JP2000012896A - Group iii nitride semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a base laminate layer by constituting a III-V compd. semiconductor single crystal substrate from GaAs, a buffer layer on the substrate surface from specified B phosphide-based III-V compd. semiconductor single crystal and a III compd. semiconductor crystal layer making a junction with the buffer layer from specified BP nitride ternary mixed crystal. SOLUTION: On a BP-based buffer layer 102, a III compd. semiconductor crystal layer advantageously acting to make the lattice-matching with an Al nitride Ga-In mixed crystal (AlxGayInzN: 0<=x, y, z<=1, x+y+z=1) is bonded and constituted from a BP nitride ternary mixed crystal 106 (BP1-xNx: 0<x<1), because BP1-xNx ca be lattice matching the AlxGayInzN mixed crystal. A base laminate layer system composed of a bond structure of the BP-based buffer layer 102 and BP1-xNx 106 which can lattice match the BP-based buffer layer 102 with the AlxGayInzN.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for forming a group III nitride semiconductor device from a laminated structure comprising a cubic group III nitride semiconductor crystal. In particular, the present invention relates to a technique for forming a group III nitride semiconductor device from a laminated structure including a buffer layer suitable for providing a continuous cubic group III nitride semiconductor crystal layer.

[0002]

2. Description of the Related Art In general, a device called a group III nitride semiconductor device includes a light emitting diode such as a short wavelength visible light emitting diode (abbreviation: LED) such as blue or a laser diode (abbreviation: LD) such as a laser diode. There is an element (Ma
t. Res. Soc. Symp. Proc. Vol.
449 (1997), pp. 509-518). Further, for example, there is an electronic device such as a Schottky junction field effect transistor (abbreviation: MESFET) (Proc. OF THE TOPICAL).
WORKSHOP ON III -V NITRIDE
S (21-23. Sept. 1995) (PERGAM
ON PRESS), pages 97-100).

[0003] These group III nitride semiconductor devices, which are not bulk devices but belong to the category of thin film devices, have a composition formula of Al _A Ga _B In _C M _{1 -Z} N _Z (0 ≦
A, B, C ≦ 1, A + B + C = 1, 0 <Z ≦ 1, symbol M
Represents a Group V element other than nitrogen. ) Is used as a material. For example, a field effect transistor (English abbreviation: FE)
T) is a mixed crystal of aluminum nitride and gallium (Al _A Ga
_{B N: 0 ≦ A ≦ 1} , A + B = 1) the active layer (and a layered structure comprising a channel layer). In addition, short-wavelength visible LEDs and LDs are made of gallium nitride-indium mixed crystal (Ga _B In _C N: 0 ≦ B ≦ 1, B + C = 1).
As a light emitting layer (active layer).

[0004] Conventional laminated structures for practical use in Group III nitride semiconductor devices include sapphire (α-Al).
Usually, an insulating hexagonal single crystal such as ₂ O ₃ single crystal or silicon carbide (6H—SiC) is used as a substrate. However, for example, the degree of lattice mismatch between the sapphire substrate and gallium nitride (GaN), which is a group III nitride semiconductor, is 13.
8% size ("Journal of Japan Society for Crystal Growth", Vo
l. 15, No. 3 & 4 (1988), pp. 74-82). Therefore, in order to alleviate the lattice mismatch, it has conventionally been general to arrange a buffer layer on the surface of the sapphire substrate (see JP-A-2-229476). Buffer _{layer, Al A Ga B N (0} ≦ A
.Ltoreq.1, A + B = 1) It is a general prior art to comprise a mixed crystal (see JP-A-2-229476 and JP-A-4-297923). The buffer layer is
Since it is formed at a relatively low temperature of about 400 ° C. to about 600 ° C. in practical use, it is called a low-temperature buffer layer (edited by Isamu Akasaki,
"III-V Group Compound Semiconductor" (May 20, 1994, first edition, published by Baifukan Co., Ltd.), page 334).

[0005] However, the conventional laminated structure using sapphire or hexagonal silicon carbide (6H-SiC) as a substrate has a number of problems in constituting a group III nitride semiconductor device. For example, (1) there is a problem of forming a smooth mirror-surface laser light resonance surface due to the substrate not exhibiting a clear cleavage. Also, (2) the location of the ohmic electrode is restricted due to electrical insulation (Elect).
ron. Lett. , 33 (23) (1997), 19
86-1987). Also, wurtzite (urzi)
te) type hexagonal low-temperature buffer layer (JP-A-2-22947)
No. 6 (see Japanese Patent Application Laid-open No. 6-316), a laminated structure composed of hexagonal group III nitride semiconductor crystal layers is formed by piezo (pi).
Ezo) effect (piezoelectric effect) appears. In a device such as an FET that utilizes the high-speed traveling property of carriers (particularly, electrons), the mobility of electrons is affected by the effects of piezoelectric scattering (see “III-V compound semiconductor” described above, page 178). There is a disadvantage that the improvement is hindered.

For this reason, instead of a hexagonal substrate such as sapphire, a cubic substrate such as a III-V compound semiconductor crystal or diamond-structured silicon (silicon) is used.
Attempts have also been made to stack group III nitride semiconductor crystals (J. Electrochem. Soc., 120 (1)
2) (1973), pages 1783-1785). In such prior art examples, gallium arsenide (GaAs)
s) and zinc blende-type cubic crystals such as gallium phosphide (GaP) are used as a substrate material (see the above-mentioned document J. Electrochem. Soc.).

[0007] Recently, gallium nitride (GaN) has been formed by bonding to a gallium phosphide (GaP) intermediate layer on a silicon (Si) single crystal substrate ("Blue Laser").
rand Light Emitting Diode
s "(Ohmsya, Ltd., 1996), 526-
See page 529). In addition, an LED is provided via a hexagonal aluminum nitride (AlN) buffer layer provided on the surface of the Si substrate.
A laminated structure for use is configured (Appl. Phy
s. Lett. , 72 (4) (1998), 415-4
See page 17). In this stacked system, the GaN layer is directly joined to the AlN buffer layer.

