _0.99 N layer in the light emitting layer from Al _0.12 Ga
It gradually decreased in the direction of the bonding interface with _0.88 N. The concentration of indium atoms is about 2 × 10 ²⁰ cm ^-3 to 1
It decreased almost linearly to × 10 ¹⁸ cm ⁻³ . on the other hand,
The concentration distribution of silicon and zinc atoms (indicated by (Si) and (Zn) in FIG. 22 respectively) and the dopants which influence the conductivity type were almost constant in the layer thickness direction inside the light emitting layer. The feature of the gallium nitride light emitting layer of Comparative Example 3 from the viewpoint of the distribution of the dopant is that the atomic concentration of indium increases in the direction to reduce the degree of lattice mismatch, as opposed to Example 1, ie, the layer thickness Are distributed so that the atomic concentration gradually becomes smaller in the direction of increasing. In summary, the concentration distribution of indium atoms in the layer thickness direction is reversed from that of the light emitting layer described in the first embodiment.

The wafers formed by the methods described in Examples 1 to 4 and Comparative Examples 1 and 2 were processed under the same conditions to produce blue light emitting diodes (LEDs). First, titanium nitride (Ti) having a film thickness of about 100 nm is formed on the entire surface of each wafer by a general high frequency sputtering method.
N) A coating was formed. A silicon nitride (SiN) film having a thickness of about 150 nm was deposited on the titanium nitride film by plasma CVD using silane gas (SiH ₄ ) and ammonia gas (NH ₃ ) as raw materials. Next, a positive type AZ-1350 photoresist was spin-coated on the silicon nitride film. Thereafter, the resist material was patterned using a known ultraviolet photolithography technique. The chip shape of the LED drawn by patterning was common to each wafer, and was a square having a side of about 350 μm.

After removing only the resist material in the area where the scribe line and the n-type electrode (positive electrode) are to be arranged on the outer periphery of the square chip with a peeling material mainly composed of an aromatic compound, the resist material is exposed to the area. The silicon nitride film thus obtained was dissolved and removed with buffered hydrofluoric acid (HF). As a result, zinc and magnesium, which are the outermost layers of the wafer, are doped only in the area where the scribe line and the n-type electrode are to be formed, and the titanium nitride film on the surface of the gallium nitride contact layer into which magnesium is ion-implanted is exposed. Was.
Next, the titanium nitride film and the constituent layers of the wafer exposed by a general plasma etching method using a mixed gas of argon / methane / hydrogen and the like were removed by etching only in a region where an n-type electrode and a scribe line were to be formed. Plasma etching was performed in Examples 1 and 2 and Comparative Examples 1 and 2.
In the four wafers described in the above section, the process was advanced until the surface portion of the n-type aluminum nitride / gallium mixed crystal deposited on the low temperature buffer layer of gallium nitride was exposed. The plasma etching was performed on the wafers described in Examples 3 and 4 until the surface portion of the n-type gallium nitride layer was exposed. Due to this etching, a step was formed between the exposed surface of the region where the n-type electrode and the scribe line were to be formed and the surface of the outermost gallium nitride layer which was not etched. After completion of the etching, the photoresist material on the silicon nitride film was peeled off with an organic solvent mixed solution, leaving only the silicon nitride film. Again, after the above photoresist material was spin-coated on the entire surface of the wafer, the resist material was exposed and developed according to the shapes of the n-type and p-type electrodes (negative electrodes) to be formed, and patterned. After this patterning, the above-mentioned titanium nitride film was exposed in a region where the resist material was removed in the shape of the p-type electrode. On the other hand, the surface layer of the n-type gallium nitride layer or the n-type aluminum / gallium nitride layer was exposed in the region where the resist material was stripped in the shape of the n-type electrode. Thereafter, rod-shaped high-purity aluminum (Al) having a nominal purity of 6N (99.9999%) was applied to the entire surface of the wafer by a vacuum evaporation method. After taking out the wafer from the vacuum deposition apparatus, the aluminum-deposited wafer was immersed in a resist stripping solution, and the aluminum-deposited film deposited on the resist material was peeled off from the resist material by a normal lift-off method. By this lift-off step, rectangular opposing n-type and p-type electrodes each having a width of about 100 μm and a length of about 300 μm were formed.

