JP3446660B2 - Nitride semiconductor light emitting device - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a light emitting diode,
Nitride semiconductors (In _X A) used for light-emitting devices such as laser diodes, or light-receiving devices such as solar cells and optical sensors.
The present invention relates to a nitride semiconductor device composed of 1 _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, and 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
A protective film made of SiO ₂ is partially formed on the aN layer, and GaN is grown again on the protective film by a vapor phase growth method such as metal organic vapor phase epitaxy (MOVPE). 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 device according to 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 made of a p-type nitride semiconductor.
A nitride semiconductor light emitting device comprising a p-type clad layer and a p-type guide layer between the active layer and the p-type clad layer, wherein the active layer is formed between the p-type guide layer and the active layer. A p-type cap layer that forms a potential barrier is formed between the two, and the p-type cap layer is grown by metal organic chemical vapor deposition using N ₂ gas so as to prevent decomposition of the active layer. The first p-type nitride semiconductor layer made of _a Ga _{1 -a} N (0 <a <1) and grown by metalorganic vapor phase epitaxy using H ₂ gas to form the potential barrier. And a second p-type nitride semiconductor layer made of Al _b Ga _{1 -b} N (0 <b <1).

Further, a third nitride semiconductor device according to the present invention comprises an n-type clad layer made of at least an n-type nitride semiconductor, an active layer made of a nitride semiconductor containing In, and a p-type cladding layer.
A p-type clad layer made of a p-type nitride semiconductor, and a p-type guide layer between the active layer and the p-type clad layer. In between, a p-type cap layer that forms a potential barrier with the active layer is formed, and the film thickness of the p-type cap layer is set to 20 Å or more and 400 Å or less, and
The p-type cap layer is made of Al _a Ga _1-a N (0 <a <1) grown to a film thickness in the range of 10Å to 100Å, and is a first p-type nitride that prevents decomposition of the active layer. A second p-type nitride semiconductor layer formed of a semiconductor layer and Al _b Ga _1-b N (0 <b <1) having fewer crystal defects than the first p-type nitride semiconductor layer and forming the potential barrier. It is characterized by having and.

In the first and second nitride semiconductor devices according to the present invention, the film thickness of the first nitride semiconductor layer is 10 Å or more and 100 Å or less, and the second nitride semiconductor layer is It is preferable that the film thickness is 10 Å or more and 300 Å or less.

In the first and second nitride semiconductor devices according to the present invention, the active layer comprises In _c Ga _1-c N (0 ≦ c <1).
A multi-quantum well structure including a well layer made of

In the first and second nitride semiconductor devices according to the present invention, the active layer is formed of In _c Ga _1-c N (0 ≦ c <1).
And a p-type clad layer of A
l _x Ga _1-x N (0 <x <1), and Al _a Ga
_{A first} p-type nitride semiconductor layer made of _1-a N (0 <a <1) and a second p-type nitride semiconductor layer made of Al _b Ga _1-b N (0 <b <1) Can be composed of layers whose compositions are set so as to satisfy x ≦ a and x ≦ b, respectively.

Further, a nitride semiconductor light emitting device having 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 case of Al _a Ga _1-a N (0 <a <1) having a larger energy gap than the p-type clad layer between the active layer and the p-type clad layer, and is grown at a lower temperature than the clad layer. There is also a device including a first p-type nitride semiconductor 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 _{1 -a} N.
By providing the first p-type nitride semiconductor layer made of (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,
Although the active layer containing In decomposes, in the second nitride semiconductor device according to the present invention, first, the first p-type nitride film is formed between the active layer and the cladding layer at a temperature lower than that of the cladding layer. Of the p-type nitride semiconductor layer is grown to prevent the active layer from being decomposed by the first p-type nitride semiconductor layer, while the p-type nitride semiconductor layer has good crystallinity.
Since the type 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.

In the above nitride semiconductor light emitting device, in order to effectively suppress decomposition of the active layer, the first p-type nitride semiconductor layer is grown by metal organic chemical vapor deposition using N ₂ gas. Can be made.

In the nitride semiconductor light emitting device, the active layer may have a multiple quantum well structure including a well layer made of In _c Ga _1-c N (0 ≦ c <1).