Further, there is disclosed a technique intended to construct the entire laminated structure including a substrate material from a cubic crystal (Japanese Patent Application Laid-Open Nos. 2-275682 and 2-2).
88371 and JP-A-2-288388. In this prior art, as a substrate material, silicon (silicon), gallium phosphide (GaP) or silicon carbide (3C-SiC) is proposed as a cubic single crystal material (Japanese Patent Laid-Open No. 2-275682). Gazette). On these cubic single-crystal substrates, cubic
A technique of disposing a buffer layer made of zinc blende-type boron phosphide (BP) to form a group III nitride semiconductor crystal layer is also disclosed (see Japanese Patent Application Laid-Open No. 2-275682 and the like). ).

BP is considered to be an excellent cubic material for forming a buffer layer for growing a cubic group III nitride semiconductor crystal layer. A laminated structure having a heterojunction between a BP buffer layer and a group III nitride semiconductor crystal layer is also disclosed (JP-A-2-275682). However, simply forming a film of BP as a buffer layer on a cubic crystal substrate of gallium phosphide (GaP) or the like does not always provide a continuous crystal layer. For example, a boron monophosphide (boron) is formed on a Si substrate.
The case where a buffer layer composed of monophosphide (BP) is formed will be described as an example. The lattice constant of Si is 5.431 ° and the lattice constant of BP is 4.538 ° (see the above “III-V compound semiconductor”, p. 148). Therefore, the degree of mismatch between the two lattices reaches 16.4% based on Si. Due to this large mismatch, a BP film simply grown on a Si substrate is actually a film lacking continuity in which pyramid-shaped growth islands are scattered (see the above-mentioned “Journal of the Japan Society for Crystal Growth”, Vol. 24, No. 2
No. (1997), p. 150). Such a discontinuous B
On the surface of the P film, of course, there is a continuity III
It is difficult to form a group III nitride semiconductor crystal layer.

Even if a buffer layer made of BP is simply provided, an upper layer, for example, a group III nitride semiconductor crystal layer, which is laminated thereon, is not always constituted mainly of cubic crystals. There is also a problem related to inconsistency in the upper layer crystal morphology. For example, a GaN film formed by bonding to a BP crystal layer on a Si single crystal substrate is actually a mixture of cubic and hexagonal crystals (Inst. Ph.
ys. Conf. Ser. , No. 129 (Inst.
of Phys. (IOP) Publishing L
td. (London, 1993), pp. 157-162). That is, at present, the conventional BP buffer layer does not reliably achieve the uniformity of the upper crystal system.

[0011]

For the purpose of avoiding the problems associated with the hexagonal system laminated structure, the prior art for constructing a laminated structure from a cubic group III nitride semiconductor crystal layer has also been proposed. As described above, there are problems to be overcome. If the technique is limited to a technique of forming a laminated structure using a boron phosphide (BP) or the like as a buffer layer on a cubic single crystal substrate, first, an upper layer made of a group III nitride semiconductor crystal having continuity is provided. The constitutional requirements of a suitable BP buffer layer are unclear.

According to the present invention, a cubic III
-BP to bring about growth of group V compound semiconductor crystal layer
The purpose is to specify the requirements that the system buffer layer should have. In particular, preferred components are clarified from the internal crystal structure.

[0013] Boron phosphide (BP) also has a lattice mismatch of about 0.6% with cubic GaN having a lattice constant of 4.510 °. However, the degree of lattice mismatch with cubic aluminum nitride (chemical formula: AlN) having a lattice constant of 4.380 ° is about 3.6% based on BP. The degree of lattice mismatch with cubic indium nitride (chemical formula: InN) having a lattice constant of 4.980 ° reaches about 9.7% based on BP. Therefore, in order to form a group III nitride semiconductor active layer that reduces the density of crystal defects caused by lattice mismatch, it is necessary to provide a lattice mismatch between the group III nitride semiconductor active layer and the BP-based buffer layer. It is advisable to insert a group III nitride semiconductor crystal layer capable of alleviating the property and form a base laminate system.

Therefore, the present invention relates to a laminated structure including a group III nitride semiconductor crystal layer joined to a buffer layer provided on the surface of a group III-V compound semiconductor single crystal substrate, as in the prior art. directly on the crystal _{layer, Al a Ga B N (0} ≦ a,
A system different from a stacked system for joining a group III nitride semiconductor crystal layer, such as B ≦ 1, A + B = 1), is presented. And a junction structure between a buffer layer having a cubic upper layer having continuity and a group III nitride semiconductor crystal layer which provides good lattice matching to a group III nitride semiconductor active layer having a low crystal defect density. It is also an object of the present invention to provide a base laminate system comprising:

[0015]

That is, the present invention has been made on the background of the above-mentioned problems of the prior art, and the invention of claim 1 is directed to a III-V compound semiconductor single crystal substrate. And a buffer layer provided on the surface of the substrate, and a group III nitride semiconductor device having a stacked structure including a group III nitride semiconductor crystal layer bonded to the buffer layer. The group-III compound semiconductor single crystal substrate is made of gallium arsenide (chemical formula: GaAs), and the buffer layer provided on the surface of the substrate is made of a boron phosphide polymer crystal (B _i P _j : i>
1, j ≧ 1) boron phosphide (B
P) A group III nitride semiconductor crystal layer composed of a III-V group compound semiconductor crystal and forming a junction with the buffer layer is formed of a ternary mixed crystal of boron phosphide (BP ₁ -XN _X : 0 <X < 1) or ternary mixed crystal of boron arsenide (BAs _1-Y N _Y : 0 <Y <1)
And a group III nitride semiconductor device characterized by comprising:

The present invention further provides, in addition to the structure described in claim 1, a crystalline material which has good lattice matching with GaAs and is convenient for forming a low-temperature buffer layer. That is, the invention of claim 2, said buffer layer, boron indium phosphide mixed crystal _{(B U In W P: 0} <U <0.3
2, U + W = 1).

