JPH04229678A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To prevent light from being absorbed near a light-radiating part in an active layer by a method wherein a band gap at a light-radiating edge part in the active layer is made larger than that at a main light-emitting part in the active layer. CONSTITUTION:A buffer layer 11, clad layers 12, 14, 16, 20, an active layer 13, an etching-stop layer 15, a cap layer 17, a current-blocking layer 18, a guide layer 19, an intermediate gap layer 21 and a contact layer 22 are formed on an n-GaAs substrate 10. A stripe-shaped opening part 18a which reaches the etching-stop layer 15 is made in the clad layer 16, the cap layer 17 and the current-blocking layer 18. At the active layer 13, a part (a main light-emitting part) directly under the stripe-shaped opening part 18a in the current-blocking layer 18 is a low-energy-gap region 13a; a part (indicated by shaded lines) under other regions of the current-blocking layer 19 is a high-energy-gap region 13b. The individual layers mentioned above are formed of an InGaAlP-based semiconductor layer and the like.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

[Industrial Application Field] The present invention relates to a semiconductor laser using a compound semiconductor material, and in particular, an active layer of InGaAl.
The present invention relates to a semiconductor laser device using P.

0002

[Prior art] In recent years, I
Red semiconductor lasers using nGaAlP-based materials have been commercialized and are expected to be used as light sources for high-density disk devices, laser beam printers, barcode readers, optical measuring instruments, and the like.

FIG. 8 is a cross-sectional view showing an example of this type of laser (37th Spring 1990 Applied Physics Conference, 29a-SA-4). In FIG. 8, 100 is n
-GaAs substrate, 101 is n-InGaAlP cladding layer, 102 is InGaP active layer, 103 is p-InGa
AlP cladding layer, 104 is n-GaAs current blocking layer, 105 is p-GaAs contact layer, 106, 10
Reference numeral 7 indicates an electrode, reference numeral 108 indicates an impurity diffusion region, and a striped ridge portion is formed in the cladding layer 103.

In this laser, in the region 108 where impurities are diffused, the natural superlattice formed in the InGaP active layer disappears and becomes a disordered layer. Since the bandgap of the disordered layer is larger than that of the original superlattice, the disordered layer becomes transparent to laser light excited in the original natural superlattice region. Making the vicinity of the output end face transparent in this way is extremely effective in eliminating light absorption in the active layer near the output end face, which causes damage to the end face during high-output operation of semiconductor lasers, and increases the maximum optical output level. improvement is expected.

However, this type of laser has the following problems. That is, the impurity diffusion region 108
After forming the current blocking layer 104 on top of the diffusion region 108, the process becomes complicated. Furthermore, impurity diffusion takes place both in the depth direction and in the lateral direction.
Controlling the diffusion distance of this lateral diffusion is difficult. Therefore, when forming the current blocking layer 104 above the diffusion region 108, it is necessary to take lateral diffusion into consideration, which poses a problem of complicating processes such as mask alignment. Further, the diffusion region (window region) 108 has no optical waveguide mechanism, the wavefront of the laser light is disturbed, and there is also the problem that the astigmatism difference is larger than in the conventional structure in which no window region is formed.

[0006]

[Problems to be Solved by the Invention] As described above, conventionally, In
In a semiconductor laser having an active layer made of GaP or the like,
There has been a problem in that the maximum optical output during continuous operation is reduced due to light absorption near the emission end face of the laser beam. Furthermore, when a window structure is applied to increase the maximum light output, there is a problem in that the manufacturing process becomes extremely complicated.

The present invention has been made in consideration of the above circumstances, and its purpose is to eliminate light absorption in the vicinity of the emission end face of laser light, and to improve the maximum light output in continuous operation. An object of the present invention is to provide an InGaAlP semiconductor laser device. [Structure of the invention]

[
0008

[Means for Solving the Problems] The gist of the present invention is to
In a semiconductor laser having an active layer made of aAlP-based material, etc., in order to avoid light absorption near the light emitting part of the active layer, the band gap of the light emitting end face of the active layer is made larger than that of the main light emitting part of the active layer. The purpose is to create a band gap difference in the active layer by changing the shape of the current confinement layer formed on the cladding layer.

That is, the present invention (claim 1) is directed to InGaAl
In a semiconductor laser device made of a P-based semiconductor material,
Formed on a compound semiconductor substrate, In1-x-y Ga
y Alx P (0≦x<1, 0≦y<1), etc., with a double hetero structure sandwiching an active layer between cladding layers, and a laser beam emitting end face formed on the double hetero structure. n with striped openings except for the top
type semiconductor layer (current blocking layer), and the active layer n
The region directly under the type semiconductor layer has a larger band gap than the region directly under the striped opening of the active layer.

[0010] The present invention (claim 2) also provides InGaAl
In a semiconductor laser device made of a P-based semiconductor material,
Formed on a compound semiconductor substrate, In1-x-y Ga
y Alx P (0≦x<1, 0≦y<1), etc., is formed on a double heterostructure portion in which an active layer is sandwiched between first and second cladding layers, and It consists of a third cladding layer in which stripe-shaped openings are provided except on the laser beam emission end face, and an n-type semiconductor layer (current blocking layer) formed on this third cladding layer, and an active layer. The portion directly under the n-type semiconductor layer is made into a region having a larger band gap than the portion directly under the striped opening of the active layer.

[0011] The present invention (claim 3) also provides InGaAl
In a semiconductor laser device made of a P-based semiconductor material,
Formed on a compound semiconductor substrate, In1-x-y Ga
y Alx P (0≦x<1, 0≦y<1), etc., with a double hetero structure sandwiching an active layer between cladding layers, and a laser beam emitting end face formed on this double hetero structure. an n-type current confinement layer having a larger bandgap than the active layer in which striped openings are provided except for the upper part; The part of the active layer directly under the n-type semiconductor layer has a larger band gap than the part directly under the striped opening of the active layer.

[0012] Also, as a preferred embodiment of the present invention,
The main surface of the substrate is 1 in the [011] direction from the {100} plane.
Using n-type GaAs with a plane inclined within 5 degrees, the lower cladding layer of the double heterostructure is n-type, the upper cladding layer is p-type, and each cladding layer is In1-z-
w Gaw AlzP(0≦z<1,0≦z<1,z>
x), or Ga1-t Alt As (0≦t<1)
Also, n-type GaAs is used as the n-type semiconductor layer. Furthermore, the present invention is characterized in that the width of the striped openings is narrower at the ends in the stripe direction.

[0013]

[Operation] According to the present invention, the stripe of the n-type semiconductor layer is not extended to the laser beam output end face, but the stripe opening is formed in the area excluding the laser beam output end face, so that the active layer A difference can be provided in the band gap between the main light emitting part of the active layer, which corresponds to the vicinity of the emission end face and the opening of the n-type semiconductor layer. Although the mechanism has not been clearly elucidated, the following is assumed.

When manufacturing a semiconductor laser device, a semiconductor substrate is placed, for example, on a high-frequency heated susceptor, and
A semiconductor layer is formed. In addition to heat conduction from the susceptor and the like, the semiconductor substrate and the semiconductor layer absorb the radiated light and are heated. Here, since the n-type semiconductor layer absorbs a large amount of free carriers, it easily absorbs radiation, and it is thought that the temperature of this n-type semiconductor layer becomes higher than other layers during the growth process. As a result, it is thought that impurities diffuse into the active layer from the p-type cladding layer region below the region where the n-type semiconductor layer is formed, causing a difference in the band gap of the active layer.

[0015] When the impurity of the p-type cladding layer is Zn, the diffusion coefficient is large and diffusion can be performed satisfactorily. In this way, the vicinity of the light-emitting end face can be made into a region with a larger band gap than the light-emitting portion, and it becomes possible to suppress heat generation and light absorption in the vicinity of the light-emitting end face.

Furthermore, if the opening of the n-type semiconductor layer is narrowed near the light-emitting end face, the band gap between the n-type semiconductor layer and the opening will be reduced in the lateral direction of the active layer (direction perpendicular to the stripe direction). A difference can be made. Therefore, the light is confined in the lateral direction, and the light is guided well even near the end face where there is no optical waveguide, and the wavefront is less disturbed and it is possible to reduce the astigmatism difference.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be explained below with reference to illustrated embodiments.

