JP2000031579A - Etch mirror type compound semiconductor laser integrated device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel compound semiconductor laser integrated device which facilitates monolithic integration with other devices such as a laser diode and has a high gain and a high stability in a laser diode alone. . SOLUTION: In an etched mirror type compound semiconductor laser integrated device in which a compound semiconductor laser device 41 and a light detecting element 43 for detecting laser light emitted from the device are integrally formed, one of end faces of a resonator of the laser device is provided. Alternatively, both are formed on the reflection surfaces 45 and 47 by etching, and Al or W is adhered to the reflection surfaces to make the reflectance higher than the reflectance of the reflection surfaces.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel etched mirror type compound semiconductor laser device having high gain, high stability and low noise performance.

[0002]

2. Description of the Related Art In general, a reflecting mirror (reflecting surface) constituting a resonator of a semiconductor laser, which uses a cleavage plane of a substrate crystal, has been widely used because it is easy to manufacture and simple.

FIG. 3 is a view showing the structure of a conventional semiconductor laser device. In the figure, 11 is n-InP (substrate), 13
Is n-InP, 15 is p-InP, 17 is n-InP,
19 is p-InP, 21 is p-GaInAsP (active region), 23 is p-GaInAsP, 25 is p-InP,
27 is p-GaInAsP, 29 is Zn diffusion region, 31
Is SiO ₂ , 33 is In, 35 is Au / Zn, 37 is A
u / Sn.

In the figure, n-InP13, p-GaI
The nAsP21 and the p-InP25 form a double hetero structure, and the n-InP17 forms a stripe structure for limiting current in the lateral direction. Note that p-GaInAs
P23 is formed in the active region 21 by melt back during crystal growth.
AMB (Anti Me
lt Back) layer, and p-InP 15 constitutes a light guide. As for the electrode, the positive electrode side has the In layer 33 and the Au /
The Zn layer 35 is formed with the Au / Sn layer 37 on the negative pole side,
Both end faces function as reflection mirrors by the cleavage planes, and constitute a Fabry-Perot resonator.

When a current flows between the upper and lower electrodes in such a semiconductor laser, injected carriers are confined by the double hetero structure, and the current is restricted by the stripe structure in the lateral direction, so that a large current density and internal quantum efficiency are obtained. Is obtained. In addition, natural light emission is effectively confined by the light guide layer, and laser oscillation is performed with a small threshold current.

FIG. 4 is a view showing an element in which a semiconductor laser and a photodiode as shown in FIG. 3 are integrated on the same substrate, for example.
43 is a photodiode, 45 and 47 are cleavage planes or etched mirror surfaces, and 49 is an etched mirror surface.

In the semiconductor laser device of FIG. 4, a compound semiconductor laser 41 and a photodiode 43 are integrally formed on the same substrate, and one or both surfaces of the compound semiconductor laser device are formed as mirror surfaces by etching. Thus, a resonator is formed.

[0008]

However, in the method as shown in FIG. 4, the reflectivity is effectively 30 to 40%, the Q value of the resonator is essentially low, and the semiconductor laser and other components are not used. So-called monolithic integration, in which elements such as light output detection photodiodes and modulation transistors are formed on the same substrate, has been extremely difficult.

Further, in a semiconductor laser device having a structure as shown in FIG. 4, an end surface mirroring by various etchings (chemical etching and vapor phase etching, and plasma assisted vapor phase etching) has been attempted (35th edition). Applied Physics-related Lectures, 1988, Proceedings 28
p-ZP-12, 28p-ZP-13, 28p-ZP-
14) However, the reflectivity of the mirror obtained by these methods is almost the same as that obtained by the cleavage plane, and although it is possible to make the mirror monolithic, the Q of the resonator having the reflecting mirror having a low reflectivity is essentially Q. The value was low, and the occurrence of unstable states such as optical feedback noise was inevitable.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to facilitate monolithic integration with other elements such as a laser diode, and to provide a laser diode with high gain and high stability. It is an object to provide a compound semiconductor laser device.

[0011]

FIG. 1 shows an embodiment in which a compound semiconductor laser device according to the present invention and a photodiode are integrally formed. 4, the same reference numerals as those in FIG. 4 indicate the same contents, and reference numeral 51 denotes a high-reflectance etched mirror surface according to the present invention.