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Cubic crystals include magnesium oxide (chemical formula: MgO) and manganese oxide (chemical formula: Mn).
O), nickel oxide (chemical formula: NiO), and cobalt oxide (chemical formula: CoO). Perovskite-type lithium niobate (chemical formula: LiNb
O ₃ ) and lithium tantalate (chemical formula: LiTaO ₃ )
Are also cubic. LiGaO ₂ or Li
AlO _{2 and the} like are also cubic crystals. There are also metals with an equiaxed cubic lattice such as nickel (element symbol: Ni). In the present invention, a cubic crystal is particularly preferably a zinc-blende structure type III-V
A substrate is composed of gallium arsenide (GaAs) single crystal, which is a group III compound semiconductor. The conductive GaAs is used for the LED because of its superiority in the arrangement of the ohmic electrode.
It is suitable as a substrate material when constituting a light emitting element such as a laser diode and an LD. In a group III nitride semiconductor device requiring electrical insulation between an active layer such as an FET and a substrate, a high-resistance semi-insulating GaAs single crystal can be used as the substrate. In addition, sphalerite crystal-type GaAs exhibits a clear cleavage property in the [011] crystal orientation. Therefore, for example, in the case of an LD using GaAs as a substrate, there is an advantage that a laser light resonance surface having a {011} plane can be easily formed.

The BP-based buffer layer of the present invention comprises the above GaAs
It is provided on the surface of the single crystal substrate by using a conventional epitaxial growth method. To form the buffer layer according to the present invention,
The vapor phase growth method (VPE method) is more suitable than the liquid phase epitaxial growth method (LPE method). Halogen VP made from chloride such as boron trichloride (BCl ₃ )
When the BP-based buffer layer according to the present invention is formed by the E method, a film formation temperature of 300 ° C. or more and 600 ° C. or less is suitable. In addition, since the buffer layer of the present invention contains phosphorus (element symbol: P) as a constituent element, a metalorganic thermal decomposition chemical vapor deposition (MOCVD) method is also particularly preferable. MO
When the buffer layer of the present invention is obtained by the CVD method, film formation at a temperature in the range of 250 ° C. or more and 500 ° C. or less is suitable. The preferable range of the film forming temperature varies depending on the growth method and the growth conditions, but is generally in the range of 250 ° C. to 600 ° C.

In such a BP-based crystal layer formed at a relatively low temperature, the region near the junction interface with the cubic substrate is mainly composed of a single crystal, and the region above it is mainly composed of amorphous. The feature is that it is done. When the film forming temperature of the BP-based crystal layer serving as the buffer layer is approximately 200 ° C. or lower, almost the whole becomes an amorphous body. At a high temperature of about 650 ° C. to over 700 ° C., on the contrary, almost the whole is composed of a single crystal.
The temperature suitable for forming the BP-based buffer layer according to the present invention is not a temperature at which a buffer layer substantially entirely composed of single crystal or amorphous is obtained, but as described above, from the bonding interface with the substrate. This is a temperature at which a buffer layer having a configuration in which a main component is changed from single crystal to amorphous in the layer thickness direction can result.

In order to explain the structure of the BP-based low-temperature buffer layer of the present invention, FIG. 1 schematically shows a cross-sectional structure of the buffer layer. FIG. 1 illustrates an internal crystal structure of a low-temperature buffer layer 102 made of boron phosphide (BP) formed on a gallium arsenide (GaAs) single crystal substrate 101. In FIG. 1, the vicinity of a bonding interface 103 with the substrate 101 in the low-temperature buffer layer 102 is a region 104 in which a single crystal (single crystal layer or single crystal grain) is mainly arranged. Above that is a region 105 mainly composed of an amorphous body. The single crystal layer or the single crystal constituting the region near the bonding interface acts so that the crystal layer formed on the surface of the low-temperature buffer layer becomes a continuous film. In particular, a low-temperature buffer layer in which a single crystal layer covers almost the entire surface of a substrate has a remarkable effect in obtaining a continuous crystal layer as an upper layer. This is because the presence of the layered single crystal promotes the growth of a two-dimensional (planar) crystal layer. The thickness (indicated by the symbol “d” in FIG. 1) of the region 104 mainly composed of a single crystal (layer) is about 1 of the entire layer thickness (indicated by the symbol “D”) of the low-temperature buffer layer 102. / 2. That is, generally, d <0.5 · D. As the film formation temperature is higher, d tends to be larger. The region 105 mainly composed of an amorphous body has the function of unifying the orientation of the crystal layer deposited as the upper layer of the low-temperature buffer layer.

Further, according to the present invention, the crystalline substances constituting the low-temperature buffer layer are regulated in a quantitative relationship. Particularly, in the present invention, boron phosphide (boron monophosphide: b) composed of boron (element symbol: B) and phosphorus (element symbol: P) atoms
The low-temperature buffer layer is mainly composed of oron monophosphide (BP). A so-called boron phosphide polymer crystal (B _i P _j : i> 1, j ≧ 1) containing a plurality of boron atoms is a modified BP crystal. Representative examples of the boron phosphide multimeric crystal include B ₆ P and B ₁₃ P ₂ having a boron atom number (i) of 6 or 13 (see Acta. Cryst., 14 (1961), p. 93). ). These multimeric crystals are rhombohedral (rhombo)
Hexagonal crystal having a hexadral crystal structure
nal) crystal (J. Amer. Cer. So
c. , 47 (1964), pp. 44-47). Therefore, when a large amount of such hexagonal crystals are present in the buffer layer, a growth layer having a hexagonal crystal morphology is likely to be grown using these crystals as growth nuclei. For this reason, it is inconvenient for the purpose of the present invention to obtain a growth layer mainly composed of cubic crystals.
To obtain a growth layer mainly composed of cubic crystals in which the volume occupied by the cubic crystals exceeds 90%, it is necessary to use B _i P _j
(Generally, i> 6 and j = 1 or 2) The content of the multimeric crystal is set to 10% or less. Preferably, it is 5% or less.