A diamond blade (cutting blade) was moved along a scribe line provided so as to intersect the outer periphery of each chip in a lattice pattern, thereby achieving isolation (insulation) between the LED chips. Insulation between each chip (i
resolution) is retained,
The main optical and electrical characteristics of the LED chip were sampled and inspected using a general prober. Table 1 summarizes the measurement results for each example and each comparative example. The light emission intensity was measured using a photodetector (abbreviated as PD) in a chip state without molding with an epoxy resin. Both forward and reverse voltages have a current value of 10
It is the voltage value in volts (V) in microamps (μA).

[0091]

[Table 1]

As summarized in Table 1, there is no significant difference in the emission center wavelength. It is presumed that the subtle difference in the emission center wavelength is due to the subtle variation in the doping concentration of zinc for each growth. It was the emission intensity that caused a particularly significant difference in characteristics. From the comparison between Example 1 and Comparative Example 2, when the atomic concentration distributions of silicon and zinc were similar, the emission intensity clearly increased when the distribution of indium atomic concentration was assigned. In the case where the concentration of indium atoms in the gallium nitride light emitting layer is gradually increased toward the bonding interface with the gallium nitride based bonding layer, which increases the degree of lattice mismatch with the light emitting layer, the atomic concentration of silicon is reduced. The emission intensity was increased by making the opposite to the increasing / decreasing tendency of the indium atom concentration (as compared with Examples 1 and 2). On the other hand, when the distribution of the atomic concentration of silicon was the same, the emission intensity was increased by assigning the distribution to the indium atom concentration (according to the comparison between Example 2 and Comparative Example 1). Even when the indium atom concentration is the same, the emission intensity obtained increases when indium is increased toward the interface with the gallium nitride-based bonding layer, which has a higher degree of lattice mismatch (δ in the text). Was achieved (by comparison between Example 1 and Comparative Example 3).

The LED chips produced from the wafers described in Examples 1 to 4 were cut into single chips along a scribe line with a diamond scriber. Thereafter, the n-type and p-type electrodes were subjected to wire bonding so that the current between the two electrodes was measured via a lead wire. Typical electron beam induced excitation current method in this state, so-called abbreviated EBIC (E lectron B aam
It was observed LED chip cross section I nduced C urrennt) method. As a result, a band-like contrast was observed in a region near the interface between the aluminum-gallium nitride mixed crystal to which zinc and magnesium were added and the n-type gallium nitride light-emitting layer to which indium, silicon, and zinc were doped. Thus, the formation of a pn junction between the two layers became clear. This EBIC measurement is a general SEM
(Scanning electron microscope), the layer thickness is about 50
It was not possible to obtain a sufficiently high magnification to image a light emitting layer as thin as 〜60 nm with high resolution. Therefore, it is clearly determined whether the region where the contrast caused by the pn junction is maximum is located at the interface between the upper cladding layer made of the aluminum nitride-gallium mixed crystal and the gallium nitride light emitting layer or inside the upper cladding layer. I could not do it.

