JPH04105384A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To make it possible to reduce a leakage current, to make a laser oscillate in a low threshold current and moreover, to make it possible to form easily a contact electrode by a method wherein lattice defects are made to introduce from an interdiffusion accelerating layer comprising an insulating film and a quantum well structure is disordered. CONSTITUTION:An n-type clad layer 2, a quantum well active layer 3, a p-type clad layer 4 and a p-type GaAs cap layer 5 are formed in order on an N-type GaAs substrate 1. Then, a mask 6, from which parallel two striped regions are removed, is formed, an etching is performed until the layer 3 is exposed and groove regions 7 are formed. At this time, a striped luminous region 8 is formed. After this, an insulating film 9 is formed, a photoresist 10 is applied, the resist 0 is etched and removed until a growth surface is exposed using oxygen ions 11 and the film 9 only exposed on the growth surface is removed. After that, a heat treatment is performed, defects, such as pores or the like, are introduced from the interior of the film 9, a semiconductor denaturation layer 12 is formed only in the parts of the groove regions 7 and the layer 3 in the vicinities of the side surfaces of the region 8 is disordered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a high-performance semiconductor laser, and more particularly to a method for manufacturing a semiconductor laser having a selectively disordered quantum well structure.

[Conventional technology]

It has been known that quantum well structures can be disordered by introducing impurities. An example of a method for manufacturing a semiconductor laser having a quantum well structure using this method is described in Electronics Letters.
etters), 1986, Vol. 22, p. 1117. This semiconductor laser manufacturing method involves forming an n-type cladding layer with a thickness of approximately 1 μm on an n-type GaAs substrate.
G a As quantum well layer and Aβ. 2 G ao,s
A quantum well active layer consisting of an As barrier layer, a p-type rad layer with a thickness of about 1 μm, and a GaA layer with a thickness of about 1000 μm.
In this manufacturing method, the s-cap layer and the s-cap layer are sequentially formed, and then the n-type cladding layer is mesa-shaped etched to the middle, and Zn is diffused over the entire surface to selectively disorder the quantum well structure.

In addition, an example of a method for manufacturing a window stripe semiconductor laser having a quantum well structure that utilizes the fact that the quantum well structure is disordered by introducing impurities is described in the Japanese Journal of Applied Physics (
Jpn, J., Appl, Phys) 1985, No. 2
It is reported in Volume 4, page L647. In this semiconductor laser manufacturing method, a p-type rad layer is formed on a p-type GaAs substrate with a thickness of about 3 μm, a p-type kite layer with a thickness of about 0.1 μm, and a G
aAs quantum well H and A 1112 G a a, s A
A quantum well active layer consisting of an S barrier layer and a quantum well active layer having a thickness of about 0.
An n-type guide layer with a thickness of 1 μm, an n-type cladding layer with a thickness of approximately 1 μm, and a GaAs cap layer with a thickness of approximately 1 μm are each formed in sequence, and then Zn is diffused into the p-type rad layer using a rectangular mask. The quantum well active layer is selectively disordered to form a buried structure and a window region. Next, a SiO□ stripe electrode is formed in accordance with the rectangular mask, and the Zn-diffused portion is separated to complete a window structure semiconductor laser.

[Problem to be solved by the invention]

However, in the above-described conventional method for manufacturing a semiconductor laser, the Zn diffusion region extends entirely in the lateral direction of the stripe, and this region has a high concentration, so the resistance is small. Therefore, there is a problem in that a large leakage current flows through this region, bypassing the quantum well structure, and the threshold current increases.

Further, it is necessary to form the p-side contact electrode only on the upper surface of the mesa, but when the mesa stripe width becomes narrow, it becomes difficult to form it using normal photolithography, and there is a problem in that a complicated manufacturing process is required.

Next, in the above-described conventional method for manufacturing a semiconductor laser having a window structure, the length of the window region is determined by the cleavage, and therefore requires several tens of micrometers.

However, since the window region has a high hole concentration due to Zn diffusion and free carrier absorption is large, there is a problem that the threshold current increases and the differential quantum efficiency decreases because the window region is several tens of micrometers long. Further, there was a problem in that the length of the window region was poorly controllable due to variations in cleavage. An object of the present invention is to provide a method for manufacturing a semiconductor laser that can reduce leakage current, oscillate with a low threshold current, and facilitate the formation of contact electrodes.