The BP-based buffer layer in which the content of the boron phosphide multimeric crystal (B _i P _j ) is suppressed to a low level can be obtained by setting the film forming temperature low. The film formation temperature is about 70 at 250 ° C. or more.
0 ° C or less is suitable. BP changes to B ₁₃ P ₂ in a high-temperature environment according to the following chemical reaction formula (1) (J. Amer. C.
hem. Soc. , 82 (1960), 1330-13
See page 32). 52 BP → 4 B ₁₃ P ₂ +11 P ₄ ... Reaction formula (1) Accordingly, in order to reduce the content of the boron phosphide multimeric crystal, it is advantageous to lower the film forming temperature of the buffer layer. Becomes In order to stably keep the content of the boron phosphide multimer crystal at 5% or less, the range of the film formation temperature is suitable for obtaining the buffer layer composed of the above-mentioned single crystal body and amorphous body. It is again convenient to set the temperature to 250 ° C. or higher and 600 ° C. or lower, which is the same as the range of the film forming temperature. By setting the content of the boron phosphide multimeric crystal to 5% or less, a growth layer mainly composed of cubic crystals can be formed.

Crystals constituting the low-temperature buffer layer, for example, B
The quantitative relationship between P and B ₁₃ P ₂ can be measured by comparing the X-ray diffraction intensity from a specific crystal plane obtained by the X-ray diffraction method. Knowing in advance the diffraction intensity from a specific crystal plane that is convenient for quantification of BP and B ₁₃ P _{2 from} a standard sample, BP
And B ₁₃ P ₂ are conveniently separated and quantified.

According to the present invention, (1) it is composed of a single crystal and an amorphous substance, and (2) the content of the boron phosphide multimer crystal such as B ₁₃ P ₂ is 5% or less. BP
On the system buffer layer, a growth layer composed mainly of cubic crystal and having excellent continuity can be joined and laminated.

Taking advantage of this advantage, in the present invention, an aluminum-gallium-indium mixed crystal (Al _X Ga _Y In _Z N: 0 ≦ X, Y, Z ≦ 1, X
+ Y + Z = 1) is bonded to a group III nitride semiconductor crystal layer which works well for achieving lattice matching. In the present invention, the group III nitride semiconductor crystal layer to be bonded to the buffer layer is composed of a ternary mixed crystal of boron nitride phosphide (BP ₁ -XN _X : 0 <X <1). Alternatively, a ternary mixed crystal of boron arsenide (BAs
_{1-Y NY} : 0 <Y <1). This is because BP _1-X N _X or BAs _1-Y N _Y can be lattice-matched to Al _X Ga _Y In _Z N mixed crystal depending on the nitrogen composition ratio (= X, Y). That is, in the present invention, the BP-based buffer layer described above,
BP _{1-X that} can achieve lattice matching with Al _X Ga _Y In _Z N
Providing a base laminate system comprising a joining structure of the N _X or BAs _1-Y N _Y.

For example, from BP _0.97 N _0.03 having a nitrogen composition ratio of 0.03 (3%), a crystal layer which performs lattice matching with cubic gallium nitride (GaN) having a lattice constant of 4.510 ° is formed. it can. Also, from BP _0.83 N _0.17 ,
Cubic aluminum nitride (AlN; lattice constant = 4.3)
80 °) and a crystal layer that performs lattice matching can be formed. BA
s ₁ -YN _Y can be used as a crystal layer that is superior in performing lattice matching with a cubic indium nitride-based mixed crystal having a relatively high indium composition ratio. For example, BAs _0.97 N _0.03 becomes a crystal layer that lattice-matches with cubic Ga _0.50 In _0.50 N having an indium composition ratio of 0.50.

The above-mentioned BP _1-X N _X or BAs _1-Y N _Y
Since the crystal layer is deposited so as to be bonded to the buffer layer according to the configuration of the present invention, continuity is provided, the crystal layer can be mainly composed of cubic crystals, and lattice matching with Al _X Ga _Y In _Z N is achieved. Therefore, an Al _X Ga _Y In _Z N crystal layer in which the density of crystal defects caused by lattice mismatch or film discontinuity is reduced is formed on the underlying laminated system having the junction structure of the present invention. Can be laminated.

The present invention further provides a low-temperature buffer layer which is favorable for providing good lattice matching with a III-V compound semiconductor single crystal substrate and providing a continuous upper layer mainly composed of cubic crystals. Material can be provided. For GaAs single crystal, B _U In _W P mixed crystal (0 <U <1, U + W
= 1) with boron composition ratio (= U) of 0.16 B
_A lattice-matched buffer layer can be formed from _0.16 In _0.84 P.
The composition ratio of the mixed crystal that achieves lattice matching with the substrate crystal is determined by Vegard's law (by Haruo Nagai et al., “III−
Group V Compound Mixed Crystal "(First Edition, Second Edition, July 30, 1993,
(Corona Co., Ltd.), page 27). When configuring the low-temperature buffer layer from B _U In _W P mixed crystal, boron compositional ratio assigned to the obtained upper layer with continuity, approximately based on the 0.16, in the range of ± 50%. Preferably, it is 0.16 ± 30%. That is, a preferable boron composition ratio is in a range of 0.11 or more and 0.21 or less.

