JP2011159897A - Semiconductor laser element and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser element reducing a contact resistance between an electrode and a cap layer without degrading an electric power conversion efficiency in an active layer, and also to provide a method for manufacturing the same. <P>SOLUTION: The semiconductor laser element 1 is equipped with: a first conduction type semiconductor substrate 1 with a first plane 1a and a second plane 1b facing each other; a first conduction type clad layer 4 formed on the first plane 1a; an active layer 5 formed on the clad layer 4; a second conduction type clad layer 6 formed on active layer 5; a second conduction type ridge 12 formed on the clad layer 6; a first electrode 14 formed on the ridge 12; and a second electrode 15 formed on the second plane 1b. The ridge 12 is an assembly film of polycrystalline films or crystalline grains, and is provided with a second conduction type contact resistance reduced film 11 connected to the first electrode 14. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a highly heat-resistant semiconductor laser device and a method for manufacturing the same.

Semiconductor laser elements are used in a wide range of fields as light sources for optical pickups, laser printers, displays, and the like.
For example, an AlGaInP (aluminum gallium indium phosphorus) -based semiconductor laser element used for DVD optical pickups has a problem with respect to heat resistance.
This is due to the large diffusion coefficient of Zn (zinc), which is generally used as a p-type dopant, and hinders operation at high temperatures and high output.

Specifically, when each semiconductor layer including the active layer and the p-type cap layer is sequentially formed on the semiconductor substrate, each semiconductor layer becomes high temperature. The p-type cap layer is doped with Zn at a high concentration in order to obtain an ohmic contact with the p-side electrode.
When Zn in the p-type cap layer is thermally diffused to the active layer during film formation, power conversion efficiency in the active layer is deteriorated. For this reason, there is a problem that the heat resistance of the semiconductor laser element is deteriorated, resulting in malfunction during high-temperature operation, or difficulty in increasing the output.

  In order to solve the above problem, Patent Document 1 discloses means for using Mg (magnesium) having a diffusion coefficient smaller than Zn as a p-type dopant instead of Zn having a large diffusion coefficient.

JP 2005-353654 A

By the way, in an AlGaInP-based semiconductor laser element as disclosed in Patent Document 1, GaAs (gallium arsenide) is generally used as a material of a p-type cap layer in order to make an ohmic contact with a p-side electrode. .
Since GaAs has a narrower band gap than an AlGaInP-based compound semiconductor, the energy barrier height at the contact interface with the p-side electrode can be made lower than that of an AlGaInP-based compound semiconductor.
Further, by making the p-type cap layer a GaAs layer doped with Zn at a high concentration, the height of the energy barrier at the contact interface between the p-side electrode and the p-type cap layer is lowered, and carriers move by the tunnel effect. As a result, the contact resistance between the p-side electrode and the p-type cap layer is reduced. Thereby, the element resistance of the semiconductor laser element is reduced.

However, in the AlGaInP-based semiconductor laser device disclosed in Patent Document 1, it is difficult to dope Mg into the p-type cap layer, which is a GaAs layer, at a high concentration. For example, the upper limit of the Mg doping concentration in the p-type cap layer, which is a GaAs layer, is about 1 × 10 ¹⁹ cm ³ .
Therefore, when Mg is used as the p-type dopant, it is difficult to sufficiently reduce the contact resistance between the p-side electrode and the p-type cap layer.

  Further, when Zn is doped together with Mg in the p-type cap layer in order to reduce the contact resistance between the p-side electrode and the p-type cap layer, since Zn is a material that easily diffuses with Mg, the p-type cap layer The Zn contained therein interdiffuses with Mg in other p-type semiconductor layers, causing problems such as a decrease in carrier concentration in the p-type semiconductor layer and diffusion of Zn into the active layer. This deteriorates the heat resistance and power conversion efficiency of the semiconductor laser element.

Further, as disclosed in Patent Document 1, when C (carbon) is doped with Mg in the p-type cap layer, C is a group III element, so GaAs or AlGaIn
In a group III-based semiconductor compound such as P, it becomes an amphoteric element that dissolves in both the group III site and the group III site, so that it acts not only as a p-type carrier but also as an n-type carrier.
Therefore, it becomes difficult to control the p-type dopant concentration of the p-type cap layer, and it is difficult to reduce the contact resistance between the p-side electrode and the p-type cap layer.

  Accordingly, an object of the present invention is to provide a semiconductor laser device and a method for manufacturing the same that can reduce the contact resistance between an electrode and a cap layer without deteriorating the power conversion efficiency in the active layer.

In order to solve the above-described problems, the present invention provides the following semiconductor laser device and manufacturing method thereof.
1) a first conductivity type semiconductor substrate (1) having a first surface (1a) and a second surface (1b) facing each other; and a first conductivity type semiconductor substrate formed above the first surface. A cladding layer (4), an active layer (5) formed on the first conductivity type cladding layer, a second conductivity type cladding layer (6) formed on the active layer, and the second layer A second conductivity type ridge (12) formed above the conductivity type cladding layer, a first electrode (14) formed on the second conductivity type ridge, and formed on the second surface The second conductivity type ridge is a polycrystalline film or an aggregate film of crystal grains, and the second conductivity type ridge is connected to the first electrode. A semiconductor laser device (20), comprising a contact resistance reducing film (11).
2) The semiconductor laser device according to 1), wherein the contact resistance reducing film contains magnesium as a second conductivity type dopant.
3) The semiconductor laser device according to 2), wherein the contact resistance reducing film contains gallium arsenide.
4) The first conductivity type first cladding is disposed above the first surface of the first conductivity type semiconductor substrate (1) having the first surface (1a) and the second surface (1b) facing each other. A layer (4), an active layer (5), a second conductivity type second cladding layer (6), a second conductivity type etching stop layer (7), a second conductivity type third cladding layer (8), and A film forming step for sequentially forming the second conductivity type cap layer (10), and after the film formation step, the second conductivity type dopant is supplied so as to become a doping limit concentration or more, and a large amount is formed on the cap layer. After the contact resistance reducing film forming step for forming the second conductivity type contact resistance reducing film (11) which is a crystal film or an aggregate film of crystal grains, and after the contact resistance reducing film forming step, The contact resistance reducing film and the carrier are exposed so that the etching stop layer is exposed. A ridge forming step of partially etching the first layer and the third cladding layer to form a second conductivity type ridge (12) in a stripe shape, and covering the side surface of the ridge after the ridge forming step. Forming a current confinement layer (13) on the etching stop layer;
After the current confinement layer forming step, an electrode forming step of forming a first electrode (14) connected to the contact resistance reducing film and forming a second electrode (15) connected to the second surface; A method for manufacturing a semiconductor laser device, comprising:
5) The method for manufacturing a semiconductor laser device according to 4), wherein magnesium is used as the second conductivity type dopant in the film formation step for reducing the contact resistance.
6) The method for manufacturing a semiconductor laser device according to 5), wherein in the step of forming the contact resistance-reducing film, the contact resistance-reducing film is formed to contain gallium arsenide.

  ADVANTAGE OF THE INVENTION According to this invention, there exists an effect that the contact resistance of an electrode and a cap layer can be reduced, without deteriorating the power conversion efficiency in an active layer.

It is typical sectional drawing for demonstrating the Example (1st process) of the semiconductor laser element of this invention. It is typical sectional drawing for demonstrating the Example (2nd process) of the semiconductor laser element of this invention. It is typical sectional drawing for demonstrating the Example (3rd process) of the semiconductor laser element of this invention. It is typical sectional drawing for demonstrating the Example (4th process) of the semiconductor laser element of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to FIGS.
Normally, a plurality of semiconductor laser elements are formed from one semiconductor wafer at a time. However, in FIG. 1 to FIG. 4, only one semiconductor laser element is shown from the beginning of the process for convenience of explanation. .

<Example>
[First step] (see FIG. 1)
An n-type first buffer layer 2, an n-type second buffer layer 3, an n-type cladding layer 4, on one surface 1a of an n-type semiconductor substrate 1 having a pair of opposed surfaces 1a and 1b, Non-doped MQW active layer (hereinafter referred to as active layer) 5, p-type cladding layer 6, p-type etching stop layer 7, p-type cladding layer 8, p-type band discontinuous relaxation layer 9, p-type cap The layer 10 and the p-type contact resistance reducing film 11 are sequentially formed by, for example, MOCVD (metal organic chemical vapor deposition).
A double heterostructure is formed by the n-type cladding layer 4, the active layer 5, and the p-type cladding layer 6.

  In the examples, Si (silicon) was used as the n-type dopant, and Mg (magnesium) having a smaller diffusion coefficient than Zn (zinc) was used as the p-type dopant.

  In the embodiment, an n-type GaAs (gallium arsenide) wafer is used as the n-type semiconductor substrate 1.

  In the embodiment, an n-type GaAs layer is formed as the n-type first buffer layer 2.

  In the example, an n-type GaInP (gallium indium phosphorus) layer was formed as the n-type second buffer layer 3.

In the example, an n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P (aluminum gallium indium phosphorus) layer was formed as the n-type cladding layer 4.

In the example, the active layer 5 has a multiple quantum well structure in which non-doped GaInP layers and non-doped (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P layers are alternately stacked.

In the example, a p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P layer was formed as the p-type cladding layer 6.

In the example, a p-type (Al _0.3 Ga _0.7 ) _0.5 In _0.5 P layer was formed as the p-type etching stop layer 7.

In the example, a p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P layer was formed as the p-type cladding layer 8.

In the embodiment, a p-type GaInP layer is formed as the p-type band discontinuous relaxation layer 9, and the Mg dopant concentration of the p-type band discontinuous relaxation layer 9 is 2.5 × 10 ¹⁸ cm ⁻³ . did.

In the example, a p-type GaAs layer was formed as the p-type cap layer 10, and the Mg dopant concentration of the p-type cap layer 10 was 1.0 × 10 ¹⁹ cm ⁻³ .

  In the embodiment, the supply amount of Mg when forming the p-type contact resistance reducing film 11 is set to an excessive amount exceeding the doping limit concentration with respect to GaAs, for example, when forming the p-type cap layer 10. A GaAs film was formed with a supply amount of three times or more of the supply amount of Mg. Thus, the formed GaAs film does not become a single crystal film but a polycrystalline film or an aggregate film of crystal grains. The GaAs polycrystal film or the aggregate film of GaAs crystal particles is the p-type contact resistance reducing film 11.

  Since the surface of the p-type contact resistance reducing film 11 does not have a uniform crystal structure, carrier recombination centers are formed in the semiconductor region at the contact interface with the p-side electrode 14 described later. For this reason, the formation of an energy barrier at the contact interface between the contact resistance reducing film 11 and the p-side electrode 14 is suppressed. Even if it is not increased, the contact resistance with the p-side electrode 14 can be reduced as compared with the prior art.

[Second step] (See FIG. 2)
Using a photolithography method, the contact resistance reducing film 11, the cap layer 10, the band discontinuous relaxation layer 9, and the cladding layer 8 are partially etched so that the etching stop layer 7 is exposed, and before the plane of the paper surface− Striped p-type ridges 12 extending in the depth direction of the paper surface are formed.

  By using an etchant whose etching rate with respect to the etching stop layer 7 is sufficiently slower than the etching rate with respect to the cladding layer 8, the partial etching can be easily stopped with the etching stop layer 7.

[Third step] (see FIG. 3)
A current confinement layer 13 is formed on the etching stop layer 7 so as to cover the side surface of the ridge 12.

  In the embodiment, an insulating film containing SiN (silicon nitride) as a main component is formed as the current confinement layer 13 by the plasma CVD method.

[Fourth step] (see FIG. 4)
A p-side electrode 14 connected to the contact resistance reducing film 11 is formed on at least the ridge 12 by using, for example, a vacuum deposition method, and an n-side electrode 15 is formed on the other surface 1b of the semiconductor substrate 1 (lower side in FIG. 4). Is formed using, for example, a vacuum deposition method.

  In the example, Ti (titanium), Pt (platinum), and Au (gold) were sequentially vacuum-deposited on the ridge 12 to form the p-side electrode 14.

  In the example, the n-side electrode 15 was formed on the other surface 1b of the semiconductor substrate 1 by vacuum deposition of an alloy containing Au (gold), Ge (germanium), and Ni (nickel).

Thereafter, the semiconductor substrate 1 that has undergone the first to fourth steps described above is cleaved in a direction perpendicular to the direction in which the ridges 12 extend, and further divided so as to divide the gap between adjacent ridges 12 into two. Thus, a plurality of semiconductor laser elements 20 shown in FIG. 4 are obtained at a time.
In FIG. 4, the front surface and the back surface of the semiconductor laser element 20 are a pair of resonator surfaces.

  By supplying current from the outside toward the n-side electrode 15 from the p-side electrode 14 of the semiconductor laser element 20, from the region corresponding to the region where the ridge 12 is formed in the active layer 5, the front side and the back side of the page. Laser light is emitted in the direction.

  As described above, according to the semiconductor laser device and the manufacturing method thereof according to the present invention, Mg having a small diffusion coefficient is used as the p-type dopant of each p-type semiconductor layer without using Zn having a large diffusion coefficient. Since the thermal diffusion to the p-type dopant in the active layer can be suppressed, the deterioration of the power conversion efficiency in the active layer can be prevented.

  In addition, according to the semiconductor laser device and the method for manufacturing the same according to the present invention, the GaAs film is formed between the p-side electrode and the cap layer by setting the supply amount of Mg to an excessive amount equal to or higher than the doping limit concentration for GaAs. By forming a p-type contact resistance reducing film that is a polycrystalline film or an aggregate film of crystal grains, formation of an energy barrier at the contact interface between the contact resistance reducing film and the p-side electrode is suppressed. Therefore, the contact resistance with the p-side electrode can be reduced as compared with the prior art without increasing the Mg dopant concentration in the contact resistance reducing film and the cap layer so much.

  The embodiment of the present invention is not limited to the configuration and procedure described above, and it goes without saying that modifications may be made without departing from the scope of the present invention.

  In some embodiments, the n-type of the semiconductor substrate and each semiconductor layer may be referred to as a first conductivity type, and the p-type may be referred to as a second conductivity type. Contrary to the embodiment, the n-type semiconductor substrate and each n-type semiconductor layer may be p-type, and each p-type semiconductor layer may be n-type. That is, the first conductivity type indicates one of n-type and p-type, and the second conductivity type indicates the other of n-type and p-type.

1_n type semiconductor substrate 1a, 1b_plane 2, 3_n type buffer layer 4_n type cladding layer 5_active layer 6, 8_p type cladding layer 7_p type etching stop layer 9_p type band discontinuous relaxation layer 10_p type cap layer 11_p-type contact resistance reducing film 12_p-type ridge 13_current confinement layer 14_p-side electrode 15_n-side electrode 20_semiconductor laser element

Claims (6)

A first conductivity type semiconductor substrate having a first surface and a second surface facing each other;
A first conductivity type cladding layer formed above the first surface;
An active layer formed on the first conductivity type cladding layer;
A second conductivity type cladding layer formed on the active layer;
A second conductivity type ridge formed above the second conductivity type cladding layer;
A first electrode formed on the ridge of the second conductivity type;
A second electrode formed on the second surface;
With
The ridge of the second conductivity type is
A semiconductor laser device comprising a second conductivity type contact resistance reducing film which is a polycrystalline film or an aggregate film of crystal grains and is connected to the first electrode.   2. The semiconductor laser device according to claim 1, wherein the contact resistance reducing film contains magnesium as a second conductivity type dopant.   3. The semiconductor laser device according to claim 2, wherein the contact resistance reducing film contains gallium arsenide. Above the first surface of the first conductivity type semiconductor substrate having a first surface and a second surface facing each other, a first conductivity type first cladding layer, an active layer, and a second conductivity type second substrate. A film forming step of sequentially forming a second cladding layer, a second conductivity type etching stop layer, a second conductivity type third cladding layer, and a second conductivity type cap layer;
After the film formation step, the second conductivity type dopant is supplied so as to be higher than the doping limit concentration, and the contact resistance of the second conductivity type, which is a polycrystalline film or an aggregate film of crystal grains, is reduced on the cap layer. A contact resistance reducing film forming step for forming a film;
After the contact resistance-reducing film forming step, the contact resistance-reducing film, the cap layer, and the third cladding layer are partially etched to expose the etching stop layer to be a second conductivity type. A ridge forming step of forming a ridge of
A current confinement layer forming step for forming a current confinement layer on the etching stop layer so as to cover a side surface of the ridge after the ridge formation step;
After the current confinement layer forming step, an electrode forming step of forming a first electrode connected to the contact resistance reducing film and forming a second electrode connected to the second surface;
A method for manufacturing a semiconductor laser device, comprising:   5. The method of manufacturing a semiconductor laser device according to claim 4, wherein magnesium is used as the second conductivity type dopant in the step of forming the contact resistance reducing film.   6. The method of manufacturing a semiconductor laser device according to claim 5, wherein, in the contact resistance reducing film forming step, the contact resistance reducing film is formed to contain gallium arsenide.

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