JPH04103187A - Semiconductor laser and manufacture thereof - Google Patents

Abstract

PURPOSE:To form a window structure which is restrained from increasing in threshold value and deteriorating in efficiency so as to enable a semiconductor laser to output a high power by a method wherein an SiO2 film is formed on the etched surface of a wafer close to the end of a resonator, Ga holes are diffused into the wafer through thermal annealing, and a multi-quantum well active layer is disordered to form a window structure. CONSTITUTION:An SiO2 film 9 is formed on the etched surface of a wafer near to the end face of a resonator, Ga holes are diffused into the wafer through thermal annealing to form a Ga hole diffusion section 13. The Ga holes are diffused into a multi-quantum well active layer 4 to induce a disordered part, and the band gap of the disordered Ga hole diffusion section 13 is larger than that of a non-disordered active layer 4. The Ga hole diffused part of the active layer 4 becomes larger than the Ga hole non-diffused part of the active layer in band gap, whereby a window structure is formed. As a disordered part is induced in an active layer, the active layer is hardly changed in impurity concentration before and after the diffusion of Ga holes, so that the active layer is prevented from increasing in loss due to the absorption of free carriers caused by an increase in impurity concentration when Zn is diffused.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser and a method for manufacturing the same, and more particularly to a semiconductor laser capable of high output operation and a method for manufacturing the same.

[Conventional technology]

FIG. 2 is a diagram showing a conventional semiconductor laser, with a portion cut away so that the end face and interior of the laser can be seen. FIG. 3 is a sectional view showing the inside of a resonator of a conventional semiconductor laser, and FIG. 4 is a view showing an end face of the conventional semiconductor laser.

In the figure, 1 is a p-GaAs substrate, 2 is a p-Alo,
z Gao, r As upper cladding layer, 3 is p-A1,,
, sGa, and sAs light guide layer. 4 is a multiple quantum well active layer, which has five GaAs well layers (not shown) with a thickness of 80 people and Aj! with a thickness of 120 people. o,tGa,,,A
It has a structure in which six s1li wall layers are alternately laminated. 5
is n Alo, tsGao, rsAS light guide layer, 6
is n-Alo, 3Cae, As upper cladding layer, 7 is n-
GaAs contact layer, 8 zinc (Zn) diffusion part, 9 SiO* film, 10 n-side electrode, 11 p-side electrode, 1
2 is a light emitting part.

Next, the operation will be explained.

When a voltage is applied between the electrodes 10.11, the current flows through nCaAs
Zero laser beams flowing through the contact layer 7 are connected to the p-type lower cladding layer 2. Multi-quantum well active layer 4, n-type upper cladding layer 6
p in the so-called double heterostructure (DH structure) consisting of
It has a structure in which a type light guide layer 3 and an n type light guide N5 are added, and the injected current causes light emission in the multi-quantum well active layer 4, leading to laser oscillation.

Furthermore, this semiconductor laser utilizes the disordering phenomenon of multiple quantum wells caused by Zn diffusion to control the transverse mode and improve the level of end face destruction.

First, we will discuss transverse mode control.

When the multi-quantum well active layer 4 is disordered, its refractive index becomes smaller than that of the multi-quantum well active layer 4 before being disordered. Therefore, as shown in FIG. 3, when both sides of the light emitting section 120 are sandwiched between the multi-quantum well active layers 4 which are disordered using Zn diffusion, light is confined in the light emitting section 12 which is not disordered. By setting the width of the non-disordered portion to about 3 μm or less, it is possible to oscillate in the fundamental transverse mode.

Next, we will discuss the improvement in the level of edge fracture.

When a semiconductor laser is operated at high output, a problem arises in that the laser emitting end facet is destroyed. The reason for this is as follows. The end facet of an AfGaAs laser has many surface states.
There are many non-radiative recombinations via this. Since the carriers injected into the multi-quantum well active layer 4 near the end face are lost by this non-radiative recombination, the density of injected carriers in the multi-quantum well active layer 4 near the end face is lower than that inside the chip.