The low-temperature buffer layer that provides good lattice matching with the substrate can be composed of a single crystal layer. In addition, a plurality of crystal layers having different composition ratios may be stacked. For example, a strained superlattice structure (strained layer structure)
There is a method of forming a buffer layer having a multi-layer structure by forming an upper layer. When constituting the buffer layer from the strained superlattice structure, the composition ratio of n-crystal layer overlaying (e.g., boron composition ratio of the above B _U In _W P mixed crystal) are crystalline and identical constituting the substrate It is preferable to design so as to give the same amount of change in the lattice constant in the increase / decrease direction based on the above composition ratio that provides the lattice constant. Such as the above-mentioned B _U I
When forming a buffer layer having a strained superlattice structure from n _W P mixed crystal,
0.16 which is a boron composition ratio that achieves lattice matching with GaAs.
± 0.08 (8%)
B _0.08 In _0.92 P and B _0.24 In _0.76 P
Are alternately layered to form a lattice-matched buffer layer having a strained superlattice structure. The boron composition ratio was 0.08 and 0.2, respectively.
The average boron composition ratio of the superlattice structure having a two-layered multilayer structure composed of two BInP crystal layers as a set of 4 is 0.1.
This is because it becomes 6. When constituting the buffer layer from the strained superlattice structure, B _U In _W P mixed crystal constituting the same structure (0 <U <
1, U + W = 1) Since the maximum fluctuation range of the boron composition ratio (= U) that the layer can take is ± 0.16, the possible range of the boron composition ratio is 0 <U <0.32. Become.

The buffer layer is smaller crystal defect density due to lattice mismatch, BP _1-X N _X or BAs excellent further crystal quality consistent with such a GaAs substrate material lattice
Contributes to providing a _{1-YN Y} crystal layer. BP _1-X N in the _X or BAs _1-Y N Y-crystal layer excellent in crystal quality, Al _X Ga _Y In _Z N crystal layer excellent in crystallinity can be deposited. From the high quality Al _X Ga _Y In _Z N crystal layer,
An active layer such as a light-emitting layer which is convenient for providing light emission excellent in intensity and a channel layer which is excellent in electron mobility can be formed. These active layers having excellent quality contribute to providing a group III nitride semiconductor device having excellent characteristics such as emission intensity and noise figure.

The thickness of the crystal layer constituting the buffer layer and the thickness of the BP _1-X N _X or BAs _1-Y N _Y crystal layer bonded to the buffer layer are not particularly strictly specified. Relatively thick crystalline layers of the order of a few μm can also be used. The upper limit of the thickness of the crystal layer is generally less than about 10 μm. In order to form a growth layer having continuity mainly composed of cubic crystals in which the proportion of cubic crystals exceeds approximately 90% in volume ratio, the buffer layer may be a monoatomic layer of about several Å.

BP _1-X N _X or B bonded to the buffer layer
The As ₁ -YN _Y crystal layer is formed by a halide VPE method (halogen VPE method) or MO as in the case of the buffer layer.
A film can be formed using a CVD method or the like. When a conductive crystal is used as a substrate for the purpose of laying an ohmic electrode on the back surface side of a substrate material such as a laminated structure used for a light emitting element, a buffer layer and a BP ₁ -XN bonded to the buffer layer are used. _It is customary to use an _X or BAs _{1-Y NY} crystal layer as the conductive layer. The conductivity of the crystal layer is not particularly limited, and can be determined in consideration of, for example, the conductivity type of the conductive substrate. N-type conductive doped donor impurities or acceptor impurities or crystal layer having a p-type conductivity, BP _1-X N _X or BAs _1-Y N _Y which is bonded to the buffer layer and the buffer layer
It can be used as a crystal layer. The n-type conductive crystal layer is made of, for example, a fourth IV material such as silicon (Si) or tin (element symbol: Sn).
It can be obtained by doping a group VI impurity such as a group VI impurity or a group VI impurity such as selenium (element symbol: Se) and sulfur (element symbol: S). The p-type crystal layer is made of, for example, a group II impurity such as zinc (element symbol: Zn) or magnesium (element symbol: M
g) or by doping with Group IV carbon (element symbol: C).

[0033]

The BP-based buffer layer formed in the temperature range according to the first aspect of the present invention has the function of using the crystal layer constituting the upper layer as a continuous film. Further, the BP-based buffer layer in which the content of the boron phosphide multimeric crystal is reduced has an effect of mainly forming a cubic crystal in the crystal layer constituting the upper layer.

Further, the BAsN or BPN mixed crystal layer provided by bonding to the BP-based buffer layer according to claim 1 is
It has an effect of providing lattice matching with the AlGaInN crystal layer constituting the active layer.

Further, the buffer layer according to the second aspect of the present invention,
This has the effect of improving the lattice matching with the GaAs substrate material.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) The present invention will be described in detail below with reference to embodiments. In the first embodiment, n-type GaAs
The light emitting device (L) shown in FIG.
The present invention will be specifically described with reference to examples constituting ED) 3.

The substrate 101 was made of n-type gallium arsenide (GaAs) doped with silicon (Si). The buffer layer 102 made of undoped n-type boron phosphide (BP) is made of boron trichloride (BCl 3).
₃ ) / phosphorus trichloride (PCl ₃ ) / hydrogen (H ₂ ) based halide VPE method. The region near the junction interface 103 with the GaAs substrate 101 is cubic boron phosphide (BP).
The film forming temperature was set to 350 ° C. in order to form the region 104 mainly composed of a single crystal (layer) and the region 104 mainly composed of the amorphous body above the region 104. In the buffer layer 102 having an overall thickness (hereinafter, represented by the symbol “D”) of about 20 nanometers (unit: nm), the thickness of the region 104 (mainly a BP single crystal layer) Hereinafter, the symbol “d”) is about 3 nm. Further, by setting the film forming temperature to 350 ° C., the buffer layer 1 is formed.
The concentration of the boron phosphide multimer crystal typified by B ₁₃ P ₂ contained in
(Boron monophosphide) of less than 2%.

On the buffer layer 102, the above halogen VP
N-type B doped with Si at 930 ° C using the E method
The crystal layer 106 made of P _0.97 N _0.03 is laminated, and the buffer layer 1
02. The thickness of the n-type BP _0.97 N _0.03 crystal layer 106 is about 0.2 μm, and the carrier concentration is about 8 × 10
¹⁸ cm ^-3 .

