JP2003283057A - Nitride semiconductor light emitting element and its fabricating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor light emitting element producing a higher output while exhibiting a higher reliability of an element as compared with a conventional case. <P>SOLUTION: The nitride semiconductor light emitting element comprises an active layer of a nitride semiconductor containing In and a p-type cap layer of Al<SB>x</SB>Ga<SB>1-x</SB>N (0<x<1) formed in contact with the active layer wherein the p-type cap layer comprises a first p-type nitride semiconductor layer of Al<SB>a</SB>Ga<SB>1-a</SB>N (0<a<1) and a second p-type nitride semiconductor layer of Al<SB>b</SB>Ga<SB>1-b</SB>N (0<b<1) having fewer crystal defects than the first p-type nitride semiconductor layer and the overall thickness of the p-type cap layer is set in the range of 10-1000 Å. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a light emitting diode,
Light-emitting devices such as laser diodes, or photovoltaic, nitride semiconductor used in the light-receiving element such as an optical sensor (an In _X A
TECHNICAL FIELD The present invention relates to a nitride semiconductor device composed of 1 _Y Ga _{1-X- Y} N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1), and particularly to a light emitting device and a laser device.

[0002]

2. Description of the Related Art In recent years, blue laser diodes made of nitride semiconductor have become practical. For example, the present inventors have proposed that the Japanese Journal of Applied Physics. Vol.37.
(1998) pp.L309-L312, G grown on sapphire
By partially forming a protective film made of SiO ₂ on the aN layer and growing GaN again on the protective film by a vapor phase growth method such as metal organic vapor phase epitaxy (MOVPE), the protective film is formed. Growth starts from a portion not formed (hereinafter referred to as a window portion), and lateral growth of GaN gradually occurs on the upper portion of the protective film, and GaN laterally grown from adjacent window portions are bonded to each other on the protective film. It is disclosed that a nitride semiconductor having extremely few crystal defects (hereinafter, sometimes referred to as dislocation) can be obtained by continuing the growth. A nitride semiconductor laser device obtained by using the obtained nitride semiconductor with few crystal defects as a substrate and forming a device structure on this nitride semiconductor substrate can achieve continuous oscillation for 10,000 hours or more. It is disclosed.

[0003]

However, the nitride semiconductor light emitting device requires further improvement in output and device reliability.

Therefore, an object of the present invention is to provide a nitride semiconductor light emitting device having higher output and higher device reliability than the conventional example.

[0005]

The present invention has achieved the above object by the following constitution. That is, the first nitride semiconductor light emitting device of the present invention includes at least an n-type cladding layer made of an n-type nitride semiconductor, an active layer made of a nitride semiconductor containing In, and a p-type nitride semiconductor.
In a nitride semiconductor light emitting device including a type clad layer, an Al _a Ga layer is provided between the active layer and the p type clad layer.
_1-a N (0 <a <1) and a first p-type nitride semiconductor layer having an energy gap larger than that of the p-type cladding layer and Al _b Ga _1-b N (0 <b <1). The second p-type nitride semiconductor layer is formed.

Further, in the first nitride semiconductor light emitting device of the present invention, it is preferable that the first p-type nitride semiconductor layer is formed in contact with the active layer.

Further, in the first nitride semiconductor light emitting device of the present invention, the film thickness of the first nitride semiconductor layer is
It is preferable that the thickness is 10 Å or more and 100 Å or less, and the film thickness of the second nitride semiconductor layer is 10 Å or more and 300 Å or less.

Further, the first nitride semiconductor light emitting device of the present invention
In the child, the active layer is In _cGa_1-cN (0
A multiple quantum well structure including a well layer of ≦ c <1)
May be.

Furthermore, in the first nitride semiconductor light emitting device of the present invention, the active _layer, In _{c Ga 1-c} N
A layer including a well layer of (0 ≦ c <1), the p-type cladding layer is Al _x Ga _1-x N (0 <x <1),
In addition, the first p-type nitride semiconductor layer made of Al _a Ga _1-a N (0 <a <1) and the Al _b Ga _1-b N (0
The second p-type nitride semiconductor layer of <b <1) can be formed of layers whose compositions are set to satisfy x ≦ a and x ≦ b, respectively.

In the second nitride semiconductor light emitting device according to the present invention, an In-type cladding layer made of an n-type nitride semiconductor and a p-type cladding layer made of a p-type nitride semiconductor are provided between the In and In layers.
In a nitride semiconductor light emitting device including an active layer made of a nitride semiconductor containing Al, _a Ga1 _- aN (0) having _a larger energy gap between the active layer and the p-type cladding layer than the p-type cladding layer. The first p-type nitride semiconductor layer is formed of <a <1) and is grown at a lower temperature than the cladding layer.

As described above, in the nitride semiconductor light emitting device, the energy gap between the active layer and the p-type cladding layer is larger than that of the p-type cladding layer, that is, Al _a Ga.
By providing the first p-type nitride semiconductor layer made of _1- aN (0 <a <1) and grown at a lower temperature than the cladding layer, the quality of the active layer can be kept good. That is, under the growth conditions for growing AlGaN having good crystallinity, the active layer containing In decomposes, but in the second nitride semiconductor device according to the present invention, first, the active layer and the cladding layer are separated from each other. In the meantime, the first p-type nitride semiconductor layer is grown at a temperature lower than that of the clad layer to prevent the active layer from being decomposed by the first p-type nitride semiconductor layer, while maintaining good p-type crystallinity. Since the nitride semiconductor layer (including the clad layer) can be formed, it is possible to provide a light emitting device including a good quality active layer and a p-type nitride semiconductor layer having good crystallinity thereon.

Further, in the second nitride semiconductor light emitting device according to the present invention, in order to effectively suppress decomposition of the active layer, the first p-type nitride semiconductor layer is an organic layer using N ₂ gas. It is preferably grown by metal vapor deposition.

Further, in the second nitride semiconductor light emitting device according to the present invention, the active layer is made of In _c Ga _{1 -c} N.
A multiple quantum well structure including a well layer of (0 ≦ c <1) can be obtained.

The second nitride semiconductor device according to the present invention is also used.
In the optical device, the active layer is In_cGa _1-cN (0 ≦ c <
The p-type cladding is a layer including a well layer consisting of 1).
Layer Al_xGa_1-xA layer composed of N (0 <x <1)
And said Al_aGa_1-aN (0 <a <1)
The first p-type nitride semiconductor layer to satisfy x ≦ a
Can be configured by setting the composition to.

Further, in the third nitride semiconductor light emitting device according to the present invention, In is provided between the n-type cladding layer made of an n-type nitride semiconductor and the p-type cladding layer made of a p-type nitride semiconductor.
An active layer made of a nitride semiconductor containing
Big _{Al y Ga 1-y N (} 0 band gap than the p-type cladding layer between the type cladding layer and the active layer <
A nitride semiconductor light emitting device having a p-type cap layer formed of y <1), wherein the p-type cap layer is p-type.
Type p-type Al _b Ga _1-a N (0 <a <1), and a p-type Al _b Ga layer formed on the first p-type nitride semiconductor layer. _1-b N (0 <b <1)
And a second p-type nitride semiconductor layer having fewer crystal defects than the first p-type nitride semiconductor layer, and the total thickness of the p-type cap layer is set to 10 Å or more and 1000 Å or less. It is characterized by

As described above, in the third nitride semiconductor light emitting device according to the present invention, the p-type cap layer is formed of Al _a.
A _first p-type nitride semiconductor layer formed of Ga _1-a N (0 <a <1) in contact with the active layer, and Al _b Ga
_1-b N (0 <b <1) second with few crystal defects
And a p-type nitride semiconductor layer of
The function of confining carriers in the active layer can be effectively exerted and the quality of the active layer can be kept good. That is, under the growth conditions for growing AlGaN having good crystallinity, since the active layer containing In decomposes, the AlGaN layer has conventionally been grown under the condition that the active layer does not decompose. It was difficult to form the p-type cap layer having good crystallinity, and it was difficult to effectively exhibit its function. Further, when an attempt is made to form a carrier confinement layer made of AlGaN having good crystallinity, the active layer is decomposed and the emission characteristics are deteriorated.

On the other hand, in the third nitride semiconductor device according to the present invention, first, the first nitride semiconductor device is provided on the side close to the active layer.
The p-type nitride semiconductor layer is grown to form a second p-type nitride semiconductor layer having good crystallinity while preventing the active layer from being decomposed by the first p-type nitride semiconductor layer. Therefore, it is possible to provide a light emitting device including an active layer with good quality and a p-type cap layer with good crystallinity. That is, in the third nitride semiconductor device of the present invention, the p-type cap layer is the first p-type nitride semiconductor layer for preventing the decomposition of the active layer, and the second p-type capping layer is for effectively confining carriers in the active layer. By forming a plurality of layers that are functionally separated from the p-type nitride semiconductor layer, the problems in the conventional trade-off relationship are solved.

In the third nitride semiconductor device of the present invention, the film thickness of the first p-type nitride semiconductor layer is 10
It is preferable to set it to Å or more and 100 Å or less. By setting it in this range, the decomposition of the active layer can be effectively prevented, and the deterioration of the crystallinity of the entire p-type cap layer can be reduced. Further, the film thickness of the second p-type nitride semiconductor layer is preferably 10 Å or more and 300 Å or less. With this setting, the crystallinity of the p-type cap layer as a whole can be kept relatively good, and electrons can be effectively confined in the active layer.

