JPH07154026A - Semiconductor laser and fabrication thereof - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser from which the dislocation, causing deterioration of reliability or increasing leakage current, is eliminated. CONSTITUTION:At least a first clad layer 4, an active layer 5, and a second clad layer 6 are formed sequentially on a GaAs substrate 1 and a stripe contact layer 8, having band gap narrower than the active layer 5, is formed on the second clad layer 6. Si is then diffused from above the second clad layer 6 except the contact layer 8 and an underlying semiconductor layer to produce a mixed crystal region 12 filling the underlying semiconductor layer. Subsequently, the surface layer of the second clad layer 6 diffused with Si is removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a visible light embedded semiconductor laser device using a mixed crystal technique by impurity diffusion and a method for manufacturing the same.

[0002]

2. Description of the Related Art A buried semiconductor laser device using a mixed crystal technique by impurity diffusion has a low threshold, a high efficiency, a stable lateral mode, a planar type, and is easy to integrate. Many are made of AlGaAs, which is a material for the optical region.

Conventionally, AlGaInP which is a material of visible light
In this system, an embedded semiconductor laser device using this technique is described in J. Appl. Phys. 66, (1989) 48
See pages 2 to 487. The laser device described in this document is manufactured as follows.

On an n-type GaAs substrate, Te-doped n-type (Al _0.9 Ga _0.1 ) _0.5 In _0.5 P having a thickness of 1 μm
The first clad layer of, with a thickness of 200 Å (Al _0.2
Ga _0.8 ) _0.5 In _0.5 P, three undoped quantum well layers, and two layers of (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P each having a thickness of 100 Å between the quantum well layers. And a Zn-doped p-type barrier layer sandwiching the barrier layer between the unconfined first confinement layer and the second confinement layer.
Type (Al _0.9 Ga _0.1 ) _0.5 In _0.5 P and thickness 1μ
m second clad layer and p-type G heavily doped with Zn
The semiconductor layer of the contact layer made of aAs is MOCVD (m
et al organic chemical vap
or deposition method.

Then, a stripe-shaped window having a width of 10 μm is formed by photolithography on a 150 Å-thick Si film deposited by electron beam evaporation.

After that, a SiO ₂ film or a PSG protective film is deposited by CVD to a thickness of about 1000 Å. This sample was put into a quartz tube of about 3 cm ³ together with 3 mg of P, and 2 × 10
^-6 Torr is evacuated to about ⁶ Torr for sealing, and heat treatment is performed at 850 ° C. for 25 hours to diffuse Si and form a Si diffusion region. As a result, the region where Si is diffused becomes a mixed crystal region, and the region where Si is not diffused is embedded in the mixed crystal region as an active region.

After the heat treatment, the sample was taken out from the quartz tube, the Si film as the diffusion source and the protective film were removed, a 1000 Å SiO ₂ film was deposited again by CVD, and further, a region where Si was not diffused by photolithography. SiO _{2 on}
A 5 μm wide window is opened in the film to provide a current injection region.

Finally, after forming a p-side electrode of Au-Zn-Au, the GaAs substrate side is polished to 100 μm, and A
An n-side electrode is formed with u-Ge.

As a result, the embedded semiconductor laser device is manufactured.

This semiconductor laser device has a GaAs contact layer and (Al _0.9 Ga _0.1 ) in a region where Si is diffused.
_{Since the 0.5} In _0.5 P second cladding layer is n-type,
Contact layer and (Al _0.9 Ga _0.1 ) _{0.5 where} the p-type semiconductor layer in the diffusion region of Si and the non-diffusion region of Si are joined
A pn junction is formed in the In _0.5 P second cladding layer.

In the (Al _X Ga _{1 -X} ) _0.5 In _0.5 P system, the forbidden band width is E = 1.872 + 0.521 depending on the value of X.
X X (eV), Ga _0.5 In _0.5 P (E
= 1.872 eV), the forbidden band width is GaAs
It is wider than the forbidden band width of (E = 1.424 eV).

Therefore, the forbidden band width of the GaAs contact layer is narrower than the forbidden band width of the (Al _0.2 Ga _0.8 ) _0.5 In _0.5 P quantum well layer which should be a layer where carriers are recombined for laser oscillation. , The turn-on voltage at which the current starts flowing in the pn junction in the GaAs contact layer is smaller than the turn-on voltage of the pn junction in the active region, and the current easily flows through the pn junction in the GaAs contact layer.

Since the recombination at the pn junction in the GaAs contact layer does not contribute to stimulated emission, the current passing through the region where Si is diffused becomes a leakage current, which causes a problem of increasing the threshold value. .

Therefore, in order to solve this problem, the band gap of the pn junction formed in a region other than the active region is made larger than the band gap of the pn junction in the active layer, so that the region other than the active region is not formed. It has been proposed to obtain a low threshold embedded semiconductor laser device having a small leakage current flowing into the pn junction, and the present applicant has filed it as Japanese Patent Application No. 5-91669.

FIG. 6 shows the structure of a visible-light-embedded semiconductor laser device using mixed crystal formation by impurity diffusion proposed in the above-mentioned prior application. In the figure, 101 is an n-type GaAs substrate, 102 is a GaAs first buffer layer, and 103 is GaI.
nP second buffer layer, 104 AlInP first cladding layer, 105 quantum well active layer, 106 AlInP second cladding layer, 107 AlGaInP intermediate layer, 108 GaAs contact layer, 109 mixed crystal region by impurity diffusion , 110 is an insulating film, 111 is a p-side electrode, and 112 is an n-side electrode.

In the method of manufacturing the semiconductor laser device shown in FIG. 6, the GaAs first buffer layer 102, the Ga _0.5 In _0.5 P second buffer layer 103, and the Ga _0.5 In _0.5 P second buffer layer 103 are formed on the n-type GaAs substrate 101.
Al _0.5 In _0.5 P first cladding layer 104, undoped Ga _0.5 In _0.5 P, 10 nm thick three well layers, and (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P, 5 nm thick barrier between the well layers. Layer, well layer and barrier layer sandwiched (Al
_0.5 Ga _0.5 ) _0.5 In _0.5 P Quantum well active layer 105 composed of two 170-nm thick optical waveguide layers, Al _0.5
In _0.5 P second cladding layer 106, (Al _0.1 G
a _0.9 ) _0.5 In _0.5 P intermediate layer 107 and a GaAs contact layer 108 are sequentially laminated by a MOCVD method. 10μ on top of this by photolithography
A stripe-shaped resist having a width of m is formed, and using this resist as a mask, NH ₄ OH: H ₂ O ₂ : H ₂ O = 1:
The GaAs contact layer 108 was formed into a stripe with a width of 5 μm (Al _0.1 Ga) with an etching solution mixed at 2: 100.
_0.9 ) _0.5 In _0.5 P Selective etching is performed on the intermediate layer. Next, as an impurity diffusion source, an electron beam heating vapor deposition apparatus was used to obtain 5 nm in a vacuum of 1.3 × 10 ⁻⁴ Pa or less.
After depositing a Si film with a thickness of 5 nm and removing the Si film on the GaAs contact layer 108 by resist lift-off, a SiO ₂ film with a thickness of 50 nm is deposited on the entire surface as a surface protection film. Seal this in a quartz tube with phosphorus,
Heat treatment is performed in an electric furnace at 850 ° C. for 3 hours to diffuse Si until reaching the second cladding layer. Next, after taking out from the quartz tube and removing the SiO ₂ film and the Si film by dry etching using CF ₄ gas, a 100 nm SiO ₂ film as a current blocking layer is deposited thereon, and a resist is formed by photolithography. Open a window with a width of 5 μm, and use this resist as a mask and buffered hydrofluoric acid to form SiO 2.
₂ Etch the film. After that, the resist is removed and p
By depositing the side electrode and the n-side electrode respectively, as shown in FIG.
The semiconductor laser device shown in is formed.

According to the semiconductor laser device proposed in the above-mentioned prior application, a pn junction having a turn-on voltage smaller than that of the active layer is not formed in the contact layer having a small bandgap, so that recombination occurs outside the active region. Leakage current can be reduced. Further, when mixed crystal occurs between the contact layer and the clad layer due to Si diffusion, dislocations are generated due to lattice misalignment due to a change in the lattice constants of both layers. If it is removed in advance or if the region in which dislocations have occurred is removed, it becomes possible to prevent the effect of dislocations, which causes deterioration of the life of the semiconductor laser.

[0018]

In this semiconductor laser device, S is formed on the (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P intermediate layer.
The i film is deposited and thermally diffused. Since In diffuses very easily into Si, (Al _0.1 Ga _0.9 ) _0.5 I when heated.
It has been found that In escapes from n _0.5 P and diffuses into the Si film, causing dislocations and defects near the surface of the semiconductor layer in the Si diffusion region. This is group III In and Al _x G
This is because lattice matching is achieved with GaAs when the ratio of a _1-x is approximately 1: 1, and when the ratio changes due to the loss of In, the lattice constant changes and lattice irregularity occurs.
Such dislocations and defects reduce the reliability of the semiconductor laser and increase the leakage current on the surface.

Therefore, an object of the present invention is to provide a semiconductor laser device in which dislocations and defects that cause a decrease in reliability of the semiconductor laser and an increase in leakage current are removed.

[0020]

According to the method of manufacturing a semiconductor laser device of the present invention, at least a first clad layer, an active layer, and a second clad layer are sequentially laminated on a semiconductor substrate, and the second clad layer is formed on the second clad layer. A stripe-shaped contact layer having a bandgap narrower than that of the active layer is formed, and a first impurity is diffused from above the second cladding layer into a region excluding the contact layer and the semiconductor layer below the contact layer. And the mixed crystallized region is formed so that the semiconductor layer under the contact layer is filled with the mixed crystallized region, and then the surface layer of the second clad layer in which the first impurity is diffused is formed. It is characterized by removing.

Further, according to the present invention, a semiconductor substrate, and at least a semiconductor layer of a first clad layer, an active layer, and a second clad layer are sequentially laminated on the semiconductor substrate, and the active layer is formed on the second clad layer. A striped contact layer having a narrow band gap is formed, and the first impurity is diffused from above the second cladding layer into a region other than the contact layer and the semiconductor layer below the contact layer to form a mixed crystal. In the semiconductor laser device in which the semiconductor layer below the contact layer is filled with the mixed crystallized region, the thickness of the second cladding layer in the mixed crystallized region in which the first impurity is diffused is It is characterized in that it is thinner than the thickness of the second cladding layer below the contact layer.

[0022]

In the manufacturing process of the semiconductor laser device, it is necessary to heat the semiconductor layer for Si diffusion. At this time, In escapes from the AlGaInP-based semiconductor and diffuses into the Si film to form a semiconductor layer in the Si diffusion region. Dislocations occur near the surface. In the present invention, after Si diffusion, the vicinity of the surface of the semiconductor layer in the Si diffusion region is removed by etching, so that dislocations generated during heating are removed and the characteristic deterioration of the semiconductor laser device is prevented.

[0023]

1 is a sectional view of a semiconductor laser device according to an embodiment of the present invention. 1 is an n-type GaAs substrate, 2 is a first buffer layer, 3 is a second buffer layer, 4 is a first cladding layer, 5 is a quantum well active layer, 6 is a second cladding layer, 7 is an intermediate layer, and 8 is a contact. A layer, 12 is a Si diffusion region, 13 is a Zn diffusion region, 14 is an insulating film, 16 is a p-side electrode, and 17 is an n-side electrode. In the Si diffusion region 12, mixed crystallization occurs between the cladding layers 4 and 6 and the quantum well active layer 5, so that the quantum well active layer in the Si non-diffusion region is embedded in the mixed crystallization region.

The manufacturing method of the embodiment of the present invention will be described with reference to FIG. First, Si-doped G on the n-type GaAs substrate 1
0.2 μm thick first buffer layer 2 made of aAs, Si
A second buffer layer 3 made of doped Ga _0.5 In _0.5 P and having a thickness of 0.2 μm, a first cladding layer 4 made of Si-doped Al _0.5 In _0.5 P and having a thickness of 1 μm, an undoped quantum well active layer 5, and Zn-doped Al _0.5. In _0.5 P thickness 0.5
μm second cladding layer 6, Zn-doped Ga _0.5 In _0.5
0.1 μm thick intermediate layer 7 of P, Zn-doped GaA
MOCVD of the contact layer 8 made of s and having a thickness of 0.1 μm
Are sequentially laminated by the method. The quantum well active layer 5 comprises three Ga _0.5 In _0.5 P well layers each having a thickness of 10 nm, and two (Al _0.5 Ga _0.5 ) _0.5 layers each having a thickness of 10 nm.
The barrier layers are separated by two In _0.5 P barrier layers, each of which has a thickness of 170 nm and is made of (Al _0.5 Ga _0.5 ) _0.5 In.
It is a structure sandwiched by two _0.5 P optical waveguide layers.

On this, as shown in FIG. 2A, a resist 9 in a stripe shape having a width of 5 μm is formed by photolithography. Next, as shown in FIG. 2B, NH ₄ OH: H ₂ O ₂ : H ₂ O is used with this resist 9 as a mask.
= 1: 2: 100 mixed with an etching solution to form a Ga _0.5 In stripe on the GaAs contact layer 8 in a stripe shape with a width of 3 μm.
_{The 0.5} P intermediate layer 7 is selectively etched. Since the Ga _0.5 In _0.5 P intermediate layer 7 is hardly etched by the etching solution used here, the width of the GaAs contact layer 8 can be controlled by side etching the GaAs contact layer 8.

Next, as shown in FIG. 2 (c), 1.3 × 10 3
A Si film 10 having a thickness of 5 nm is vapor-deposited in a vacuum of ^-4 Pa or less with the resist 9 left. At this time, the GaAs contact layer 8 under the resist 9 and the Ga _0.5 In _0.5 P intermediate layer 7 under the resist 9 exposed on the surface by the side etching of the GaAs contact layer 8 are masked by the resist 9. Si is not deposited. Thereafter, as shown in FIG. 2D, the resist 9 is removed to remove the Si film 10 on the GaAs contact layer 8 by lift-off.

Next, as shown in FIG. 3A, a Si ₃ N ₄ film 11 having a thickness of 50 nm is deposited on the entire surface as a surface protection film. In the surface protective film of the semiconductor laser device of the present invention,
It can be used as long as it has heat resistance at 850 ° C. or higher and does not diffuse In or is sufficiently small during heat treatment. This was sealed in a quartz tube with phosphorus and 850 in an electric furnace.
Heat treatment is performed at ° C for 3 hours to diffuse Si until reaching the second cladding layer 4 to form a Si diffusion region 12, as shown in FIG. The Si diffusion region 12 becomes n-type and G
Between the a _0.5 In _0.5 P intermediate layer 7 and the Al _0.5 In _0.5 P second cladding layer 6, and between the Al _0.5 In _0.5 P second cladding layer 6, the quantum well active layer 5 and the first cladding layer 4. Mixed crystals occur. In addition, the surface layer of the Si diffusion region 12 is tens of n
Dislocations and defects occur in m due to the escape of In.

After being taken out from the quartz tube, as shown in FIG. 3 (c), S was obtained by dry etching using CF ₄ gas.
The i ₃ N ₄ film 11 and the Si film 10 are removed. After that, FIG.
As shown in (d), an etching solution mixed with H ₃ PO ₄ : HCl = 6: 1 or HCl: CH ₃ COO
By etching with an etching solution mixed with H: H ₂ O ₂ = 3: 150: 1, the GaAs contact layer 8 is not etched and the Ga _0.5 In _0.5 P intermediate layer 7 in the Si diffusion region 12 and the Si non-diffusion region 7 is etched. And Al _0.5 In _0.5
The P second cladding layer 6 is etched. As a result, dislocations and defects generated in the surface layer of the Si diffusion region 12 are removed. At this time, the thickness of the second cladding layer 6 in the mixed crystallized region 12 in which Si is diffused is preferably 200 to 500 nm thinner than the thickness of the second cladding layer 6 below the contact layer 8. If this difference is less than 200, there is the inconvenience that dislocations and defects may remain.
If it is larger than 0 nm, the effective refractive index difference between the active region and the mixed crystal region becomes large, and there is a disadvantage that a high-order transverse mode is generated.

This was sealed again in a quartz tube together with zinc, phosphorus and arsenic and heat-treated in an electric furnace at 550 ° C. for 20 minutes to diffuse Zn on the entire surface as shown in FIG. 4 (a). , Zn diffusion regions 13 are formed. Since Zn is a p-type dopant, a pn junction is formed with the region where Si is diffused. Therefore, the p-side electrode is directly exposed to S due to the displacement of the photolithography when forming the current blocking layer.
Even when in contact with the i diffusion region, current leakage is suppressed by the pn junction formed here. Also, due to Zn diffusion, G
Since the doping level of the aAs contact layer 8 is increased, a good ohmic contact is formed.

On this, as shown in FIG. 4B, a 100 nm SiO ₂ film 14 is deposited as a current blocking layer. The current blocking layer may be made of any material such as a Si ₃ N ₄ film that is electrically insulating and does not react with GaAs. Next, as shown in FIG. 4C, S on the GaAs contact layer is
A resist 15 having a window with a width of 5 μm is formed by photolithography so that the iO ₂ film 14 is exposed. Then, as shown in FIG. 5A, the SiO ₂ film 14 is etched using the resist 15 as a mask and buffered hydrofluoric acid to form a window for current injection. Next, as shown in FIG. 5B, the resist is removed.

After that, the semiconductor laser device shown in FIG. 1 is formed by depositing the p-side electrode and the n-side electrode respectively.

[0032]

According to the present invention, dislocations and defects caused by lattice misalignment due to In loss are removed by etching. Therefore, it is possible to eliminate a decrease in reliability and an increase in leakage current due to dislocations and defects. it can.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an embedded semiconductor laser device that is an embodiment of the present invention.

FIG. 2 is a sectional view showing a manufacturing procedure of the embedded semiconductor laser device according to the embodiment of the present invention.

FIG. 3 is a cross-sectional view showing the manufacturing procedure following FIG.

FIG. 4 is a cross-sectional view showing the manufacturing procedure following FIG.

FIG. 5 is a cross-sectional view showing the manufacturing procedure following FIG.

FIG. 6 is a cross-sectional view of a conventional embedded semiconductor laser device.

[Explanation of symbols]

1, 101 ... GaAs substrate, 2, 102 ... GaAs first buffer layer, 3, 103 ... GaInP second buffer layer,
4, 104 ... AlInP first cladding layer, 5, 105 ...
Quantum well active layer, 6, 106 ... AlInP second cladding layer, 7 ... GaInP intermediate layer, 8, 108 ... GaAs contact layer, 9, 15 ... Resist, 10 ... Si film, 11 ...
Si ₃ N ₄ film, 12, 109 ... Si diffusion region, 13 ... Z
n diffusion region, 14, 110 ... SiO ₂ film, 16, 111
... p-side electrode, 17, 112 ... n-side electrode, 107 ... AlG
aInP intermediate layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiromi Otoma Fuji Xerox Co., Ltd. 2274 Hongo, Ebina City, Kanagawa Prefecture

Claims (4)

[Claims] 1. A semiconductor substrate comprising at least a first clad layer, an active layer and a second clad layer, which are sequentially laminated on a semiconductor substrate, and a striped pattern having a band gap narrower than that of the active layer on the second clad layer. Forming a contact layer, diffusing the first impurity from above the second clad layer into a region excluding the contact layer and the semiconductor layer below the contact layer to form a mixed crystal, and this mixed crystal formation A method for manufacturing a semiconductor laser device, characterized in that a semiconductor layer below the contact layer is filled with a region, and then a surface layer of the second cladding layer in which the first impurity is diffused is removed. 2. The sequentially stacked semiconductor layers are made of AlG.
2. The method for manufacturing a semiconductor laser device according to claim 1, wherein the semiconductor laser device is made of an aInP-based semiconductor. 3. A semiconductor substrate, and at least a first clad layer, an active layer, and a semiconductor layer of a second clad layer are sequentially laminated on the semiconductor substrate, and a forbidden band width is formed on the second clad layer more than the active layer. Mixed crystal in which a narrow stripe-shaped contact layer is formed, and the first impurity is diffused from above the second cladding layer into a region excluding the contact layer and the semiconductor layer below the contact layer. In the semiconductor laser device in which the semiconductor layer below the contact layer is filled with a crystallization region, the thickness of the second clad layer in the mixed crystallized region in which the first impurity is diffused is smaller than that in the contact layer below. A semiconductor laser device having a thickness smaller than that of the second cladding layer. 4. The sequentially stacked semiconductor layers are made of AlG.
4. The semiconductor laser device according to claim 3, wherein the semiconductor laser device is composed of an aInP-based semiconductor.