On the n-type BP _0.97 N _0.03 crystal layer 106,
A lower cladding layer 107 (layer thickness (t) = 1.5 μm, carrier concentration (n) = 1.0 × 10 ¹⁸ cm ⁻³ ) made of Si-doped n-type gallium nitride (GaN), undoped n-type gallium nitride Indium mixed crystal (Ga _0.88 In _0.12 N)
Light-emitting layer 108 (t = 0.1 μm, n = 2.1 ×
10 ¹⁸ cm ^-3 ) and magnesium (Mg) -doped p-type aluminum-gallium nitride mixed crystal (Al _0.10 Ga
_0.90 N) upper cladding layer 109 (t = 0.1 μm)
m and a carrier concentration (p) of 4.1 × 10 ¹⁷ cm ⁻³ ) were sequentially laminated to form a light emitting section 2 having a pn junction type double hetero structure. Each of the layers 107 to 109 constituting the light-emitting portion 2 deposited on the cubic n-type BP _0.97 N _0.03 crystal layer 106 includes:
It was composed of cubic crystals. Further, G constituting the light emitting layer 108
a _0.88 In _0.12 N was used as a crystal layer having a multiphase structure composed of a plurality of phases having different indium concentrations. p
On the Al _0.10 Ga _0.90 N layer 109, a Mg-doped p-type GaN layer (t = 0.1 μm, p = 1.0 × 10 ¹⁸ c
m ⁻³ ) was laminated as a contact layer 110 to obtain a laminated structure 1 for LED use.

On the contact layer 110, which is the outermost layer of the multilayer structure 1, a p-type ohmic electrode 111 made of a gold (Au) vapor deposited film was arranged. On the other hand, the n-type ohmic electrode 112 was provided on the back surface of the n-type GaAs substrate 101 as a "solid" full-surface electrode. Thereafter, the above laminated structure 1 is cleaved in the [011] crystal direction of the GaAs substrate orthogonal to each other to form a group III nitride semiconductor LED 3 shown in FIG. 2 as a square chip having a side of about 300 μm. did. Originally, GaAs had a cleavage property in the [011] crystal direction, so that it could be formed into a chip easily and with little chipping.

Ohmic electrodes 1 provided above and below LED 3
An operating current was passed in the forward direction between 11 and 112, and light emission in a blue band was obtained. A forward current of 20 mA (m
The center wavelength of light emission when set in A) was about 430 nm. The half-width of the main emission spectrum was about 20 nm, which indicated that the emission was excellent in monochromaticity. Also,
The forward voltage (so-called Vf) is about 2.
8 volts (V). LED according to the configuration of the present embodiment
Unlike conventional short-wavelength LEDs using sapphire as a substrate, there was no need to cut out a part of the light-emitting surface in order to lay the n-side electrode, and a wide light-emitting area could be maintained. Reflecting this, the light emission output of the resin mold (mold) lamp covered with the condenser lens is about 1.2 candela (cd), and an LED excellent in light emission intensity is provided.

(Second Embodiment) In the second embodiment, the crystal layer 106 described in the first embodiment is _replaced with an n-type BP _0.97 N
_0.03 to boron arsenide mixed crystal (BAs _1-Y N _Y : 0 <Y <
The laminated structure 4 shown in FIG. 3 was configured by changing to 1).
Nitrogen composition ratio of the crystal layer 106 made of BAs _1-Y N Y cubic (= Y) was set to 0.19 (19%).

In FIG. 3, the procedure up to laminating the buffer layer 102 is the same as in the first embodiment. Buffer layer 102
Was changed to a mixed crystal of boron arsenide (BAs _{1 -Y} N _Y , where Y = 0.19) as described above. On the Si-doped n-type BAs _0.81 N _0.19 crystal layer 106, an n-type gallium-indium nitride mixed crystal (Ga _0.90 In _0.10 ) mainly composed of a cubic crystal lattice-matching with BAs _0.81 N _0.19 (lattice constant = 4.557 °) N) of the lower cladding layer 107 (t = 0.5 μm, n = 2.0 × 10 ¹⁸ cm)
^-3 ), a luminescent layer 10 composed of n-type Ga _0.82 In _0.18 N mainly composed of cubic crystals doped with zinc (Zn) and Si.
8, and an upper cladding layer 109 made of Mg-doped p-type GaN were sequentially laminated to form a light emitting section 5 having a pn junction double hetero structure.

A p-type ohmic electrode 111 and an n-type ohmic electrode 112 similar to those of the first embodiment are formed on the laminated structure 4 having the upper cladding layer 109 made of p-type GaN mainly composed of cubic crystals as the outermost layer. LED6 (Fig. 3
reference). An operating current was passed through the LED 6 in the forward direction, and blue light emission was obtained. A forward current of 20 mA (m
The center wavelength of light emission when set in A) was about 450 nm. The half width of the main emission spectrum was about 40 nm. Further, the forward voltage (so-called Vf) became about 2.6 volts (V) when 20 mA was applied. Unlike the conventional short-wavelength LED using sapphire as a substrate, the LED 6 according to the configuration of the second embodiment does not need to cut out a part of the light emitting surface for laying the n-side electrode, and can maintain a wide light emitting area. Therefore, a resin mold (mol
d) The luminous output of the lamp was about 1.0 candela (cd), and an LED having excellent luminous intensity was provided.

