JPH065986A - Semiconductor laser manufacturing method - Google Patents

Abstract

(57) [Summary] [Objective] To provide a manufacturing method for mass-producing high-power semiconductor lasers with excellent reliability and high yield. [Configuration] p-type cladding layer, the active layer, n-type cladding layer each _{p- (Al 0. 6 Ga 0.4)} 0.5 In 0.5 P, an undoped _{Ga 0.5 In 0.5 P, n- (} Al 0.6 Ga 0.4) 0.5 I
The resonator end face of the laser bar 11 (n _0.5 P) (R
Both sides of the region) are irradiated with plasma of phosphine excited by the RF coil 13 while controlling the temperature of the laser bar 11 at 400 ° C. or less, and hydrogen atoms are injected in the vicinity of the end face of the resonator. As a result, a high resistance region is formed with a precision of 1 μm or less in a thin range of several microns in the vicinity of the end face of the resonator, without deterioration of crystallinity due to phosphorus defects caused by damage. As a result, it is possible to easily manufacture a high-yield semiconductor laser with high linearity of IL characteristics, low drive current, and high COD level with high yield.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor laser capable of high power operation, and more particularly to a method of manufacturing a high power visible light semiconductor laser using AlGaInP type crystal.

[0002]

2. Description of the Related Art Since an AlGaInP / GaAs semiconductor laser has an oscillation wavelength of around 680 nm, it has been attracting attention as a light source for laser beam printers, optical discs, etc., and higher output is required more and more.
However, in a semiconductor laser, when the optical output limit (COD level) is exceeded, catastrophic damage that instantaneously disables oscillation occurs. This is because at the crystal facets that make up the resonator, the recombination velocity is faster due to the surface states, the bandgap is substantially narrowed, and the absorption of laser light increases, so that when the laser light output increases, Fever increases,
This is because the crystals will eventually be destroyed.

In order to prevent this, a structure in which a current non-injection region is provided on the resonator end face has been proposed as a structure for increasing the output of a conventional semiconductor laser.

For example, in Japanese Patent Laid-Open No. 153090/1993, as shown in FIG. 5, an AlGaInP-based semiconductor laser is formed on an n-GaAs substrate 41 and n-GaInP.
A buffer layer 42, an n-AlGaInP clad layer 43,
On the stacked structure of the GaInP active layer 44, in the current injection region (A region) inside the resonator, the p-AlGaInP cladding layer 45, the p-GaInP cap layer 46, and the p-GaA are formed.
The s contact layer 48 is sequentially laminated (X- in FIG. 5A).
(Shown in (b) in the X cross section), in the current non-injection region (B region) near the end face, the p-AlGaInP cladding layer 45, p
A laser having a structure in which -GaAs contact layers 48 are sequentially stacked is described. In this structure, p-AlGa
InP clad layer 45 and p-GaAs contact layer 48
The structure is such that the current is cut off by utilizing the hetero barrier formed between the two. The method of forming the current non-injection region is as follows: n-GaAs substrate 41, n-GaInP buffer layer 42, n-AlGaInP clad layer 43, GaI.
nP active layer 44, p-AlGaInP clad layer 45,
The p-GaInP cap layer 46 is sequentially laminated by the MOCVD method. Next, using a photolithography technique, Si is formed on the ridge top portion 45a of the cap layer 46 and the P-type cladding layer 45.
After forming an O ₂ mask and etching away portions other than the ridge top portion 45a to form stripes, the n-GaAs block layer 47 is selectively grown. Next, after removing the portion other than the current injection region (A region) of the SiO ₂ mask, the p-GaInP cap layer 46 on the ridge top portion 45a of the B region is removed.
Are removed by selective etching. Next, after removing the SiO ₂ mask entirely, the p-GaAs contact layer 48 is removed.
Are stacked. Finally, the positive electrode 40 and the negative electrode 49 are formed. With respect to the wafer formed as described above, cleaving the bar,
Cleavage of chips is performed sequentially. Here, the cavity length of the laser is 500 μm, and the length of the current non-injection region (B region) is 30.
μm. This laser can output up to 40 mW.

[0005]

However, in the conventional manufacturing method, as shown in FIG. 6, the width of the current non-injection region 62 is 3 μm to 10 μm generated when the wafer 61 is cleaved into bars.
However, it is difficult to control on the order of several microns, and about 20 μm or more is required. Therefore, when a wide current non-injection region is present on the end face of the resonator as in the conventional case, a phenomenon of supersaturation absorption occurs, and as shown in FIG. There is a problem that the linearity is deteriorated due to the jump and the driving current becomes large because there is no gain in the current non-injection region. As a matter of course, since there are variations of the order of several microns that occur during cleavage, variations in the characteristics of the laser such as the threshold current have been a serious problem.

The present invention solves the above problems and creates a current non-injection region in a thin region of several microns in the vicinity of the end face of a resonator with high precision, thereby manufacturing a highly reliable high-power semiconductor laser with high yield. It is an object of the present invention to provide a novel method of manufacturing a semiconductor laser suitable for manufacturing.

[0007]

In order to achieve the above object, the present invention irradiates a laser bar having a resonator surface with a plasma composed of active species of elements constituting the laser bar and active species of hydrogen, A method of manufacturing a semiconductor laser is characterized in that hydrogen atoms are injected into a range of several microns near an end face of a resonator with an accuracy of 1 μm or less.

Preferably, the laser bar is set in a temperature range of 400 ° C. or lower to carry out the above method in the method of manufacturing a semiconductor laser.

In particular, the method of manufacturing an AlGaInP semiconductor laser is characterized in that the cavity facet is irradiated with phosphine plasma.

[0010]

Function: The active layer is AlGaInP crystal or GaIn
When a phosphine is irradiated in a plasma state on a cavity end face of a laser bar in which the clad layer is a P crystal and is made of AlGaInP crystal, hydrogen atoms are injected into a certain depth near the cavity end face depending on the temperature of the laser bar, and a dopant is introduced. To lower the activation rate and increase the resistance at a certain depth near the end face of the resonator. As a result, the current flowing through the resonator end face can be suppressed and the temperature rise can be reduced, so that the COD level can be raised. Here H contained in the phosphine plasma, P, P-H, the active species of the _{P-H 2, P-H} 3 , the active layer, and prevent the phosphorus of defects due to damage to the cladding layer end surface is generated Since the penetration range of hydrogen atoms can be controlled with an accuracy of 1 μm or less by changing the temperature of the laser bar,
A highly reliable semiconductor laser can be manufactured with a high yield.
Furthermore, since the high resistance region can be formed in a thin region having a thickness of several microns, the phenomenon of supersaturation absorption does not occur and good IL characteristics can be obtained.

[0011]

EXAMPLES Examples of the present invention will be described in detail below.

As shown in FIG. 1, a laser bar 11 having a resonator surface is placed on a metallic target 12 of a reactor 14 with one surface of the laser bar resonator end surface (R region) facing the upstream side of plasma. A phosphine gas is flown from a phosphine cylinder 15 connected to the reactor 14, and this is excited by the high frequency coil 13 to be in a plasma state. The target 12 is biased, and the laser bar resonator end face (R
The region) is irradiated with phosphine plasma. Reactor 1
The pressure inside 4 is 0.2 Torr, and the metallic target 12
Is kept at 350 ° C by heater 17 and bias is -1
Apply 00V. An RF frequency of 10 MHz is applied to the high frequency coil 13. The processing time is 30 minutes.

Next, the same step as the phosphine plasma irradiation is applied to the other surface of the laser bar resonator end surface (R region).

FIG. 2 shows the recording used in the manufacturing method of the embodiment of the invention.
This is the element structure of the server bar. 21 in FIG.
Au-Ge / Ni negative electrode, 22 is n-GaAs substrate, 2
3 is an n-GaAs buffer layer, 24 is n- (Al_0.6G
a_0.4)_0.5In_0.5P clad layer, 25 is undoped G
a_0.5In_0.5P active layer, 26 is p- (Al_0.6Ga_0.4)
_0.5In_0.5P cladding layer, 27 is n-GaAs current constriction
Layer, 28 is p-Ga_0.5In_0.5P cap layer, 29 is p
-GaAs contact layer, 30 is Cr / Au / Pt / A
u positive electrode.

The above device structure is (100) n-GaAs
The substrate was subjected to three times of low pressure MOVPE crystal growth and etching process.

As a source gas, TMG (trimethylgallium), TMA (trimethylaluminum), TMI (trimethylindium), AsH ₃ (arsine), PH
₃ (phosphine), Si ₂ H ₆ (disilane) and DMZ (dimethyl zinc) were used.

First, in the first crystal growth step, n-GaAs is used.
The n-GaAs buffer layer 23, n- (Al
_0.6Ga_0.4)_0.5In_0.5P clad layer 24, Ga_0.5I
n_0.5P active layer 25, p- (Al_0.6Ga_0.4)_0.5In
_0.5P clad layer 26, p-Ga _0.5In_0.5P cap
Each layer of the layer 28 is sequentially laminated. Then SiO₂Use a mask
P- (Al_0.6Ga_0.4)_0.5In_0.5P clad layer 2
6 is etched and trapezoidal <1-10> direction mesas
After forming the tripe, the mesa is formed in the second crystal growth step.
The n-GaAs current confinement layer 25 is selected on both sides of the stripe.
Selective embedded growth. Then SiO₂Remove the mask,
The p-GaAs contact layer 29 is formed in the third crystal growth step.
After stacking, a positive electrode 21 and a negative electrode 30 using a mask
To form.

Next, the wafer produced in the crystal growth step is cleaved to produce the laser bar having a cavity length of 400 μm shown in FIG.

When the phosphine gas is excited by the RF coil, H, P, P-H, P-H ₂ and P-H ₃ active species are generated, and when these are irradiated to the laser bar resonator end face (R region), Hydrogen atoms can be injected into the laser bar resonator end face (R region) to form a high resistance region. As a method of directly injecting hydrogen into the cavity end face, a method using hydrogen plasma may be considered. In this method, hydrogen is also injected into the cavity end face at the time of plasma irradiation, but at the same time, a new defect is generated in the active layer. . As a result, the semiconductor laser deteriorates. As in the present invention, H, P, P-H, and P- are used as a means for injecting hydrogen into the cavity end face without making defects in the active layer.
By using the active species of H ₂ and P-H ₃ , n-
(Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 24, undoped Ga _0.5 In _0.5 P active layer 25, p- (Al _0.6 G
a _0.4 ) _0.5 In _0.5 P It is possible to suppress the generation of phosphorus defects that are likely to occur due to plasma irradiation damage in the cladding layer 26, and to suppress the generation of new non-radiative centers due to such defect levels. Has been confirmed by photoluminescence measurement and the like.

By irradiating with phosphine plasma, hydrogen atoms are injected in the vicinity of the end face of the resonator of the laser bar. However, if the materials forming the layers are different or the same materials have different p and n characteristics, the hydrogen profile will be different. different.
Here, p- (Al _0.6 which has the most effect of suppressing the current is particularly used.
The concentration profile of hydrogen atoms in the Ga _0.4 ) _0.5 In _0.5 P cladding layer 26 by SIMS was 300 ° C., 32
The results of measurement at temperatures of 0 ° C. and 350 ° C. are shown in FIG. By controlling the temperature in the range of 400 ° C. or less in this way, it can be seen that the sharp injection control of hydrogen atoms can be performed within the range of 5 μm from the cavity end face with an accuracy of 1 μm or less. Moreover, the temperature of the laser bar is set to 300 ° C. by using the active species of H, P, PH, PH ₂ , and PH _3.
It can be performed at relatively low temperatures such as front and back. If annealing is performed in a hydrogen or phosphine atmosphere at a high temperature of 400 ° C. or higher, problems such as dopant diffusion and phosphorus release occur.
The production method of the present invention, which can be performed at a low temperature of ℃ or less, can avoid these problems. Further, FIG. 3B also shows the carrier profile of holes measured by CV. The hole concentration is reduced to about 1/10 at the lowest point, and the current between the p- (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P clad layer 24 and the undoped Ga _0.5 In _0.5 P active layer 25 is reduced at the cavity end face. It turns out that is suppressed.

According to the manufacturing method of the present invention described above, as shown in FIG. 2B, a high resistance region (R region) having a thickness of 5 μm or less is formed over the entire vicinity of the end facet of the laser resonator.
It can be easily manufactured with an accuracy of μm or less. As a result, the current flowing through the end face of the resonator is reduced and the temperature rise is suppressed, so that not only the COD level of the semiconductor laser rises and high output operation is possible, but also a thin high resistance layer of a few microns from the end face of the resonator. By accurately manufacturing, the I-L characteristic jump and the drive current increase in the vicinity of the threshold current which occur when the current non-injection region near the resonator end face is several tens of microns do not occur. In addition, since a high resistance layer can be accurately formed in the vicinity of the end faces of the resonators for all the laser chips constituting the laser bar, it is possible to perform mass production in which the characteristics such as the threshold current are constant and the yield is good.

A laser chip was prepared from the thus obtained laser bar by cleavage (cleavage in FIGS. 2a and 2b), and the IL characteristics were examined. As a result, as shown in FIG. 4 (a), the COD level was 50 mW. Up to the threshold value, the IL characteristics did not jump near the threshold value, and the drive current did not increase.

In the present embodiment, phosphine is used as the active species of the elements composing the semiconductor laser, but the same effect can be obtained by using organic phosphorus or the like as the gas for supplying the active species of the elements.

Further, in the present embodiment, the laminated structure of the laser is explained by using GaInP crystal as the active layer and AlGaInP crystal as the cladding layer, but the active layer with shorter wavelength is AlGaI.
The same effect can be obtained by the above method even with a semiconductor laser having an nP crystal and an AlGaInP crystal for the cladding layer. Needless to say, the same effect can be obtained by irradiating AsH ₃ (arsine) plasma if the active layer and the cladding layer are semiconductor lasers of AlGaAs crystal.

Even in a semiconductor laser composed of another II-VI group semiconductor crystal, similar effects can be obtained by using plasma containing active species of its constituent elements and active species of hydrogen.

[0026]

As described above, according to the present invention, it is possible to reduce the steps of the photolithography and the etching process required for manufacturing the conventional current non-injection region when increasing the output of the semiconductor laser. In addition, defects are not generated at the stacking interface during re-growth as in the conventional case,
A high-power semiconductor laser can be easily manufactured. In addition, hydrogen atoms can be injected without creating new defect levels in the active layer and cladding layer regions of the semiconductor laser cavity end face, and the thickness of the high resistance region in the vicinity of the semiconductor laser cavity facet is on the order of a few microns. Since it can be controlled with an accuracy of 1 μm or less in the thin range, it is possible to easily realize mass production with a high yield of a high output semiconductor laser having a highly linear CO characteristic and a highly reliable COD level. .

[Brief description of drawings]

FIG. 1 is a schematic diagram of a plasma irradiation apparatus and an irradiation method according to an embodiment of the present invention.

FIG. 2 is a diagram showing a device structure of a semiconductor laser bar according to an embodiment of the invention.

FIG. 3 is a diagram showing a hydrogen atom profile and a hole carrier profile in a p-type AlGaInP crystal according to an example of the present invention.

FIG. 4A is an IL characteristic diagram of a semiconductor laser according to an embodiment of the present invention. FIG. 4B is an IL characteristic of a conventional semiconductor laser in which a laminated structure of a current non-injection region is formed on an end face of a resonator. Figure

FIG. 5 is a view showing a conventional element structure in which a laminated structure of a current non-injection region is formed on an end face of a resonator.

FIG. 6 is a diagram showing variations in a position where a current non-injection region of a wafer is cleaved into a bar.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyoshi Ohnaka 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A method of manufacturing a semiconductor laser, wherein at least one surface of the semiconductor laser resonator surface is irradiated with plasma containing active species of constituent elements of the semiconductor laser and active species of hydrogen. 2. The method for manufacturing a semiconductor laser according to claim 1, wherein the plasma irradiation temperature is set to a temperature of 400 ° C. or lower.