1 and 2 are for explaining the schematic structure of a semiconductor laser according to a first embodiment of the present invention. FIG. 1 is a perspective view showing the overall structure, and FIG. 2(a) is a current diagram. FIG. 2(b) is a plan view showing the block layer pattern, and FIG.
) shows a cross-sectional view of the laser element corresponding to the cross section taken along arrow B-B in (a). 10 in the figure is an n-GaAs substrate, and on this substrate 10, an n-GaAs buffer layer 11, an n-I
n0.5 (Ga0.3 Al0.7 )0.5 P first cladding layer 12, undoped In0.5 G
a0.5 P active layer 13, p-In0.5 (
Ga0.3 Al0.7 )0.5 P second cladding layer 14, p-In0.5 Ga0.5 P etching stop layer 15, p-In0.5 (Ga
0.3 Al0.7 ) 0.5 P third cladding layer 16
, p-In0.5Ga0.5P cap layer 17, and n-GaAs current blocking layer 18 are laminated.

Striped openings 18a reaching the etching stop layer 15 are provided in the third cladding layer 16, the cap layer 17, and the current blocking layer 18. This opening 18a does not reach the end face of the emitted light. The p-
In0.5 (Ga0.5 Al0.5)0.5 P
A light guide layer 19 is grown. On this optical guide layer 19, p-In0.5 (Ga0.3
Al0.7)0.5P fourth cladding layer 20,
p-In0.5 Ga0.5 P intermediate bandgap layer 21, p-GaAs contact layer 22

00
20] are each grown and formed. AuZn is formed as a p-side electrode 23 on the contact layer 22, and AuGe is formed as an n-side electrode 24 on the lower surface of the substrate 10.

Here, in the active layer 13, the part directly below the striped opening 18a of the current blocking layer 18 (main light emitting part) is a low energy gap region 13a, and the other part under the current blocking layer region This is a high energy gap region 13b (indicated by diagonal lines). The reason for the difference in energy gap between the low energy gap region 13a and the high energy gap region 13b is thought to be that although the compositions are the same, the atomic arrangement in the crystal is different. In fact, the band gap energy of the low energy gap region 13a determined by photoluminescence evaluation is the same as that of the high energy gap region 13a.
It is about 20 to 90 meV smaller than b.

The oscillation wavelength of the device with this structure is determined by the low energy gap region 1 of the active layer 13 where current injection is mainly performed.
It is determined by the bandgap of 3a. The absorption coefficient of the high energy gap region 13b for light of this wavelength is smaller than that of the low energy gap region 13a, and the absorption coefficient near the output light end face is smaller than that in the case where a uniform energy gap region is formed up to the output light end face. The deterioration mode due to self-absorption can be suppressed, thereby improving the maximum optical output level.

Note that the buffer layer 11 is made of InGaP, and the etching stop layer 15 is made of InGaAlP or GaA.
lAs, current blocking layer 18 is n-type or semi-insulating InGaAlP, or n-type or semi-insulating GaAlA
s, the optical guide layer 19 is a p-InGaAlP layer or a p-InGaAlP layer
-GsAlAs, the intermediate bandgap layer 21 is p-Ga
The same effect as described above can be obtained even when the third cladding layer 16 is made of n-InGaAlP.

3 and 4 are for explaining the schematic structure of a semiconductor laser according to a second embodiment of the present invention. FIG. 3 is a perspective view showing the overall structure, and FIG. 4(a) is a current diagram. FIG. 4(b) is a plan view showing the block layer pattern, FIG. 4(c) is a plan view showing the cap layer pattern, and FIG. 4(c) is a plan view showing the block layer pattern.
The cross-sectional view of the laser element corresponding to cross-section A, FIG. 4(d), is (
A cross-sectional view of the laser element corresponding to the cross section taken along arrow B-B in a) is shown. 30 in the figure is an n-GaAs substrate, and on this substrate 30, an n-GaAs buffer layer 31, an n-I
n0.5 (Ga0.3 Al0.7 )0.5 P first cladding layer 32, undoped In0.5 G
a0.5 P active layer 33, p-In0.5 (
Ga0.3 Al0.7 )0.5 P second cladding layer 34, p-In0.5 Ga0.5 P etching stop layer 35, n-In0.5 (Ga
0.3 Al0.7 ) 0.5 P current blocking layer 36
, n-GaAs cap layer 37 are laminated.

The current blocking layer 36 is provided with a striped opening 36a that reaches the etching stop layer 35, and the cap layer 37 is provided with an opening 37a that reaches the current blocking layer 36. This opening 37
a does not reach the output light end face. Current blocking layer 36
On the etching stop layer 35 exposed in the opening of the p-In0.5 (Ga0.5 Al0.5
)0.5P light guide layer 38 is grown. On this light guide layer 38, p-In0.5 (
Ga0.3Al0.7)0.5P third cladding layer 39, p-In0.5Ga0.5P intermediate bandgap layer 40, p-GaAs contact layer 41

[0026] is grown and formed. AuZn is formed as a p-side electrode 42 on the contact layer 41, and AuGe is formed as an n-side electrode 43 on the lower surface of the substrate 30.

[0027] In this embodiment as well, by the same effect as in the previous embodiment, it is possible to suppress the deterioration mode due to self-absorption in the vicinity of the output light end face, and it is possible to improve the maximum optical output level.

4 and 6 are for explaining the schematic structure of a semiconductor laser according to a third embodiment of the present invention. FIG. 5 is a perspective view showing the overall structure, and FIG. 5(a) is a current diagram. FIG. 6(b) is a plan view showing the block layer pattern, and FIG.
) shows a cross-sectional view of the laser element corresponding to the cross section taken along arrow B-B in (a). Note that the same parts as in FIGS. 1 and 2 are given the same reference numerals, and detailed explanation thereof will be omitted.

In the figure, reference numeral 10 denotes an n-GaAs substrate, and on this substrate 10, as in the first embodiment, an n-GaAs buffer layer 11, an n-InGaAlP first cladding layer 12, an undoped InGaP active layer 13, and a p-type InGaP active layer 13 are formed. -InGaAlP second cladding layer 14 and p-InGaP etching stop layer 15 are laminated, and n-GaAs
A current blocking layer 18 is formed in a laminated manner.

The current block layer 18 is provided with striped openings 18a that reach the etching stop layer 15. This opening 18a becomes narrow near the output light end face and does not reach the output light end face. A p-GaAs contact layer 22 is grown on the etching stop layer 15 exposed in the opening of the current blocking layer 18 and further on the current blocking layer 18 . A p-side electrode 23 is formed on the contact layer 22, and an n-side electrode 24 is formed on the lower surface of the substrate 10.

Here, in the active layer 13, as in the first embodiment, the portion (main light emitting portion) directly below the striped opening 18a of the current blocking layer 18 is a low energy gap region 13a. The portion below the other current block layer 18 region (indicated by diagonal lines) is a high energy gap region 13b.

Even with this configuration, the low energy gap region 13 of the active layer 13 is
The oscillation wavelength is determined by the band gap of a, and the deterioration mode due to self-absorption near the output light end face can be suppressed, and the maximum optical output level can be improved.

Furthermore, as shown in FIG. 6(c), since a region 13b with a high energy gap is formed outside the region 13a with a low energy gap, light can be guided well. Furthermore, since the aperture area that enters the window area where there is no waveguide mechanism is narrowed, the light is condensed in the window area. Therefore, the light is guided without spreading in the window region and has a uniform wavefront, thereby reducing the astigmatism difference.

FIG. 7 is a plan view showing a current blocking layer pattern, for explaining the main structure of the fourth embodiment of the present invention. Note that the same parts as in FIG. 2 are given the same reference numerals, and detailed explanation thereof will be omitted.

In this embodiment, the shape of the striped openings 18a formed in the current blocking layer 18 in the first embodiment is changed, and other parts are completely the same as the first embodiment. The opening 18a is narrower near the output light end face, similar to the third embodiment. Here, the opening 18a
In each part, the width of the center part M = 5 μm, the width of the end face N =
2 μm, and the length L of the tapered portion was 10 μm. In order to condense the light and prevent it from spreading in the window area, the ranges of L=5 to 30, M=3 to 10, and N=1 to 8 are desirable. Alternatively, N=0 and the end portion may have a sharp shape.

It should be noted that the present invention is not limited to the above-mentioned embodiments. In the example, In1-y (Ga1
The Al composition, expressed as -x Alx )y P, is set to x = 0 in the active layer and x = 0.7 in the cladding layer, but this Al composition has a band gap of the cladding layer that is sufficiently larger than that of the active layer. It may be determined as appropriate within a larger range. Furthermore, the Al composition of the optical guide layer is not limited to x=0.5, but can be changed as appropriate within a range that is smaller than the cladding layer and larger than the active layer. Furthermore, although y=0.5 was used this time, y=0.5±0.12 is also effective. others,
Various modifications can be made without departing from the spirit of the invention.

[0037]

[Effects of the Invention] As detailed above, according to the present invention, I
In a semiconductor laser having an active layer made of nGaAlP or the like, the band gap of the light emitting end face of the active layer is made larger than that of the main light emitting part of the active layer, thereby preventing light absorption near the light emitting part of the active layer. This makes it possible to improve the maximum optical output in continuous operation. Furthermore, since the aperture area that enters the window area where there is no optical waveguide mechanism is narrowed, the light can be focused in the window area and the wavefronts can be made uniform, thereby making it possible to reduce the astigmatism difference. Furthermore, by utilizing the difference in atomic arrangement in the crystal to create a difference in band gap energy, the above-mentioned semiconductor laser can be manufactured by a simple process, and its usefulness is enormous.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a schematic configuration of a semiconductor laser according to a first embodiment;

FIG. 2 is a plan view and a sectional view showing the configuration of each part of the first embodiment;

FIG. 3 is a perspective view showing a schematic configuration of a semiconductor laser according to a second embodiment;

FIG. 4 is a plan view and a sectional view showing the configuration of each part of the second embodiment;

FIG. 5 is a perspective view showing a schematic configuration of a semiconductor laser according to a third embodiment;

FIG. 6 is a plan view and a sectional view showing the configuration of each part of the third embodiment;

FIG. 7 is a plan view showing the main part configuration of the fourth embodiment;

[Figure 8
] A perspective view showing a schematic configuration of a conventional semiconductor laser.

[Explanation of symbols]

10,30...n-GaAs substrate, 12,32...n-In
GaAlP first cladding layer, 13, 33... InGaP active layer, 13a... low energy gap region, 13b... high energy gap region, 14, 34... p-InGaA
lP second cladding layer, 16,39...p-InGaAlP
Third cladding layer, 17...p-InGaP cap layer, 1
8...n-GaAs current blocking layer, 18a, 36a, 3
7a... Opening, 19, 38... p-InGaAlP light guide layer, 20... p-InGaAlP fourth cladding layer, 21
, 40...p-InGaP intermediate bandgap layer, 22,
41...p-GaAs contact layer, 23, 24, 42,
43... Electrode, 36... n-InGaAlP current blocking layer, 37... n-GaAs cap layer.

Claims (4)

[Claims] Claim 1: A double heterostructure in which an active layer is sandwiched between cladding layers, and a p-type on the opposite side of the double heterostructure to the substrate.
an n-type semiconductor layer formed on a cladding layer of the mold, and provided with a stripe-shaped opening except over the laser beam emission end face, and the band gap of the active layer region under the n-type semiconductor layer region A semiconductor laser device characterized in that the bandgap is larger than that of other active layer regions. 2. A double heterostructure in which an active layer is sandwiched between first and second cladding layers, and a p-type second cladding layer on the opposite side of the double heterostructure to the substrate; It consists of a third cladding layer in which a striped opening is provided except on the laser beam emission end face, and an n-type semiconductor layer formed on the third cladding layer, and the n-type semiconductor layer region A semiconductor laser device characterized in that a lower active layer region has a band gap larger than that of other active layer regions. 3. A double heterostructure in which an active layer is sandwiched between cladding layers, and a p-type on the opposite side of the double heterostructure to the substrate.
an n-type current confinement layer having a larger band gap than the active layer, which is formed on the type cladding layer and has a stripe-shaped opening except over the laser beam emission end face;
an n-type semiconductor layer formed on the laser beam emitting end surface on the type current confinement layer, and the bandgap of the active layer region under the n-type semiconductor layer region is larger than the bandgap of other active layer regions. A semiconductor laser device characterized by: 4. The semiconductor laser device according to claim 1, wherein the stripe-shaped opening is formed to have a narrow width at an end in the stripe direction.