JPH0758409A - Surface emitting semiconductor laser element - Google Patents

Abstract

PURPOSE:To reduce threshold current by forming a current diffusion layer on the side of a semiconductor layer in contact with a distributed Bragg reflector, and further forming a first electrode on the current diffusion layer without interposing the distributed Bragg reflector in-between. CONSTITUTION:Current injected through a p-electrode 20 is diffused in a p<+>-InP current diffusion layer 17 without passing through a DBR layer 19, and flows into an active layer 13 through a p-InP cladding layer 14. Since the active layer 13 is surrounded with a p-InP buried layer 15 and n-InP buried layer 16 formed on the circumference thereof, current passes only through the active layer 13, and threshold voltage is almost a half of that in conventional ways. Thus a current diffusion layer is formed between a semiconductor layer and a distributed Bragg reflector, and further a first electrode is formed on the current diffusion layer without interposing the distributed Bragg reflector in-between; therefore, element resistance is reduced and threshold current is reduced as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed Bragg reflection (DBR) type surface emitting semiconductor laser device used as a light source for optical communication.

[0002]

2. Description of the Related Art In a vertical cavity surface emitting semiconductor laser device that emits laser light in a vertical direction from a substrate, it is important to form a high reflectivity reflecting mirror in order to perform a low threshold operation. A distributed Bragg reflector (DBR) made of a semiconductor multilayer film is regarded as a promising reflector with high reflectance.

A conventional vertical cavity surface emitting semiconductor laser device has, for example, a structure as shown in FIG. In the figure,
1 is an n-InP substrate, 2 is an n-DBR layer, 3 is GaIn
AsP active layer, 4 p-InP clad layer, 5 p-I
nP buried layer, 6 is n-InP buried layer, 7 is p-
The DBR layer, 8 is a p ⁺ -InGaAs contact layer, 9 is a p electrode, and 10 is an n electrode. N consisting of semiconductor multilayer film
The -DBR layer 2 and the p-DBR layer 7 have a relatively high refractive index and a small band gap energy of GaInA.
The sP layer and the InP layer having a relatively low refractive index and a large band gap energy are repeatedly formed, and have a high reflectance. The layer thicknesses are each 1/4 optical wavelength with respect to the oscillation wavelength.

By the way, since the semiconductor multi-layered film DBR has a band structure peculiar to the hetero structure, there is a problem that the element resistance becomes high due to repetition of the hetero barrier. Therefore, in order to reduce this resistance, it is necessary to increase the impurity concentration of the semiconductor multilayer film, and in particular, p-DB having a low mobility is required.
In R, it is necessary to increase the impurity concentration above n-DBR. As another method of lowering the resistance, only the layer having a larger band gap energy of the semiconductor multilayer film may be doped to carry out modulation doping to partially increase the impurity concentration, which further lowers the resistance. be able to.

[0005]

However, even if the impurity concentration of the semiconductor multilayer film DBR is increased as described above, p
-In the case of DBR, there is a limit to the reduction of resistance, so p-
When the DBR is used, the influence of heat generation due to it cannot be avoided. Further, when the impurity concentration becomes high, the absorption loss of light also becomes high, and there is a problem that the threshold current increases.

[0006]

SUMMARY OF THE INVENTION The present invention provides a surface-emitting semiconductor laser device that solves the above-mentioned problems, including a semiconductor substrate, a semiconductor layer including an active layer provided on the semiconductor substrate, A distributed Bragg reflector made of a semiconductor multilayer film provided on a semiconductor layer, and the distributed Bragg reflector has a light emitting portion for emitting laser light in a vertical direction, and is provided on the light emitting portion side. In a surface emitting semiconductor laser device including a first electrode and a second electrode provided on the semiconductor substrate side, a current diffusion layer is provided between the semiconductor layer and the distributed Bragg reflector, and the first electrode is the It is characterized in that it is provided on the current diffusion layer without a distributed Bragg reflector.

[0007]

As described above, when the current diffusion layer is provided on the side of the semiconductor layer in contact with the distributed Bragg reflector, and the first electrode is provided on the current diffused layer without the distributed Bragg reflector, the injected current is The active layer can be injected from the first electrode through the current diffusion layer without passing through the distributed Bragg reflector. Therefore, the resistance to the injection current of the element is reduced, heat generation can be prevented, and since it is not necessary to inject the impurity for reducing the resistance into the distributed Bragg reflector, the light absorption loss is reduced, and therefore, The threshold current is reduced.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is a sectional view of an embodiment of a surface emitting semiconductor laser device according to the present invention. In the figure, 11 is an n-InP substrate, 12 is an n-DBR layer, and 13 is GaIn.
AsP active layer (λ _g = 1.3 to 1.6 μm), 14 is p
-InP clad layer, 15 is a p-InP buried layer, 1
6 is an n-InP buried layer, 17 is a p ⁺ -InP current diffusion layer, 18 is a p ⁺ -InGaAs contact layer, 19 is a non-doped DBR layer which is non-doping to reduce light absorption loss, 20 is a p-electrode, 21 Is the n-electrode. n-
The DBR layer 12 and the non-doped DBR layer 19 are 25-
It is composed of 30 pairs of GaInAsP well layers and InP barrier layers, and the thicknesses of the well layers and barrier layers are each 1/4 optical wavelength. The p ⁺ -InP current diffusion layer 17 has a thickness of 0.1 μm or less and an impurity concentration of 5 × 10 ¹⁸ cm 2.
^-3 or more.