(Third Embodiment) FIG. 4 shows the laminated structure manufactured in the third embodiment. In the third embodiment, first, trimethyl boron ((CH ₃ ) ₃ B) is converted from a boron (B) source to cyclopentadienyl indium (I) (C ₅ H ₅ In).
(I)) is converted to an indium (In) source and phosphine (P
The H ₃₎ normal atmospheric pressure MOCVD method using a phosphorus (P) source, a buffer layer 102 composed of boron indium phosphide mixed crystal (B _U In _W P) on Zn-doped p-type GaAs single crystal substrate 101 Provided. For the buffer layer 102, a Zn-doped p-type B _0.16 In _0.84 P mixed crystal having a boron composition ratio of 0.16 was used. A region 104 in the vicinity of a junction interface 103 with the GaAs substrate 101 is mainly composed of a single crystal (layer) made of cubic B _0.16 In _0.84 P, and an upper region 105
The buffer layer 102 was grown at 420 ° C. in order to mainly form the amorphous body composed of B, In and P. At the same time, the growth temperature increases the content of the boron phosphide multimer crystal such as B ₁₃ P ₂ or B ₆ P by 5% in the entire buffer layer 102.
% Is set. In the buffer layer 102 having an overall layer thickness (hereinafter, referred to as a symbol “D”) of about 15 nm, the thickness of the region 104 mainly occupied by the single crystal body (layer) (hereinafter, the symbol “d”) ") Is about 1.
5 nm. That is, d / D = 0.10.

Buffer layer 1 of B _0.16 In _0.84 P described above
02 on the surface of Zn-doped p-type BP _0.95
N _0.05 mixed crystal layer 106 (t = 3.0 μm, p = 2.5 × 1
0 ¹⁸ cm ⁻³ ) was formed at 930 ° C. by a normal pressure MOCVD method using ammonia (NH ₃ ) as a nitrogen (N) source.
The X-ray diffraction spectrum showed that the layer 106 was mainly composed of cubic crystals.

On the p-type BP _0.95 N _0.05 mixed crystal layer 106,
M of lattice constant (= 4.491 °) corresponding to the same layer 106
p-type Al _0.15 Ga _0.85 N mainly composed of g-doped cubic crystal
Mixed crystal layer (t = 0.1 μm, p = 5.0 × 10 ¹⁷ cm ⁻³ )
As the lower cladding layer 107. On the lower cladding layer 107, an undoped n-type Ga _0.90 In _0.10 N mixed crystal layer (t = 9 nm, n to 5 × 10
¹⁷ cm ^-3 ) was laminated as the light emitting layer 108. Light emitting layer 10
On top of n is a cubic crystal doped with Si.
GaN layer (t = 3.3 μm, 2.3 × 10 ¹⁸ cm ⁻³ )
Was laminated as an upper cladding layer 109 to construct a laminated structure 7 for an LED as shown in FIG. 4 having a light emitting portion 8 having a pn junction type double hetero structure.

On the surface of the upper cladding layer 109, an n-type ohmic electrode 112 made of an aluminum (Al) vapor-deposited film
Was formed. On the back side of the p-type GaAs substrate 101, a gold (Au) -Zn alloy was vacuum-deposited to form a p-type ohmic electrode 111 to constitute the LED 9 (see FIG. 4). The center wavelength of light emission when a forward current of 20 mA (mA) was passed between the ohmic electrodes 111 and 112 was about 460 nm. The half width of the main emission spectrum was about 25 nm. In addition, a forward voltage (so-called V
f) became about 2.8 volts (V) when a current of 20 mA was supplied. Unlike the conventional short-wavelength LED using sapphire as a substrate, the LED 9 according to the configuration of the present embodiment does not have to cut out a part of the light emitting surface to lay the p-side electrode, and can maintain a wide light emitting area. The light emission output of the resin mold (mold) lamp covered with the condenser lens was about 1.4 candela (cd), and an LED having excellent light emission intensity was provided.

The internal crystal structure of the light emitting section 8 was observed by a cross-sectional TEM technique using a transmission electron microscope (abbreviation: TEM). The light emitting unit 8 of the third embodiment is the GaAs substrate 1
A buffer layer 102 composed of B _0.16 In _0.84 P lattice-matched with 01, and a BP _0.95 N _0.05 mixed crystal layer 106 bonded to the buffer layer 102 and lattice-matched to the lower cladding layer 107
Since the lamination is performed on the underlying lamination system composed of the following, the dislocation penetrating into the light emitting layer region from the region near the interface 103 between the substrate and the buffer layer is clearly small, and the crystallinity is excellent.
It was composed of a group III nitride semiconductor crystal layer. In the light-emitting portion 8 of the laminated structure 9 according to the third embodiment, the dislocation density obtained by simply belonging to the linear black contrast imaged in the cross-sectional TEM image as being caused by the dislocation is:
It was about 10 ³ to about 10 ⁴ cm ^-2 . This density is higher than the dislocation density in the lattice-mismatched light emitting portion provided on the conventional sapphire substrate, which is about 10 ¹⁰ cm ^-2 (Appl. Phys. Lett., 66 (199).
5), 1249. (See Reference). That is, it was shown that a light emitting portion having few crystal defects such as dislocations and excellent in crystallinity was laminated on the buffer layer according to the structure of the present invention.

[0050] (Fourth Embodiment) A fourth embodiment, in alternative to the buffer layer 102 composed of a single layer of B _0.16 In _0.84 P mixed crystal according to a third embodiment of the, Zn-doped p Type B
First crystal layer 113 composed of _0.01 In _0.99 P mixed crystal and Zn
The buffer layer 102 having a strained superlattice structure was formed by alternately stacking the second crystal layers 114 made of a doped p-type B _0.31 In _0.69 P mixed crystal. FIG. 5 shows a laminated structure 10 according to the fourth embodiment. The boron composition ratio of the first and second crystal layers 113 and 114 forming the buffer layer 102 having the strained superlattice structure is as follows:
Each is a boron composition ratio of 0.1, which is lattice-matched to GaAs.
The value was increased / decreased to an equivalent of ± 0.15 based on 16. The composition of increase or decrease to an equal amount from the reference value is, B _0.01 In _0.99 the first crystal layer 113 made of P mixed crystal and a Zn-doped p-type B _0.31
The average composition in a two-layer structure composed of a combination with the second crystal layer 114 composed of In _0.69 P mixed crystal is 0.16.
This is because

The above-mentioned first and second crystal layers 113 and 11
No. 4 was formed by the atmospheric pressure MOCVD method described in the third embodiment. Each of the crystal layers 113 and 114 is formed at 380 ° C. in order to mainly include a cubic crystal and to make the content of a boron phosphide polymer crystal represented by B ₁₃ P ₂ less than 3%. did. The first and second crystal layers 11
The thicknesses of the layers 3 and 114 were both set to about 8 nm.