Another object of the present invention is to provide a method for manufacturing a semiconductor laser in which absorption loss in the window region is small and the length of the window region can be formed with good controllability.

[Means to solve the problem]

The present invention has two aspects, one of which is a method for manufacturing a semiconductor laser with a buried structure having a quantum well active layer and a structure in which the quantum well active layer is disordered, in which a first cladding layer is formed; forming a quantum well active layer including at least one quantum well on the first cladding layer; forming a second cladding layer on the quantum well active layer; After this step, a step of forming a striped light emitting region sandwiched between etched groove regions until it reaches at least the quantum well active layer, and a step of forming an interdiffusion promoting layer including at least an insulating film on the entire surface. After this step, there is a step of removing only the interdiffusion promoting layer on the growth surface. After this step, a heat treatment is performed to form a semiconductor metamorphic layer only in the groove region, and a quantum well near the side surfaces of the stripe is removed. 1. A method of manufacturing a semiconductor laser, comprising a step of partially disordering an active layer.

A second aspect of the present invention includes a step of forming a first cladding layer on a semiconductor substrate, and a step of forming at least one cladding layer on the first cladding layer.
forming a quantum well active layer including one quantum well;
A step of forming a second cladding layer on this quantum well active layer, and after this step, forming a rectangular light emitting region surrounded by a groove region etched away at least until reaching the quantum well active layer. a step of forming an interdiffusion promoting layer including at least an insulating film on the entire surface after this step; and a step of performing heat treatment after this step to form a semiconductor transformation layer in the groove region, and forming a semiconductor transformation layer in the groove region at least on the resonator end face. A method of manufacturing a semiconductor laser is characterized by comprising a step of partially disordering a quantum well active layer near a side surface.

[Effect]

A simple and effective method for forming a buried structure is to disorder the side surfaces of the quantum well active layer, but if impurities are used in this case, this layer becomes highly concentrated, which reduces leakage current flowing through this layer. This is undesirable as it may cause the occurrence of irradiation and increase absorption loss. However, according to the semiconductor laser manufacturing method of the present invention, the quantum well structure is disordered by introducing lattice defects from the interdiffusion promoting layer, so the above-mentioned problem does not occur. However, in this case, if lattice defects are also introduced from the growth surface, this will affect the active layer of the light emitting region, resulting in a decrease in light emission efficiency and an increase in contact resistance of the electrode portion. However, according to the semiconductor laser manufacturing method of the present invention, it is possible to form a good buried structure without reducing luminous efficiency or increasing contact resistance, as described below, and even if the stripe width is narrow. Contact electrodes can be easily formed. First, since the area of the groove region is significantly smaller than the entire area, it is possible to apply the crucian carp/cyst evenly in one process. Thereafter, by etching the photoresist in parallel using a dry etching method or the like, it is possible to expose only the growth surface in a convenient manufacturing process step. Therefore, it becomes possible to remove by etching only the growing surface portion of the insulating film that has been previously deposited over the entire surface. When heat treatment is performed thereafter, lattice defects such as vacancies are introduced into the insulating film, so that a semiconductor metamorphic layer is formed, and the sides of the quantum well active layer are disordered and a buried structure is formed. At this time, since the insulating film is formed only in the groove region, no defects are introduced from the growth surface.

Therefore, a good buried structure can be formed without reducing luminous efficiency or increasing contact resistance. After this, if an electrode is formed, a contact electrode can be formed on the upper part of the stripe. Next, by forming an interdiffusion promoting layer on the resonator end face and introducing lattice defects through heat treatment, the quantum well active layer near the resonator end face can be disordered and a window region can be formed. At this time, since no impurity is introduced into the window region, no increase in absorption loss occurs, and problems such as an increase in threshold value and a decrease in quantum efficiency do not occur. Furthermore, since the length of the window region is determined by the diffusion distance of the lattice defects, it can be formed with good controllability depending on the heat treatment conditions.