Further, in the third nitride semiconductor device according to the present invention, the active layer is made of In _c Ga _{1 -c} N (0≤c <
A multiple quantum well structure including the well layer of 1) can be obtained, and in this case, the excellent light emitting function of the active layer having the multiple quantum well structure can be more effectively exhibited.

That is, in the conventional nitride semiconductor light emitting device, even if the active layer having the multiple quantum well structure is adopted, the hole diffusion length is short, and the offset on the carrier side is insufficient, so that overflow easily occurs. Since the function of the active layer of the multiple quantum well structure cannot be fully exhibited, the device characteristics could not be improved as much as expected compared with the single quantum well structure. However, in the third nitride semiconductor light emitting device of the present invention, the active layer has a multiple quantum well structure having a plurality of well layers made of InGaN, and the p-type cap layer is
By comprising the first p-type nitride semiconductor layer and the second p-type nitride semiconductor layer, carriers can be effectively confined in the active layer having the multiple quantum well structure, and carriers to the well layer can be effectively confined. Can be injected well. As a result, the characteristics of the active layer having the multiple quantum well structure can be fully utilized, and good light emission characteristics can be realized.

A method of manufacturing a nitride semiconductor light emitting device according to the present invention is characterized in that an active layer made of a nitride semiconductor containing In is formed,
A method for manufacturing a nitride semiconductor light emitting device, comprising the step of growing a p-type cap layer made of Al _x Ga _1-x N (0 <x <1), wherein the step of growing the p-type cap layer comprises: the active layer metal organic chemical vapor deposition method using nitrogen gas on, Al a _Ga 1- a N first growth step of growing the first p-type nitride semiconductor layer made of _{(0 <a <1)} And Al _b Ga _1-b N on the first p-type nitride semiconductor layer by a metal organic chemical vapor deposition method using hydrogen gas.
A second growth step of growing a second p-type nitride semiconductor layer of (0 <b <1), wherein the first p-type nitride semiconductor layer and the second p-type nitride semiconductor layer are included. The p-type cap layer having a thickness of 10 Å or more and 1000 Å or less is grown.

In the above-described method for manufacturing a nitride semiconductor light emitting device according to the present invention, the first growth step uses the nitrogen gas capable of growing a semiconductor layer on the active layer at a relatively low temperature in the first growth step. Since the p-type nitride semiconductor layer is grown, the Al _a G layer is formed without decomposing the active layer containing In.
An a1 _- aN (0 <a <1) layer can be formed.
Further, in the second growth step, Al _b Ga _1-b N (0 <
Since the second p-type nitride semiconductor layer is grown using hydrogen gas capable of growing b <1), the first p-type nitride semiconductor layer prevents decomposition of the active layer. The second p-type nitride semiconductor layer having good crystallinity can be grown. In addition, In in the active layer containing In
It is also possible to suppress variations in the light emission characteristics between the elements due to the in-plane distribution of, and it is possible to improve the manufacturing yield. Furthermore, by forming the second p-type nitride semiconductor layer in an atmosphere different from that of the first p-type nitride semiconductor layer,
Layers having different crystal growth forms can be formed and the functions can be separated.

As described above, in the method for manufacturing a nitride semiconductor light emitting device according to the present invention, since the p-type cap layer can be formed without impairing the crystal quality of the active layer, the light emitting characteristics are extremely excellent and the variation is large. It is possible to manufacture a nitride semiconductor light emitting device with less power consumption.

In the method for manufacturing a nitride semiconductor light emitting device according to the present invention, it is preferable that the growth temperature in the second growth step is set higher than the growth temperature in the first growth step. By doing so, the second p-type nitride semiconductor layer having better crystallinity can be grown.

In the method for manufacturing a nitride semiconductor light emitting device according to the present invention, the growth temperature in the first growth step may be set to be substantially the same as the growth temperature when growing the active layer. preferable. In this way, In
It is possible to more effectively prevent the decomposition of the active layer containing Al, and it is possible to further maintain the crystal quality of the active layer.

Further, in the method for manufacturing a nitride semiconductor light emitting device according to the present invention, in the first growing step, the first p-type nitride semiconductor layer is grown to a film thickness of 10 Å or more and 100 Å or less, In the second growth step, the second
It is preferable that the p-type nitride semiconductor layer is grown to a film thickness of 10 Å or more and 300 Å or less. In this manner, the first p-type nitride semiconductor layer is grown to have a film thickness of 10 to 100Å and the second p-type nitride semiconductor layer is grown to have a film thickness of 10 to 300Å. As a result, both the function of protecting the active layer in the growth of the first p-type nitride semiconductor layer and the function of confining carriers by the second p-type nitride semiconductor layer can be exhibited well.

This is because the first p-type nitride semiconductor layer having relatively poor crystallinity is limited to the minimum film thickness capable of protecting the active layer, and the first p-type nitride semiconductor layer is interposed. By making the second p-type nitride semiconductor layer capable of good crystal growth relatively thick, good offset with respect to the active layer is realized. That is, with only the first p-type nitride semiconductor layer having the above-mentioned thickness, the outflow of electrons from the active layer due to the tunnel effect becomes a problem, but with the second p-type nitride semiconductor layer, the active layer is formed. Good carrier confinement inside can be realized.

Further, in the method for manufacturing a nitride semiconductor light emitting device of the present invention, the growth temperature in the first growth step is set to a temperature of 850 ° C. or higher and 950 ° C. or lower, and the growth temperature in the second growth step is set. Is preferably set to a temperature of 950 ° C. or higher. By setting the growth temperature in such a temperature range, the protection of the active layer by the above-mentioned first p-type nitride semiconductor layer can be more effectively achieved, and the second p-type nitriding having even better crystallinity can be achieved. The object semiconductor layer can be grown.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Nitride according to an embodiment of the present invention
The semiconductor light emitting device, as shown in FIG.
P-type Al on the active layer 6 composed of a semiconductor._xGa
_1-xN (0 <x <1) and carriers in the active layer 6
A p-type cap layer 7 having a confining function is formed
In the nitride semiconductor light emitting device, the p-type cap layer 7 is
p-type Al _aGa_1-aFirst consisting of N (0 <a <1)
P-type nitride semiconductor layer 7a and p-type Al_bGa_1-b
Second p-type nitride semiconductor layer 7 made of N (0 <b <1)
and b.

The p-type cap layer 7 is formed as a layer for confining carriers in the active layer 6, and has to have a band gap larger than that of the active layer 6 and have good crystallinity. It is said that When a layer satisfying these conditions is formed in contact with the active layer, a good potential barrier (offset) is formed between the layer and the active layer, and the carrier confining function can be effectively exhibited. However, in the nitride semiconductor light emitting device including the active layer containing In to which the present invention is applied, as the p-type cap layer 7,
P-type Al _x Ga _1-x N (0 <x <where the Al content is adjusted so that the size of the band gap becomes a desired value.
The 1) layer is mainly used, but has the following problems.

That is, in order to grow an AlGaN layer with few crystal defects and good crystallinity, the AlGaN layer is grown at a relatively high temperature (using H ₂ as a carrier gas) in an H ₂ atmosphere using a metal organic chemical vapor deposition method. However, it is necessary to grow the AlGaN layer into the active layer 6 containing In in an H ₂ atmosphere.
There is a problem that the active layer is decomposed when it is directly grown on the surface. For this reason, p-type Al _x Ga _1-x
Even if the p-type cap layer 7 made of N (0 <x <1) with good crystallinity can be formed, it deteriorates the active layer 6 itself, and eventually obtains expected light emission characteristics. Was difficult. AlGa in H ₂ atmosphere
When the growth temperature of the N layer is increased, the crystallinity of the grown AlGaN layer can be further improved, but the decomposition of the active layer containing In becomes more severe, which causes the emission lifetime to be shortened. In the present specification, simply referring to AlGaN means a nitride semiconductor in which a part of Ga in GaN is replaced by Al.

The present invention has found that an AlGaN layer can be formed on an active layer containing In without growing the H ₂ atmosphere and growing the AlGaN layer in an N ₂ atmosphere at a low temperature without decomposing the active layer. , It was completed focusing on that point. That is, in the nitride semiconductor light emitting device according to the embodiment of the present invention, a relatively thin p-type Al is formed on the active layer 6 made of a nitride semiconductor containing In so as not to decompose the active layer in advance in an N ₂ atmosphere. _a Ga _1-a N
First p-type nitride semiconductor layer 7a made of (0 <a <1)
Is formed to a thickness not deteriorating the electron confinement function, and is protected by the first p-type nitride semiconductor layer 7a from decomposing the active layer, while p-type Al _b Ga _{1 is formed in} an H ₂ atmosphere. The second p-type nitride semiconductor layer 7b made of _-bN (0 <b <1) is formed.

The embodiment of the present invention will be described below with reference to FIG.
Will be described in more detail. FIG. 1 illustrates one embodiment of the present invention.
In the form of a nitride semiconductor light emitting device (nitride semiconductor laser
FIG. 3 is a schematic cross-sectional view showing the element). Nitride semiconductor in Figure 1
Body laser devices are different from nitride semiconductors such as sapphire.
ELOG-grown nitride half on the top surface of heterogeneous substrate 100
Dope an n-type impurity (for example, Si) on the conductor substrate 1.
Become Al_kGa_1-kN type consisting of N (0 <k <1)
Contact layer 2, Si-doped In_gGa_1-gN
A crack prevention layer 3 made of (0.05 ≦ g ≦ 0.2),
Al_eGa_1-eContains N (0.12 ≦ e <0.15)
N-type clad layer 4 of a multi-layered film, undoped GaN
N-type guide layer 5 made of In_cGa_1-cN (0≤c
<1) active layer 6 having a multiple quantum well structure, Mg
Al_dGa_1-dLess consisting of N (0 <d ≦ 1)
Two or more p-type cap layers 7, undoped GaN
P-type guide layer 8 made of Al_fGa _1-fN (0 <f
P-type clad layer 9 composed of a multilayer film containing ≦ 1), Mg
P-type contact layer 10 made of GaN,
Type contact layer 10 to n-type contact layer 2 have a predetermined width
Etched to form a ridge-shaped stripe 200
It will be done. The p-electrode is a ridge-shaped stripe 2
00 to be in contact with the uppermost p-type contact layer 10
Formed on the one side of the ridge-shaped stripe 200.
It is formed on the exposed n-type contact layer 2.

The individual elements will be described in detail below. (Regarding ELOG Growth) ELOG growth is a growth method in which vertical growth of a nitride semiconductor is temporarily stopped at least partially and growth in the horizontal direction is used to suppress the generation of dislocations. Is. Specifically, a protective film made of a material in which a nitride semiconductor does not grow or is hard to grow is partially formed on a heterogeneous substrate made of a material different from that of the nitride semiconductor, and the nitride semiconductor is grown on the protective film. By doing so, the growth of the nitride semiconductor is started from the portion where the protective film is not formed, and by continuing the growth, the nitride semiconductor is grown laterally, and as a result, the entire heterogeneous substrate is covered. A relatively thick film nitride semiconductor is formed.

Various substrates can be used as the heterogeneous substrate. For example, insulating properties such as sapphire having C-plane, R-plane, and A-plane as main surfaces shown in FIG. 2 and spinel (MgA1 ₂ O ₄ ). Substrate, SiC (including 6H, 4H, 3C), Z
Substrate materials different from conventionally known nitride semiconductors can be used, such as nS, ZnO, GaAs, Si, and oxide substrates lattice-matched to nitride semiconductors.

Among the above, a preferable different type of substrate is sapphire, more preferably the C plane of sapphire. Further, the C-plane of sapphire is off-angled stepwise, and the off-angle angle θ (θ shown in FIG. 3) is 0.
It is even more preferable to use one having a range of 1 ° to 0.3 ° because it is possible to prevent the generation of fine cracks inside the nitride semiconductor obtained by ELOG growth. Off-angle angle θ
Is less than 0.1 °, fine cracks are likely to occur inside the ELOG-grown nitride semiconductor, and an off-angle angle θ of 0.1 ° or more is formed on the crack. The characteristics of the laser element can be stabilized. If the off-angle angle exceeds 0.3 °, EL
If the surface of the OG-grown nitride semiconductor is stepped and a device is formed on it, the steps are slightly emphasized in each semiconductor layer, which causes a short circuit of the device and an increase in threshold value, which is not preferable.

A protective film is directly or once grown on a heterogeneous substrate such as sapphire off-angled in steps as described above, and then partially (for example,
The surface of the dissimilar substrate is exposed at regular intervals). As the protective film, various materials having a property that a nitride semiconductor does not grow or does not easily grow on the surface of the protective film can be used, and examples thereof include silicon oxide (SiO _X ), silicon nitride (Si _X N _Y ), and oxide. Titanium (TiO _X ), zirconium oxide (ZrO _X ), or other oxides and nitrides, multilayer films of these, and a metal having a melting point of 1200 ° C. or higher can be used. Preferred protective film materials include SiO ₂ and SiN.

As a method of forming the protective film material on the surface of the nitride semiconductor or the like, a vapor phase film forming technique such as vapor deposition, sputtering or CVD can be used. In addition, as a method of forming partially (selectively), a photomask having a predetermined shape is formed by using a photolithography technique,
A method of forming a vapor phase film of the above material through the photomask can be used. The shape of the protective film is not particularly limited, but it can be formed, for example, in the shape of dots, stripes, or a checkerboard shape, preferably in the shape of a stripe, and the stripes serve as orientation flat surfaces (A surface of sapphire). Form vertically.

Further, it is preferable that the ratio of the surface area of the surface of the heterogeneous substrate on which the protective film is formed is made larger than the surface area of the portion on which the protective film is not formed. It is possible to prevent dislocations that occur and obtain a nitride semiconductor substrate having good crystallinity. For example, when the protective film is formed in a stripe shape, the stripe width of the protective film is preferably 10 or more when the width of the portion (window portion) where the protective film is not formed is 3. In this case, it is more preferable that the stripe width w1 of the protective film is set to satisfy w1: w2 = 16 to 18: 3 as the width w2 of the portion (window portion) where the protective film is not formed. When the protective film is formed in a stripe shape, if the stripe width of the protective film and the width of the window are set to the above relationship, the nitride semiconductor can easily cover the protective film and dislocations can be effectively prevented. . The stripe width of the protective film is, for example, 6
˜27 μm, preferably 11 to 24 μm, and the width of the window is, for example, 2 to 5 μm, preferably 2 to 4 μm.
And

When a device is formed on a nitride semiconductor obtained by ELOG growth and a ridge-shaped stripe 200 is formed in a p-type nitride semiconductor layer, the ridge-shaped stripe 200 is a stripe-shaped protective film. Is above
In addition, it is preferable to be formed so as to avoid the center line (the center line parallel to the longitudinal direction). By doing so, the threshold value can be lowered and the reliability of the element can be improved. . That is, the crystallinity of the nitride semiconductor located in the upper portion of the protective film is better than that in the upper portion of the window portion, and in the vicinity of the center line of the protective film, adjacent nitride semiconductors grown from the window portion are adjacent to each other. It is a portion to be joined by lateral growth, and a void may be formed at such a joined portion, and a ridge-shaped stripe 20 is formed on the upper portion of this void.
When 0 is formed, dislocations are likely to propagate from the void during the operation of the laser element, which may deteriorate the reliability of the element.

The protective film may be directly formed on the foreign substrate, but the buffer layer 101 grown at a low temperature on the foreign substrate.
Is preferably formed, and the buffer layer 102 made of a nitride semiconductor grown at a high temperature is further grown thereon to be formed, and in this case, the nitride semiconductor substrate having less dislocations and excellent crystallinity is formed. Can grow. In addition, the substrate that can be used to form the nitride semiconductor light emitting device according to the present invention is the above-mentioned ELOG.
It is not limited to the grown nitride semiconductor substrate. In the present invention, for example, undoped GaN may be grown on a sapphire substrate as a base layer having a thickness of several μm to several tens of μm, and the device may be formed thereon. The low temperature growth buffer layer 101 used for ELOG growth is, for example, AlN, GaN, A
One of lGaN, InGaN, and the like grown at a temperature of 900 ° C. or lower and 200 ° C. or higher with a film thickness of several tens of angstroms to several hundreds of angstroms can be used. These buffer layers can alleviate the lattice constant mismatch between the heterogeneous substrate and the nitride semiconductor layer grown at a relatively high temperature, and can prevent the generation of dislocations in the grown layer.

As the buffer layer 102 made of a nitride semiconductor grown at a high temperature, undoped GaN, n-type impurity-doped GaN, or Si-doped GaN can be used, and preferably undoped GaN is used. Further, these nitride semiconductors have high temperatures, specifically, 9
It is grown on the buffer layer 101 at 00 ° C to 1100 ° C, preferably 1050 ° C. In the present invention, the thickness of the buffer layer 102 is not particularly limited, but is, for example, 1 to 20 μm, preferably 2 to 10 μm.

Next, a nitride semiconductor is subjected to ELOG growth by MOCVD or the like, after forming a protective film, to obtain a nitride semiconductor substrate 1. In this case, as the nitride semiconductor to be grown, undoped GaN or impurities (for example, Si,
GaN doped with Ge, Sn, Be, Zn, Mn, Cr, and Mg) can be used. The growth temperature is, for example, 900 ° C. to 1100 ° C., more specifically 10
Grow at a temperature around 50 ° C. When impurities are doped, the generation of dislocations in the growth layer can be suppressed,
preferable.

In this ELOG growth, MOCVD (Metal Organic Chemical Vapor Deposition) or the like, which makes it easy to control the growth rate, is performed in the initial stage of growth, and the growth after the protective film is covered with the nitride semiconductor of the ELOG growth is performed. It may be grown by HVPE (halide vapor phase epitaxy) or the like. As described above, in the present embodiment, nitride semiconductor substrate 1 is formed on a heterogeneous substrate by ELOG growth.

(Formation of Nitride Semiconductor Layers on Nitride Semiconductor Substrate 1) In the present embodiment, first, n-type contact layer 2 is grown on nitride semiconductor substrate 1. As the n-type contact layer 2, Al _a Ga _1-a N (0 <a <1) doped with an n-type impurity (preferably Si) is grown. As the n-type contact layer 2, a is preferably 0.0
1 to 0.05 to grow the set _Al a _{Ga 1-a} N a. If the n-type contact layer 2 is formed of a ternary mixed crystal containing Al, even if minute cracks are generated in the nitride semiconductor substrate 1, it is possible to prevent the minute cracks from propagating, and there is a conventional problem. The nitride semiconductor substrates 1 and n
It is possible to prevent the generation of fine cracks in the n-type contact layer due to the difference in lattice constant and thermal expansion coefficient from the type contact layer 2, which is preferable. The doping amount of n-type impurities is 1
× a ^{10 1 8 / cm 3 ~5 ×} 10 18 / cm 3. An n electrode 21 is formed on the n-type contact layer 2. n
The thickness of the mold contact layer 2 is 1 to 10 μm. In addition, in the present embodiment, undoped Al _a Ga _1-a N is provided between the nitride semiconductor substrate 1 and the n-type contact layer 2.
(0 <a <1) may be grown. If this undoped layer is grown, the crystallinity of the n-type contact layer 2 may be improved and the life characteristics may be improved. in this case,
The film thickness of the undoped n-type contact layer is several μm.

Next, the crack prevention layer 3 is grown on the n-type contact layer 2. As the crack prevention layer 3, Si is used.
Doped In _g Ga _1-g N (0.05 ≦ g ≦ 0.2)
Was grown, and In with g set to 0.05 to 0.08
It is preferable to grow _g Ga _1-g N. It is preferable to form the crack prevention layer 3 on the n-type contact layer 2 because it is possible to prevent the occurrence of cracks in the device. The doping amount of Si is 5 × 10 ¹⁸ / cm ³ . However, in the present invention, the crack prevention layer 3 may be omitted.

Further, when the crack prevention layer 3 is grown, it is preferable to increase the In mixed crystal ratio (x ≧ 0.1). In this case, the crack prevention layer 3 is separated from the n-type cladding layer 4. The leaked light generated in the active layer 6 can be absorbed, and the far field pattern of the laser light can be prevented from being disturbed. The film thickness of the crack prevention layer is, for example, 0.05 to 0.3 μm, which is a thickness that does not impair its own crystallinity.

Next, the n-type cladding layer 4 is grown on the crack prevention layer 3. The n-type cladding layer 4 is made of Al _e Ga.
It is formed as a layer of a multilayer film including a nitride semiconductor containing _1-e N (0.12 ≦ e <0.15). The multilayer film shows a multilayer structure obtained by laminating nitride semiconductor layers having different compositions from each other, for _{example, Al e Ga 1-e N} (0.12 ≦ e <
0.15) layer and, different mixed crystal ratio of the _{Al e Ga 1-e} N different nitride semiconductor compositions, for example Al, I
A ternary mixed crystal containing n or a layer formed by combining a layer made of GaN or the like. Preferred combinations in _this, Al _{e Ga 1-e} N and G
It is a multilayer film formed by laminating aN. By doing so, a nitride semiconductor layer having good crystallinity can be stacked at the same temperature. A more preferable multilayer film is undoped Al _e.
Ga1 _- eN and Ga doped with n-type impurities (for example, Si)
N is combined and laminated. In this case n
Type impurity _may be doped in the Al _{e Ga 1-e} N. The doping amount of the n-type impurity is 4 × 10 ¹⁸ / cm ³ to
It is 5 × 10 ¹⁸ / cm ³ . If the n-type impurity is doped in this range, the resistivity can be lowered and the n-type cladding layer 4 can be formed without impairing the crystallinity.

In this multilayer film, a nitride semiconductor layer having a single layer thickness of 100 angstroms or less, preferably 70 angstroms or less, more preferably 40 angstroms or less, and preferably 10 angstroms or more is laminated. Configured by When the single film thickness is 100 angstroms or less, the n-type clad layer has a superlattice structure, and although Al is contained, generation of cracks can be prevented and crystallinity can be improved. The total film thickness of the n-type cladding layer 4 is 0.7.
~ 2 μm.

The average composition of the entire n-type cladding layer is
When the average composition is represented by Al _k Ga _1-k N, k
Is preferably 0.05 to 0.1. When the Al content is within this range, cracks can be formed without causing a crack, and a sufficient difference in refractive index from the laser waveguide can be obtained. Next, the n-type guide layer 5 is grown on the n-type cladding layer 4. As the n-type guide layer 5, a nitride semiconductor made of undoped GaN is grown. The film thickness of the n-type guide layer 5 is preferably set to 0.1 to 0.07 μm, and by doing so, the threshold value can be lowered. In addition, it is preferable that the n-type guide layer 4 be undoped, whereby the propagation loss in the laser waveguide can be reduced and the threshold value can be lowered.

Next, the active layer 6 is grown on the n-type guide layer 5. In this embodiment, the active layer is In _c Ga.
It has a multiple quantum well structure including _1-c N (0 ≦ c <1). In the active layer 6, the well layer has c of 0.1 to 0.1.
0.2 In _c Ga _1-c N, and the barrier layer has c of 0 to 0.
0.01 of _{In c Ga 1-c} N. Further, one or both of the well layer and the barrier layer forming the active layer 6 may be doped with impurities. In this case, it is preferable to dope the barrier layer with impurities because the threshold value can be lowered. The film thickness of the well layer is 30 to 60 angstroms, and the film thickness of the barrier layer is 90 to 150 angstroms.

The active layer 6 having a multi-quantum well structure may start from a barrier layer and end with a well layer, start with a barrier layer and end with a barrier layer, or start with a well layer and end with a barrier layer.
Also, it may start from the well layer and end at the well layer. Preferably, starting from the barrier layer, the well layer and the barrier layer are paired by 2 to
It is preferable to repeat 5 times, preferably to repeat the pair of the well layer and the barrier layer 3 times, to lower the threshold value and improve the life characteristics.

Next, the p-type cap layer 7 is grown on the active layer 6. As the p-type cap layer 7, Mg-doped A
at least 2 consisting of l _d Ga _1-d N (0 <d ≦ 1)
Layers are grown and constructed. The mixed crystal ratio of the p-type cap layer 7 is preferably set so that d is 0.1 or more and 0.5 or less. The first constituting the p-type cap layer in the present invention
The mixed crystal ratio in the above range is applied to the p-type nitride semiconductor layer and the second p-type nitride semiconductor layer, but each layer will be described in detail later. The total thickness of the p-type cap layer 7 is 10 angstroms or more and 1000 or more.
The thickness is set to be less than or equal to angstrom, preferably more than or equal to 20 angstrom and less than or equal to 400 angstrom. The thickness of the entire p-type cap layer 7 is set in such a range for the following reason. That is, when the p-type cap layer 7 is an AlGaN layer, the carrier confinement function can be effectively exhibited.
The aN layer has a higher bulk resistance than a gallium nitride-based semiconductor containing no Al. Therefore, since it is necessary to suppress an increase in the resistance value of the light emitting element due to the formation of the p-type cap layer, it is set to 1000 angstroms or less, preferably 400 angstroms or less. The original function of the p-type cap layer 7 is the above-mentioned carrier confinement function, and the film thickness thereof is set to 10 angstroms or more, preferably 20 angstroms or more in order to effectively exhibit the function.
Therefore, when the film thickness is in the above range, carriers can be effectively confined in the active layer 6 and the bulk resistance can be suppressed low.

Also, the doping amount of Mg in the p-type cap layer 7
Is 1 × 10¹⁹/ Cm^Three~ 1 x 10 ²¹/ Cm^ThreeTosu
It Setting the doping amount in this range lowers the bulk resistance.
In addition to lowering it, grow it with undoped as described below.
Mg is diffused into the p-type guide layer, and p is a relatively thin layer.
1 × 10 of Mg in the mold guide layer 8¹⁶/ Cm^Three~ 1 x 10
¹⁸/ Cm^ThreeIt can be contained in the range of.

[0055] Especially where, p type cap layer 7 in the present _embodiment, Al a _{Ga 1-a} and the first p-type nitride semiconductor layer 7a that N consists, _Al thereon b _{Ga 1-b} N The second p-type nitride semiconductor layer 7b is composed of two layers. However, the present invention is not limited to this, and may be two or more layers, and, for example, the second p
The type nitride semiconductor layer 7b may be formed by stacking a plurality of layers.

The Al mixed crystal ratio of each layer is particularly limited.
Not a thing. However, Al_aGa _1-aRepresented by the N layer
In the first p-type nitride semiconductor layer 7a,
If the ratio a is 0 or more, the decomposition of the active layer is effectively suppressed.
can do. To make full use of this function,
More preferably, Al with a> 0_aGa_1-aN-layer, nitriding
Among the semiconductors, a layer that has a relatively high melting point and is chemically stable,
It can be provided closer to (preferably in contact with) the active layer.
Can more effectively suppress decomposition of the active layer.
It In the present invention, the first p-type nitride semiconductor
Al mixed crystals of the layer 7a and the second p-type nitride semiconductor layer 7b
The ratio a, b is preferably greater than 0.1, and more preferably
If it is larger than 0.2, it is good with the active layer.
It is possible to take a large offset (form a potential barrier)
Good carrier injection without carrier overflow
Can be realized. At this time, the first p-type nitride half
The conductor layer 7a and the second p-type nitride semiconductor layer 7b are the same
Is preferable, that is, a = b.
Under such conditions, each source gas and impurity gas may be
It is possible to easily adjust the amount of gas supplied and to improve controllability.
The first p-type nitride semiconductor layer and the second p-type nitride semiconductor layer.
The stable semiconductor layer can be grown with high accuracy.
It

Next, growth conditions for the first p-type nitride semiconductor layer 7a and the second p-type nitride semiconductor layer 7b will be described. As the growth temperature, it is preferable to grow the second p-type nitride semiconductor layer at a temperature higher than that of the first p-type nitride semiconductor layer. Particularly, when the specific growth temperature of the first p-type nitride semiconductor layer is set to about 850 to 950 ° C. and the same temperature as the temperature for growing the active layer is set, the decomposition of the active layer 6 containing In is prevented. Is preferred and is preferable. And the second
The growth temperature of the p-type nitride semiconductor layer is preferably set to, for example, about 100 ° C. higher than the growth temperature of the active layer, whereby AlGa having better crystallinity is obtained.
An N layer can be formed.

Further, the first p-type nitride semiconductor layer and the second p-type nitride semiconductor layer
The atmosphere during the growth of the p-type nitride semiconductor layer is preferably different. That is, the first p-type nitride semiconductor is preferably grown in the same atmosphere as the active layer, and by doing so, decomposition of the active layer can be prevented. Further, the second p-type nitride semiconductor is grown in a preferable atmosphere to form a good offset. By doing this, due to the difference in crystal growth morphology between the two layers,
The first p-type nitride semiconductor layer can be a layer that prevents decomposition of the active layer, and the second p-type nitride semiconductor can be a layer that is responsible for realizing good offset, and each layer can have a unique function. . Specifically, the growth atmosphere of the first p-type nitride semiconductor layer is set to N _2, and the growth atmosphere of the second p-type nitride semiconductor layer is set to H ₂ , so that the layers each having the above-mentioned function are formed. Since it can be formed, the obtained device has good light emission characteristics.

Further, the p-type cap layer 7 is provided with at least 2 described above.
In the case where the first p-type nitride semiconductor layer is composed of layers, the thickness of each layer is 10 to 10 in order to suppress a rise in Vf (forward voltage) of the light emitting element due to the formation of the p-type cap layer. The range of 100 angstroms and the range of the second p-type nitride semiconductor layer are preferably set to 10 to 300 angstroms. Further, in order to suppress the increase in Vf to a smaller level, the first p-type nitride semiconductor layer is formed in an amount of 10 to 30.
Å range, the second p-type nitride semiconductor layer 10-100 Å
It is more preferable to set it in the angstrom range. Next, the p-type guide layer 8 is grown on the p-type cap layer 7. The p-type guide layer 8 is formed by growing a nitride semiconductor layer made of undoped GaN. The film thickness is 0.1
˜0.07 μm is preferable, and the film thickness in this range can lower the threshold value. Further, as described above, the p-type guide layer 8 is grown as an undoped layer, but the Mg doped in the p-type cap layer 7 diffuses and 1 × 10 ¹⁶ / cm ³ to 1 × 10 ¹⁸ / cm ³ is diffused. Mg is contained in the range.

Next, the p-type cladding layer 9 is replaced with the p-type guide layer 8
Grow up. As the p-type cladding layer 9, Al_fG
a_1-fNitride semiconductor containing N (0 <f ≦ 1)
Layer, preferably Al_fGa_1-fN (0.05 ≦ f ≦
Multilayer film having a nitride semiconductor layer containing 0.15)
It is preferably a layer. The composition differs from that of a multilayer film.
A layer having a multi-layered film structure in which nitride semiconductor layers are laminated.
Yes, for example, Al_fGa _1-fN layer and Al_fGa
_1-fA mixture of N and a nitride semiconductor having a different composition, for example, Al.
Different crystal ratios, ternary mixed crystals containing In,
Alternatively, it is formed by combining and stacking with a layer made of GaN or the like.
It is a thing. Among these, especially Al_fGa_1-fN and Ga
At the same temperature, a multilayer film formed by combining N and N
It is preferable because a nitride semiconductor layer with good crystallinity can be stacked with
Yes. A more preferable multilayer film is undoped Al._fG
a_1-fGaN doped with N and p-type impurities (eg Mg)
It is a combination formed by stacking and. The p-type impurity is A
l_fGa_1-fN may be doped. of p-type impurities
Dope amount is 1 × 10¹⁷/ Cm^Three~ 1 x 10¹⁹/ C
m ^ThreeIs. p-type impurities are doped in this range
And bulk resistance with a doping amount that does not impair crystallinity
Can be lowered.

In this multilayer film, the thickness of a single layer is 10
The thickness is 0 angstroms or less, preferably 70 angstroms or less, more preferably 40 angstroms or less, and preferably 10 angstroms or more. Single film thickness is 100
When the thickness is less than or equal to angstrom, the n-type cladding layer has a superlattice structure, and although Al is contained, generation of cracks can be prevented and the crystallinity of the entire n-type cladding layer can be improved. The total film thickness of the p-type cladding layer 9 is preferably 0.4 to 0.5 μm, and the forward voltage (Vf) can be reduced by setting it in this range.

The average Al composition of the entire p-type cladding layer 9 is expressed as Al _s Ga _1-s N, where s is 0.
It is preferable to set it in the range of 05 to 0.1. By doing so, it is possible to suppress the generation of cracks and obtain a good refractive index difference with the laser waveguide. Next, the p-type contact layer 10 is grown on the p-type cladding layer 9. The p-type contact layer is a layer obtained by growing a nitride semiconductor layer made of Mg-doped GaN. The film thickness is set to 10 to 200 angstrom. Doping amount of Mg is 1 × ^{10 1 9}
/ Cm ³ to 1 × 10 ²² / cm ³ . By adjusting the film thickness and the doping amount of Mg in this way, the carrier concentration of the p-type contact layer can be increased, and good ohmic contact can be formed with the p-electrode.

In the device of the present invention, the ridge-shaped stripe 200 is formed by etching from the p-type contact layer to a predetermined depth. In the present embodiment, for example, a ridge-shaped stripe 200 formed by etching from the p-type contact layer 10 to the middle of the p-type cladding layer 9 as shown in FIG. 1, or the p-type contact layer 10.
It is possible to apply various ridge-shaped stripes 200 such as the ridge-shaped stripe 200 formed by etching from to the n-type contact layer 2.

The side surface of the ridge-shaped stripe 200 formed by etching and the plane of the nitride semiconductor layer continuous to the side surface have a value smaller than the refractive index of the laser waveguide region, for example, as shown in FIG. The insulating film 62 is formed. The insulating film formed on the side surface of the stripe or the like is selected from the group consisting of Si, V, Zr, Nb, Hf, and Ta having a refractive index of about 1.6 to 2.3, for example. Oxide containing at least one element, B
N, AlN and the like are mentioned, and preferably, one or more elements selected from oxides of Zr and Hf and BN.

Further, the p-type contact layer 1 which is the uppermost layer of the ridge-shaped stripe 200 via the insulating film 62.
A p-electrode is formed on the surface of 0. The width of the ridge-shaped stripe 200 formed by etching is 0.
The thickness is 5 to 4 μm, preferably 1 to 3 μm. When the width of the ridge-shaped stripe 200 is set in this range, the horizontal transverse mode can be set to the single mode. Further, it is preferable to form the ridge-shaped stripe 200 by etching deeper than the interface between the p-type clad layer 9 and the laser waveguide region, because the aspect ratio can be close to 1.

As described above, the ridge-shaped stripe 2
00, the stripe width, and the refractive index of the insulating film on the side surface of the stripe are preferably set so that a single-mode laser beam can be obtained and the aspect ratio is closer to a circular shape. Easy lens design. Further, in the device of the present invention, various conventionally known ones can be appropriately selected and used as the p electrode, the n electrode and the like.

The present invention is not limited to the layer structure described in the embodiment, and the following modifications are possible. Modified Example In the nitride semiconductor light emitting device according to the embodiment, the first p layer for preventing the decomposition of the active layer 6 is formed as a part of the p-type cap layer 7.
Although the type nitride semiconductor layer 7a is formed, in the present invention, at least one first p-type nitride semiconductor layer may be formed between the p-type cladding layer 7 and the active layer. That is, in the nitride semiconductor light emitting device according to the present invention, the first band gap between the p-type cladding layer 7 and the active layer is lower than that of the p-type cladding layer 7 and has a bandgap larger than that of the p-type cladding layer. When the p-type nitride semiconductor layer is formed, it is possible to maintain the crystal quality of the active layer and form the p-type clad layer having good crystallinity. Further, in this modified example, the band gap of the first p-type nitride semiconductor layer is set to be larger than that of the cladding layer, so that a certain carrier confinement function can be exhibited. Therefore, the nitride semiconductor light emitting device of this modification can have higher output and device reliability as compared with the conventional example.

[0068]

The following is an example of an embodiment of the present invention. However, the present invention is not limited to this. In addition, although the present embodiment shows MOVPE (metalorganic vapor phase epitaxy), the method of the present invention is not limited to MOVPE, and for example, HVPE (halide vapor phase epitaxy),
All known methods for growing nitride semiconductors can be applied, such as MBE (Molecular Beam Vapor Deposition).

Example 1 As Example 1, the nitride semiconductor laser device according to one embodiment of the present invention shown in FIG. 1 is manufactured. As a heterogeneous substrate, as shown in FIG. 3, a C-plane off-angled in a step-like manner is used as a main surface, an off-angle angle θ = 0.15 °, a step difference of about 20 Å, and a terrace width W of about 800 Å. A sapphire substrate whose surface is the A surface and steps are perpendicular to the A surface is prepared.

