JP2001007447A - Nitride semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance lifetime characteristics by employing a quantum well structure having a specified total number of well layers in an active layer and specifying the oscillation wavelength thereby lowering the threshold current density. SOLUTION: An n-type contact layer 2 is grown on an nitride semiconductor substrate 1, an anti-clad layer 3 is grown thereon and an n-type clad layer 4 is grown further thereon. Subsequently, an n-type guide layer 5 is grown on the n-type clad layer 4. An nitride semiconductor layer of undoped GaN is grown as the n-type guide layer. Thereafter, an active layer 6 is grown on the n-type guide layer 5. The active layer 6 is a quantum well structure active layer comprising one or two well layers of InGaN having an In compositional ratio adjusted such that the oscillation wavelength will be 420 nm or longer. Finally, a p-type electron confinement layer 7 is grown on the active layer 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light emitting diode,
A nitride semiconductor (In _X A) used for a light emitting element such as a laser diode or a light receiving element such as a solar cell or an optical sensor.
1 _Y Ga _{1 -XYN} , 0 ≦ X, 0 ≦ Y, X + Y ≦ 1) A nitride semiconductor laser device having an oscillation wavelength of 420 nm or more, in which the threshold current density is low and the life characteristics are improved. The present invention relates to a semiconductor laser device.

[0002]

2. Description of the Related Art In recent years, research on a laser device made of a nitride semiconductor has been advanced to a practical level as a blue laser device having a wavelength of about 400 nm. For example, researchers including the present inventor have described the Japanese Journal of Aplide Physic
s.Vol.37 (1998) pp.L1020-L1022, ELOG (Epitaxia
lly laterally overgrown GaN) as a substrate, an element structure is formed on the substrate, and light having a wavelength of
A nitride semiconductor laser device capable of continuously oscillating at an output of 5 mW for about 160 hours under an environment temperature of ° C. has been announced.

Further, the present inventor has been studying a laser device having an oscillation wavelength of 420 nm or more, which is used for a laser display, color copying, and the like. Oscillation wavelength is 420
In order to obtain a laser beam of nm or more, the active layer In
It is necessary to increase the In composition ratio of the well layer of the GaN layer and reduce the band gap energy.

[0004]

However, in general, when the In composition ratio of InGaN is increased, its crystallinity is deteriorated, and the self-absorption ratio is increased in a laser device, and the quantum efficiency is also reduced. As a result, the threshold current density was increased, and a laser device having high reliability could not be obtained.

Accordingly, an object of the present invention is to obtain a highly reliable laser device having an oscillation wavelength of 420 nm or more.
An object of the present invention is to provide a nitride semiconductor laser device capable of lowering the threshold current density and improving the life characteristics.

[0006]

That is, the present invention can achieve the object of the present invention by the following constitutions (1) to (8). (1) At least an n-type nitride semiconductor, In
In a nitride semiconductor laser device in which an active layer having a quantum well structure having a well layer containing and a p-type nitride semiconductor are sequentially stacked, the active layer has a total number of well layers of 2
And the oscillation wavelength is 42
A nitride semiconductor laser device having a thickness of 0 nm or more. (2) The nitride semiconductor according to (1), wherein the active layer has a single quantum well structure in which the total number of well layers is 1, and further has an oscillation wavelength of 430 nm or more. Laser element. (3) The quantum well structure of the active layer is formed of a well layer and a barrier layer, and the barrier layer has an n-type impurity concentration of 1 × 1.
The nitride semiconductor laser device according to the above (1) or (2), wherein the content is 0 ¹⁹ / cm ² or less. (4) The barrier layer has an n-type impurity of 5 × 10 ¹⁸ / cm.
^2. The nitride semiconductor laser device according to the above (3), wherein the nitride semiconductor laser device comprises ² or less. (5) The well layer has an n-type impurity of 1 × 10 ¹⁸ / cm.
(1) to (4), characterized by comprising ² or less.
The nitride semiconductor device according to any one of the above. (6) The nitride semiconductor laser device according to any one of (1) to (5), wherein the well layer has a thickness of 40 Å or less. (7) The nitride semiconductor laser device according to any one of (1) to (6), wherein the well layer has a thickness of 30 Å or less. (8) The quantum well structure of the active layer is formed of a well layer and a barrier layer, and the barrier layer has a thickness of 100 Å or more. Nitride semiconductor laser device. (9) The nitride semiconductor laser device according to (8), wherein the barrier layer has a thickness of 100 to 200 Å. (10) The nitride semiconductor laser device is formed on a heterogeneous substrate or a nitride semiconductor substrate made of a material different from that of the nitride semiconductor by using lateral growth of the nitride semiconductor. The nitride semiconductor laser device according to any one of the above (1) to (9), which is grown.

That is, according to the present invention, the oscillation wavelength is 420 nm.
By forming an active layer having a quantum well structure in which the In composition ratio of the well layer is adjusted as described above with the total number of well layers being 2 or less, continuous operation for a long time at a low threshold current density can be achieved. It is possible to provide a nitride semiconductor laser device that can oscillate.

[0008] In the above J.P. J. A. P. Describes that the threshold current density decreases most when the number of stacked layers is two, but the threshold current density increases sharply when the number of stacked layers is one. This indicates that when the oscillation wavelength is around 400 nm, it is difficult to obtain a gain by reducing the number of stacked well layers. FIG. 3 shows that the oscillation wavelength is 400 nm.
4 is a graph showing the relationship between the threshold current density and the number of stacked well layers in a nearby laser element.

On the other hand, according to the present invention, as described above, despite the high In composition ratio at which crystallinity is expected to decrease, and the number of stacked well layers for confining carriers is reduced. In addition, the threshold current density can be reduced, and good life characteristics can be achieved. The reason why a large gain can be obtained even when the number of stacked well layers is reduced is probably that if the In composition ratio is increased so that the oscillation wavelength becomes 420 nm or more, the In composition ratio where the oscillation wavelength becomes about 400 nm is obtained. It is thought that good carrier confinement, which cannot be obtained, can be achieved. That is, In
If the composition ratio is large, the In composition non-uniformity due to the compositional separation of InGaN becomes large, and a deep localized level is formed. It is considered that a large gain is easily obtained in order to obtain a quantum dot effect. Also, regarding the loss in the active layer,
Generally, it is considered that if the In composition ratio is increased, the crystallinity is reduced, so that the self-absorption ratio is increased and the internal loss is increased. However, as described above, the present invention relates to a well layer in which the crystallinity is easily reduced. Since the total number of layers is set to 2 or less, the ratio of self-absorption is reduced to reduce the internal loss.

As described above, the present inventor has conducted various studies on the increase in the gain and the reduction in the loss in order to reduce the threshold current density.
It has been found that there is a great difference in the degree of non-uniformity of the In composition ratio between the In composition ratio of not less than m and the In composition ratio at a wavelength shorter than 420 nm. By repeating the theory and experiments based on theory, a large gain can be obtained even when the total number of well layers is 2 or less at a high In composition ratio where the oscillation wavelength is 420 nm or more. The internal loss is reduced, and as a result, the threshold current density is reduced. Furthermore, in the present invention, the life characteristics are improved more than expected with respect to the decrease in the threshold current density, and probably the large non-uniform In composition has some positive effect on the prevention of the deterioration of the device. It is expected.

Incidentally, when the In composition ratio is such that oscillation near 400 nm is possible, the In composition becomes non-uniform as in the case where oscillation above 420 nm is possible.
Since the degree of n composition non-uniformity is small, and the effect of the localized level formed by the small In composition non-uniformity is small, a large gain obtained at 420 nm or more cannot be obtained near 400 nm. Guessed.

Further, in the present invention, when the oscillation wavelength of the laser element is 430 nm or more and the active layer has a single quantum well structure in which the total number of well layers is 1, the threshold current density is reduced, and This is preferable from the viewpoint of improving the life characteristics of the device. Further, in the present invention, when the barrier layer forming the quantum well structure of the active layer contains an n-type impurity of 1 × 10 ¹⁹ / cm ² or less, preferably 5 × 10 ¹⁸ / cm ² or less,
This is preferable in that the threshold current density is reduced and the life characteristics are improved. Still further, in the present invention, the well layer is formed of n
It is preferable to include the type impurity of 1 × 10 ¹⁸ / cm ² or less in that the threshold current density is reduced and the life characteristics are improved. Furthermore, in the present invention, the well layer has a thickness of 4
A thickness of 0 Å or less, preferably 30 Å or less, is preferable in that the threshold current density is reduced and the life characteristics are improved without impairing the crystallinity of InGaN. Still further, in the present invention,
When the quantum well structure of the active layer is formed of a well layer and a barrier layer, and the barrier layer has a thickness of 100 Å or more, preferably 100 to 200 Å,
This is preferable from the viewpoint of improving the life characteristics.