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of a semiconductor laser crystal at each manufacturing process for explaining one embodiment of the present invention. First, a first cladding layer is formed on an n-type GaAs substrate 1 with an impurity concentration of 1 to 3 x 10''cm-3 and an Au composition ratio X of 0.
An n-type cladding layer 2 having a thickness of about 1 μm and made of Aρx Ga 1-x As having a value of 5 to 0.7 is formed. Next, on this n-type cladding layer 2, an impurity concentration of about 1×10170−
3 and n-type A 1213G a m? A p-type AI with an A s confinement layer of about 1000 layers and a GaAs quantum well layer with a thickness of about 100 layers and an impurity concentration of about I x 1017 cm-3.
I Q, 30 a or A S confinement layer approx. 100
A quantum well active layer 3 consisting of 0 people is formed. A second Crabstone layer is formed on this quantum well active layer 3 with an impurity concentration of 1 to 3 X L O"am-3 and an A1 composition ratio of 0.5
~0.7 A I! A p-type cladding layer 4 made of x Ga + -xAs is formed to a thickness of about 1 μm. The impurity concentration on this p-type cladding layer 4 is about IX 10"Cm-3
And a p-type GaAs key? Approximately 1000 to 500 Tsubu layer 5
Form 0 people.

The process so far has been molecular beam epitaxy (
MEE) method etc. Next, SiO is grown on the grown substrate.
2. Apply an insulating film such as SiN or photoresist to about 30%
A mask 6 is formed by removing two parallel stripe-shaped regions having a width of approximately 3 μm to 10 μm and an interval of 1 μm to 100 μm by photolithography.

After that, use this mask 6 to perform CI! Using a dry etching technique such as reactive ion beam etching (RIEE) using two plasmas, etching is performed until at least the quantum well active layer 3 is exposed, thereby forming a groove region 7 (FIG. 1(a)). At this time, striped light emitting regions 8 sandwiched between the groove regions 7 are formed. After this, an insulating film 9 such as a 5iCh or SiN film is formed on the entire surface, and then a photoresist 10 is applied on the entire surface so that the groove region 7 is filled.

At this time, since the area of the groove region 7 is extremely small compared to the entire surface area, the photoresist 10 is applied almost evenly due to its viscosity (FIG. 1(b)). Thereafter, using a dry etching technique such as reactive ion beam etching (RIE) using oxygen ions 11, the photoresist 10 is etched away until the growth surface is exposed (FIG. 1(C)). After this, only the insulating film 9 exposed on the growth surface is removed. After this step, for example, using the face-to-face method etc.,
Heat treatment is performed at 0°C. Through this step, defects such as vacancies are introduced into the insulating film 9, a semiconductor metamorphic layer 12 is formed only in the groove region 7, and the quantum well active layer near the side surfaces of the light emitting region 8 is disordered, resulting in a buried structure. is formed (Fig. 1(d)). At this time, since the insulating film is not present on the growth surface, no defects are introduced from the growth surface, and problems such as reduction in luminous efficiency and increase in electrode contact resistance do not occur. Thereafter, CF/Au is formed on the entire surface as the n-side electrode 13, and then the Ct/Au other than the striped light emitting region 8 is etched away by photolithography. Finally, on the back surface of the n-type GaAs substrate 1, as the n-side electrode 14, A u G e N i / A u N
i is formed, and the semiconductor laser shown in FIG. 1(e) is completed.

Next, another embodiment of the present invention will be described. FIGS. 2(a) and 2(b) are a perspective view and a sectional view of a semiconductor laser for explaining one embodiment of the present invention. first,
Each semiconductor layer is grown as in the previous example. Next, on the surface of the grown semiconductor layer, an insulating film such as SiO21SiN or photoresist is formed to a thickness of approximately 3000 to 5 μm.
A rectangular region with a width of about 3 μm to 10 μm is removed by photolithography to form a mask. Thereafter, using this mask (12), etching is performed by a dry etching technique such as reactive ion beam etching (RIBE) using plasma until at least the quantum well active layer is exposed to form a groove region 7. At this time, the groove region 7 is formed. The rectangular light emitting region 8 surrounded by the region 7 and the resonator end face 15 can be formed at the same time.