As a result, the multi-quantum well active layer 4 near the end face becomes an absorption region for the maximum gain wavelength (laser wavelength) created by the high internal carrier density. As the optical power density increases, local heat generation in the absorption region increases, the temperature rises, and the bandgap decreases. As a result, the absorption coefficient further increases and the temperature rises, causing positive feedback, which melts the crystal at the end face and causes breakage of the end face. In the semiconductor laser shown in FIG. 2, in order to prevent this phenomenon, the multi-quantum well active layer 4 near the end face is disordered by Zn diffusion. When disordered, the band gap of the multi-quantum well active layer 4 increases, so that it no longer absorbs the laser light generated inside. That is, a window structure is formed. Then, end face destruction occurs.

Further, the resonator length is 300 to 400 μm, and the window length (in the resonator direction) is usually 15 to 20 μm. This is determined by the cleavage position accuracy when forming the laser end face by cleavage. By the way, in order to disorder the multi-quantum well layer 4 by diffusion of Zn,
A Zn concentration on the order of 1.-" is required. As the Zn concentration increases, light loss increases due to free carrier absorption.

In the undiffused region inside the resonator, the loss α is l0C
II-' ~ 20 cm-', whereas the loss α in the window section where diffusion is performed is 225 cra-' ~ 450 C
It becomes large as 11-'. In order to cause laser oscillation, the gain obtained by injecting current must be greater than the loss, so as the loss increases, the threshold current increases.

[Problems to be solved by the invention] Conventional semiconductor lasers are configured as described above, and therefore have problems such as large loss near the cavity end face, high threshold current, and poor efficiency. .

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a semiconductor laser that has a low threshold value and is capable of efficient high-output operation, and a method for manufacturing the same.

[Means to solve the problem]

A semiconductor laser and a method for manufacturing the same according to the present invention are 5i
ozllll is formed on the wafer surface only in the vicinity of the resonator end face, and thermal annealing is performed to disorder the multi-quantum well active layer under the Si0g film.

[Effect]

In this invention, a 340W film is formed on the wafer surface only near the resonator end face, and thermal annealing is performed to
Since the multi-quantum well active layer under the two films is disordered to form a window structure, loss due to absorption of free carriers can be reduced, thereby preventing the upper threshold limit and efficiency deterioration.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a semiconductor laser and a method for manufacturing the same according to an embodiment of the present invention, and for the sake of simplicity, shows an example of a structure in which the transverse mode is not controlled. In the figure, the same reference numerals as in FIGS. 2 and 3 indicate the same or corresponding parts, and 6a indicates n Aj! near the resonator end face. o,s Gao
, q As upper cladding layer, 6b is n A inside the resonator
/! o, s Gao, 7As upper cladding layer, 13 is Ga
This is a hole diffusion part.

Next, the manufacturing process will be explained.

P Aj! onto the p-GaAs substrate 1! o,s Gao,
wAs lower cladding layer 2. Multi-quantum well active layer 4. n
Aj! 6.30ao, t As Kurind Jii6a,
6b.

An n-CyaAs contact layer 7 is continuously grown.

Next, the thickness of the upper cladding layer 6a near the resonator end face is 0.5
The contact layer 7 and a part of the upper cladding layer 6b are removed by etching from the surface to a thickness of about .mu.m. Next, S is deposited on the etched wafer surface near the cavity end face.
An iOz film 9 is formed. Sio2 has the property of absorbing Ga, and the above-mentioned Sin and CaAs 6 a directly under the film 9
Ga vacancies of about 1017 Crl' are generated therein. Next, Ga vacancies are diffused by annealing at 950° C. for about 15 seconds. In this annealing, the Si0g film 9 and /lG
The stress caused by the difference in thermal expansion coefficient between the aAs crystals accelerates the diffusion of the Ga vacancies, and the Ga vacancies diffuse into the wafer by approximately 0.5 μm in 15 seconds at 950°C, causing the Ga vacancy diffusion part 13 to Form. Finally, electrodes 10.11 are formed to complete the wafer process.