This sapphire substrate was set in a reaction vessel, the temperature was set to 510 ° C., hydrogen was used as a carrier gas, ammonia and TMG (trimethylgallium) were used as source gases, and low temperature growth of GaN was performed on the sapphire substrate. The buffer layer is grown to a film thickness of 200 Å. After growing the buffer layer, stop only TMG and raise the temperature to 10
The temperature is raised to 50 ° C., and when it reaches 1050 ° C., TMG, ammonia, and silane gas are used as source gases, and a high-temperature grown buffer layer made of undoped GaN is grown to a thickness of 5 μm.

Next, a stripe-shaped photomask is formed on the wafer on which the high-temperature grown buffer layer is laminated, and the CV is formed.
A protective film made of SiO _{2 having a} stripe width of 18 μm and a window width of 3 μm is formed with a film thickness of 0.1 μm by the D device. The stripe direction of the protective film is perpendicular to the sapphire A surface. After forming the protective film, the wafer is transferred to a reaction container, and TMG and ammonia are used as source gases at 1050 ° C. to grow a nitride semiconductor layer made of undoped GaN to a thickness of 15 μm to obtain a nitride semiconductor substrate 1. . Using the obtained nitride semiconductor as the nitride semiconductor substrate 1, the following element structure is grown.

(Undoped n-type contact layer) [not shown in FIG. 1] 105 on the nitride semiconductor substrate 1
TMA (trimethylaluminum) as a source gas at 0 ° C,
Undoped Al using TMG and ammonia gas
The n-type contact layer composed of _0.05 Ga _{0.9 5} N 1
Grow with a film thickness of μm.

(N-type contact layer 2) Next, at the same temperature, TMA, TMG, and ammonia gas are used as source gases, and silane gas (SiH ₄ ) is used as an impurity gas.
The 3 × ¹⁰ 18 / cm ³ doped with _{Al 0.05} Ga
_The n-type contact layer 2 made of _0.95 N is grown to a film thickness of 3 μm. No fine cracks are generated in the grown n-type contact layer 2, and the generation of fine cracks is well prevented. Further, even if minute cracks are generated in the nitride semiconductor substrate 1, the propagation of the minute cracks can be prevented by growing the n-type contact layer 2 and an element structure having good crystallinity can be grown. The crystallinity is improved more by growing the undoped n-type contact layer as described above than in the case of only the n-type contact layer 2.

(Crack prevention layer 3) Next, the temperature is set to 800.
℃, TMG, TMI (trimethylin
) And ammonia, using silane gas as an impurity gas.
5 × 10 Si ¹⁸/ Cm^ThreeDoped In
_0.08Ga_0.92The crack prevention layer 3 made of N
Grow with a film thickness of 0.15 μm.

(N-type clad layer 4) Next, the temperature is set to 105.
At 0 ° C., TMA, TMG, and ammonia are used as source gases, and an A layer made of undoped Al _0.14 Ga _0.86 N is grown to a film thickness of 25 Å. Then, TMA is stopped and impurity gas is added. Then, a silane gas is used, and a B layer made of GaN doped with Si at 5 × 10 ¹⁸ / cm ³ is grown to a film thickness of 25 Å.
Then, this operation is repeated 160 times to stack the A layer and the B layer to grow the n-type cladding layer 4 formed of a multilayer film (superlattice structure) having a total film thickness of 8000 angstroms.

(N-type guide layer 5) Next, at the same temperature,
Using TMG and ammonia as a source gas, an n-type guide layer made of undoped GaN is grown to a thickness of 0.075 μm. (Active layer 6) Next, the temperature is set to 800 ° C., TMI, TMG, and ammonia are used as source gases, silane gas is used as an impurity gas, and N ₂ is used as a carrier gas.
The reaction vessel was filled with N ₂ atmosphere and Si was added at 5 × 10 ¹⁸ /
A barrier layer of cm ³ -doped In 0 _{.01Ga 0 .99N} is grown to a thickness of 100 Å.
Then, the silane gas was stopped and undoped In _0.11
A well layer made of Ga _0.89 N is grown to a film thickness of 50 Å. This operation is repeated three times, and finally, the active layer 6 having a multiple quantum well structure (MQW) having a total film thickness of 550 angstroms in which barrier layers are laminated is grown.

(P-type cap layer 7) Next, at the same temperature,
In a similar atmosphere (N ₂ ), TMA, TMG, and ammonia are used as source gases, Cp ₂ Mg (cyclopentadienyl magnesium) is used as an impurity gas, and Mg is 1 ×.
A first p-type nitride semiconductor layer 7a made of Al _0.4 Ga _0.6 N doped with 10 ¹⁹ / cm ³ is grown to a film thickness of 20 Å. Next, after changing the carrier gas to H ₂ to create an H ₂ atmosphere and raising the temperature to 960 ° C., Mg
Of Al _0.4 Ga doped with 1 × 10 ¹⁹ / cm ³
_A second p-type nitride semiconductor layer 7b made of _0.6 N is grown to a film thickness of 70Å. The first p-type nitride semiconductor layer and the second p-type nitride semiconductor layer are used to form the p-type cap layer 7 with a layer thickness of 90Å.

(P-type guide layer 8) Next, the temperature is set to 1050.
C., using TMG and ammonia as the source gas, the p-type guide layer 8 made of undoped GaN is added to 0.075.
Grow with a film thickness of μm. This p-type guide layer 8 is grown as undoped, but M from the p-type cap layer 7 is grown.
Due to the diffusion of g, the Mg concentration becomes 5 × 10 ¹⁶ / cm ³ , which indicates p-type.

(P-type clad layer 9) Next, at the same temperature, using TMA, TMG and ammonia as source gases,
Two A layers made of undoped Al _0.1 Ga _0.9 N
It is grown to a thickness of 5 Å, followed by TMA
Stop, and use Cp ₂ Mg as an impurity gas,
2 × 10 ¹⁸ / cm ³ B layer of GaN
Grow with a thickness of 5 Å. Then, this operation is repeated 100 times to stack the A layer and the B layer to grow the p-type cladding layer 9 composed of a multilayer film (superlattice structure) having a total film thickness of 5000 angstroms.

(P-type contact layer 10) Next, at the same temperature, TMG and ammonia were used as source gases, Cp ₂ Mg was used as an impurity gas, and Mg was 1 × 10 ²⁰ / c.
A p-type contact layer 10 made of m ³ -doped GaN is grown to a film thickness of 150 Å. After completion of the reaction, the wafer was placed in a reaction vessel in a nitrogen atmosphere at 70
Annealing is performed at 0 ° C. to further reduce the resistance of the p-type layer. After annealing, remove the wafer from the reaction vessel,
A protective film made of SiO ₂ is formed on the surface of the uppermost p-side contact layer, and is etched with SiCl ₄ gas using RIE (reactive ion etching) to form an n-electrode as shown in FIG. The surface of the n-side contact layer 2 is exposed.

Next, as shown in FIG. 4A, p of the uppermost layer is
On the almost entire surface of the side contact layer 10, by a PVD device,
After forming a first protective film 61 made of Si oxide (mainly SiO ₂ ) with a film thickness of 0.5 μm, a mask having a predetermined shape is applied on the first protective film 61, and a photoresist is used. The third protective film 63 has a stripe width of 1.8 μm.
m and the thickness is 1 μm. Next, as shown in FIG. 4B, after forming the third protective film 63, a CF ₄ gas is used by a RIE (reactive ion etching) device, and the third protective film 63 is used as a mask to remove the first protective film 63. The protective film is etched to form stripes. After that, the photoresist is treated with an etching solution to remove only the photoresist.
As shown in (c), a first protective film 61 having a stripe width of 1.8 μm can be formed on the p-side contact layer 10.

Further, as shown in FIG. 4D, after the stripe-shaped first protective film 61 is formed, S is again formed by RIE.
The p-side contact layer 10 and the p-side clad layer 9 are etched using iCl ₄ gas to obtain a stripe width of 1.
An 8 μm ridge-shaped stripe 200 is formed. However, as shown in FIG. 1, the ridge-shaped stripe 200 is formed so as to avoid the central portion of the protective film above the protective film formed during the ELOG growth.

After forming the ridge stripe, the wafer is PVd.
4E, the second protective film 62 made of Zr oxide (mainly ZrO ₂ ) is formed on the first protective film 61 and the p exposed by etching as shown in FIG.
It is continuously formed on the side clad layer 9 with a film thickness of 0.5 μm. When the Zr oxide is formed in this manner, it is preferable because the pn plane is insulated and the transverse mode is stabilized. Next, the wafer is dipped in hydrofluoric acid, and then, as shown in FIG.
As shown in, the first protective film 61 is removed by the lift-off method.

Next, as shown in FIG. 4G, the surface of the p-side contact layer exposed by removing the first protective film 61 on the p-side contact layer 10 is made of Ni / Au.
The electrode 20 is formed. However, the p electrode 20 has a stripe width of 100 μm and is formed over the second protective film 62 as shown in this figure. After forming the second protective film 62,
As shown in FIG. 1, on the exposed surface of the n-side contact layer 2, an n electrode 21 made of Ti / Al is formed in a direction parallel to the stripe.

