JPH06291414A - Surface emitting type semiconductor laser element - Google Patents

Abstract

PURPOSE:To provide a surface emitting type semiconductor laser element, which has a low threshold current and is capable of making a high-speed response. CONSTITUTION:A lower optical confinement layer 32, a lower clad layer 33, an active layer 34 and an upper optical confinement layer 40 are laminated in order on a semi-insulative semiconductor substrate 31, an N electrode 41 is provided on the layer 40, P electrodes 42 are provided on lower clad layers 36 and 37 and holes are injected in the layer 34 through the lower surface or the side surfaces of the layer 34 without going through the layer 32.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-emitting type semiconductor laser device capable of high-speed response, which is used for optical communication, optical measurement and the like.

[0002]

2. Description of the Related Art Surface-emitting type semiconductor laser devices have attracted attention as promising devices used for optical interconnection, parallel transmission, etc., and several structures have been proposed so far. For example, 1) In the structure shown in FIG.
An nGaAs strained quantum well layer is used and grown on an n-GaAs substrate 1 together with semiconductor multilayer reflective films 2 and 4 made of a pair of GaAs-AlAs arranged above and below the nGaAs strained quantum well layer, and a mesa of a light emitting portion is formed by etching. . But,
In this structure, the active layer temperature rises due to the high resistance of the semiconductor multilayer reflective film 4 on the p-electrode 7 side (due to the bandgap difference generated at the GaAs-AlAs interface), so the oscillation threshold current rises. However, there is a problem that the efficiency is lowered (see Document 1). 5 is GaAs
A semiconductor multilayer reflective film made of a pair of -AlAs, 6 is a polyimide insulating layer, and 8 is a non-reflective film. Reference numeral 9 is an n electrode having a light extraction window. 2) This tendency shows that the wavelength used for optical communication is 1.3 to 1.5.
This is particularly remarkable in InP-based materials that emit light in the vicinity of μm.
For example, as shown in FIG. 3, even in the embedded surface emitting semiconductor laser device, the threshold current is as high as 100 mA or more, which is a practical problem. Up to now, room temperature continuous oscillation has not been realized in InP-based surface emitting semiconductor laser devices (see References 2 and 3). In the figure, 11 is n-Ga
As substrate, 12 is n-GaAlAs clad layer? , 13
Is an n-GaAlAs / AlAs semiconductor multilayer reflective film, 14
Is a p-GaAs active layer, 15 is a p-GaAlAs cladding layer, 16 is an n-GaAs current confinement layer, and 17 is p-Ga.
As current confinement layer, 18 is p-GaAlAs cap layer,
Reference numeral 19 is a p-electrode, and 20 is an n-electrode. 3) In the mesa-type surface-emitting semiconductor laser device, as shown in FIG. 4, a dielectric multilayer film is used as the reflection films 26 and 27, and the p electrode 28 is directly provided on the upper surface of the p-InP buffer layer 23. The structure reduces the series resistance as much as possible. As a result, the oscillation threshold value at room temperature was also reduced to 50 mA (pulse drive), but continuous oscillation has not yet been reached. The main reasons are the resistance value of the thin p-InP cladding layer 23 and the poor heat dissipation due to the mesa shape.
For example, the injection current density is non-uniform (see Reference 4). In the figure, 21 is a p-InP substrate and 22 is a p-InG substrate.
aAsP stop etch layer, 24 is p-InGaAsP
An active layer, 25 is an n-InP clad layer, 29 is an n electrode,
30 is a polyimide insulating layer. Reference 1: 48th Device Research Conference., 53A-1, J
une, 1990. Reference 2: IEEE J. Quantum. Electron., QE-24, No. 9, pp.
1845-1855, Sept. 1988. Reference 3: 48th Device Research Conference., Post Dea
dline Paper, 5B-2, June, 1990. Reference 4: 49th Device Research Conference., Post Dea
dline Paper, 3A-8, June, 1991.

[0003]

The problems of the prior art as described above can be summarized as follows. That is, 1) the semiconductor multilayer film can be formed at the same time in the same growth apparatus,
Moreover, since the film thickness controllability is good, it is often used as a reflective film of this type of surface emitting semiconductor laser device, but the resistance value of the semiconductor multilayer film on the p-electrode side becomes high. Particularly, in the case of InP-based multilayer film, this resistance value becomes high. 2) When forming a cavity, in a conventional buried structure using a current blocking layer with a pn junction, a large parasitic capacitance is generated and high-speed modulation becomes impossible. 3) In the example of Reference 4, high-speed modulation is possible, but the heat dissipation of the mesa-type active layer 24 is poor and the characteristics deteriorate. Also,
The current in the active layer 24 is concentrated in the peripheral portion of the active layer 24 close to the p-electrode 28, and the current density in the central portion of the active layer 24 is reduced. The value current increases.

[0004]

SUMMARY OF THE INVENTION The present invention provides a surface-emitting type semiconductor laser device which solves the above problems, and includes a lower optical confinement layer, a lower cladding layer, an active layer and an upper layer on a semi-insulating semiconductor substrate. Light confinement layers are sequentially stacked, and n
The electrode is provided on the upper optical confinement layer, the p-electrode is provided on the lower clad layer, and holes are injected into the active layer from the lower surface or the side surface of the active layer without passing through the lower optical confinement layer. It is a thing.