A region near the interface between the gallium nitride light-emitting layer and the aluminum-gallium nitride mixed crystal layer bonded thereto was observed by a cathodoluminescence (CL) method using a high-resolution analytical electron microscope (abbreviation: analytical electron microscope). As the sample, a chip obtained by thinning a chip used in the above EBIC method by an ion etching method using argon ions was used.
It is increased toward the interface between the Al _0.12 Ga _0.88 N mixed crystal layer that the atomic concentration of indium larger lattice mismatch between the gallium nitride light emitting layer ([delta] in the text) as described in Example 1 In some cases, the CL intensity near the interface between the upper cladding layer and the light emitting layer was found to be stronger than in other regions. In a light emitting layer in which indium atoms are present at a substantially constant concentration as in Comparative Examples 1 and 2, C
There was no tendency for the L intensity to increase. In a chip in which indium atoms are increased toward an Al _0.01 Ga _0.99 N mixed crystal layer that _{reduces the} degree of lattice mismatch with gallium nitride constituting the light emitting layer (see Comparative Example 3), Al _0.01 Ga
It was observed that the CL intensity at the interface between the _0.99 N mixed crystal layer and the gallium nitride light emitting layer was slightly increased as compared with the other regions. Regardless of the distribution of CL intensity in the light emitting layer, it is a qualitative judgment for visual observation, but the overall intensity from the light emitting layer is expressed by It was the largest when increasing toward the larger bonding layer. Conversely, when the concentration distribution of indium atoms is increased in the direction of the interface with the bonding layer where δ is small, the CL intensity is rather weak as compared with the case where the atomic concentration distribution of indium in the light emitting layer is substantially constant. Met. In the case where the atomic concentration distribution of indium is the same, the distribution of the doping concentration is given to either the donor or the acceptor impurity (in the present embodiment and this comparative example, the donor impurity is given a concentration distribution) to increase the CL intensity. An increasing trend was observed. In particular, the CL intensity increased when the atomic concentration distribution of doped silicon was substantially opposite to that of indium atoms. The magnitude of the CL intensity matched the magnitude of the emission intensity (see the emission intensity of Examples 1 and 2 in Table 1). When the indium atom concentration is increased in the interface direction of the bonding layer where δ is large and the silicon atom concentration distribution is substantially reversed, the CL intensity observed from the light emitting layer portion is obtained by doping the light emitting layer with indium. It further increased by joining the gallium nitride based compound semiconductor layer. Since the CL intensity is arranged below the light emitting layer, it seems that the CL intensity tends to increase as the number of indium-doped gallium nitride-based compound semiconductor layers increases. This increase in CL intensity was considered to correspond to the tendency of increase in light emission intensity of the LED chips of Examples 3 and 4 shown in Table 1.

The magnitude of the CL intensity substantially corresponds to the intensity of the light emission intensity of the LED chip. Here, if the key points inferred from the CL measurement result are simply described,
The CL intensity is increased when the concentration distribution of indium atoms is increased in the direction of the interface between the nitride compound semiconductor constituting the light emitting layer and the bonding layer having a large degree of lattice mismatch.
Although the cause cannot be conclusively determined, the doping of indium in the junction region where lattice strain exists due to lattice mismatch in the first place in a larger amount than in other regions results in the accumulation of more indium in that region. Is also presumed to be relevant. It is presumed that even if the concentration of indium atoms is distributed so as to increase in the direction of the interface having a small degree of lattice mismatch, the lattice strain is small, so that accumulation of indium at a very small concentration does not occur. It is considered that an appropriate doping concentration range of indium atoms for increasing the emission intensity is determined depending on the amount of indium accumulated at this interface. It is not clear whether or not indium accumulated toward the junction interface locally causes further strain near the interface, and influences on the electronic state such as emission center impurities near the interface.

[0096]

According to the present invention, there is provided a light emitting device made of a nitride compound semiconductor, which has an effect of increasing light emission intensity.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of a conventional blue LED.

FIG. 2 is a schematic sectional view showing the structure of a conventional green LED.

FIG. 3 is a diagram showing a relationship between an indium concentration and photoluminescence intensity.

FIG. 4 is a diagram illustrating an indium concentration distribution inside an active layer according to the present invention.

FIG. 5 is a diagram for explaining an initial concentration (N ₀ ) and a final concentration (N) of indium.

FIG. 6 is a diagram showing a difference in luminescence intensity in comparison.

FIG. 7 is a schematic plan view of a blue LED according to the first embodiment.

8 is a schematic cross-sectional view of the LED shown in FIG. 7 taken along a broken line AA ′.

FIG. 9 is a diagram showing a change over time in the temperature of the substrate during the growth process of the laminate described in Example 1.

FIG. 10 is a diagram showing a change over time of a hydrogen gas flow rate in Example 1.

FIG. 11 is a diagram showing a change over time in the flow rate of argon gas in Example 1.