As described above, the sapphire substrate of the wafer on which the n electrode and the p electrode were formed was polished to 70 μm, and then cleaved in a bar shape from the substrate side in the direction perpendicular to the striped electrodes, A resonator is formed on the cleavage plane (11-00 plane, plane corresponding to side surface of hexagonal columnar crystal = M plane).
A dielectric multilayer film made of SiO ₂ and TiO ₂ is formed on the cavity surface, and finally the bar is cut in a direction parallel to the p-electrode to obtain a laser device as shown in FIG. The resonator length is 3
It is desirable that the thickness is from 00 to 500 μm. The obtained laser device was placed on a heat sink, and each electrode was wire-bonded, and laser oscillation was attempted at room temperature.

As a result, the threshold value is 2.5 k at room temperature.
A / cm ² , threshold voltage 5 V, oscillation wavelength 400 nm
The continuous oscillation was confirmed, and it has a life of 10,000 hours or more at room temperature. Furthermore, when driven at 30 mW, Vf was greatly reduced by 0.5 V as compared with Comparative Example 1. This results in that the p-type cap layer has at least the above-mentioned two-layer structure and thus the Ith does not increase and the device life is improved. At 2.0 mA, V
Although f shows a decrease of about 0.1 to 0.2 V, it can be seen that the device characteristics of the light emitting device of the present invention are greatly improved from those of the conventional device at high output.

[Comparative Example 1] A nitride semiconductor laser device is manufactured in the same manner as in Example 1, except that the p-type cap layer 7 is composed of one layer as follows. (P-type cap layer 7) After growing the active layer, TMA, TMG, and ammonia are used as source gases at the same temperature (800 ° C.) and the same atmosphere (N ₂ atmosphere), and Cp ₂ Mg ( Cyclopentadienyl magnesium)
Al doped with Mg at 5 × 10 ¹⁸ / cm ³
_The p-type cap layer 7 made of _0.4 Ga _0.6 N is grown to a film thickness of 100 Å. The obtained laser device had higher Vf and shorter device life than those of Example 1.

[Example 2] N as a carrier gas_TwoRaw material
TMA, TMG, ammonia in gas, Cp in impurity gas_Two
Using Mg (cyclopentadienyl magnesium),
At a temperature of 800 ° C, that is, at a temperature similar to that at the time of growing the active layer.
In the same atmosphere, Mg with a film thickness of 30Å is added to 1 × 10¹⁹
/ Cm^ThreeDoped Al_0.4Ga_0.6The first consisting of N
No. 1 p-type nitride semiconductor layer 7a is grown, and carrier gas
To H_TwoAfter heating to 960 ° C. under a hydrogen atmosphere,
Mg of 1 × 10 with a film thickness of 100Ź⁹/ Cm^ThreeDoped
Al _0.4Ga_0.6N is grown and p-type
In the same manner as in Example 1 except that the cap layer is formed, the laser
The device is formed. The obtained laser device is the same as that of Example 1.
It has almost the same good element reliability and output
With respect to the characteristics as well, the threshold current Ith rises at the same Vf.
However, it was a device capable of continuous oscillation at high output.

The film thicknesses of the first p-type nitride semiconductor layer and the second p-type nitride semiconductor layer are 100 Å,
100 Å, then 100 Å and 400 Å respectively,
Investigate changes in device characteristics. When the thickness of each layer is 100Å,
Although there is no significant change in the device characteristics, an increase in Vf begins to appear, and the output characteristics tend to be slightly inferior. At respective film thicknesses of 100Å and 400Å, this tendency becomes remarkable,
An increase in Vf due to an increase in film thickness, and an increase in threshold current due to this, were observed.

Example 3 A laser device is formed in the same manner as in Example 1 except that the composition of the first p-type nitride semiconductor layer is Al _0.2 Ga _0.8 N. The obtained laser device has almost the same output characteristics as in Example 1, which means that the first p-type nitride semiconductor layer acts as a potential barrier with the active layer, confines electrons, and It shows that the p-type nitride semiconductor layer does not contribute as much as that of the p-type nitride semiconductor layer, and that it contributes to good crystal growth of the upper second p-type nitride semiconductor layer and protection of the active layer. It is shown. Therefore, the element reliability, especially the element life,
Similar to Example 1, it exhibited good life characteristics.

[Fourth Embodiment] A fifth embodiment will be described with reference to FIG. Substrate 100 made of sapphire (C surface) M
Set in the reaction vessel of OVPE, while flowing hydrogen,
The temperature of the substrate is raised to 1050 ° C., and the substrate is cleaned. (Buffer layer 101) Then, the temperature is lowered to 510 ° C., hydrogen is used as a carrier gas, and ammonia and TM are used as a source gas.
G (trimethylgallium) is used to form G on the substrate 100.
A buffer layer 101 made of aN is grown to a film thickness of about 150 Å.

(Undoped GaN Layer 103) After growing the buffer layer 101, only TMG is stopped and the temperature is raised to 1050 ° C. When the temperature reaches 1050 ° C., TMG and ammonia gas are similarly used as the source gas, and the undoped GaN layer 103 is grown to a film thickness of 1.5 μm.

(N-Type Contact Layer 104) Then 105
At 0 ° C., TMG, ammonia gas was used as the source gas, and silane gas was used as the impurity gas, and Si was added at 4.5 × 10 ¹⁸ /
cm ³ -doped GaN n-type contact layer 104
Are grown to a film thickness of 2.25 μm.

(N-type clad layer 105) Next, only silane gas is stopped, and an undoped GaN layer is grown to a thickness of 75 angstroms at 1050 ° C. using TMG and ammonia gas, and then silane gas is added at the same temperature. S
A GaN layer doped with i of 4.5 × 10 ¹⁸ / cm ³ is grown to a film thickness of 25 Å. In this way
A consisting of 75 angstrom undoped GaN layer
A pair consisting of a layer and a 25 Å B layer with a Si-doped GaN layer is grown. And pair 2
Five layers are stacked to have a thickness of 2500 Å, and an n-type first multilayer film layer 5 made of a multilayer film having a superlattice structure is grown.

(N-type buffer layer 106) Next, at a similar temperature, a first layer of undoped GaN is grown to 40 Å, and then the temperature is set to 800 ° C.
Undoped In _0.13 G using G, TMI, and ammonia
A second layer of _0.87 N a is grown to 20 Å. Then, these operations are repeated so that 10 layers are alternately laminated in the order of the second layer + the first layer, and finally GaN is formed.
The n-type buffer layer 106 formed of a multi-layered film having a superlattice structure in which the second layer formed of
It is grown to a film thickness of angstrom.

(Active layer 107) Next, the carrier gas is changed to N 2.
_{In place of 2} , a barrier layer made of undoped GaN was grown to a thickness of 200 Å in a nitrogen atmosphere,
Subsequently, the temperature is set to 800 ° C., and a well layer made of undoped In _0.4 Ga _0.6 N is grown to a thickness of 30 Å using TMG, TMI, and ammonia. Then, the barrier layer is 5 in the order of barrier + well + barrier + well.
An active layer 10 having a multiple quantum well structure having a total film thickness of 1120 angstroms, which is formed by alternately stacking four layers and well layers.
Grow 7

(P-type cap layer 108) Same as active layer
And N as carrier gas_TwoWith the active layer growth
TMA, TM as the source gas under the same atmosphere and temperature
G, ammonia, Cp for impurity gas_TwoMg (cyclopen
Tadienyl magnesium) with a film thickness of 20 Å
1 x 10 of ROHM Mg¹⁹/ Cm^ThreeDoped Al
_0.4Ga_0.6First p-type nitride semiconductor layer made of N
7a is grown and carrier gas is H_TwoInstead of hydrogen atmosphere
After raising the temperature to 960 ° C under air, the film thickness is 60 Å.
1 × 10 for Mg ¹⁹/ Cm^ThreeDoped Al
_0.4Ga_0.6N is grown and the film thickness is 80
A ngstrom p-type cap layer is formed.

(P-type Multilayer Clad Layer 109) Next, TMG, TMA, ammonia, Cp ₂ M at a temperature of 1050 ° C.
g (cyclopentadienyl magnesium), Mg
1 × 10 ²⁰ / cm ³ -doped p-type Al _0.2 Ga _0.8 N having a thickness of 40 Å was grown as a first layer, and the temperature was then raised to 800 ° C. to obtain TMG, TMI, ammonia, and Cp ₂ A second layer of In _0.03 Ga _0.97 N doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is grown to a thickness of 25 Å. Then, these operations are repeated, and five layers are alternately laminated in the order of first and second,
Finally, a p-type multilayer clad layer 109 made of a multilayer film having a superlattice structure in which the first layer is grown to a thickness of 40 angstroms is grown to a thickness of 365 angstroms.

(P-type GaN contact layer 110) Next, at 1050 ° C., a p-type contact layer 110 made of p-type GaN doped with Mg of 1 × 10 ²⁰ / cm ³ was used to have a thickness of 700 Å using TMG, ammonia and Cp 2 Mg. Grow with film thickness. After the reaction is completed, the temperature is lowered to room temperature, and the wafer is annealed at 700 ° C. in a reaction vessel in a nitrogen atmosphere to further reduce the resistance of the p-type layer. After annealing, the wafer is taken out from the reaction container, a mask having a predetermined shape is formed on the surface of the uppermost p-type contact layer 110, and etching is performed from the p-type contact layer side by an RIE (reactive ion etching) device. As shown in FIG. 5, the surface of the n-type contact layer 104 is exposed.