The reason why the contact layer 7 and part of the upper cladding layer 6b are removed by etching only near the cavity end face is to reduce the distance from the SiOg film 9 to the active layer 4. If the diffusion time due to annealing is increased, the Ga vacancies will diffuse deeper, but
Since there is a possibility that the doping profile in the vicinity may change and remote junctions may occur, degrading the characteristics, the distance between the 5in2 film 9 and the multi-quantum well active layer 4 is set to 0°5
The thickness is about μm.

Next, the operation will be explained. When the Ga vacancies diffuse into the multi-quantum well active layer 4, disordering occurs, and the bandgap of the disordered Ga vacancy diffusion region 13 is larger than the bandgap of the active layer 4 which is not disordered. Become. Moreover, since the SiO□ film 9 is formed only near the cavity end face, the band gap of the multi-quantum well active layer 4 in which the Ga vacancies are diffused near the cavity end face is
The bandgap becomes larger than that of the multi-quantum well active layer 4 without a-vacancies, and a window structure is formed. In this example, G
Since disorder is caused by the a-vacancies, the impurity concentration does not change before and after diffusion, and there is no increase in loss due to free carrier absorption caused by an increase in the impurity concentration as in the case of Zn diffusion.

As described above, according to this embodiment, the SiO□ film 9 is formed on the etched wafer surface near the resonator end face, and Ga vacancies are diffused into the wafer by thermal annealing, and the diffusion of the Ga vacancies causes multiplexing. Since the quantum well active layer 4 is disordered to form a window structure, it is possible to form a window structure without raising the threshold value or deteriorating efficiency, and enables high output operation.

In the above embodiment, a semiconductor laser without a transverse mode control mechanism has been described as an example, but a semiconductor laser with a transverse mode control mechanism may also be used, and the same effects as in the above embodiment can be obtained.

Furthermore, in the above embodiment, AffiGaAsff-GaAs
However, an AlGa InP laser may be used, and the same effects as in the above embodiment can be expected. Also,
In the above embodiment, a semiconductor laser having a p-type substrate has been explained as an example, but a semiconductor laser having an n-type substrate may also be used (the same effect as in the above embodiment can be obtained).

〔Effect of the invention〕

As described above, according to the present invention, a 5in2 film is formed on the etched wafer surface near the cavity end face, Ga vacancies are diffused into the wafer by thermal annealing, and the multi-quantum well active layer is thereby disordered. Since the window structure is formed using the same method, it is possible to form a window structure without raising the threshold value or deteriorating the efficiency, and there is an effect that a semiconductor laser capable of high output operation can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a semiconductor laser according to an embodiment of the present invention, and FIG. 2 is a perspective view of a conventional semiconductor laser, with a portion of the laser cut away to show the end face and the inside at the same time. . Figure 3 is a cross-sectional structural diagram showing the inside of Figure 1;
FIG. 4 is a cross-sectional structural diagram showing the end face portion of FIG. 1. In the figure, 1 is a p-GaAs substrate, 2 is a p-Aj! o
, s Gao, t As lower cladding layer, 3 is p-Aj!
6. x*G ao, ysA s light guide layer,
4 is a multi-quantum well active layer, 5 is n A lo, t
sG a O,? ! , A S light guide layer, 6 is n A
j! a,s f:yao,? 6a is the upper cladding layer near the cavity end face, 6b is the upper cladding layer inside the cavity, 7 is the n-CaAs contact layer, and 8 is the Zn upper cladding layer.
9 is a 5in2 film, 10 is an n-side electrode, 11 is a p-side t8i, 12 is a light emitting portion, and 13 is a Ga vacancy diffusion portion. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (2)

[Claims] (1) In a semiconductor laser having an active layer with a quantum well structure, SiO formed on the wafer surface only near the cavity end facets
A semiconductor laser comprising: a _2 film; and a multi-quantum well active layer under the SiO_2 film, which is disordered by annealing. (2) A method for manufacturing a semiconductor laser having a window structure, which includes a step of forming a SiO_2 film on the wafer surface only in the vicinity of the cavity end face, and a step of annealing to disorder the multi-quantum well active layer under the SiO_2 film. A method for manufacturing a semiconductor laser, comprising: