JPH01187987A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To realize a TJS laser using an MQW layer as an active layer by selectively forming a first mask having nontransmission to an impurity and a second mask having transmission to the impurity, diffusing the impurity and forming a first diffusion region in a high impurity concentration and a second diffusion region in a low impurity concentration. CONSTITUTION:A first mask 9 having nontransmission to an impurity conducting doping and a second mask 10 having an opening section 11 and transmission to said impurity are respectively formed selectively onto a semiconductor wafer in which an active layer 3 is held by first conductivity type two clad layers 2, 4. Said impurity is diffused from the upper section of said wafer, and a second conductivity type high impurity concentration first diffusion region 5 reaching at least the active layer 3 and a second conductivity type low impurity- concentration second diffusion region 7 are shaped. Zn is thermally diffused to the double hetero-structure wafer for a fixed time at a temperature of 650-700 deg.C, using the Si3N4 film 9 and the SiO2 film 10 as masks, and the p<+>- diffusion region 5 and the p-diffusion region 7 are formed simultaneously.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor laser having both p and n electrodes in the same plane, suitable for integration with electronic devices, and having a small operating current. It is.

[Conventional technology]

A laser that has both p and n electrodes in the same plane and is suitable for integration with electronic devices is TJS (Trans-v
5 tripe) lasers are well known. This laser forms an n-type double heterostructure on a semi-insulating GaAs substrate, and then
A portion of the double heterostructure is inverted to p-type by two-step diffusion of Zn into the substrate to form an active region. A low threshold current of about 20 mA is achieved because the current is efficiently confined in the active layer due to the difference in built-in potential between the active region and the cladding layer.

In general, the active region is formed using a multi-quantum well (Multi Quad well).
It has been experimentally confirmed that the threshold current density decreases when the N-tum Well (M' Q W') structure is used, and there are attempts to make the active layer of the TJS laser an MQW, but the reason is explained below. As a result, TJS (hereinafter referred to as MQW-T) with satisfactory characteristics of MQW in the active layer
JS) laser has not yet been realized.

FIGS. 3(a) and 3(b) are cross-sectional views for explaining the manufacturing method of a conventional <7) MQW-TJS laser. In this figure, 1 is a substrate made of semi-insulating GaAs, and 2 and 4 are Cladding layer made of n-AJ2GaAs, 3 is GaAs
- a multiple quantum well (hereinafter referred to as MQW) layer made of AllGaAs; 5 is a p"-diffusion region formed by diffusion as a first diffusion region; 6 is an MQW layer disordered by impurity diffusion; 7 is a second p- as the diffusion region of
The diffusion region 8 is an MQW layer disordered by heat treatment.

Next, the manufacturing process will be explained.

First, a cladding layer 2 made of n-AJ2GaAs is sequentially formed on a substrate 1 made of semi-insulating GaAs by molecular beam epitaxial growth (MB'E) or fi metal vapor phase epitaxy (MOCVD). MWQ layer 3 and n-AJ2Ga
A cladding layer 4 made of As is grown. Next, in order to convert a part of the wafer into p-type, for example, a 650 t.
to diffuse Zn until it reaches the substrate 1 and form the po-diffusion region 5.
(Figure 3(a)). At this time, the MQW layer 3 is mixed with GaAs and AfLGaAs as impurities diffuse, and becomes an Al1GaAs layer with an averaged composition (referred to as disordering of the multiple quantum well layer).

Next, the p-diffusion region 7 is essential for TJS lasers.
Heat treatment is performed at a high temperature of about 950 t to form.

A normal TJS laser that does not use MQW as an active layer requires heat treatment for about 2 hours, but under the same conditions, MQW-TJ
When the S laser heat treatment is performed, disorder occurs even in areas where impurities are not diffused due to the high temperature, causing the disadvantage that the MQW layer 3 disappears over the entire surface of the wafer (FIG. 3(b)). Attempts were made to extremely shorten the heat treatment time to several minutes, but due to the high temperature of 950° C., partial disorder occurred and desired laser characteristics could not be obtained.