In the above nitride semiconductor light emitting device, the active layer is a layer including a well layer made of In _c Ga _1-c N (0 ≦ c <1), and the p-type clad layer is Al _x Ga. _1-x N
(0 <x <1) and the Al _a Ga _1-a
The first p-type nitride semiconductor layer made of N (0 <a <1) can be formed by setting the composition so as to satisfy x ≦ a.

Further, in the first nitride semiconductor light emitting device according to the present invention, the first p-type nitride semiconductor layer and the second p-type nitride semiconductor layer are provided.
The total thickness of the p-type nitride semiconductor layers is 10Å or more 100
It is preferably set to 0 Å or less.

In the nitride semiconductor light emitting device according to the present invention constructed as described above, 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
The second p-type nitride semiconductor layer containing N (0 <b <1) and having few crystal defects makes it possible to effectively exhibit the function of confining carriers in the active layer and to improve the quality of the active layer. Can be kept at That is, under the growth conditions for growing AlGaN having good crystallinity, I
Since the active layer containing n is decomposed, the AlGaN layer is conventionally grown under the condition that the active layer is not decomposed. Therefore, it is difficult to form a p-type cap layer using AlGaN with good crystallinity. Therefore, it was difficult to effectively exert its function. Also, AlGa with good crystallinity
When a carrier confinement layer made of N is formed,
Decomposition of the active layer occurred, resulting in deterioration of light emitting characteristics.

On the other hand, in the nitride semiconductor device according to the present invention, first, the first p-type nitride semiconductor layer is grown on the side close to the active layer, and the first p-type nitride semiconductor layer is grown. Since it is possible to form the second p-type nitride semiconductor layer having good crystallinity while preventing decomposition of the active layer in the semiconductor layer,
It is possible to provide a light emitting device including a high-quality active layer and a p-type cap layer having good crystallinity.

That is, the nitride semiconductor device of the present invention is
A plurality of p-type cap layers functionally separated into a first p-type nitride semiconductor layer for preventing decomposition of the active layer and a second p-type nitride semiconductor layer for effectively confining carriers in the active layer. By forming the layer with the above-mentioned layer, the problems that have been related to the conventional trade-off relationship are solved.

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 nitride semiconductor light emitting device of the present invention, the active layer has a multiple quantum well structure having a plurality of InGaN well layers, and the p-type cap layer is the first p-type nitride semiconductor layer. And the second p-type nitride semiconductor layer, carriers can be effectively confined in the active layer of the multiple quantum well structure, and carriers can be well injected into the well layers. 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.

In the method for manufacturing a nitride semiconductor light emitting device according to the present invention, at least an n-type clad layer made of an n-type nitride semiconductor, an active layer made of a nitride semiconductor containing In, and a p-type made of a p-type nitride semiconductor. In the method for manufacturing a nitride semiconductor light emitting device having a type clad layer, Al _{a is} deposited on the active layer by a metal organic chemical vapor deposition method using nitrogen gas.
A _first growth step of growing a first p-type nitride semiconductor layer made of Ga _1-a N (0 <a <1), and hydrogen gas is used on the first p-type nitride semiconductor layer. A second growth step of growing a second p-type nitride semiconductor layer made of Al _b Ga _1-b N (0 <b <1) by the above-mentioned metal-organic chemical vapor deposition method. .

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 can be formed without decomposing the active layer containing In.
An a _1-a N (0 <a <1) layer can be formed. In the second growth step, Al _b Ga _1-b N (0 <b <0) having good crystallinity is formed on the first p-type nitride semiconductor layer.
Since the second p-type nitride semiconductor layer is grown using hydrogen gas capable of growing 1), the first p-type nitride semiconductor layer prevents the active layer from being decomposed while crystallizing. The second p-type nitride semiconductor layer having good properties can be grown. In addition, it is possible to suppress variations in the light emission characteristics between devices due to the in-plane distribution of In in the active layer containing In, 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 As shown in FIG. 1, a nitride semiconductor light emitting device according to an embodiment of the present invention has a p-type Al _x Ga ₁ layer formed on an active layer 6 made of a nitride semiconductor containing In. _-x N
A nitride semiconductor light emitting device, which is formed of (0 <x <1) and has a p-type cap layer 7 having a function of confining carriers in the active layer 6, wherein the p-type cap layer 7 is a p-type A layer.
l _a Ga _1-a N and a first p-type nitride semiconductor layer 7a composed of (0 <a <1), p -type _{Al b Ga 1-b N (} 0 <b <1)
And a second p-type nitride semiconductor layer 7b made of.

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 <1) in which the content of Al is adjusted so that the band gap has a desired value
The layer is mainly used, but has the following problems.

That is, in order to grow an AlGaN layer having few crystal defects and good crystallinity, metalorganic vapor phase epitaxy is used in an H ₂ atmosphere (using H ₂ as a carrier gas).
Although it is necessary to grow the AlGaN layer at a relatively high temperature,
There is a problem that the active layer is decomposed when the AlGaN layer is grown directly on the active layer 6 containing In in the H ₂ atmosphere. Therefore, p-type Al _x Ga _1-x N (0 <
Even if it is possible to form the p-type cap layer 7 having good crystallinity of x <1), the active layer 6 itself is deteriorated, and it is difficult to obtain expected light emission characteristics. It was When the growth temperature of the AlGaN layer in the H ₂ atmosphere is increased, the crystallinity of the grown AlGaN layer can be further improved, but the decomposition of the active layer containing In becomes more intense, which causes the emission lifetime to be shortened. It was In the present specification, simply referring to AlGaN means a nitride semiconductor in which a part of Ga in GaN is replaced by Al.

According to the present invention, H is formed on the active layer containing In.₂Atmosphere
N instead of surrounding air₂Growth of AlGaN layer in atmosphere and at low temperature
Forming an AlGaN layer without decomposing the active layer.
Find out what can be done and pay attention to that point
It was made. That is, the embodiment of the present invention
Nitride semiconductor light emitting device is a nitride semiconductor containing In
N on the active layer 6 made of₂Decompose the active layer beforehand in the atmosphere
Relatively thin p-type Al to prevent_aGa_1-aN (0 <
The first p-type nitride semiconductor layer 7a composed of a <1) is electrically charged.
It is formed to a thickness that does not deteriorate the child confinement function.
The active layer is decomposed by the first p-type nitride semiconductor layer 7a of
H to protect against ₂P-type Al in the atmosphere_bG
a_1-bSecond p-type nitride semiconductor consisting of N (0 <b <1)
The body layer 7b is formed.

The embodiment of the present invention will be described in more detail below with reference to FIG. FIG. 1 is a schematic sectional view showing a nitride semiconductor light emitting device (nitride semiconductor laser device) according to an embodiment of the present invention. The nitride semiconductor laser device shown in FIG. 1 is formed by doping an n-type impurity (for example, Si) with Al on a nitride semiconductor substrate 1 which is ELOG-grown on the upper surface of a heterogeneous substrate 100 different from a nitride semiconductor such as sapphire. n-type contact layer 2 made of _k Ga _1-k N (0 <k <1), Si-doped In _g Ga _1-g N (0.05 ≦
g ≦ 0.2) crack preventive layer 3, Al _e Ga _1-e
N of a multilayer film containing N (0.12 ≦ e <0.15)
-Type cladding layer 4, n-type guide layer 5 made of undoped GaN, active layer 6 of multiple quantum well structure made of In _c Ga _1-c N (0 ≦ c <1), Mg-doped Al _d Ga _1-d N
From a multilayer film including at least two p-type cap layers 7 (0 <d ≦ 1), p-type guide layers 8 made of undoped GaN, and Al _f Ga _{1 -f} N (0 <f ≦ 1) The p-type clad layer 9 and the p-type contact layer 10 made of Mg-doped GaN, and the ridge-shaped stripe 200 is formed by etching the p-type contact layer 10 to the n-type contact layer 2 to a predetermined width. . The p electrode is formed in contact with the p-type contact layer 10 which is the uppermost layer of the ridge-shaped stripe 200, and is formed on the n-type contact layer 2 exposed on one side of the ridge-shaped stripe 200.

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, an insulating material 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), Zn
Substrate materials different from conventionally known nitride semiconductors can be used, such as S, ZnO, GaAs, Si, and oxide substrates lattice-matched with 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.