FIG. 12 is a diagram showing a change over time in the flow rate of ammonia gas in Example 1.

FIG. 13 shows a growth process of the laminate described in Example 1.
It is a figure which shows the change of the supply amount of a group III raw material.

FIG. 14 is a diagram illustrating a change in the supply amount of trimethylgallium during the growth process of the stacked body described in Example 1.

FIG. 15 is a diagram showing a change in the supply amount of trimethylaluminum during the growth process of the laminate described in Example 1.

FIG. 16 is a diagram showing current-voltage characteristics for a surface layer portion of the laminate described in Example 1.

FIG. 17 is a diagram showing a concentration distribution in the depth direction of a constituent element and a dopant inside the laminate described in Example 1.

FIG. 18 is a view showing a growth temperature profile of Example 2.

FIG. 19 is a diagram showing a change over time in the flow rate of a raw material carrier gas in Example 2.

FIG. 20 is a diagram showing a change over time in a flow rate of a dopant gas in Example 2.

FIG. 21 is a diagram showing a concentration distribution of a dopant in a depth direction in Example 2.

FIG. 22 is a diagram showing a concentration distribution in a depth direction of a dopant of Comparative Example 3.

[Explanation of symbols]

(101) Substrate (102) Buffer layer (103) Lower cladding layer (104) Active layer (light emitting layer) (105) Upper cladding layer (106) Contact layer (107) Intermediate layer (108) Joining to active layer Bonding layer (109) bonding layer bonded to the active layer (110) bonding interface between the active layer and the bonding layer that increases the degree of lattice mismatch between the active layer and (111) a curve showing the concentration distribution of indium atoms. (112) Distribution curve indicating that the concentration of indium atoms is increasing stepwise (113) Other distribution curve indicating that the concentration of indium atoms is increasing stepwise (114) 5 is a diagram showing a room temperature photoluminescence spectrum of Example 1; (116) A diagram showing a room temperature photoluminescence spectrum of Comparative Example 1. FIG. (117) Lower cladding layer (118) Active layer (light emitting layer) (119) Upper cladding layer (120) Current after forming nitride compound semiconductor laminate
Curve indicating voltage characteristics (121) Curve indicating current-voltage characteristics after ion-implanting and annealing a nitride compound semiconductor laminate (122) P-type electrode (123) N-type electrode (124) Active layer and Bonding interface with the bonding layer to make the degree of lattice mismatch with the active layer smaller

Claims (5)

[Claims] 1. A gallium (Ga) -based III on a single crystal substrate
A nitride having a junction structure composed of an active layer made of a group III nitride compound semiconductor, a first nitride compound semiconductor layer of a first conductivity type, and a second nitride compound semiconductor layer of a second conductivity type Compound semiconductor device, wherein the active layer has an atomic concentration of not less than 8 × 10 ¹⁷ cm ^{−3 and not} more than 4 × 10 ²⁰ cm ⁻³ , and a concentration distribution is applied in one direction of the layer thickness to form indium (In). A nitride compound semiconductor device, which is doped. 2. The active layer has a concentration distribution that increases the atomic concentration of indium toward a junction interface with a first or second nitride compound semiconductor that increases the degree of lattice mismatch with the active layer. The nitride compound semiconductor device according to claim 1, wherein: 3. An active layer doped with both a donor and an acceptor impurity, wherein one of the donor and the acceptor is doped at a substantially constant atomic concentration in the thickness direction of the active layer, and the other is doped with the other impurity. 3. The nitride compound semiconductor device according to claim 1, wherein the impurity is doped in a layer thickness direction with a concentration distribution substantially inversely proportional to an atomic concentration of indium. 4. An active layer, wherein one of the first and second nitride compound semiconductor layers to be joined to the active layer is made of the same nitride compound semiconductor material as the active layer doped with indium. 4. The nitride compound semiconductor device according to claim 1, wherein 5. The nitride according to claim 5, wherein the first or second nitride compound semiconductor layer doped with indium is joined to the nitride compound semiconductor layer doped with indium. Compound semiconductor device.