[0005]

As described above, when the p-electrode is provided on the lower clad layer and holes having low mobility are injected into the active layer from the lower surface or the side surface of the active layer without passing through the lower optical confinement layer, the injection current is reduced. Is uniformly injected into the active layer and does not pass through the high-resistance lower optical confinement layer, so that the series resistance of the device is reduced. Further, since the n and p electrodes are formed on the substrate surface without facing each other, there is no stray capacitance such as a pn junction,
High-speed response characteristics are also possible.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the embodiments shown in the drawings. 1A and 1B are a cross-sectional view and a top view of an embodiment of a surface emitting semiconductor laser device according to the present invention. This structure is similar to the quantum well semiconductor laser device (normal cleaved edge emitting type) proposed by the present inventor in Japanese Patent Application No. 4-105388. The device of this example was manufactured by the following steps. That is, 1) First, a semi-insulating semiconductor multilayer film 32 (an InGaAsP layer 2000Å having a band gap wavelength λ _g = 1.4 μm) is also formed on a semi-insulating InP substrate 31 by a metal organic chemical vapor deposition (MOCVD) method or the like. , 30 pairs of InP layers 2000 Å), 1 μm thick 5 × 10 ¹⁷ cm ⁻³
Zn-doped p-InP layer 33, 0.6 μm
An undoped InGaAsP active layer 34 (bandgap wavelength λ _g = 1.5 μm) having a thickness and an undoped InP layer 35 having a thickness of 0.2 μm are sequentially epitaxially grown. 2) Next, a thin film of SiO ₂ or the like is formed on the undoped InP layer 35 by the plasma CVD method or the like, and processed into a circular shape having a diameter of 4 μm by photolithography. 3) Next, using this circular SiO ₂ film as a mask,
Chemical etching that reaches the surface of the semi-insulating semiconductor multilayer film 32 is performed to form a circular mesa. 4) Next, using the SiO ₂ film as a selective growth mask,
5 × 10 ¹⁷ cm ⁻³ by the second metalorganic vapor phase epitaxy
Zn-doped p-InP layer 36, 1 × 10 ¹⁹
p-InGaAsP layer 3 doped with Zn at cm ^-3 or more
7 (bandgap wavelength λ _g = 1.3 μm), a Fe-doped semi-insulating InP layer 38 for current confinement is grown to fill the periphery of the previously processed circular mesa. 5) Next, after removing the SiO ₂ mask, an n-InP layer 39 having a carrier concentration of about 1 × 10 ¹⁸ cm ⁻³ and a semi-insulating semiconductor multilayer film 32 are formed by the third metal organic chemical vapor deposition. An n-type semiconductor multilayer film 40 having the same structure but doped to about 1 × 10 ¹⁸ cm ⁻³ is formed. further,
An n-electrode 41 having a diameter of about 10 μm is formed, and the n-electrode 4
1 is used as a mask to etch the p-InGaAsP layer 37 to form a mesa, and a p-electrode 42 is formed around the mesa. In the present embodiment, the injected current does not pass through the semi-insulating semiconductor multilayer film 32 from the p-electrode 42, but is p- which is the lower cladding layer.
The InGaAsP active layer 34 passes through the InP layers 33 and 36.
Is injected from the bottom and sides. Therefore, the injection current is uniformly injected into the active layer 34. The injected current is confined by the semi-insulating InP layer 38, and the n-electrode 41 and the p-electrode 4
Since Nos. 2 do not face each other, high-speed response characteristics are not impaired.

[0007]

As described above, according to the present invention, a lower optical confinement layer, a lower cladding layer, an active layer and an upper optical confinement layer are sequentially stacked on a semi-insulating semiconductor substrate,
The electrode is provided on the upper optical confinement layer, the p electrode is provided on the lower clad layer, and holes are injected into the active layer from the lower surface or the side surface of the active layer without passing through the lower optical confinement layer.
There is an excellent effect that a surface-emitting type semiconductor laser device having a low threshold current and capable of high-speed response can be obtained.

[Brief description of drawings]

1A and 1B are respectively a cross-sectional view and a top view of an embodiment of a surface-emitting type semiconductor laser device according to the present invention.

FIG. 2 is a sectional view of a conventional surface-emitting type semiconductor laser device.

FIG. 3 is a sectional perspective view of another conventional surface-emitting type semiconductor laser device.

FIG. 4 is a sectional view of still another conventional surface-emitting type semiconductor laser device.

[Explanation of symbols]

 31 InP substrate 32, 40 Semiconductor multilayer film 33, 36 p-InP layer 34 InGaAsP active layer 35 InP layer 37 p-InGaAsP layer 38 Semi-insulating InP layer 39 n-InP layer 41 n-electrode 42 p-electrode

Claims (1)

[Claims] 1. A lower optical confinement layer, a lower clad layer, an active layer and an upper optical confinement layer are sequentially stacked on a semi-insulating semiconductor substrate, an n-electrode is provided on the upper optical confinement layer, and a p-electrode is a lower clad. A surface-emitting type semiconductor laser device provided on the layer, wherein holes are injected into the active layer from the lower surface or side surfaces of the active layer without passing through the lower optical confinement layer.