The off-angle is stepped as described above.
Of the protective film directly or on the dissimilar substrate such as sapphire
Once the nitride semiconductor is grown, it can be partially (eg,
So that the surface of the dissimilar substrate is exposed at regular intervals)
It As a protective film, nitride semiconductor grows on the surface of the protective film.
Various materials that have the property of not growing or being difficult to grow
It can be used, for example, silicon oxide (SiO 2_X),
Silicon oxide (Si_XN_Y), Titanium oxide (TiO_X), Oxidation
Zirconium (ZrO_X) Oxides, nitrides, etc.
These multilayer films have a melting point of 1200 ° C or higher
A metal or the like can be used. As a preferred protective film material
For SiO ₂And 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 0.01 to
Grow Al _a Ga _1-a N set to 0.05. n
When the mold contact layer 2 is formed of a ternary mixed crystal containing Al,
Even if minute cracks are generated in the nitride semiconductor substrate 1, the propagation of the minute cracks can be prevented, and the lattice between the nitride semiconductor substrate 1 and the n-type contact layer 2 which has been a conventional problem. It is possible to prevent the generation of fine cracks in the n-type contact layer due to the difference in the constant and the coefficient of thermal expansion, which is preferable. The doping amount of n-type impurities is 1 × 10 ^18.
/ Cm ^{3 to} 5 × 10 ¹⁸ / cm ³ . An n electrode 21 is formed on the n-type contact layer 2. The film thickness of the n-type contact layer 2 is 1 to 10 μm. In addition, in the present embodiment, undoped Al _a Ga _1-a N (0 <a <1) may be grown between the nitride semiconductor substrate 1 and the n-type contact layer 2. When the layer is grown, the crystallinity of the n-type contact layer 2 can be improved and the life characteristics can be improved. In this case, the film thickness of the undoped n-type contact layer is set to 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.
Dog In _g Ga _1-g N (0.05 ≦ g ≦ 0.2) was grown and In _g G with _g set to 0.05 to 0.08
It is preferred to grow a1 _-gN . 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. Si
The doping amount 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 _1-e.
It is formed as a layer of a multilayer film including a nitride semiconductor containing N (0.12 ≦ e <0.15). The multilayer film refers to a multilayer film structure in which nitride semiconductor layers having different compositions are stacked, and for example, Al _e Ga _1-e N (0.12 ≦ e <0.1
5) a layer and a nitride semiconductor having a composition different from that of Al _e Ga _{1 -e} N, for example, a material having a different mixed crystal ratio of Al, a material of a ternary mixed crystal containing In, or a layer made of GaN or the like It is formed by combining and stacking. Among them, a preferable combination is a multilayer film formed by stacking Al _e Ga _1-e N and GaN. By doing so, a nitride semiconductor layer having good crystallinity can be stacked at the same temperature. A more preferable multilayer film is a stack of undoped Al _e Ga _{1 -e} N and n-type impurity (for example, Si) doped GaN in combination. In this case, the n-type impurity is Al _e G
It may be doped into a _1-e N. The doping amount of the n-type impurity is 4 × 10 ¹⁸ / cm ^{3 to} 5 × 10 ¹⁸ / cm ³ . n
When the type impurities are 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 the present 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.
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 two layers of l _d Ga _{1 -d} N (0 <d ≦ 1) are grown and formed. 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 mixed crystal ratio in the above range is applied to the first p-type nitride semiconductor layer and the second p-type nitride semiconductor layer forming the p-type cap layer in the present invention, but each layer will be described in detail later. It is as follows. The thickness of the entire p-type cap layer 7 is set to 10 angstroms or more and 1000 angstroms or less, preferably 20 angstroms or more and 400 angstroms or less. Setting the film thickness of the entire p-type cap layer 7 in such a range is as follows.
The reason is as follows. That is, when the p-type cap layer 7 is an AlGaN layer, the carrier confinement function can be effectively exhibited.
The layer has a higher bulk resistance than a gallium nitride based semiconductor that does not contain 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.

The doping amount of Mg in the p-type cap layer 7 is 1 × 10 ¹⁹ / cm ³ to 1 × 10 ²¹ / cm ³ . When the doping amount is set in this range, in addition to lowering the bulk resistance, Mg is diffused into the p-type guide layer to be grown by undoped described later, and Mg is added to the p-type guide layer 8 which is a relatively thin layer. × 10 ¹⁶ / cm ³ to 1 × 10 ¹⁸ / cm ³
It can be contained in the range of.

Here, in particular, in the present embodiment, the p-type cap layer 7 is the first p-type nitride semiconductor layer 7a made of Al _a Ga _1-a N, and Al _b Ga _1-b N is formed on the first p-type nitride semiconductor layer 7a. 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. For example, the second p-type nitride semiconductor layer 7b may be formed by laminating a plurality of layers.

The Al mixed crystal ratio of each layer is not particularly limited. However, in the first p-type nitride semiconductor layer 7a represented by the Al _a Ga _{1 -a} N layer, the Al mixed crystal ratio a
Is 0 or more, decomposition of the active layer can be effectively suppressed. In order to exert this function, preferably, an Al _a Ga _1-a N layer with a> 0 is used. Among the nitride semiconductors, _a layer having a relatively high melting point and chemically stable is provided on the side closer to the active layer. Can be provided (preferably in contact), and decomposition of the active layer can be suppressed more effectively. Also,
In the present invention, the Al mixed crystal ratios a and b of the first p-type nitride semiconductor layer 7a and the second p-type nitride semiconductor layer 7b, respectively.
Is preferably greater than 0.1, more preferably 0.
When it is larger than 2, a good offset can be obtained (a potential barrier is formed) with the active layer, and good carrier injection without carrier overflow can be realized. At this time, the first p-type nitride semiconductor layer 7a
It is preferable that the second p-type nitride semiconductor layer 7b and the second p-type nitride semiconductor layer 7b have the same composition, that is, a = b. Since it can be easily performed and the controllability can be improved, the first p-type nitride semiconductor layer and the second p-type nitride semiconductor layer can be stably and accurately grown.

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 _f G
a _1-f N (0 <f ≦ 1) -containing nitride semiconductor layer,
Preferably Al _f Ga _1-f N (0.05 ≦ f ≦ 0.15)
A multilayer film layer having a nitride semiconductor layer containing is preferable. The multi-layer film is a layer having a multi-layer film structure in which nitride semiconductor layers having different compositions are laminated, for example, an Al _f Ga _1-f N layer and a nitride having a different composition from Al _f Ga _1-f N. Semiconductors, such as those having different mixed crystal ratios of Al, I
A ternary mixed crystal containing n or a layer formed by combining a layer made of GaN or the like. Among them, a multilayer film obtained by combining Al _f Ga _{1 -f} N and GaN is preferable because a nitride semiconductor layer having good crystallinity can be stacked at the same temperature. A more preferable multilayer film is a combination of undoped Al _f Ga _{1 -f} N and p-type impurity (eg, Mg) -doped GaN. p-type impurity may be doped in the Al _f Ga _1-f N. The p-type impurity doping amount is 1 × 10 ¹⁷ / cm ³ to
It is 1 × 10 ¹⁹ / cm ³ . When the p-type impurity is doped in this range, the amount of doping is such that the crystallinity is not impaired and the bulk resistance 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 clad layer 9 is 0.05 when s is expressed as Al _s Ga _{1 -s} N.
It is preferable to set in the range of 0.1 to 0.1. By doing so, it is possible to suppress the occurrence 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. The doping amount of Mg is 1 × 10 ¹⁹ / cm
^{It is set to 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 portion 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] TM is used as a source gas at 1050 ° C. on the nitride semiconductor substrate 1.
An n-type contact layer made of undoped Al _0.05 Ga _0.95 N is grown to a thickness of 1 μm using A (trimethylaluminum), TMG, and ammonia gas.

(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 impurity gas.
The n-type contact layer 2 made of Al _0.05 Ga _0.95 N doped with 3 × 10 ¹⁸ / cm ³ 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 improvement in crystallinity is n
It becomes better by growing the undoped n-type contact layer as described above than in the case of only the 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/ Cm³Doped In
_0.08Ga_0.920.15μ of the crack prevention layer 3 made of N
Grow with a film thickness of m.