After etching, a light-transmitting p-electrode 111 containing Ni and Au having a film thickness of 200 angstrom is formed on almost the entire surface of the p-type contact layer which is the uppermost layer, and the p-electrode 111.
A p-pad electrode (not shown) made of Au for bonding is formed thereon with a film thickness of 0.5 μm. On the other hand, an n-electrode 112 containing W and Al was formed on the surface of the n-type contact layer 104 exposed by etching to obtain an LED element. This LED element has a forward current of 20 mA,
It showed pure green light emission of 520 nm and Vf was 3.5V. As described above, the LED element also shows a good Vf, and the element life is p as well as the laser element.
LED with a mold cap layer having a structure as in Comparative Examples 1 and 2
Compared to the device, the device has high output with suppressed increase of Vf, and high device reliability supported by favorable growth of the second p-type nitride semiconductor.

[Comparative Example 2] As a p-type cap layer, H ₂ was used as a carrier gas in a hydrogen atmosphere at a temperature of 960 ° C.
And Al _0.2 doped with Mg at 1 × 10 ¹⁹ / cm ³
A laser device was obtained in the same manner as in Example 1 except that Ga _0.8 N was formed to a film thickness of 70Å. The obtained laser device is
Although Vf was slightly higher than that in Example 1, the difference in oscillation was not so large, but the device life was extremely poor and did not reach as long as 10,000 hours. It was found that there were many causes due to decomposition of the active layer at the time of driving.

[0102]

According to the present invention, the first p-type nitride semiconductor layer prevents decomposition of the active layer, in particular, evaporation and separation of In, and the second p-type nitride semiconductor layer has good crystallinity. Since it is formed, it is possible to take a good offset with the active layer,
The resulting light emitting device has a reduced Vf and an improved device life, which is improved.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a nitride semiconductor laser device according to an embodiment of the present invention.

FIG. 2 is a unit cell diagram showing a plane orientation of sapphire.

FIG. 3 is a schematic cross-sectional view showing a partial shape of an off-angled dissimilar substrate.

FIG. 4 is a schematic cross-sectional view showing a partial structure of a wafer in each step of the method which is an embodiment of forming a ridge-shaped stripe 200.

FIG. 5 is a schematic cross-sectional view of an LED element of Example 5 according to the present invention.

[Explanation of symbols]

1 ... Nitride semiconductor substrate, 2 ... n-type contact layer, 3 ... Crack prevention layer, 4 ... n-type cladding layer, 5 ... n-type guide layer, 6 ... Active layer, 7a ... a first p-type nitride semiconductor layer, 7b: second p-type nitride semiconductor layer, 7 ... p-type cap layer, 8 ... p-type guide layer, 9 ... p-type cladding layer, 10 ... p-type contact layer.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5F041 AA40 AA43 AA44 CA04 CA05                       CA12 CA40 CA46 CA65 CA88                 5F045 AA04 AB14 AB17 AC01 AC08                       AC12 AC15 AD13 AD14 AD15                       AF09 AF13 BB13 CA09 CA13                       DA53                 5F073 AA13 AA45 AA51 AA55 AA74                       AA77 AA83 AA89 CA07 CB05                       DA05 DA25 EA24 EA28

Claims (18)

[Claims] 1. An n made of at least an n-type nitride semiconductor
A nitride semiconductor light emitting device comprising: a clad layer, an active layer made of a nitride semiconductor containing In, and a p-type clad layer made of a p-type nitride semiconductor, wherein the active layer and the p-type clad layer are provided between the active layer and the p-type clad layer. , _Al a Ga
_1-a N (0 <a <1) and a first p-type nitride semiconductor layer having an energy gap larger than that of the p-type cladding layer and Al _b Ga _1-b N (0 <b <1). A second p-type nitride semiconductor layer having the following structure. 2. The nitride semiconductor light emitting device according to claim 1, wherein the first p-type nitride semiconductor layer is formed in contact with the active layer. 3. The film thickness of the first nitride semiconductor layer is 1
The nitride semiconductor light emitting device according to claim 1, wherein the thickness is 0 Å or more and 100 Å or less, and the thickness of the second nitride semiconductor layer is 10 Å or more and 300 Å or less. 4. The active layer comprises In _c Ga _1-c N (0
The nitride semiconductor light emitting device according to claim 1, which has a multiple quantum well structure including a well layer of ≦ c <1). 5. The active layer comprises In _c Ga _1-c N (0
≦ c <1), the p-type cladding layer is made of Al _x Ga _1-x N (0 <x <1),
In addition, the first p-type nitride semiconductor layer made of Al _a Ga _1-a N (0 <a <1) and the Al _b Ga _1-b N (0
2. The nitride semiconductor light emitting device according to claim 1, wherein the second p-type nitride semiconductor layer of <b <1) has a composition set so as to satisfy x ≦ a and x ≦ b, respectively. 6. A nitride semiconductor light emitting device comprising an active layer made of a nitride semiconductor containing In between an n-type clad layer made of an n-type nitride semiconductor and a p-type clad layer made of a p-type nitride semiconductor. In, the energy gap between the active layer and the p-type cladding layer is larger than that of the p-type cladding layer, that is, Al _a Ga _1-a N.
A nitride semiconductor light-emitting device comprising a first p-type nitride semiconductor layer made of (0 <a <1) and grown at a lower temperature than the cladding layer. 7. The nitride semiconductor light emitting device according to claim 6, wherein the first p-type nitride semiconductor layer is grown by a metal organic chemical vapor deposition method using N ₂ gas. 8. The active layer comprises In _c Ga _1-c N (0
The nitride semiconductor light emitting device according to claim 6, which has a multiple quantum well structure including a well layer of ≦ c <1). 9. The active layer comprises In _c Ga _1-c N (0
≦ c <1), the p-type cladding layer is made of Al _x Ga _1-x N (0 <x <1),
7. The nitride according to claim 6, wherein the composition of the first p-type nitride semiconductor layer made of Al _a Ga _1-a N (0 <a <1) is set to satisfy x ≦ a. Semiconductor light emitting device. 10. An active layer made of a nitride semiconductor containing In is provided between an n-type clad layer made of an n-type nitride semiconductor and a p-type clad layer made of a p-type nitride semiconductor, and the p-type clad is provided. big Al y _{Ga 1-y} N band gap than the p-type cladding layer between the layer active layer
A nitride semiconductor light emitting device having a p-type cap layer made of (0 <y <1), wherein the p-type cap layer is a p-type Al _a Ga _1-a N (0
<A <1) first p-type nitride semiconductor layer, and p-type Al _b G formed on the first p-type nitride semiconductor layer
a _1-b N (0 <b <1) and a second p-type nitride semiconductor layer having fewer crystal defects than the first p-type nitride semiconductor layer, and A nitride semiconductor light emitting device having a thickness of 10 Å or more and 1000 Å or less. 11. The nitride semiconductor light emitting device according to claim 10, wherein the first p-type nitride semiconductor layer is grown on the active layer by a metal organic chemical vapor deposition method using N ₂ gas. 12. The film thickness of the first p-type nitride semiconductor layer is 10 Å or more and 100 Å or less, and the film thickness of the second p-type nitride semiconductor layer is 10 Å or more and 300 Å or less. The nitride semiconductor light emitting device according to claim 10, which has a thickness. 13. The active layer comprises In _c Ga _1-c N.
The nitride semiconductor light emitting device according to claim 10, which has a multiple quantum well structure including a well layer of (0 ≦ c <1). 14. An activity comprising a nitride semiconductor containing In.
On the layer, Al_yGa _1-yP consisting of N (0 <y <1)
Nitride semiconductor light emission including the step of growing a mold cap layer
A method of manufacturing an element, comprising: The step of growing the p-type cap layer comprises: A metal-organic vapor phase epitaxy method using nitrogen gas on the active layer
From Al_aGa_{1- a}First consisting of N (0 <a <1)
A first growth step of growing the p-type nitride semiconductor layer of Hydrogen gas was used on the first p-type nitride semiconductor layer.
Al by the metal organic chemical vapor deposition method_bGa_1-bN (0 <
growing a second p-type nitride semiconductor layer of b <1)
And a second growth step, The first p-type nitride semiconductor layer and the second p-type nitride semiconductor
The p-type cap layer having a body layer is 10 Å or more 1
Nitriding characterized by growing to a thickness of 000Å or less
Method for manufacturing semiconductor light emitting device. 15. The method for manufacturing a nitride semiconductor light emitting device according to claim 14, wherein the growth temperature in the second growth step is set higher than the growth temperature in the first growth step. 16. The method for manufacturing a nitride semiconductor light emitting device according to claim 14, wherein the growth temperature in the first growth step is set to be substantially the same as the growth temperature when growing the active layer. 17. In the first growth step, the first p-type nitride semiconductor layer is grown to a film thickness of 10 Å or more and 100 Å or less, and in the second growth step, the second p-type nitride semiconductor layer is formed.
15. The method for manufacturing a nitride semiconductor light emitting device according to claim 14, wherein the p-type nitride semiconductor layer is grown to a film thickness of 10 Å or more and 300 Å or less. 18. The growth temperature in the first growth step is set to 850 ° C. or higher and 950 ° C. or lower, and the growth temperature in the second growth step is set to 950 ° C. or higher.
A method for manufacturing the nitride semiconductor light emitting device according to.