JPH10154844A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a higher output stable operation by coating the edge for emitting a laser light with indium nitride InN or gallium nitride GaN thereby suppressing deterioration of emission edge and reflection edge. SOLUTION: An n-(Al0.7 Ga0.3 )InP layer 43, a strained quantum well active layer 44, a p-(Al0.7 Ga0.3 )InP layer 45, a p-GaInP layer 46 and a p-GaAs layer 47 are formed sequentially on a substrate 42. The strained quantum well active layer 44 comprises three strained quantum well layers 44a sandwiching barrier layers 44b of (Al0.4 Ga0.6 )0.5 In0.5 P. Subsequently, an n-GaAs layer 48 is formed on the layer 45 on the opposite sides of a mesa stripe being formed except the central region while filling the etched part before depositing an alumina 51 and a silicon 52 sequentially on a cleavage plane CF8. According to the structure, upper limit of optical density causing no deterioration of emission edge and reflection edge is elevated and aging of the optical output can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly to a semiconductor laser having two cleavage planes facing each other in the longitudinal direction of an active layer. Semiconductor laser having the same.

[0002]

2. Description of the Related Art In recent years, a semiconductor laser has become important as a light source of an optical information processing apparatus such as an optical disk, and further higher output stable operation is demanded. Conventionally, as a factor that hinders high-output stable operation of a semiconductor laser, deterioration of an end face, ie, an emission end face and a reflection end face, that is, COD (Catastro
There is a problem that phic optical damage occurs.

[0003] At the end face of a semiconductor laser, there is a surface level which becomes a recombination center of carriers.
Carriers injected into the active layer undergo non-radiative recombination via the recombination centers. Due to the heat generated by the recombination, the temperature rises in the vicinity of the end face, the forbidden band width of the active layer becomes small, and the laser beam is easily absorbed. When the laser beam is absorbed, the heat is generated and the temperature is further increased, and the non-radiative recombination is further increased. Ultimately, the laser breaks down due to COD (Catastrophic Optical Damage) that melts and destroys the end face. Such a vicious cycle occurs when the laser light exceeds a certain light density, which hinders high output stable operation.

[0004] It is known that the surface state density at the end face increases as the laser operation becomes longer and the end face oxidizes. In order to reduce this, as shown in FIG. 6, an alumina film (Al ₂ O ₃ film) and a silicon oxide film (Si) are formed on a main light extraction end face CF1 (hereinafter referred to as a front end face).
O ₂ film) or silicon nitride film (SiN film)
It is known that by controlling the film thickness so that the end face reflectivity is 5 to 10%, the end face CF1 is suppressed from being oxidized and a high output stable operation can be performed. In FIG. 6, 1 is an n-GaAs substrate, 2 is n- (Al _0.7 Ga
_0.3 ) InP layer, 3 is an active layer made of a lattice-matched GaInP film, 4 is a p- (Al _0.7 Ga _0.3 ) InP layer, 5 is a p-GaInP layer, 6 is
p-GaAs layer, 7 is n-GaAs layer, 8 is p-GaAs layer, 10 is alumina film, 11 is Si film, alumina film 10 and Si film 11
Thereby, the reflectance of the rear end face CF2 is about 80%.

On the other hand, in the semiconductor lasers shown in FIGS. 7A and 7B, particularly the quantum well laser, the thickness of the quantum well layer 14a and the barrier layer 14b constituting the active layer 14 is set to be equal to or less than the de Broglie wavelength of the carrier. It is formed in such a thin single layer or multilayer. In such a quantum well laser, threshold current density and high-temperature operation characteristics are improved by introducing compressive strain into the quantum well layer 14a and the like, and the forbidden band width of the quantum well layer 14a is increased. It has been known. Also in this case, the above-mentioned end face covering film 20 is formed to prevent oxidation of the front end face CF3. 7A and 7B, reference numeral 12 denotes an n-GaAs substrate,
13 is an n- (Al _0.7 Ga _0.3 ) InP layer, 15 is p- (Al _0.7 Ga _0.3 ) InP
P layer, 16 is p-GaInP layer, 17 is p-GaAs layer, 18 is n-Ga
As layer, 19 is a p-GaAs layer, 21 is an alumina film, and 22 is a Si film. In FIG. 7B, Ec represents a conduction band, and Ev represents a valence band.