Still further, according to the present invention, the nitride semiconductor laser device is grown on a heterogeneous substrate or a nitride semiconductor substrate made of a material different from the nitride semiconductor by utilizing the lateral growth of the nitride semiconductor. Nitride semiconductor (hereinafter E
When grown on an ELOG substrate or simply an ELOG substrate by LOG growth), a nitride semiconductor with reduced dislocations is used as a substrate, so that an element structure with few dislocations can be formed. Can improve the crystallinity of a well layer having a large thickness, which is preferable in terms of reduction in threshold current density and improvement in life characteristics.

Further, other preferred embodiments of the present invention will be described below. In the present invention, an ELOG substrate is used, and the n-type contact layer grown on the ELOG substrate is made of Al _a Ga _1-a N (0 <a <1, preferably 0.
01 ≦ a ≦ 0.05), even if an n-type contact layer is formed on an ELOG substrate, which tends to have a different coefficient of thermal expansion from that of the n-type contact layer, it is possible to prevent generation of minute cracks inside. This is preferable in terms of lowering the threshold current density and improving the life characteristics. In order to grow a plurality of layers having various functions of the laser element on the n-type contact layer, n
The better the crystallinity of the mold contact layer is, the more an element having good crystallinity can be manufactured, and the element characteristics can be improved. In the present invention, EL
When a heterogeneous substrate for growing an OG substrate is one in which the C-plane of sapphire is off-angled in a stepwise manner, it is preferable in terms of reducing dislocations and obtaining a good surface state. The element structure grown on the substrate is also favorable, which is preferable in that the effects of the present invention can be obtained. Furthermore,
If the off-angle angle of the sapphire substrate that is off-angled in a step shape is 0.1 ° to 0.3 °, ELO is performed.
The G substrate can be satisfactorily grown, which is preferable in terms of reduction in threshold current density and improvement in life characteristics.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The nitride semiconductor laser device according to the present invention will be described below in more detail. The nitride semiconductor laser device of the present invention is a device in which at least an n-type nitride semiconductor, an active layer having a quantum well structure having a well layer containing In, and a p-type nitride semiconductor are sequentially stacked on a substrate. In this case, the active layer is formed with the total number of well layers being 2 or less, and the In composition ratio of the well layer is adjusted so that the oscillation wavelength becomes 420 nm or more. An element structure is formed below.

(Active Layer) In the present invention, the active layer
Means that at least the well layer contains In. _bGa_1-b
It is a quantum well structure composed of N (0 ≦ b <1). Soshi
Therefore, the active layer having the quantum well structure has an oscillation wavelength of 420 nm or less.
The In composition ratio is adjusted to be above. Active layer
In adjusting the In composition ratio, the In composition ratio of the well layer is adjusted.
The vibration wavelength is adjusted to be 420 nm or more. Well layer
As for the In composition ratio, the oscillation wavelength is 420 nm or more.
There is no particular limitation as long as the In composition ratio is
For example, the value obtained from the following formula
It can be cited as an approximate value. But actually
The oscillation wavelength obtained by operating the laser element is
Because a quantum level with a structure is formed, the energy of the oscillation wavelength
Energy (Eλ) is the band gap energy of InGaN
-It becomes larger than (Eg) as shown in Fig. 2,
From the oscillation wavelength calculated from
There is a direction.

[Calculation formula of theoretical value] Eg = (1-χ) 3.40 + 1.95χ-Bχ (1-
χ) wavelength (nm) = 1240 / Eg Eg: band gap energy of InGaN well layer χ: composition ratio of In 3.40 (eV): band gap energy of GaN 1.95 (eV): band gap energy of InN B : Indicates a bowing parameter, which is 1 to 6 eV. The variation of the Boeing parameter like this is
In recent studies, from SIMS analysis and the like, it has been conventionally assumed that the crystal has no distortion, but it is set to 1 eV. It is becoming clear that

Although there is a slight difference between the oscillation wavelength considered from the specific In composition ratio obtained from the SIMS analysis of the well layer and the like as described above and the oscillation wavelength when actually oscillated, the actual oscillation wavelength is slightly different. When the lasing wavelength is 420 nm or more, if the total number of the active layer well layers is 2 or less, the threshold current density can be reduced and the life characteristics can be improved. Can be provided. Although the reason for this is not clear, it was probably not obtained when the oscillation wavelength was around 400 nm. However, in the case of an element having an oscillation wavelength of 420 nm, the non-uniform In composition became large and a deep localized level was formed. It is considered that a large gain can be obtained even if the total number of well layers is 2 or less in order to obtain a quantum dot effect, and as a result, the threshold current density can be reduced. Further, when the number of stacked well layers is two or less, the lifetime tends to be longer when the thickness of the barrier layer is set to be 100 Å or more, preferably 100 to 200 Å. Thus, the threshold current density can be reduced and the life characteristics can be improved. Furthermore, since a better life characteristic than the degree of decrease in the threshold current density is obtained, it is considered that the large non-uniformity of the In composition has some positive effect on the prevention of device deterioration.

The total number of the well layers forming the quantum well structure of the active layer is 2 or 1 when the oscillation wavelength is 420 nm or more, and more preferably 1 when the oscillation wavelength is 430 nm or more.
It is. As described above, the threshold current density can be favorably reduced by changing the In composition ratio due to the oscillation wavelength and adjusting the number of stacked well layers. FIG. 1A shows the relationship between the number of stacked well layers and the threshold current density when the oscillation wavelength is 420 nm, and FIG.
A graph is shown for the case of m. First, as shown in FIG. 1A, when the oscillation wavelength is 420 nm, the threshold current density is lowest when the number of stacked well layers is 1 and 2, and when the number of stacked well layers is 3 and 4. It tends to rise sharply.
Further, as shown in FIG. 1B, the oscillation wavelength is 430 nm.
The threshold current density decreases most when the number of stacked well layers is one, and increases when the number of stacked well layers is increased to two or three. Also, when the wavelength is longer than 430 nm, as in the case of 430 nm, when the number of stacked well layers is 1, the threshold current density becomes the minimum value.

In the present invention, the well layer may be undoped or doped with an impurity. However, it is preferable that the well layer be doped with an impurity (eg, Si) even when undoped or doped with an impurity, so as not to impair the crystallinity. 1 × 10
Those containing ¹⁸ / cm ² or less are preferable. If the well layer has good crystallinity, it is preferable in terms of lowering the threshold current density and improving the life characteristics. The thickness of the well layer is not particularly limited, but is not more than 40 Å, preferably not more than 30 Å from the viewpoint of reduction in threshold current density. The lower limit of the thickness of the well layer is not particularly limited, but is about 10 angstroms.

The barrier layer forming the quantum well of the active layer is not particularly limited, but may be a barrier layer having a composition having a band gap energy larger than at least the well layer. For example, specifically, In _b Ga _{1− b} N (0 ≦ b <0.
The nitride semiconductor shown in 1) is mentioned. The barrier layer is
It may be undoped or doped with impurities,
Preferably, in order to lower the threshold current density, an impurity (for example, Si or the like) containing 1 × 10 ¹⁹ / cm ² or less, preferably 5 × 10 ¹⁸ / cm ² or less is preferable. The thickness of the barrier layer is not particularly limited,
100 angstrom or more, preferably 100 to 20
0 Angstrom. With such a film thickness,
The element is less likely to deteriorate, which is preferable from the viewpoint of improving the life characteristics.

When the number of the well layers of the active layer is two, at least two well layers need only be stacked, and the well layer may start from the barrier layer and end at the well layer, or may start from the barrier layer and end at the barrier layer. It may start with a well layer and end with a barrier layer, or start with a well layer and end with a well layer. Preferably, starting at the barrier layer and ending at the barrier layer is preferable for lowering the threshold current density and improving the life characteristics. Also,
When the active layer has a single quantum well structure in which the number of stacked well layers is 1, the barrier layer is preferably formed so as to sandwich the well layer. In the case of a single quantum well structure, it is preferable to form a barrier layer in terms of lowering threshold current density and improving life characteristics. In the case where the active layer has a single quantum well structure, an element structure without a barrier layer may be used.