On the buffer layer 102 having a strained superlattice structure, a third
P having the same configuration as the laminated structure described in the embodiment of
BP _0.95 N _0.05 mixed crystal layer 106 and lower cladding layer 1
07, a light emitting layer 108 and an upper cladding layer 109 were laminated to form a laminated structure 10 for LED use shown in FIG. Surface of upper cladding layer 109 constituting the outermost layer of laminated structure 10 and p-type GaAs substrate 1
Ohmic electrode 11 similar to the third embodiment
1 and 112 were provided to form the LED 12 (see FIG. 5).
Cross section T using transmission electron microscope (abbreviation: TEM)
According to the observation by the EM technique, the light emitting unit 11 of this embodiment is
Is a BP _0.95 N _0.05 mixed lattice-matched with the lower cladding layer 107 on a buffer layer 102 having a strained superlattice structure made of a BInP mixed crystal lattice-matched with a GaAs substrate 101 having an average boron composition ratio of 0.16. Since the layers are stacked with the crystal layer 106 interposed therebetween, the dislocation penetrating into the light emitting layer region starting from the region near the interface 103 between the substrate and the buffer layer is clearly small, and the group III nitride semiconductor crystal layer excellent in crystallinity is obtained. It was composed of The dislocation density obtained by simply assigning the linear black contrast captured in the cross-sectional TEM image to the dislocation due to the dislocation was about 10 ³ to about 10 ⁴ cm ⁻² .

[0053]

According to the first aspect of the present invention, the BP-based low-temperature buffer layer provided on the conductive GaAs substrate has an effect of providing an upper layer (group III nitride semiconductor crystal layer) having excellent continuity. By utilizing this, a light-emitting portion composed of a group III nitride semiconductor crystal layer mainly composed of cubic crystals and having a low crystal defect density can be formed. For this reason, there is an effect of providing a group III nitride semiconductor light emitting device that emits short-wavelength visible light having excellent characteristics both optically and electrically.

Further, in the base laminate system comprising the BP-based buffer layer according to the first aspect of the present invention and a BPN mixed crystal or BAsN mixed crystal layer having excellent continuity bonded thereto, these mixed crystals are formed of a cladding layer. This is effective in forming a light emitting portion having good crystallinity in order to lattice-match with the AlGaInN crystal layer constituting the structure.

In particular, according to the invention described in claim 2, G
a low-temperature buffer layer made of a material lattice-matched to the aAs substrate;
It is possible to provide a base laminated system including a group III nitride semiconductor crystal layer constituting a light emitting portion and a layer capable of lattice matching. The underlying laminate system is effective for laminating a light emitting portion having good crystallinity, and is particularly effective for providing a group III nitride semiconductor light emitting device having excellent light emitting characteristics.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a crystal structure inside a low-temperature buffer layer made of boron phosphide (BP) on a gallium arsenide (GaAs) substrate.

FIG. 2 is a cross-sectional view schematically showing a configuration of the LED described in the first embodiment.

FIG. 3 is a cross-sectional view schematically illustrating a configuration of an LED according to a second embodiment.

FIG. 4 is a cross-sectional view schematically showing a configuration of an LED described in a third embodiment.

FIG. 5 is a cross-sectional view schematically illustrating a configuration of an LED described in a fourth embodiment.

[Explanation of symbols]

 Reference Signs List 1 laminated structure 2 light emitting unit 3 light emitting diode (LED) 4 laminated structure 5 light emitting unit 6 light emitting diode (LED) 7 laminated structure 8 light emitting unit 9 light emitting diode (LED) 10 laminated structure 11 light emitting unit 12 light emitting diode (LED) LED) 101 Gallium arsenide (GaAs) single crystal substrate 102 Low temperature buffer layer 103 Junction interface between GaAs substrate and low temperature buffer layer 104 Region mainly composed of single crystal (layer) 105 Region mainly composed of amorphous material 106 BPN Mixed crystal layer or BAsN mixed crystal layer 107 Lower cladding layer 108 Light emitting layer 109 Upper cladding layer 110 Contact layer 111 p-type ohmic electrode 112 n-type ohmic electrode 113 First crystal layer constituting superlattice structure 114 Superlattice structure Second crystal layer

Claims (2)

[Claims] A group III-V compound semiconductor single crystal substrate;
A buffer layer provided on the surface of the substrate; and II joined to the buffer layer.
In a group III nitride semiconductor device comprising a laminated structure having a group I nitride semiconductor crystal layer, a group III-V compound semiconductor single crystal substrate is made of gallium arsenide (chemical formula: GaAs); buffer layer provided on the surface of, boron phosphide multimeric crystals _{(B i P j: i>} 1, j ≧ 1) a boron phosphide (BP) based III -V group to 5% or less content of A group III nitride semiconductor crystal layer formed of a compound semiconductor crystal and forming a junction with the buffer layer is formed of a ternary mixed crystal of boron phosphide (BP ₁ -XN _x : 0 <X <1) or a boron arsenide nitride. Original mixed crystal (BAs _1-Y N _Y : 0 <Y <
A group III nitride semiconductor device comprising: 1). Wherein said buffer layer, boron indium phosphide mixed crystal _{(B U In W P: 0} <U <0.32, U + W = 1)
3. The method of claim 1, further comprising:
Group III nitride semiconductor device.