In the present invention, after an etched mirror surface is formed by a wet method or a dry method (reactive ion etching or the like), a metal (Al, W, or the like) is selectively CVD (chemical vapor deposition). Is formed on the surface of the etched mirror. In addition, the etched mirror surface 5
1 has a refractive index smaller than that of the laser device 2
More than one kind of materials are stacked alternately or sequentially so that the product of the film thickness and the refractive index is な る of the oscillation wavelength of the laser device. By forming the etched mirror surface in this way, the reflectivity can be dramatically improved as described later, and the Q value of the resonator can be improved. Then, a stable oscillation output can be obtained by detecting light from the laser device with a photodiode and controlling the injection current into the laser device based on the detected output. Since the photodiode side is also manufactured by the same process as the laser device, the light incident surface of the photodiode is formed as an etched mirror surface. However, since the etched mirror surface is not necessarily required on the photodiode side, a step of masking the photodiode side may be added when the etched mirror surface is not formed.

The present invention can be applied to a semiconductor laser device based on any material such as InP and GaAs.

Next, the calculation of the reflectance by the multilayer structure will be described.

For example, consider a multilayer film composed of N layers as shown in FIG. 2, and each film thickness is _represented by D _k (k = 1, 2,...,
N), the refractive index is _nk (k = 1, 2,..., N), and when the light of wavelength λ ₀ is vertically incident (φ = 90 °), the following optical matrix A _k corresponds to each layer. I do.

[0016]

(Equation 1)

[0017]

(Equation 2) It is expressed as

According to the present invention, a metal thin film or a multilayer insulating layer is deposited on a mirror surface formed by etching of a compound semiconductor laser device, and an etched mirror is selected by selecting a film thickness of a metal to be deposited or a deposition structure of two or more kinds of substances. The reflectivity of the surface can be arbitrarily varied within a range from 30 to 40% to 100%, and when the photodiode element and the laser diode element are integrally formed, the reflectivity is set to 90% to 95%. However, a small amount of light output reaches the photodiode side, and not only can it function as an optical output monitor, but also the laser diode element side can increase the Q value of the resonator and achieve high output and high stability. Can be.

[0019]

Embodiments of the present invention will be described below. (Example 1) Conditions for manufacturing an etched mirror are as follows. Reactive ion etching (RIE) was used, and Cl ₂ / Ar was used as an etching gas. The discharge power was 50 W, the reaction pressure was 1.0 × 10 ⁻² Torr, the etching time was 80 minutes, and the etching depth in the vertical portion of the mirror surface was about 4 μm.

Metal deposition conditions are chemical vapor deposition (CVD)
Method, an Al film thickness of 1000 ° is formed, and the reflectance R =
95% was obtained. (Embodiment 2) The fabrication conditions of the etched mirror are the same as those of Embodiment 1, and the formation conditions of the laminated film are as follows.

At an oscillation wavelength of 870 nm, the multilayer film is made of SiNx
/ SiNxOy.

SiNx has a refractive index n = 2.0 (film thickness 109).
nm), SiNxOy has a refractive index n = 1.7 (film thickness 128).
nm), and when 15 layers are laminated as a set,

[0023]

(Equation 3) Met.

[0024]

As described above, according to the present invention, the reflectivity can be improved by attaching or forming a metal thin film or a multilayer insulating layer on the end face mirror surface formed by etching. It is possible to manufacture a resonator having
It is possible to realize a compound semiconductor laser device with high stability and low noise.

[Brief description of the drawings]

FIG. 1 is a perspective view of an integrated structure of an etched mirror type compound semiconductor laser device and a photodiode according to the present invention.

FIG. 2 is a diagram for explaining the reflectance of a multilayer structure.

FIG. 3 is a diagram showing an example of the structure of a conventional semiconductor laser.

FIG. 4 is a diagram illustrating an example of an integrated device of a semiconductor laser and a photodiode having an etched mirror structure.

[Explanation of symbols]

41: Compound semiconductor laser device, 43: Photodiode, 45, 47: Cleavage surface or etched mirror surface, 4
9, an etched mirror surface, 51 a high reflectance etched mirror surface.

Claims (1)

[Claims] 1. An etched mirror type compound semiconductor laser integrated device in which a compound semiconductor laser device and a photodetector for detecting laser light emitted from the device are integrally formed, one of end faces of a resonator of the laser device, or Both are formed on the reflecting surface by etching, and Al
Alternatively, an etched mirror type compound semiconductor laser integrated device, wherein W is attached to make the reflectivity higher than the reflectivity of the reflection surface.