(N-type clad layer 4) Next, the temperature is set to 105.
The temperature is set to 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.
Stop MA, use silane gas as impurity gas,
A B layer made of GaN doped with 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 / c.
m ³ doped an In _0.01 Ga _0. consisting ₉₉ N barrier layer 1
It is grown to a film thickness of 00 angstrom. Then, the silane gas is stopped, and a well layer made of undoped In _0.11 Ga _0.89 N is grown to a film thickness of 50 Å. This operation was repeated three times, and finally, a multiple quantum well structure (M
QW) active layer 6 is grown.

(P-type cap layer 7) Next, at the same temperature,
In the same 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 20Å. Next, H ₂ is used as a carrier gas to create an H ₂ atmosphere,
After raising the temperature to 960 ° C., Mg was added to 1 × 10 6 in the same manner.
^A second p-type nitride semiconductor layer 7b made of Al _0.4 Ga _0.6 N doped with ¹⁹ / cm ³ is grown to a film thickness of 70Å.
With the first p-type nitride semiconductor layer and the second p-type nitride semiconductor layer, the p-type cap layer 7 is formed, and the layer thickness 90
Form with Å.

(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 and} p-type is exhibited.

(P-type clad layer 9) Next, at the same temperature, using TMA, TMG and ammonia as source gases,
An A layer made of undoped Al _0.1 Ga _0.9 N is grown to have a film thickness of 25 Å, then TMA is stopped, Cp ₂ Mg is used as an impurity gas, and Mg is 5 × 1.
A B layer made of GaN doped with 0 ¹⁸ / cm ³ is grown to a film thickness of 25 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 / cm ^3.
The p-type contact layer 10 made of doped GaN 15
It is grown to a film thickness of 0 angstrom. After the reaction,
Wafers in a reaction vessel at 700 ° C. in a nitrogen atmosphere
Annealing is performed to further reduce the resistance of the p-type layer. After annealing, the wafer is taken out of the reaction container, a protective film made of SiO ₂ is formed on the surface of the uppermost p-side contact layer, and S using RIE (reactive ion etching).
Etching with iCl ₄ gas, as shown in FIG.
The surface of the n-side contact layer 2 on which the n-electrode is to be formed 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, CF ₄ gas is used by a RIE (reactive ion etching) apparatus, the third protective film 63 is used as a mask, and the first protective film 63 is removed. 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.
4D, a second protective film 62 made of Zr oxide (mainly ZrO ₂ ) is formed on the first protective film 61 and 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 30
It is desirable to set it to 0 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 the active layer is grown, 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)
Used, 5 × the Mg 10 ¹⁸ / cm ³ doped with Al _0.4 G
The p-type cap layer 7 made of a _0.6 N is grown to a film thickness of 100Å. The obtained laser device had higher Vf and shorter device life than those of Example 1.

[Embodiment 2] N _{2 as} a carrier gas, TMA, TMG and ammonia as a source gas, and Cp _{2 as} an impurity gas.
Mg (cyclopentadienyl magnesium) was used at a temperature of 800 ° C., that is, at the same temperature as in the growth of the active layer and in the same atmosphere, to obtain Mg with a film thickness of 30 × 1 × 10 ¹⁹ /
cm ³ a first p-type nitride semiconductor layer 7a composed of doped Al _0.4 Ga _0.6 N was grown, under a hydrogen atmosphere with a carrier gas H _2, the temperature was raised to 960 ° C., thickness 10
Al _0.4 Ga doped with Mg at 1 × 10 ¹⁹ / cm ^{3 at} 0Å
_A laser element is formed in the same manner as in Example 1 _except that _0.6 N is grown and the p-type cap layer is formed of these two layers. The obtained laser device has good device reliability almost as in the first embodiment, Vf of output characteristics is similar, and the threshold current Ith does not increase, and continuous oscillation at high output is possible. It was an element.