After this, an insulating film 9 such as a 5iOz or SiN film is formed over the entire surface. Thereafter, in the same manner as in the previous embodiment, only the insulating film 9 exposed on the growth surface is removed and heat treatment is applied to form the semiconductor metamorphic layer 12 only in the groove region 7. At this time, the side surface of the rectangular light emitting region 8 and the cavity end surface 15
The Dojiwell active layer in the vicinity of is disordered, and the buried structure and window region 16 can be formed at the same time.

At this time, since the window region 16 is formed by introducing lattice defects, problems such as an increase in free carrier loss due to the introduction of impurities do not occur. Further, the length of the window region 16 can be formed with good controllability depending on the heat treatment conditions. Furthermore, the thickness of the insulating film 9 on one side of the resonator end face 15 is set to λ/
4n(λ: Laser oscillation wavelength determined approximately by the forbidden band width of the quantum well active layer.

n: refractive index of the insulating film), this resonator end face becomes non-reflective, so if this resonator end face is set as the laser beam emission side, high output light can be obtained.

Finally, electrodes are formed in the same manner as in the above embodiments, and the window type semiconductor laser is completed by cleaving to expose the resonator end face on the emission side or by etching away the semiconductor layer in front of the resonator end face. .

In the above embodiments, the quantum well active layer is a single quantum well, but the present invention is applicable to multiple quantum wells as well.

In the above example, the material system is G a A s / A
Although the material is made of GaAs, the present invention is also applicable to other material systems such as InGaAsP/InP.

〔Effect of the invention〕

As described above, according to the present invention, a semiconductor laser that can reduce leakage current, oscillate with a low threshold current, and can easily form contact electrodes can be obtained through a simple manufacturing process. Further, according to the present invention, a semiconductor laser with small absorption loss in the window region and in which the length of the window region can be formed with good controllability can be obtained through simple process steps.

[Brief explanation of the drawing]

The first section is a cross-sectional view of a semiconductor laser in the middle of manufacturing for explaining an embodiment of the first invention. Figure 2 (a
) and (b) are a perspective view and a sectional view of a semiconductor laser for explaining an embodiment of the second invention. In the figure, l
is an n-type GaAs substrate, 2 is an n-type cladding layer, 3 is a quantum well active layer, 4 is a p-type rad layer, 5 is a GaAs cap layer, 6 is a mask, 7 is a groove region, and 8 is a light emitting region ,9
is an insulating film, 10 is a photoresist, 11 is an oxygen ion,
12 is a semiconductor transformation layer, 13 is a p-side electrode, 14 is an n-side electrode, 15 is a resonator end face, and 16 is a window region. Agent: Patent Attorney Susumu Uchihara (d) Party 1 Figure 1 Figure

Claims (2)

[Claims] (1) forming a first cladding layer; forming a quantum well active layer including at least one quantum well on the first cladding layer; Step 2 of forming a cladding layer and after this step,
A step of forming a striped light emitting region sandwiched between etched groove regions until reaching at least the quantum well active layer, and after this step, forming an interdiffusion promoting layer including at least an insulating film over the entire surface. After this step, a step of removing only the interdiffusion promoting layer on the growth surface portion; After this step, a heat treatment is applied to form a semiconductor metamorphic layer only in the groove region, and the quantum layer near the side surfaces of the stripe is removed. 1. A method of manufacturing a semiconductor laser, comprising at least the step of partially disordering a well active layer. (2) forming a first cladding layer on the semiconductor substrate; forming a quantum well active layer including at least one quantum well on the first cladding layer; and forming the quantum well active layer on the first cladding layer. forming a second cladding layer thereon; and after this step forming a rectangular light emitting region surrounded by a trench region etched away at least up to the quantum well active layer; After the step, a step of forming an interdiffusion promoting layer including at least an insulating film on the entire surface, and after this step, a heat treatment is performed to form a semiconductor transformation layer in the groove region, and at least the side surface which will become the end face of the resonator is subjected to heat treatment. 1. A method for manufacturing a semiconductor laser, comprising at least the step of partially disordering a nearby quantum well active layer.