[0006]

In the above-described semiconductor laser, an alumina film (Al ₂ O ₃ film), a silicon oxide film (SiO ₂ film), or a silicon nitride film is used as the end face coating films 9 and 20 of the semiconductor laser. (SiN films) are used, but the materials of these films are not necessarily stable materials. Interdiffusion with the semiconductor material occurs during operation of the semiconductor laser, and a level is generated in the forbidden band of the semiconductor. Make it. For this reason, when the semiconductor laser is operated for a long time, COD is generated via its level.
There is a problem that deterioration such as the above occurs, which hinders a high output stable operation of the semiconductor laser.

Further, the semiconductor laser in which a compressive strain is introduced into the active layer 14 has the following problem in addition to the above-mentioned interdiffusion. That is, since the distortion of the active layer 14 is released in the vicinity of the front end face CF3 of the semiconductor laser, the forbidden band width becomes narrow in the vicinity of the active layer 14, and the laser light is easily absorbed. For this reason, deterioration of COD or the like occurs, and high-output stable operation is hindered.

The present invention has been made in view of the above-mentioned problems of the prior art, and is applicable to a semiconductor laser having a lattice-matched active layer as well as a semiconductor laser having a strained active layer. It is an object of the present invention to provide a semiconductor laser capable of achieving a higher output stable operation by suppressing the occurrence of the above-described problem, and a method of manufacturing the same.

[0009]

According to a first aspect of the present invention, there is provided a first cladding layer having one conductivity type formed on a substrate, the first cladding layer being formed on the first cladding layer, An active layer that generates laser light lattice-matched to the substrate, a second cladding layer having an opposite conductivity type formed on the active layer, and an end face coating film formed on an emission end face of the laser light Wherein the end face coating film is an indium nitride (InN) film or a gallium nitride (GaN) film, which is solved by the semiconductor laser according to the second invention. A first cladding layer having one conductivity type formed thereon, an active layer formed on the first cladding layer and generating a laser beam which is strained due to lattice mismatch with the substrate, Anti formed on the layer In a semiconductor laser having a second cladding layer having a conductivity type and an end face coating film formed on the emission end face of the laser beam, the end face coating film is a film that gives compressive strain to the active layer. The third aspect of the present invention, which is solved by a semiconductor laser, comprises: an end face coating film for giving a compressive strain, an aluminum nitride film (AlN film), a boron nitride film (BN film), and a gallium nitride film (GaN). The semiconductor laser according to the second invention is characterized in that the semiconductor laser is any one of a film, an indium nitride film (InN film), and a thallium nitride film (TIN).

In the present invention, indium nitride (In) is applied to the emission end face of a semiconductor laser having an active layer lattice-matched.
N) or an end face coating film made of gallium nitride (GaN). By the way, the indium nitride film is chemically stable and has a property that mutual diffusion hardly occurs with the semiconductor layer. For this reason, even if the carriers recombine via the surface level of the end face serving as the non-radiative recombination center and generate heat, the reaction between the indium nitride film and the semiconductor layer and the interdiffusion therebetween are suppressed. .

As a result, it is possible to suppress the deterioration with time of the COD light output, which is determined depending on the deterioration of the end face by the conduction test, and to improve the life. In addition, an end face coating film which gives a compressive strain to the active layer on the emission end face of the semiconductor laser having the strained active layer, for example, an aluminum nitride film (AlN
Film), boron nitride film (BN film), gallium nitride film (Ga
N film), an indium nitride film (InN film), or a thallium nitride film (TIN).