The nitride semiconductor laser device of the present invention has at least an active layer whose In composition ratio is adjusted so as to obtain the total number of well layers and an oscillation wavelength of 420 nm or more as described above. Other device structures are not particularly limited, but a specific embodiment is, for example, a laser device having the device structure shown in FIG. It is preferable that the laser element be combined with the element structure shown in FIG. 5 and the specified active layer such as the above-mentioned well layer in terms of reduction of threshold current density and improvement of life characteristics.
However, the present invention is not limited to this.

FIG. 5 is a schematic sectional view showing a nitride semiconductor laser device according to one embodiment of the present invention. FIG. 5 shows Al _a Ga _1-a N (0 <a <1) obtained by doping an n-type impurity (for example, Si) on a nitride semiconductor substrate 1 grown by ELOG on a heterogeneous substrate such as sapphire. Consisting of n
Type contact layer 2, Si-doped In _g Ga _1-g N (0.
05 ≦ g ≦ 0.2), crack prevention layer 3, Al _e
N _- type cladding layer 4 of a multilayer film containing Ga _1-e N (0.12 ≦ e <0.15), n-type guide layer 5 made of undoped GaN, In _b Ga _1-b N (0 ≦ b <1), an active layer 6 having a quantum well structure and Mg-doped Al _d Ga _{1 -d}
At least one or more p-type electron confinement layers 7 made of N (0 <d ≦ 1), a p-type guide layer 8 made of undoped GaN, and Al _f Ga _{1 -fN} (0 <f ≦ 1) A nitride semiconductor laser device having a ridge-shaped stripe composed of a p-type cladding layer 9 of a multilayer film and a p-type contact layer 10 of Mg-doped GaN is shown. The p-electrode is formed on the uppermost layer of the ridge-shaped stripe, and the n-electrode is formed on the n-type contact layer. Hereinafter, the substrate and each layer will be described in more detail.

(ELOG Growth) First, ELOG growth will be described below. In the present invention, as the ELOG growth that can be used, any growth method that can at least partially temporarily stop vertical growth of a nitride semiconductor and suppress dislocations by using horizontal growth can be used. It is not particularly limited.

For example, as a specific example, a protective film made of a material on which a nitride semiconductor does not grow or hardly grows is partially formed on a heterogeneous substrate made of a material different from that of a nitride semiconductor. By growing the semiconductor, the nitride semiconductor grows from a portion where the protective film is not formed, and by continuing to grow laterally toward the protective film, a thick nitride semiconductor (EL) is formed.
(OG substrate) can be obtained. As such a growth method, for example, Japanese Patent Application No. 10-275826
No., Japanese Patent Application No. 10-119377, Japanese Patent Application No. 10-146
431, Japanese Patent Application No. 11-37826, and the methods described in each specification.

Another specific example is a method that does not use a protective film, in which irregularities are formed on a nitride semiconductor grown on a heterogeneous substrate made of a material different from that of the nitride semiconductor. A growth method for obtaining a nitride semiconductor (ELOG substrate) by growing a nitride semiconductor again is given. In addition, there is a method in which the surface of the nitride semiconductor is partially modified without using a protective film so that the lateral growth of the nitride semiconductor is intentionally performed. As such a growth method, for example, Japanese Patent Application Nos. 11-378227 and 11-378227.
168080, Japanese Patent Application No. 11-142400, and the method described in each specification.

Further, a nitride semiconductor obtained by the above-described ELOG growth or the like is used as a substrate, and the above-described protective film is used on the nitride semiconductor, or a method such as forming unevenness is used. There is a growth method for obtaining a nitride semiconductor in which dislocation is favorably reduced by repeating ELOG growth. As such a growth method, for example, Japanese Patent Application No.
80288.

The above-mentioned ELOG growth is preferably a method of growing without using a protective film, and a method of growing ELOG on a nitride semiconductor. Such a method is preferable in terms of reducing dislocations, and it is preferable to form an element structure on an ELOG substrate in which dislocations are reduced in terms of reduction in threshold current density and improvement in life characteristics. The details of the ELOG growth method mentioned above are as described in the above-listed specifications, but a preferred example is shown below. However, the present invention is not limited to this.

An embodiment of a preferred ELOG growth that can be used in the present invention will be described below with reference to FIG. FIG. 4 (a-1 to a-4) is a schematic view illustrating stepwise an embodiment of a nitride semiconductor growing method. First, in the first step of FIG.
1 is grown on the first nitride semiconductor 42, and FIG.
In the second step of 2), irregularities are formed on the first nitride semiconductor 42. Subsequently, in the third step of FIG. 4A-3, the first nitride semiconductor 42 having the irregularities is formed. above,
The second nitride semiconductor 43 is grown under normal pressure or higher pressure conditions.

Hereinafter, each of the above steps will be described in more detail with reference to FIG. (First Step) FIG. 4A-1 is a schematic step view in which a first step of growing a first nitride semiconductor 42 on a heterogeneous substrate 41 is performed. In the first step, as the heterogeneous substrate 41 that can be used, for example,
Surface, and sapphire to either the main surface of the surface A, the insulating substrate such as spinel _{(MgA1 2 O 4), SiC} (6
H, 4H, 3C), ZnS, ZnO, GaAs,
Si, and oxide substrates lattice-matched with nitride semiconductors, etc.
A substrate material different from a conventionally known nitride semiconductor can be used. Preferred heterosubstrates include sapphire and spinel. When sapphire is used as a dissimilar substrate, the orientation of the nitride semiconductor on the upper portion of the projection and the side surface of the depression when the unevenness is formed tends to be specified depending on which surface is the main surface of the sapphire. Because the growth rate of nitride semiconductors is slightly different,
The main surface may be selected such that a plane orientation that facilitates growth is provided on the side surface of the concave portion.

Further, in the first step, the heterogeneous substrate 41
Before growing the first nitride semiconductor 42 thereon, a buffer layer (not shown) may be formed on the heterogeneous substrate 41. AlN, GaN, AlG
aN, InGaN or the like is used. The buffer layer is 90
At a temperature of 0 ° C. or less and 300 ° C. or more, a film thickness of 0.5 μm to 10 μm
Growing in Angstrom. Thus, the heterogeneous substrate 1
When the buffer layer is formed thereon at a temperature of 900 ° C. or lower, the lattice constant between the heterogeneous substrate 41 and the first nitride semiconductor 42 is reduced, and the crystal defects of the first nitride semiconductor 42 tend to be reduced. .

In the first step, as the first nitride semiconductor 42 formed on the heterogeneous substrate 41, undoped (undoped) GaN, S
GaN doped with n-type impurities such as i, Ge, and S can be used. The first nitride semiconductor 42 is grown on the heterogeneous substrate 41 at a high temperature, specifically, higher than about 900 ° C. to 1100 ° C., preferably 1050 ° C. When grown at such a temperature, first nitride semiconductor 42 becomes a single crystal. Although the thickness of the first nitride semiconductor 42 is not particularly limited, the thickness of the first nitride semiconductor 42 can be adjusted so that the growth in the vertical direction inside the concave portion can be suppressed and the growth in the horizontal direction can be promoted. And preferably at least 50
The film is formed to have a thickness of 0 Å or more, preferably 5 μm or more, more preferably 10 μm or more.

(Second Step) Next, FIG. 4A-2 shows that after the first nitride semiconductor 42 is grown on the heterogeneous substrate 41, the first nitride semiconductor 42 is partially formed on the first nitride semiconductor 42. Forming unevenness at a depth such that the first nitride semiconductor 42 slightly remains;
FIG. 4 is a schematic cross-sectional view in which a first nitride semiconductor 42 is exposed on a side surface of a concave portion.

In the second step, forming the unevenness partially means that the first nitride semiconductor 4 is formed on at least the side surface of the concave portion.
A recess may be formed in the direction of the heterogeneous substrate 41 from the surface of the first nitride semiconductor 42 so that 2 is exposed. Irregularities may be provided in the first nitride semiconductor 42 in any shape. For example, they can be formed in random depressions, stripes, grids, or dots. A preferable shape is a stripe shape, and this shape is preferable because it has less abnormal growth and is buried more flat. First nitride semiconductor 4
2 are partially provided on the first nitride semiconductor 4.
2 or formed at a depth reaching the heterogeneous substrate,
Preferably, the depth is such that the heterogeneous substrate is exposed.
When the heterogeneous substrate is exposed at the bottom of the recess, the growth from the bottom of the recess is easily suppressed, and the dislocation of the second nitride semiconductor 43 that grows to a thick film from the opening of the recess is easily reduced, which is preferable.

The shape of the unevenness is not particularly limited, such as the length of the side surface of the concave portion, the width of the upper portion of the convex portion, and the width of the bottom portion of the concave portion. At least growth in the vertical direction in the concave portion is suppressed, and It is preferable that the second nitride semiconductor 43 grown in the film is adjusted so as to grow laterally from the side surface of the concave portion. When the shape of the unevenness is a stripe shape, the shape of the stripe is not particularly limited. For example, the stripe width (width of the upper portion of the convex portion) is 1 to 20 μm, preferably 1 to 10 μm, and the stripe interval (width of the lower portion of the concave portion). Having a thickness of 3 to 20 μm, preferably 10 to 19 μm. Having such a stripe shape is preferable in terms of reducing dislocations and improving the surface state. Increasing the portion of the second nitride semiconductor 43 that grows from the opening of the concave portion can be achieved by increasing the width of the bottom portion of the concave portion and decreasing the width of the upper portion of the convex portion, thereby reducing dislocations. Can be more. When the width of the bottom of the recess is increased, it is preferable to increase the depth of the recess in order to prevent the growth in the vertical direction that may grow from the bottom of the recess.

As a method of providing the unevenness in the second step,
Any method may be used as long as the first nitride semiconductor 42 can be partially removed, and examples thereof include etching and dicing. When unevenness is formed partially (selectively) on the first nitride semiconductor 42 by etching, using a mask pattern of various shapes in photolithography technology, a photomask such as a stripe shape or a grid shape is used. Fabricate the resist pattern first
Formed on the nitride semiconductor 2 and then etched. The photomask is removed after etching to form irregularities. When dicing is performed, for example, it can be formed in a stripe shape or a grid shape.

The method of etching the nitride semiconductor in the second step includes wet etching, dry etching and the like, and dry etching is preferably used to form a smooth surface. Dry etching includes, for example, devices such as reactive ion etching (RIE), reactive ion beam etching (RIBE), electron cyclotron etching (ECR), and ion beam etching. It can be formed by etching a nitride semiconductor. For example, a specific nitride semiconductor etching means described in Japanese Patent Application Laid-Open No. H8-17803 previously filed by the present applicant can be used. In the case where the unevenness is formed by etching, the etched surface (the side surface of the concave portion) is formed as shown in FIG.
As shown in 2), there may be a shape in which the end face is substantially perpendicular to the heterogeneous substrate, a forward mesa shape or an inverted mesa shape, or a shape formed in a step shape. Preferably, from the viewpoint of reduction of dislocation and good surface condition,
Inverse mesas, forward mesas, and more preferably vertical.

(Third Step) Next, FIG.
First nitride semiconductor 42 having irregularities by etching
On top of the second nitride semiconductor 4
FIG. 13 is a schematic cross-sectional view showing a state where a third step of growing a third layer is performed. As the second nitride semiconductor 43, the same as the first nitride semiconductor 42 can be used. Second
The growth temperature of the nitride semiconductor 43 is the same as that for growing the first nitride semiconductor 42, and the second nitride semiconductor 43 grown at such a temperature is a single crystal. Further, when growing the second nitride semiconductor 43, impurities (for example, Si, Ge, Sn, Be, Zn, Mn, Cr,
And Mg, etc.), or the molar ratio of the group III and group V components (III
/ Molar ratio) is preferred in that the growth in the lateral direction is promoted as compared with the growth in the vertical direction to reduce dislocations, and the surface state of the surface of the second nitride semiconductor 43 is further improved. Is preferable in that the

The above-mentioned pressurizing condition above normal pressure is a condition in which the device is adjusted from normal pressure (pressure in which no pressure is intentionally applied) to intentionally apply pressure to obtain a pressurizing condition. To perform the reaction. The specific pressure is not particularly limited as long as it is equal to or higher than normal pressure, but is preferably from normal pressure (approximately 1 atm) to 2.5 atm.
Normal pressure to 1.5 atm. It is preferable to grow the second nitride semiconductor under such a pressure condition in that the surface state of the surface of the second nitride semiconductor is improved.

In the third step, the inside of the concave portion may grow laterally from the side surface of the concave portion, and may grow vertically from the bottom portion of the concave portion. The second nitride semiconductors grown from the side surfaces are bonded to each other to suppress the growth from the bottom of the concave portion. As a result, almost no dislocation is seen in the second nitride semiconductor grown from the opening of the concave portion. The growth rate in the vertical direction from the bottom of the concave portion seems to be slower than that in the lateral direction from the side surface of the concave portion. In addition, when the surface of the bottom of the concave portion is a heterogeneous substrate such as sapphire, the growth of the second nitride semiconductor from the bottom of the concave portion is suppressed, and the growth of the second nitride semiconductor from the side surface of the concave portion is improved. It is preferable in terms of reduction of the amount.

On the other hand, in the second nitride semiconductor portion grown from the upper portion of the convex portion, dislocations slightly larger than those grown from the opening portion of the concave portion are found, but the vertical growth starts in the upper portion of the convex portion. The nitride semiconductor also tends to grow in the lateral direction toward the opening of the concave portion rather than in the vertical direction, and dislocations are reduced as compared with the case where the nitride semiconductor is grown in the vertical direction without forming irregularities. Further, by repeating the second and third steps of the present invention, dislocations at the upper portion of the convex portion can be eliminated. In addition, the second nitride semiconductor grown from the upper portion of the convex portion and the inside of the concave portion is joined during the growth process, and becomes as shown in FIG.

Further, in the third step, when growing the second nitride semiconductor, the pressure is adjusted to a pressure condition equal to or higher than the normal pressure, so that the surface of the second nitride semiconductor becomes abnormally grown. A good and flat surface state is obtained.

In the present invention, when the second and third steps are repeated, as shown in FIG.
The second nitride semiconductor is partially formed with projections and depressions such that the projections are located above the depressions formed in the nitride semiconductor and the depressions are located above the projections formed in the first nitride semiconductor. Then, the third nitride semiconductor 4 is grown on the second nitride semiconductor having the unevenness. The third nitride semiconductor 4 is preferably a nitride semiconductor having few dislocations as a whole. As the third nitride semiconductor, the same as the second nitride semiconductor is grown. Further, when the second and third steps are repeated, the second nitride semiconductor is grown slightly thinner than when it is not repeated, and the bottom of the concave portion formed in the second nitride semiconductor is made of sapphire. Etching the second nitride semiconductor so as to form a heterogeneous substrate surface such as that described above is preferable because a third nitride semiconductor having less dislocations and a good surface state can be obtained.

The second nitride semiconductor 43 serves as a substrate on which a nitride semiconductor having an element structure is grown. The formation of the element structure is performed after removing a different kind of substrate in advance. In some cases, the process is performed while leaving a different substrate or the like. In some cases, the heterogeneous substrate is removed after the element structure is formed. The thickness of the second nitride semiconductor 5 when removing a heterogeneous substrate or the like is 50 μm or more, preferably 100 μm or more.
m, preferably 500 μm or less. When the thickness is in this range, the second nitride semiconductor 43 is less likely to be broken even when the heterogeneous substrate, the protective film, and the like are polished and removed, so that handling is preferable.

The thickness of the second nitride semiconductor 43 in the case of performing the process while leaving a heterogeneous substrate or the like is not particularly limited.
It is 0 μm or less, preferably 50 μm or less, more preferably 20 μm or less. Within this range, warpage of the wafer due to the difference in thermal expansion coefficient between the heterogeneous substrate and the nitride semiconductor can be prevented, and a nitride semiconductor having an element structure can be favorably grown on the second nitride semiconductor 45 serving as an element substrate. Can be done.

In the method for growing a nitride semiconductor of the present invention, the method for growing the first nitride semiconductor 42 and the second nitride semiconductor 43 is not particularly limited.
MOVPE (metalorganic vapor phase epitaxy), HVPE (halide vapor phase epitaxy), MBE (molecular beam epitaxy), M
All methods known for growing nitride semiconductors, such as OCVD (metal organic chemical vapor deposition), can be applied. As a preferable growth method, when the film thickness is 100 μm or less, the growth rate can be easily controlled by using the MOCVD method. When the film thickness is less than 100 μm, HVPE has a high growth rate and is difficult to control.

In the present invention, a nitride semiconductor having an element structure can be formed on the second nitride semiconductor 43. Therefore, in the specification, the second nitride semiconductor is referred to as an element substrate or a nitride. It may be called a semiconductor substrate.

Further, it is preferable to use a substrate in which the main surface of the material to be the heterogeneous substrate in the first step is off-angled, and further a substrate whose stepped off-angle is used. When a substrate with an off-angle is used, three-dimensional growth is not observed on the surface, and step growth appears, so that the surface tends to be flat. Furthermore, when the direction (step direction) along the step of the sapphire substrate that is off-angled in a step shape is formed perpendicular to the A-plane of sapphire, the step surface of the nitride semiconductor is aligned with the cavity direction of the laser. Matches,
This is preferable because laser light is less likely to be irregularly reflected due to surface roughness.

More preferred heterogeneous substrates include (000
1) Sapphire whose main surface is plane [C-plane], (112-0)
Sapphire whose main surface is the [A-plane] or spinel whose main surface is the (111) plane. Here, the heterogeneous substrate is (00
01) When the sapphire has the [C-plane] as the main surface, the uneven stripe shape formed on the first nitride semiconductor or the like is different from the (112-0) -plane [A-plane] of the sapphire. [It is preferable to form a stripe in a direction parallel to the (101-0) [M plane] of the nitride semiconductor], and the off angle off angle θ (see FIG. 7). Θ) shown is 0.1 ° to 0.5 °, preferably 0.1 ° to 0.2 °. Also (112-0)
When the sapphire is a sapphire whose main surface is the plane [A-plane], the stripe shape of the irregularities is (11-02) plane of the sapphire.
It is preferable that the spinel has a stripe shape perpendicular to the [R-plane]. When the spinel has a (111) plane as a main surface, the uneven stripe shape is in relation to the (110) plane of the spinel. And preferably have a vertical stripe shape. Here, the case where the irregularities are in the form of stripes is described. However, in the present invention, the nitride semiconductor easily grows in the lateral direction on the A and R planes of sapphire and the (110) plane of spinel. Nitride semiconductor 2 such that an end face of the first nitride semiconductor is formed.
In order to form a step, it is preferable to consider formation of a protective film.

The heterogeneous substrate used in the present invention will be described in more detail with reference to the drawings. FIG. 6 is a unit cell diagram showing the crystal structure of sapphire. First, in the method of the present invention, a case will be described in which sapphire having a C-plane as a main surface is used, and the unevenness has a stripe shape perpendicular to the sapphire A-plane. For example, FIG. 8 is a plan view of a sapphire substrate on the main surface side. In this figure, the sapphire C plane is the main surface, and the orientation flat (orientation flat) surface is the A surface. As shown in FIG.
The stripes are formed parallel to each other in a direction perpendicular to the plane. As shown in FIG. 8, when a nitride semiconductor is selectively grown on a sapphire C plane, the nitride semiconductor is
It tends to grow in a direction parallel to the plane and hard to grow in a direction perpendicular to the plane. Therefore, when the stripes are provided in the direction perpendicular to the A-plane, the nitride semiconductors between the stripes are connected to each other and grow easily.
It is thought that the crystal growth as described in (1) can be easily performed, but the details are not clear.

Next, when a sapphire substrate having the A surface as the main surface is used, similarly to the case where the C surface is the main surface, for example, if the orientation flat surface is an R surface, the orientation flat surface is perpendicular to the R surface. By forming stripes parallel to each other, a nitride semiconductor tends to grow in the stripe width direction, so that a nitride semiconductor layer with few crystal defects can be grown.

Next, also for spinel (MgAl ₂ O ₄ ), the growth of the nitride semiconductor is anisotropic, the growth surface of the nitride semiconductor is (111) plane, and the orientation flat surface is (11).
When the plane is the 0) plane, the nitride semiconductor tends to grow in a direction parallel to the (110) plane. Therefore, (11
When a stripe is formed in the direction perpendicular to the 0) plane, the nitride semiconductor layer and the adjacent nitride semiconductor are connected to each other at the upper portion of the protective film, and a crystal having few crystal defects can be grown. The spinel is not shown in the figure because it is tetragonal.

In the following, the direction along the steps of the sapphire substrate that has been off-angled corresponds to the A of the sapphire substrate.
The case of being formed perpendicular to the plane will be described with reference to FIG. The dissimilar substrate such as sapphire that is off-angled in a step shape has a substantially horizontal terrace portion A and a step portion B as shown in FIG. Terrace part A
Have few surface irregularities and are almost regularly formed.
The step portion having such an off angle θ is desirably formed continuously over the entire substrate, but may be formed particularly partially. Note that the off angle θ
Means the angle between the straight line connecting the bottoms of the plurality of steps and the horizontal plane of the uppermost step, as shown in FIG. The off-angle of the heterogeneous substrate is 0.1 ° to 0.5 °, preferably 0.1 ° to 0.2 °. When the off angle is in the above range, the surface of the first nitride semiconductor 42 has a fine streak morphology, and the epitaxial growth surface (the surface of the second nitride semiconductor 43) has a wavy morphology.
The nitride semiconductor device obtained using this substrate is smooth,
Characteristics with long life, high efficiency, high output, and improved yield can be obtained.

Further, when a nitride semiconductor obtained by further performing ELOG growth on the nitride semiconductor substrate obtained by the above-described ELOG growth or the like is used as a substrate having an element structure, reduction of dislocation and reduction of warpage are excellent. Which is preferable for obtaining the effects of the present invention. A preferred embodiment of the present invention is described in Japanese Patent Application No. 11-80288. For example, as a preferable example, a thick film, for example, a third nitride semiconductor having a thickness of, for example, 80 to 500 μm is further grown on the second nitride semiconductor 43 obtained by the process shown in FIG. After that, the heterogeneous substrate is removed to make only the third nitride semiconductor, and a fourth nitride semiconductor is grown by HVPE or the like on the surface of the third nitride semiconductor opposite to the surface from which the heterogeneous substrate is removed. Let it. The thickness of the fourth nitride semiconductor is adjusted so that the sum of the thickness of the third nitride semiconductor and the thickness of the fourth nitride semiconductor is, for example, preferably about 400 to 80 μm. Is done. Repeated ELOG growth on such a nitride semiconductor composed of the third and fourth nitride semiconductors can provide a nitride semiconductor substrate with reduced dislocations, which is preferable for obtaining the effects of the present invention. .

When a nitride semiconductor having few dislocations as described above is used as a substrate and an element structure is formed on this substrate, an element having good crystallinity can be obtained, and the threshold current density can be reduced and the life characteristics can be improved. It is preferred in terms of.

Obtained by ELOG growth as described above
An element structure is grown on the nitride semiconductor substrate 1. (N-type contact layer 2) First, the n-type contact layer 2 is nitrided.
Grown on the nitride semiconductor substrate 1. n-type contact layer and
The n-type impurity (preferably Si)
Al_aGa_1-aGrow N (0 <a <1), preferably
a is 0.01 to 0.05 Al_aGa_1-aGrow N
You. an n-type contact layer is formed of a ternary mixed crystal containing Al
Then, fine cracks occur in the nitride semiconductor substrate 1.
Can prevent the propagation of fine cracks,
Further, the nitride semiconductor substrate 1 and the n-type
N due to the difference in lattice constant and thermal expansion coefficient from the contact layer
To prevent micro cracks in the mold contact layer
This is preferable. The doping amount of the n-type impurity is 1
× 10¹⁸/ Cm^Three~ 5 × 10¹⁸/ Cm^ThreeIt is. This n-type
An n-electrode is formed on contact layer 2. n-type contact
The thickness of the layer 2 is 1 to 10 μm. Also, nitriding
Between the semiconductor substrate 1 and the n-type contact layer 2
Al _aGa_1-aN (0 <a <1) may be grown
When this undoped layer is grown, good crystallinity is obtained.
This is preferable for improving the life characteristics. Undoped
The thickness of the n-type contact layer is several μm.

(Crack prevention layer 3) Next, the crack prevention layer 3 is grown on the n-type contact layer 2. As the crack prevention layer 3, Si-doped In _g Ga _{1 -g} N (0.0
5 ≦ g ≦ 0.2), and preferably g is 0.05
Growing to 0.08 of In _g Ga _1-g N. Although the crack preventing layer 3 can be omitted, it is preferable to form the crack preventing layer 3 on the n-type contact layer 2 to prevent cracks from occurring in the device. The doping amount of Si is 5 × 10 ¹⁸ / cm ³ . Further, when growing the crack prevention layer 3, the mixed crystal ratio of In is increased (x
When ≧ 0.1), the crack prevention layer 3 can absorb the light emitted from the active layer 6 and leaked from the n-type cladding layer 4, and can prevent the disturbance of the far field pattern of the laser light. preferable. The thickness of the crack prevention layer is a thickness that does not impair the crystallinity, and is specifically, for example, 0.05 to 0.3 μm.

(N-type cladding layer 4) Next, the n-type cladding layer 4 is grown on the crack preventing layer 3. As the n-type cladding layer 4, Al _e Ga _{1 -e} N (0.12 ≦ e <0.1
5) It is formed as a layer of a multilayer film containing a nitride semiconductor including the above. The multilayer film refers to a multilayer structure in which nitride semiconductor layers having different compositions are stacked, for example, Al _e Ga _{1 -e} N
(0.12 ≦ e <0.15) layer and this Al _e Ga _1-e N
Semiconductors having different compositions from each other, for example, those having a different mixed crystal ratio of Al, those having a ternary mixed crystal containing In, or Ga.
It is formed by combining and laminating layers made of N or the like. Among them, a preferable combination is Al _e Ga
_A multilayer film formed by laminating _1-eN and GaN is preferable because a nitride semiconductor layer having good crystallinity can be laminated at the same temperature. More preferred multilayer film is undoped Al _e G
This is a combination of a _{1 -e} N and GaN doped with an n-type impurity (for example, Si). The n-type impurity is Al
_e Ga _{1 -e} N may be doped. The doping amount of the n-type impurity is 4 × 10 ¹⁸ / cm ^{3 to} 5 × 10 ¹⁸ / cm ³ .
When the n-type impurity is doped in this range, the resistivity can be lowered and the crystallinity is not impaired. Such a multilayer film,
A single layer is formed by stacking nitride semiconductor layers having a thickness of 100 Å or less, preferably 70 Å or less, more preferably 40 Å or less, preferably 10 Å or more. If the single film thickness is less than 100 angstroms, the n-type cladding layer has a superlattice structure, so that cracks can be prevented and the crystallinity can be improved irrespective of containing Al. The total thickness of the n-type cladding layer 4 is 0.7 to 2 μm. The average composition of Al in the entire n-type cladding layer is 0.05 to 0.1. When the average composition of Al is within this range, the composition ratio is such that cracks are not generated, and is a preferable composition ratio for sufficiently obtaining a difference in refractive index from the laser waveguide.

(N-Type Guide Layer) Next, an n-type guide layer 5 is grown on the n-type clad layer 4. As the n-type guide layer 5, a nitride semiconductor made of undoped GaN is grown. The thickness of the n-type guide layer 5 is 0.15 to
When the thickness is 0.07 μm, the threshold value decreases, which is preferable. By making the n-type guide layer 4 undoped, propagation loss in the laser waveguide is reduced, and the threshold value is lowered, which is preferable.

(Active Layer 6) Next, the active layer 6 is grown on the n-type guide layer 5. The active layer 6 is an active layer having a quantum well structure formed by laminating two or one well layers of InGaN whose In composition ratio is adjusted so that the above-mentioned oscillation wavelength is 420 nm or more. .

(P-type electron confinement layer 6) Next, a p-type electron confinement layer 7 is grown on the active layer 6. As the p-type electron confinement layer 7, Mg-doped Al _d Ga _{1 -d} N (0 <
At least one layer of d ≦ 1) is grown. Preferably, it is Mg-doped Al _d Ga ₁ -dN having d of 0.1 to 0.5. The thickness of the p-type electron confinement layer 7 is 10 to 1000 angstroms, preferably 5 to 1000 angstroms.
0 to 200 angstroms. When the film thickness is in the above range, electrons in the active layer 6 can be satisfactorily confined, and the bulk resistance can be suppressed low, which is preferable.
The doping amount of Mg in the p-type electron confinement layer 7 is 1 × 1
0 ¹⁹ / cm ³ to 1 × 10 ²¹ / cm ³ . When the doping amount is within this range, in addition to lowering the bulk resistance, Mg is added to the p-type guide layer grown by undoping described later.
Is diffused well, and Mg is added to the p-type guide layer 8 which is a thin film layer.
Can be contained in the range of 1 × 10 ¹⁶ / cm ³ to 1 × 10 ¹⁸ / cm ³ . The p-type electron confinement layer 7 is preferably grown at a low temperature, for example, at a temperature similar to the temperature at which the active layer is grown at about 850 to 950 ° C., because decomposition of the active layer can be prevented. The p-type electron confinement layer 7 is
A layer grown at a low temperature and a high temperature, for example, 1
It may be composed of two layers, a layer grown at a temperature of about 00 ° C. In this way, if it is composed of two layers,
The overall growth is better because the low temperature grown layer prevents the decomposition of the active layer and the high temperature grown layer reduces the bulk resistance. When the p-type electron confinement layer 7 is composed of two layers, the thickness of each layer is not particularly limited.
The thickness of the high-temperature growth layer is preferably 50 to 150 angstroms.

(P-type guide layer 8) Next, the p-type guide layer 8
Is grown on the p-type electron confinement layer 7. The p-type guide layer 8 is grown as a nitride semiconductor layer made of undoped GaN. The film thickness is 0.15
The thickness is preferably 0.07 μm, and within this range, the threshold value is lowered. Further, as described above, the p-type guide layer is grown as an undoped layer, but the p-type electron confinement layer 7 is formed.
Is diffused, and 1 × 10 ¹⁶ / cm
Mg is contained in the range of ³ to 1 × 10 ¹⁸ / cm ³ .

(P-type cladding layer 9) Next, the p-type cladding layer 9 is grown on the p-type guide layer 8. As the p-type cladding layer, a nitride semiconductor layer containing Al _f Ga _1-f N (0 <f ≦ 1), preferably Al _f Ga _1-f N (0.05 ≦ _f)
f ≦ 0.15) is formed as a layer of a multilayer film having a nitride semiconductor layer. The multilayer film is a multilayer film structure in which nitride semiconductor layers having different compositions are stacked, for example, an Al _f Ga _1-f N layer and a nitride semiconductor having a different composition from Al _f Ga _1-f N, for example, Those having different mixed crystal ratios of Al,
A ternary mixed crystal containing In or a layer obtained by combining and stacking layers with GaN or the like. Preferred combinations in this, Al _f Ga _1-f N and Ga
A multilayer film formed by laminating N is preferable because a nitride semiconductor layer having good crystallinity can be laminated at the same temperature. And more preferred multilayer film is a combination formed by laminating a GaN undoped Al _f Ga _1-f N and p-type impurities (e.g., Mg) doped. p-type impurity may be doped in the Al _f Ga _1-f N. The doping amount of the p-type impurity is 1 × 10 ¹⁷
/ Cm ³ to 1 × 10 ¹⁹ / cm ³ . It is preferable that the p-type impurity is doped in this range because the doping amount is such that the crystallinity is not impaired and the bulk resistance is low. Such a multilayer film is formed by stacking nitride semiconductor layers each having a single layer thickness of 100 Å or less, preferably 70 Å or less, more preferably 40 Å or less, and preferably 10 Å or more. If the single film thickness is less than 100 angstroms, the n-type cladding layer has a superlattice structure, so that cracks can be prevented and the crystallinity can be improved irrespective of containing Al. The total thickness of the p-type cladding layer 9 is 0.4 to 0.5 μm, and is preferably in this range in order to reduce the forward voltage (Vf). Also p
The average composition of Al in the entire mold cladding layer is 0.05 to
0.1. This value is preferable for suppressing the occurrence of cracks and obtaining a difference in refractive index from the laser waveguide.

(P-type contact layer 10) Next, the p-type contact layer 10 is grown on the p-type cladding layer 9. The p-type contact layer is formed by growing a nitride semiconductor layer made of Mg-doped GaN. The film thickness is 10
~ 200 angstroms. Mg doping amount is 1
× 10 ¹⁹ / cm ³ to 1 × 10 ²² / cm ³ . By adjusting the film thickness and the doping amount of Mg in this manner, the carrier concentration of the p-type contact layer increases, and ohmic contact with the p-electrode is easily obtained.

In the device of the present invention, the ridge-shaped stripe is formed by being etched from the p-type contact layer to the lower side (substrate side) than the p-type contact layer. For example, a stripe formed by etching from the p-type contact layer 10 to the middle of the p-type cladding layer 9 as shown in FIG.
To the n-type contact layer 2.

On the side surface of the ridge-shaped stripe formed by etching or on the plane of the nitride semiconductor layer continuous with the side surface, for example, as shown in FIG. 5, an insulating material having a value smaller than the refractive index of the laser waveguide region is provided. A film is formed.
As the insulating film formed on the side surface of the stripe or the like, for example, S has a refractive index of about 1.6 to 2.3.
an oxide containing at least one element selected from the group consisting of i, V, Zr, Nb, Hf, and Ta, BN, Al
N and the like, and preferably one or more elements of oxides of Zr and Hf, and BN. Further, a p-electrode is formed on the surface of the p-type contact layer 10 at the uppermost layer of the stripe via the insulating film. The width of the ridge-shaped stripe formed by etching is 0.5
４4 μm, preferably 1-3 μm. When the width of the stripe is in this range, the horizontal / lateral mode is easily changed to a single mode, which is preferable. Further, the etching is performed in the p-type cladding layer 9.
It is preferable to make the aspect ratio close to 1 when the distance is set to be closer to the substrate than the interface between the laser waveguide region and the laser waveguide region. As described above, when the etching amount of the ridge-shaped stripe, the stripe width, and the refractive index of the insulating film on the side surface of the stripe are specified, a single-mode laser beam can be obtained, and the aspect ratio can be made closer to a circle. This is preferable because the design of the laser beam and the lens becomes easy. When forming a ridge-shaped stripe, if the substrate for forming the element structure is an ELOG substrate, and if ELOG growth is performed using a protective film, an ELO substrate is provided above the protective film.
When G growth is performed with irregularities, a ridge-shaped stripe is preferably formed above the concave portion from the viewpoint of improving the reliability of the device. In addition, it is preferable in terms of reliability to avoid the respective upper portions of the central portion of the protective film and the central portion of the concave portion. In the device of the present invention, various types of conventionally known p-electrodes and n-electrodes can be appropriately selected and used.

Combining the above-described element structures with adjusted impurity concentration, film thickness, composition, etc., narrow ridge-shaped stripes, etc., can reduce the threshold current density and improve the life characteristics. preferable.

[0069]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment which is an embodiment of the present invention will be described below. However, the present invention is not limited to this. In addition, although the present embodiment shows MOVPE (metal organic chemical vapor deposition), the method of the present invention is not limited to MOVPE, for example, HVPE (halide vapor phase epitaxy),
All known methods for growing nitride semiconductors, such as MBE (Molecular Beam Epitaxy), can be applied. Also,
As described in the detailed description of the invention, the value of the formula for calculating the theoretical value of the In composition ratio differs from the actual oscillation wavelength due to a shift to a short wavelength due to the formation of a quantum level having a quantum well structure. The In composition ratio of the active layer of the example is an approximate value.

Example 1 As Example 1, a nitride semiconductor laser device according to an embodiment of the present invention shown in FIG. 5 is manufactured.

As shown in FIG. 7, the main surface of the heterosubstrate 41 is a stepwise off-angled C-plane, an off-angle angle θ = 0.15 °, a step height of about 20 angstroms, and a terrace width W of about 800 angstroms. A sapphire substrate having an orientation flat surface as an A surface and a step perpendicular to the A surface is prepared. The sapphire substrate was set in a reaction vessel, the temperature was raised to 510 ° C., hydrogen was used as a carrier gas, ammonia and TMG (trimethylgallium) were used as source gases, and Ga was placed on the sapphire substrate.
A low-temperature buffer layer of N is grown to a thickness of 200 Å. After the growth of the buffer layer, only TMG was stopped, and the temperature was increased to 1050 ° C.
, The first nitride semiconductor layer made of undoped GaN is formed to a thickness of 2 μm using TMG and ammonia as source gases.
It is grown to a thickness of m. Next, a stripe-shaped photomask is formed on the wafer on which the first nitride semiconductor layer is laminated, and a stripe width (a part to be the upper part of the convex part) 5 μm and a stripe interval (a part to be the concave part bottom part) by a sputtering apparatus. By forming an SiO ₂ film patterned to 10 μm, and then etching the first nitride semiconductor layer in a portion where the SiO ₂ film is not formed by RIE until sapphire is exposed to form irregularities. Then, the first nitride semiconductor layer is exposed on the side surface of the concave portion. After forming the irregularities, the SiO ₂ film on the convex portions is removed. The stripe direction is formed in a direction perpendicular to the orientation flat surface as shown in FIG. Next, the substrate is set in a reaction vessel, and a second nitride semiconductor layer made of undoped GaN is grown at a normal pressure using TMG and ammonia as source gases to a thickness of 15 μm to obtain a nitride semiconductor substrate 1. Using the obtained nitride semiconductor as a nitride semiconductor substrate 1, the following element structure is stacked and grown.

(Undoped n-type contact layer) [not shown in FIG. 5] On the nitride semiconductor substrate 1, a source gas of TM
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, silane gas (SiH ₄ ) is used as impurity gas, and Si is 3 × 10 ^18.
An n-type contact layer 2 made of Al _0.05 Ga _0.95 N doped with / cm ³ is grown to a thickness of 3 μm. Fine cracks are not generated in the grown n-type contact layer 2, and the generation of fine cracks is well prevented.
In addition, even if a fine crack is generated in the nitride semiconductor substrate 1, the growth of the n-type contact layer 2 can prevent the propagation of the fine crack and grow an element structure having good crystallinity. The improvement in the crystallinity can be improved by growing the undoped n-type contact layer as described above, as compared with the case where only the n-type contact layer 2 is used.

(Crack prevention layer 3) Next, the temperature was set to 800
℃, TMG, TMI (trimethyl in
Silane and ammonia as impurity gas
5 × 10 ¹⁸/ Cm^ThreeDoped In
_0.08Ga_0.920.15 μm of crack prevention layer 3 made of N
It is grown to a thickness of m.

(N-type cladding layer 4) Next, the temperature was set to 105
At 0 ° C., a layer A of undoped Al _0.14 Ga _0.86 N is grown to a thickness of 25 Å using TMA, TMG and ammonia as source gases,
Stop MA, use silane gas as impurity gas, Si
Is grown at a thickness of 25 angstroms from a B layer made of GaN doped with 5 × 10 ¹⁸ / cm ³ . This operation is repeated 160 times to laminate the A layer and the B layer to grow the n-type cladding layer 4 composed of a multilayer film (superlattice structure) having a total film thickness of 8000 Å.

(N-type guide layer 5) Next, at the same temperature,
Using TMG and ammonia as source gases, an n-type guide layer made of undoped GaN is grown to a thickness of 0.075 μm.

(Active Layer 6) Next, the temperature was raised to 800 ° C., and TMI, TMG and ammonia were used as raw material gases.
Using silane gas as an impurity gas, Si is 5 × 10 ¹⁸
A barrier layer of In _0.01 Ga _0.99 N doped with / cm ³ is grown to a thickness of 120 Å. Subsequently, the silane gas is stopped, and a well layer made of In _0.1 Ga _0.9 N is grown to a thickness of 20 Å. This operation was repeated once, and finally, a total film thickness of 40
An active layer 6 having a multiple quantum well structure (MQW) of 0 Å is grown.

(P-type electron confinement layer 7) Next, at the same temperature, TMA, TMG and ammonia are used as source gases, Cp ₂ Mg (cyclopentadienyl magnesium) is used as an impurity gas, and Mg is reduced to 1 ×. A p-type electron confinement layer 7 of 10 ¹⁹ / cm ³ doped Al _0.4 Ga _0.6 N is grown to a thickness of 100 Å.

(P-type guide layer 8) Next, the temperature was set to 1050
° C, and using TMG and ammonia as source gases, a p-type guide layer 8 made of undoped GaN was set to 0.075.
It is grown to a thickness of μm. The p-type guide layer 8 is grown as undoped, but the Mg concentration becomes 5 × 10 ¹⁶ / cm ³ due to the diffusion of Mg from the p-type electron confinement layer 7, indicating p-type.

(P-type cladding layer 9) Next, at the same temperature, using TMA, TMG and ammonia
An A layer made of undoped Al _0.1 Ga _0.9 N is grown to a thickness of 25 Å, followed by stopping TMA, using Cp ₂ Mg as an impurity gas, and adding 5 × 1 Mg.
A B layer of GaN doped with 0 ¹⁸ / cm ³ is grown to a thickness of 25 Å. This operation is repeated 100 times to stack the A layer and the B layer, thereby growing the p-type cladding layer 9 composed of a multilayer film (superlattice structure) having a total thickness of 5000 Å.

(P-type contact layer 10) Next, at the same temperature, TMG and ammonia are used as source gases, Cp ₂ Mg is used as an impurity gas, and Mg is 1 × 10 ²⁰ / cm ^3.
The p-type contact layer 10 made of doped GaN is
It is grown to a thickness of 0 Å.

After the reaction, the wafer is annealed in a nitrogen atmosphere at 700 ° C. in a reaction vessel to further reduce the resistance of the p-type layer. After annealing, the wafer is taken out of 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 by SiCl ₄ gas using RIE (reactive ion etching). As shown, the surface of the n-side contact layer 2 where the n-electrode is to be formed is exposed. Next, as shown in FIG. 9A, almost the entire surface of the uppermost p-side contact layer 10 is
Si oxide (mainly SiO ₂ ) by PVD equipment
After forming a first protective film 61 of 0.5 μm in thickness, a mask of a predetermined shape is applied on the first protective film 61, and a third protective film 63 of a photoresist is It is formed with a width of 1.8 μm and a thickness of 1 μm. Next, as shown in FIG. 9B, after forming the third protective film 63, RIE is performed.
(Reactive ion etching) The first protective film is etched into a stripe shape by using a CF ₄ gas with the third protective film 63 as a mask. Thereafter, the photoresist is removed by treating with an etching solution, thereby forming the p-side contact layer 1 as shown in FIG.
A first protective film 61 having a stripe width of 1.8 μm can be formed on the first protective film 61.

Further, as shown in FIG. 9D, after forming the first protection film 61 in the form of a stripe, S is again formed by RIE.
The p-side contact layer 10 and the p-side cladding layer 9 are etched using iCl ₄ gas to obtain a stripe width of 1.
An 8 μm ridge-shaped stripe is formed. However, as shown in FIG.
It is formed so as to avoid the central portion of the recess above the recess formed during the growth. After the formation of the ridge stripe, the wafer is transferred to a PVD apparatus and, as shown in FIG. 9E, a _{second layer of} Zr oxide (mainly ZrO ₂ ) is formed.
Is formed continuously on the first protective film 61 and on the p-side cladding layer 9 exposed by etching with a thickness of 0.5 μm. The formation of the Zr oxide in this way is preferable because the pn plane is insulated and the transverse mode can be stabilized. Next, the wafer is immersed in hydrofluoric acid, and as shown in FIG. 9F, the first protective film 61 is removed by a lift-off method.

Next, as shown in FIG. 9 (g), the first protective film 61 on the p-side contact layer 10 is removed and the exposed surface of the p-side contact layer is made of Ni / Au.
An 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 FIG. After forming the second protective film 62,
As shown in FIG. 5, 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.

After the sapphire substrate of the wafer on which the n-electrode and the p-electrode have been formed is polished to 70 μm as described above, the wafer is cleaved in a bar shape from the substrate side in a direction perpendicular to the stripe-shaped electrodes. A resonator is formed on a cleavage plane (11-00 plane, a plane corresponding to the side surface of a 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 element was set on a heat sink, and the respective electrodes were wire-bonded, and laser oscillation was attempted at room temperature. As a result, the obtained laser element was confirmed to have a continuous oscillation of 50 ° C., a threshold current density of 5 kA / cm ² , an output of 5 mW, and an oscillation wavelength of 420 nm, and showed a life of 300 hours or more.

[Embodiment 2] In the embodiment 1, the active layer 6
As described below so that the oscillation wavelength becomes 430 nm.
A nitride semiconductor laser device is manufactured in the same manner except that the n composition ratio is adjusted and the number of stacked well layers is adjusted. (Active Layer 6) Next, the temperature was set to 800 ° C., TMI, TMG and ammonia were used as source gases, silane gas was used as an impurity gas, and In _0.01 Ga _0.99 N doped with 5 × 10 ¹⁸ / cm ^{3 of} Si was used. A barrier layer is grown to a thickness of 160 Å. Subsequently, the silane gas is stopped, and a well layer made of In _0.12 Ga _0.88 N is grown to a thickness of 20 Å. Subsequently, an active layer 6 having a single quantum well structure (SQW) having a total film thickness of 340 Å in which barrier layers similar to the above are stacked is grown. When the laser element thus obtained was oscillated under the same conditions as in Example 1, the threshold current density was low and good life characteristics were obtained, almost as in Example 1.

Example 3 A laser device is manufactured in the same manner as in Example 2, except that the In composition ratio of the well layer of the active layer is adjusted so that the oscillation wavelength becomes 450 nm. When the laser device obtained was oscillated under the same conditions as in Example 2, the results were almost the same as those in Example 2.

[0087]

According to the present invention, the threshold current density is reduced by setting the high In composition ratio so that the oscillation wavelength becomes 420 nm or more, and further reducing the total number of the well layers to 2 or less, thereby reducing the lifetime characteristic. Can be provided.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the number of stacked active layers of the active layer of the laser device of the present invention and the threshold current density.

FIG. 2 is a schematic cross-sectional view showing band gap energy (Eg) of an InGaN well layer and energy (Eλ) of an oscillation wavelength due to formation of a quantum level.

FIG. 3 is a graph showing the relationship between the number of stacked active layers of the active layer of the conventional laser device and the threshold current density.

FIG. 4 shows an ELOG that can be used in the present invention.
It is a typical sectional view showing the structure of each process of one embodiment of growth.

FIG. 5 is a schematic cross-sectional view showing a nitride semiconductor laser device according to one embodiment of the present invention.

FIG. 6 is a unit cell diagram showing a plane orientation of sapphire.

FIG. 7 is a schematic cross-sectional view showing a partial shape of an off-angled heterogeneous substrate.

FIG. 8 is a plan view of the main surface of the substrate for explaining the stripe direction of the unevenness.

FIG. 9 is a schematic cross-sectional view showing a partial structure of a wafer in each step of a method according to an embodiment for forming a ridge-shaped stripe.

[Explanation of symbols]

 DESCRIPTION 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 7 ... p -Type electron confinement layer 8 ... p-type guide layer 9 ... p-type cladding layer 10 ... p-type contact layer

Claims (10)

[Claims] 1. A nitride semiconductor laser device comprising a substrate in which an n-type nitride semiconductor, an active layer having a quantum well structure having a well layer containing In, and a p-type nitride semiconductor are sequentially stacked on a substrate. A nitride semiconductor laser device in which the active layer has a quantum well structure in which the total number of well layers is 2 or less, and has an oscillation wavelength of 420 nm or more. 2. The active layer has a single quantum well structure in which the total number of stacked well layers is 1, and further has an oscillation wavelength of 430.
2. The nitride semiconductor laser device according to claim 1, wherein the thickness is not less than nm. 3. The quantum well structure of the active layer is formed of a well layer and a barrier layer, and the barrier layer has an n-type impurity concentration of 1 × 10 ¹⁹ / cm ² or less. The nitride semiconductor laser device according to claim 1. 4. The barrier layer according to claim 1, wherein said barrier layer contains n × 5 × 10 ¹⁸
4. The nitride semiconductor laser device according to claim 3, wherein the content of the nitride semiconductor laser device is not more than / cm ² . 5. The semiconductor device according to claim 1, wherein said well layer contains 1 × 10 ¹⁸ n-type impurities.
/ Cm ² or less.
The nitride semiconductor device according to any one of the above. 6. The nitride semiconductor laser device according to claim 1, wherein said well layer has a thickness of 40 Å or less. 7. The nitride semiconductor laser device according to claim 1, wherein said well layer has a thickness of 30 Å or less. 8. The nitride according to claim 1, wherein the quantum well structure of the active layer is formed of a well layer and a barrier layer, and the barrier layer has a thickness of 100 Å or more. Semiconductor laser device. 9. The nitride semiconductor laser device according to claim 8, wherein said barrier layer has a thickness of 100 to 200 Å. 10. A nitride semiconductor, wherein the nitride semiconductor laser device is grown on a heterogeneous substrate or a nitride semiconductor substrate made of a material different from that of the nitride semiconductor by utilizing lateral growth of the nitride semiconductor. The nitride semiconductor laser device according to claim 1, wherein the nitride semiconductor laser device is grown thereon.