This embodiment was manufactured by the process shown in FIG.
That is, 1) First, the n-DBR layer 1 is formed on the n-InP substrate 11.
2, the GaInAsP active layer 13, and the p-InP clad layer 14 are sequentially stacked (FIG. 2A). 2) Then, after forming a circular or rectangular mesa, p-I
The nP burying layer 15 and the n-InP burying layer 16 are buried (FIG. 2B). 3) Then, p-InP clad layer 14, p ⁺ -InP
Current diffusion layer 17, p ⁺ -InGaAs contact layer 18
Are sequentially laminated (FIG. 2C). 4) Next, using the p ⁺ -InP current diffusion layer 17,
After removing the contact layer 18 on the mesa by selective etching, a non-doped DBR layer 19 is laminated (FIG. 2).
(D)). 5) Next, the DBR layer 19 other than the upper part of the active layer 13 is removed by etching to expose the contact layer 18 on the surface, and the p electrode 20 is formed thereon. Also, on the back surface of the substrate 11,
The electrode 21 is formed (FIG. 2E).

In this embodiment, the current injected from the p-electrode 20 does not pass through the DBR layer 19 but diffuses in the p ⁺ -InP current diffusion layer 17, passes through the p-InP clad layer 14, and then becomes active layer 13. to go into. Since the periphery of the active layer 13 is filled with the p-InP burying layer 15 and the n-InP burying layer 16, the current flows only in the active layer 13. In this example, the threshold voltage was reduced by half compared to the conventional example shown in FIG.

FIG. 3 is a sectional view of another embodiment. In the present embodiment, the part corresponding to the lower part of the active layer 13 of the n-InP substrate 11 is removed, and the dielectric multilayer film mirror 25 is formed there. 23 is an n-InP clad layer, 24
Is an n-GaInAsaP etching stop layer.
In this embodiment, the DBR on the substrate 11 side is the same as in the previous embodiment.
Since no current passes through the layer 12, the device resistance is further reduced.

[0012]

As described above, according to the present invention, a distribution including a semiconductor substrate, a semiconductor layer including an active layer provided on the semiconductor substrate, and a semiconductor multilayer film provided on the semiconductor layer. A Bragg reflector, and the distributed Bragg reflector has a light emitting portion for emitting laser light in a vertical direction, a first electrode provided on the light emitting portion side, and a semiconductor substrate side. In a surface emitting semiconductor laser device including a second electrode, a current diffusion layer is provided between the semiconductor layer and the distributed Bragg reflector, and the first electrode is provided on the current diffused layer without the distributed Bragg reflector. Since it is provided, there is an excellent effect that the element resistance is reduced and the threshold current is reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of a surface emitting semiconductor laser device according to the present invention.

2 (a) to 2 (e) are explanatory views of a manufacturing process of the above embodiment.

FIG. 3 is a sectional view of another embodiment of the present invention.

FIG. 4 is a sectional view of a conventional surface emitting semiconductor laser device.

[Explanation of symbols]

 11 substrate 12 n-DBR layer 13 active layer 14 p-InP clad layer 15 p-InP buried layer 16 n-InP buried layer 17 current diffusion layer 18 contact layer 19 non-doped DBR layer 20 p-electrode 21 n-electrode 23 n-InP clad Layer 24 n-GaInAsaP etching stop layer 25 Dielectric multilayer film mirror

Claims (1)

[Claims] 1. A semiconductor substrate, a semiconductor layer including an active layer provided on the semiconductor substrate, and a distributed Bragg reflector made of a semiconductor multilayer film provided on the semiconductor layer,
The distributed Bragg reflector has a light emitting portion for emitting laser light in a vertical direction, and includes a first electrode provided on the light emitting portion side and a second electrode provided on the semiconductor substrate side. In the surface emitting semiconductor laser device, a current diffusion layer is provided between the semiconductor layer and the distributed Bragg reflector, and the first electrode is provided on the current diffused layer without the distributed Bragg reflector. Surface emitting semiconductor laser device.