[Problem to be solved by the invention]

In the conventional semiconductor laser manufacturing method as described above, 95
Although heat treatment at about 0t is essential, it is extremely difficult to maintain the MQW structure unchanged, and it has been impossible to realize a good TJS laser using MQW as an active layer.

An object of the present invention is to obtain a method for manufacturing a semiconductor laser that can realize a TJS laser using an MQW layer as an active layer.

(Means for Solving the Problems) A method for manufacturing a semiconductor laser according to the present invention is a semiconductor laser having an active layer sandwiched between two cladding layers of a first conductivity type. A step of selectively forming a first mask having transparency and a second mask having an opening and being transparent to impurities, and diffusing impurities from above the wafer to at least activate the The first layer has a second conductivity type and a high impurity concentration.
and a step of forming a second diffusion region of a second conductivity type and a low impurity concentration.

[Effect]

In this invention, by one-time sales promotion at low temperature, the second
A first diffusion region with a high impurity concentration and a second diffusion region with a low impurity concentration are simultaneously formed under the opening of the mask and under the second mask in a portion where the first mask is not formed, respectively.

〔Example〕

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

FIGS. 1(a) and 1(b) are cross-sectional views for explaining one embodiment of the method for manufacturing a semiconductor laser of the present invention. In these figures, the same symbols as in FIGS. 3(a) to (c) indicate the same things, and 9 indicates 5izN4i as the first mask.
1! , 10 is a 5in2 film as a second mask, and 11 is an opening in the SiO□ film 10.

Next, the manufacturing process will be explained.

First, 'after growing each layer in the same manner as before,
A Si3N film 9 is formed over the entire surface by a VD method or the like. If the film thickness is 500 angstroms or more, it acts as a non-transparent diffusion mask. Next, a Si3N4 film 9 is formed using an ordinary photolithography technique. An opening having the shape necessary for diffusion is provided, and an opening 11 is formed from the opening end of the Si3N4 film 9 to cover a part of the opening.
2 films 1o are formed. It is appropriate that the film thickness is 100 angstroms to several hundred angstroms, and the width is 5 to 10 μm (FIG. 1(a)).

Next, the Si3N4 film 9 is applied to the double heterostructure wafer.
Then, using the 5in2 film 10 as a mask, the film is heated to Z for a predetermined time at, for example, 650'C to 7°0C by a closed tube diffusion method or the like.
Perform n thermal diffusion.

The diffusion of Zn proceeds simultaneously through the opening 11 and through the portion of the 5i02 film 10 where the Si3N4 film 9, which is impermeable to Zn, is not formed therebelow. In the diffusion from the opening 11, since there is no film that obstructs the diffusion, a p + -diffusion region 5 is formed, and the Zn concentration is as high as about 10+20 cm-3.

When the active region is formed of multiple quantum wells, GaAs and Aj2GaAs are mixed with this impurity diffusion, resulting in an AflGaAs layer with an averaged composition (referred to as disordered multiple quantum wells).

On the other hand, in the case of diffusion through the 5in2 film 10, the SiO□ film acts like a blocking film for 102n, so the diffusion rate is slow, and the impurity concentration is about one to two orders of magnitude lower than that in the p+- diffusion region 5. A p-diffusion region 7 is formed (FIG. 1(b)).

Note that the impurity concentration of the p- diffusion region 7 can be controlled by the thickness of the 5in2 film 10.

By combining a mask with a non-permeable membrane and a permeable membrane in this way, a single diffusion at a relatively low temperature can
The p''-pn structure, which is essential for TJS lasers, can be created in the active layer.The multiple quantum well structure of the p-diffusion region 7, which has a low concentration due to the low temperature, remains unbroken and the multiple quantum well structure is A TJS laser with a quantum well as an active region has been realized, and it is possible to obtain a laser with a low threshold of several mA.In addition, because the manufacturing process is low temperature, thermal damage to the wafer is small, and the TJS laser
After the laser is fabricated, electronic devices such as FETs can be integrated on the surface of the sea urchin without reducing performance.

FIGS. 2(a) and 2(b) are sectional views for explaining another embodiment of the present invention. In these figures, Figure 1 (
The same reference numerals as in a) and (b) indicate the same parts, 9a is a Si3N4 film for preventing abnormal diffusion, and 12 is an opening between the Si3N4 film 9 and the Si3N4 film 9a.

In the manufacturing method shown in FIGS. 1(a) and 1(b), the end of the 5in2 film 10, which is permeable to Zn, reaches the opening 11, so depending on the film formation conditions such as temperature, diffusion may occur. Sometimes abnormal diffusion occurs in the lateral direction along the interface between the 5i02 film 1o and the wafer. In order to prevent this abnormal diffusion, in this example, as shown in FIG. 2(a),
Diffusion is performed by leaving a non-permeable Si3N4 film 9a for preventing abnormal diffusion under the edge of the 5i02 film 10 that reaches the opening 11. As a result, the p-diffusion region 7 is formed as shown in FIG.
As shown in b), it is formed only by diffusion from the opening 12, and no abnormal diffusion occurs in the lateral direction.

In the above embodiment, a GaAs-based TJS laser has been described, but it is obvious that the present invention can be applied to a TJS laser made of other materials such as an InP-based TJS laser.

It is also clear that Mg and Be can be used in addition to Zn as the p-type impurity, and it is also clear that the diffusion mask is not limited to the dielectric film mentioned above.

Furthermore, it goes without saying that the quantum well structure is not limited to a multiple quantum well structure.

(Effects of the Invention) As explained above, the present invention provides a semiconductor wafer in which an active layer is sandwiched between two cladding layers of a first conductivity type.
The first layer is non-permeable to impurities for doping.
selectively forming a second mask having openings and being transparent to impurities, and diffusing impurities from above the wafer to reach at least the active layer. Since it includes a step of forming a first diffusion region of a conductivity type with a high impurity concentration and a second diffusion region of a second conductivity type and a low impurity concentration, it is possible to perform a one-time low-temperature expansion process.
1 has the effect of forming a diffusion region necessary for a TJS laser. It is particularly effective for realizing a TJS laser having a quantum well structure in the active layer, and a semiconductor laser with a low threshold current can be obtained. In addition, since diffusion is performed at low temperatures, there is less damage to the surface of the sea urchin after diffusion, and high-performance FETs can be placed on this surface.
Another effect is that it becomes possible to easily create electronic technology such as the following.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view for explaining one embodiment of the semiconductor laser manufacturing method of the present invention, FIG. 2 is a cross-sectional view for explaining another embodiment of the present invention, and FIG. FIG. 2 is a cross-sectional view for explaining a method of manufacturing a laser. In the figure, 1 is a substrate made of semi-insulating GaAs; 2.
4 is a crat layer made of n-AuGaAs, 3 is GaA
s-Afl, MQW layer made of GaAs, 5 is po-diffusion region, 6 is MQW disordered by impurity diffusion
layer, 7 is p-diffused region, 9.9a is Si3N4 film, 10
is a SiO2 film, M and 12 are openings. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent Masuo Oiwa (2 others) Figure 1] Opening Figure 2

Claims (1)

[Claims] A semiconductor wafer in which an active layer is sandwiched between two cladding layers of a first conductivity type is provided with a first mask that is non-transparent to impurities to be doped, and an opening that is transparent to the impurities. a step of selectively forming a second mask having transparency through the wafer; and a step of diffusing the impurity from above the wafer to reach at least the active layer.
1. A method of manufacturing a semiconductor laser, comprising the steps of: forming a first diffusion region of a conductivity type and a high impurity concentration; and a second diffusion region of a second conductivity type and a low impurity concentration.