Incidentally, the aluminum nitride film or the like has a compressive stress sufficient to prevent the strain of the active layer in contact with the film from being released and to maintain the strain as it is. The width of the forbidden band of the well layer is maintained sufficiently wide, and the absorption of laser light is suppressed. For this reason, heat generation and temperature rise due to absorption of laser light at the emission end face are suppressed.

[0013] This makes it possible to increase the upper limit of the light density at which COD, which is determined depending on the end face deterioration due to the current test, does not occur, and to suppress the COD light output from deteriorating over time and to improve the life. it can.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. (1) First Embodiment FIG. 3 is a side view showing a configuration of a solid source ECRCVD apparatus for depositing an end face coating film of a semiconductor laser according to a first embodiment.

As shown in FIG. 3, a plasma generation chamber 51 and a film formation chamber 52 are connected through a plasma gas flow port 53. A microwave waveguide 55 having a frequency of 2.45 GHz is connected to the plasma generation chamber 51, and a cylindrical permanent magnet or coil 56 is installed around the plasma generation chamber 51 to form a film from the plasma generation chamber 51. A magnetic field directed toward the chamber 52 is generated. In addition, energy is applied by electron cyclotron resonance in N ₂ and Ar gas was introduced into the plasma generating chamber 51 from the gas inlet 54, N ₂ and Ar gases are plasma.

A target 60 made of an annular aluminum plate is provided above the substrate mounting table 59 in the film forming chamber 52, and is connected to a high frequency power supply 61 having a frequency of 13.56 MHz. When plasma is generated in a state where high-frequency power is applied to the target 60, Ar ⁺ ions flowing from the plasma generation chamber 51 to the film formation chamber 52 are emitted from the target 6.
The aluminum element is sputtered by colliding with 0, and the activated nitrogen reacts with the aluminum element to deposit an aluminum nitride film (AlN film) on the substrate 101 mounted on the substrate mounting table 59. When a plate made of another element, for example, boron, gallium, indium, or thallium is used as the target 60 instead of the aluminum plate, a boron nitride film (BN film), a gallium nitride film (GaN)
Film), an indium nitride film (InN film), a thallium nitride film (TIN), or the like.

Further, an exhaust port 58 is formed in the film forming chamber 52, and an exhaust device (not shown) is connected to reduce the pressure in the plasma generating chamber 51 and the film forming chamber 52 to a predetermined pressure. Next, a method of manufacturing the semiconductor laser according to the first embodiment will be described with reference to FIGS.
1A and 1B are perspective views. First, FIG.
As shown in FIG. 3, a 2 μm-thick n- (A
l _0.7 Ga _0.3 ) InP layer (first cladding layer) 32, thickness 50
An active layer 33 made of a GaInP film having a thickness of 2 nm and a p-
(Al _0.7 Ga _0.3 ) InP layer (second cladding layer) 34, 500 nm-thick p-GaInP layer 35, 500 nm-thick p-Ga
The As layer 36 is sequentially deposited.

Next, p-Ga is left except for a central region having a width of 5 μm.
The mesa stripe (MS) is formed by etching from the surface of the As layer 36 to the middle of the p- (Al _0.7 Ga _0.3 ) InP layer 34. The direction in which the mesa stripe extends is the longitudinal direction of the semiconductor laser. Next, p- (Al _0.7 Ga _0.3 ) on both sides of the mesa stripe
An n-GaAs layer 37 is formed on the InP layer 34 to bury the etching trace. The current for supplying electrons and holes flows intensively in this mesa stripe portion.

Next, n- on the mesa stripe and on both sides thereof
A p-GaAs layer 38 having a thickness of 5 μm is formed on the GaAs layer 37.
Next, a substrate 31 having a length of 700 μm along the longitudinal direction.
Then, the substrate 31 and the laminate on the substrate 31 are cleaved across the mesa stripe so that the laminate on the substrate 31 remains. As a result, the active layer 33 is exposed on the cleavage planes CF5 and CF6.

Next, the solid source ECR-CV shown in FIG.
The workpiece 101 is placed in the D device, and microwave power is applied while high-frequency power is applied to the target 60 made of an indium plate. As a result, indium nitride is generated, which is maintained for a predetermined time, and one cleavage plane CF5 is coated with an indium nitride film 39 having a thickness of 60 nm. At this time, as shown in FIG. 5, the film thickness (d) is adjusted so that the reflectance becomes about 10%. Note that n in FIG. 5 is the refractive index of the end surface coating film such as the indium nitride film 39,
λ is the oscillation wavelength of the laser light.

Next, an Al ₂ O ₃ film 4 is formed on the other cleavage plane CF 6.
0 and the Si film 41 are sequentially coated. At this time,
The film thickness was adjusted so that the reflectance was about 80%. Thereafter, a p-electrode and an n-electrode (not shown) are formed, and both upper and lower surfaces are covered with an insulating film, whereby a semiconductor laser having a cavity length of 700 μm is completed. The semiconductor laser oscillated at a wavelength of 670 nm by passing a current between both electrodes of the semiconductor laser thus fabricated.

The lifetime determined depending on the degradation of the end face was measured by a current test at a temperature of 60 ° C. and a power of 30 mW. The lifetime of the sample of the conventional Al ₂ O ₃ film was 4,000 hours. On the other hand, the sample coated with the indium nitride film had a life of 7000 hours. Note that the lifetime used in the following description refers to the following. That is, the output of the semiconductor laser stops when the COD light output decreases and becomes about the same as the operation output. The time from the start of energization to the stop of the output of the semiconductor laser.

As described above, in the case of the present invention, it is possible to suppress the temporal deterioration of the COD light output as compared with the case of the conventional example. This is because the indium nitride film is chemically stable and has a property that interdiffusion between the indium nitride film and the semiconductor layer does not easily occur. It is considered that even if the heat is generated by recombination, the reaction between the indium nitride film 39 and the semiconductor layer and the mutual diffusion therebetween are suppressed.

In the first embodiment described above, an example is described in which the indium nitride film (InN film) 39 is used as the end face covering film, but the gallium nitride film (GaN film) is used.
The same effect can be obtained by using. (2) Second Embodiment FIG. 2A is a perspective view showing a semiconductor laser having a quantum well active layer according to a second embodiment and a method for manufacturing the same. FIG. 2B is a band structure diagram of the quantum well active layer.

First, as shown in FIG. 2A, an n- (Al _0.7 Ga _0.3 ) InP layer (first layer) having a thickness of 2 μm is formed on an n-GaAs substrate 42.
2B), a strained quantum well active layer (strained active layer) 44 shown in FIG. 2B, and a 2 μm-thick p- (A
l _0.7 Ga _0.3 ) InP layer (second cladding layer) 45 and film thickness 1
00 nm p-GaInP layer 46 and 500 nm p-GaAs
The layers 47 are sequentially deposited. The above strained quantum well active layer 44
Is a 6 nm-thick film with a compressive strain of 1% sandwiching a barrier layer 44b made of a (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P film having a thickness of 5 nm between layers.
In this example, three strained quantum well layers 44a made of an In _0.55 Ga _0.45 P film are stacked. In FIG. 2B, Ec represents a conduction band, and Ev represents a valence band.

Next, p-Ga is left except for a central region having a width of 5 μm.
The mesa stripe (MS) is formed by etching from the surface of the As layer 47 to the middle of the p- (Al _0.7 Ga _0.3 ) InP layer 45. The current for supplying electrons and holes flows intensively in this mesa stripe portion. Next, an n-GaAs layer 48 is formed on the p- (Al _0.7 Ga _0.3 ) InP layer 45 on both sides of the mesa stripe to bury an etching mark.

Next, n- on the mesa stripe and on both sides thereof
A p-GaAs layer 49 having a thickness of about 5 μm is formed on the GaAs layer 48. Then, 700 along the longitudinal direction of the mesa stripe.
The substrate 42 and the stack on the substrate 42 are cleaved across the mesa stripe such that the μm-long substrate 42 and the stack on the substrate 42 remain. Thereby, the cleavage planes CF7, CF8
Then, the strained quantum well active layer 44 is exposed.

Next, the processed substrate is placed in a solid source ECR-CVD apparatus, and a target 6 made of an aluminum plate is placed.
While applying a high-frequency power of 600 W to 0, a microwave power of 400 W is applied. As a result, aluminum nitride is generated, which is maintained for a predetermined time, and a 60 nm-thick aluminum nitride film (AlN) is formed on one cleavage plane CF7.
Coating 50). At this time, the reflectance is about 1
The film thickness is adjusted so as to be 0%. Also, a stress of about 1 × 10 ⁶ dyne / cm ² was generated on the end face CF7. In this case, as shown in FIG. 4, since the N ₂ aluminum nitride film by adjusting the gas flow rate (AlN film) can be adjusted 50 stress, was approximately 5sccm the N ₂ gas flow rate in accordance with the data.

Next, an alumina film (Al ₂ O ₃ film) 51 and a silicon film (Si film) 52 are sequentially coated on the other cleavage plane CF 8. At this time, the film thickness is adjusted so that the reflectance becomes about 80%. Thereafter, a p-electrode (not shown) and n
When the electrodes are formed and the upper and lower surfaces are covered with insulating films, a semiconductor laser having a cavity length of 700 μm is completed.

When a current was applied between both electrodes of the semiconductor laser, the semiconductor laser oscillated at a wavelength of 685 nm.
Further, when the COD of the semiconductor laser of the present invention described above was compared with the COD of the semiconductor laser coated with an Al ₂ O ₃ film having the same end face reflectance, the COD light of the semiconductor laser coated with the Al ₂ O ₃ film was compared. Output is 40-50m
Whereas the COD light output of the semiconductor laser coated with the aluminum nitride film of the present invention is 70
８０80 mW. Thus, the semiconductor laser of the present invention was able to improve the COD light output.

The lifetime determined depending on the deterioration of the end face was measured by a current test at a temperature of 60 ° C. and a power of 30 mW. As a result, the life of the sample of the conventional Al ₂ O ₃ film was 3000 hours. On the other hand, the sample coated with the indium nitride film had a life of 30,000 hours. As described above, in the case of the present invention, as compared with the conventional example, it is possible to increase the upper limit of the light density that does not generate COD determined depending on the deterioration of the end face due to the energization test, and the COD light output deteriorates with time. Was able to be suppressed.

This is considered to be due to the following reasons. That is, the aluminum nitride film 50 has a compressive stress sufficient to prevent the strain of the active layer 44 in contact therewith from being released and to maintain the strain as it is. Therefore, the active layer 44, particularly the strained quantum well layer 44, is formed on the emission end face CF7.
This is considered to be because the width of the forbidden band a is maintained sufficiently wide and the absorption of laser light is suppressed, so that heat generation and temperature rise due to absorption of laser light at the emission end face CF7 are suppressed.

In the second embodiment, although the aluminum nitride film 50 is used as the end face covering film, a boron nitride film (BN film), a gallium nitride film (GaN film), and an indium nitride film (InN film) are used. ), Thallium nitride film (TIN)
Etc. can be used. Further, a combination of a substrate material and an active layer material (hereinafter, referred to as a substrate material / active layer material).
Although GaAs / GaInP is used as GaAs / GaInPs, it is not limited to this. GaAs / GaInPAs, InP / GaInPAs, GaAs / InGaAs
Are also possible.

[0034]

As described above, in the present invention, the end face coating film made of indium nitride (InN) or gallium nitride (GaN) is formed on the emission end face of a semiconductor laser having a lattice-matched active layer. . The indium nitride film is chemically stable and has a property that mutual diffusion hardly occurs with the semiconductor layer. For this reason, it is possible to suppress the deterioration with time of the COD light output, which is determined depending on the deterioration of the end face due to the conduction test, and to improve the life.

Further, an end face coating film for applying a compressive strain to the active layer is formed on an emission end face of the semiconductor laser having an active layer in which a compressive strain is applied. The end face coating film that gives compressive strain prevents the strain of the active layer in contact with the end face film from being released, and maintains the strain as it is. For this reason, the width of the forbidden band of the active layer is maintained sufficiently wide, and the absorption of laser light is suppressed.
As a result, it is possible to suppress deterioration with time of the COD light output, which is determined depending on the deterioration of the end face due to the conduction test, and to improve the life.

[Brief description of the drawings]

FIGS. 1A and 1B are perspective views showing a method for manufacturing a semiconductor laser according to a first embodiment of the present invention.

FIG. 2A is a perspective view showing a semiconductor laser having a strained quantum well active layer according to a second embodiment of the present invention and a method for manufacturing the same. FIG. 2B is an energy band diagram of the strained quantum well active layer.

FIG. 3 is a side view of a solid-source ECRCVD apparatus used for the method of manufacturing a semiconductor laser according to the embodiment of the present invention.

FIG. 4 is a characteristic diagram illustrating stress adjustment of an end face coating film of a semiconductor laser having a strained quantum well active layer according to a second embodiment of the present invention.

FIG. 5 is a characteristic diagram illustrating a relationship between a film thickness of an end face coating film and a reflectance of a semiconductor laser having a strained quantum well active layer according to a second embodiment of the present invention.

FIG. 6 is a perspective view illustrating a method for manufacturing a semiconductor laser according to a conventional example.

FIG. 7A is a perspective view showing another conventional semiconductor laser having a strained quantum well active layer and a method for manufacturing the same. FIG. 7B is an energy band diagram of the strained quantum well active layer.

[Explanation of symbols]

31, 42 n-GaAs substrate, 32, 43 n- (Al _0.7 Ga _0.3 ) InP layer (first cladding layer), active layer composed of 33 GaInP film, 34, 45 p- (Al _0.7 Ga _0.3 ) InP layer (Second cladding layer), 35, 46 p-GaInP layer, 36, 47 p-GaAs layer, 37, 48 n-GaAs layer, 38, 49 p-GaAs layer, 39 indium nitride film (end face coating film) , 50 aluminum nitride film (end face coating film), 40,51 alumina film, 41,52 Si film, 44 strained quantum well active layer (strained active layer), 44a strained quantum well layer, 44b barrier layer, 51 Plasma generation chamber, 52 Film formation chamber, 53 Plasma gas flow port, 54 Gas inlet, 55 Waveguide, 56 Permanent magnet or coil, 58 Exhaust port, 59 Substrate mounting table, 60 Target, 61 High frequency power supply.

Claims (3)

[Claims] A first cladding layer having one conductivity type formed on a substrate; an active layer formed on the first cladding layer and generating laser light lattice-matched to the substrate; In a semiconductor laser having a second cladding layer having an opposite conductivity type formed on the active layer and an end face coating film formed on an emission end face of the laser beam, the end face coating film is formed by nitriding. A semiconductor laser, which is an indium (InN) film or a gallium nitride (GaN) film. 2. A first cladding layer having one conductivity type formed on a substrate, and a laser beam formed on the first cladding layer and strained due to lattice mismatch with the substrate. A semiconductor laser comprising: an active layer to be generated; a second cladding layer having an opposite conductivity type formed on the active layer; and an end face coating film formed on an emission end face of the laser light. A semiconductor laser, wherein the coating film is a film that gives compressive strain to the active layer. 3. The film that gives a compressive strain includes an aluminum nitride film (AlN film), a boron nitride film (BN film), a gallium nitride film (GaN film), and an indium nitride film (InN film).
3. The semiconductor laser according to claim 2, wherein the semiconductor laser is one of a film and a thallium nitride film (T1N).