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 laser device obtained is
It 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.
It is shown that the electron confinement does not contribute as much as that of the second p-type nitride semiconductor layer, and better crystal growth of the upper second p-type nitride semiconductor layer and the active layer It shows that the contribution to protection is large. For this reason, the element reliability, especially the element life, is also the same as in Example 1.
Almost the same as above, it showed 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.
_A nitrogen atmosphere was used instead of _2, and a barrier layer made of undoped GaN was grown to a film thickness of 200 Å,
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 gas₂With the active layer growth
TMA, TM as the source gas under the same atmosphere and temperature
G, ammonia, Cp for impurity gas₂Mg (cyclopen
Tadienyl magnesium) with a film thickness of 20 Å
1 x 10 of ROHM Mg¹⁹/ Cm³Doped Al_0.4G
a_0.6Growing the first p-type nitride semiconductor layer 7a made of N
The carrier gas to H₂Under a hydrogen atmosphere instead of 9
After the temperature was raised to 60 ° C, the film thickness was 60 Å and the Mg
1 x 10¹⁹/ Cm ³Doped Al_0.4Ga_0.6Form N
The two layers of p-type film with a thickness of 80 angstroms
Form a cap layer.

(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 Ga doped with Mg at 1 × 10 ¹⁹ / cm ³
A laser element was obtained in the same manner as in Example 1 except that _0.8 N was formed with a film thickness of 70 Å. The obtained laser device had a slightly higher Vf than that of Example 1, but did not cause a large difference in oscillation, but the device life was extremely poor, and
It was not as long as 10,000 hours, and the cross section of the device was observed. It was found that the active layer was often decomposed during growth or 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.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-10-290027 (JP, A) JP-A-9-148678 (JP, A) JP-A-9-214051 (JP, A) JP-A-10- 65213 (JP, A) JP 10-75008 (JP, A) JP 9-36430 (JP, A) Japanese Journal of Applied Physics, 1996, Vol. 35 Part2 No. 1B, L74-76 (58) Fields investigated (Int.Cl. ⁷ , DB name) H01S 5/00-5/50 H01L 33/00

Claims (6)

(57) [Claims] 1. An n made of at least an n-type nitride semiconductor
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, and a p-type guide layer between the active layer and the p-type clad layer. In the nitride semiconductor light emitting device, a p-type cap layer that forms a potential barrier between the p-type guide layer and the active layer is formed between the p-type guide layer and the active layer, and the p-type cap layer is the active layer. _{Al a Ga 1-a N (} 0 , which is grown by metal organic chemical vapor deposition method using N ₂ gas to prevent degradation of
A first p-type nitride semiconductor layer made of <a <1) and Al _b Ga _1-b N (which is grown by metal organic chemical vapor deposition using H ₂ gas so as to form the potential barrier. 0 <b
A nitride semiconductor light emitting device comprising: a second p-type nitride semiconductor layer made of <1). 2. An n made of at least an n-type nitride semiconductor
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, and a p-type guide layer between the active layer and the p-type clad layer. In the nitride semiconductor light emitting device, a p-type cap layer that forms a potential barrier between the p-type guide layer and the active layer is formed between the p-type guide layer and the active layer, and the film thickness of the p-type cap layer is The thickness is set to 20 Å or more and 400 Å or less, and the p-type cap layer is formed of Al _a Ga grown to a film thickness in the range of 10 Å to 100 Å.
_{A first} p-type nitride semiconductor layer formed of _1-a N (0 <a <1) for preventing decomposition of the active layer, and having less crystal defects than the first p-type nitride semiconductor layer A
_{l b Ga 1-b N (} 0 <b <1) made from a second p-type nitride semiconductor layer and the nitride semiconductor light emitting device characterized by comprising a forming the potential barrier. 3. The film thickness of the first nitride semiconductor layer is 1
The nitride semiconductor light emitting device according to claim 1 or 2, 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 ≦ c
The nitride semiconductor light emitting device according to any one of claims 1 to 3, which has a multiple quantum well structure including a well layer made of <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), and the Al _a Ga _1-a N (0 <a <1 ) And a second p-type nitride semiconductor layer made of Al _b Ga _1-b N (0 <b <1), respectively, where x ≦ a and x ≦
The composition is set so as to satisfy b.
9. The nitride semiconductor light emitting device according to any one of the above. 6. The total thickness of the first p-type nitride semiconductor layer and the second p-type nitride semiconductor layer is 10 Å or more 10
The nitride semiconductor light emitting device according to claim 1, wherein the nitride semiconductor light emitting device is set to 00 Å or less.