JPS616886A - Distributed feedback type semiconductor laser - Google Patents

Abstract

PURPOSE:To improve reproducibility and yield by forming a current constriction layer with a striped window into a clad layer shaped onto a region in which beams are mainly confined. CONSTITUTION:A diffraction grating surface 2 at a fixed pitch having wavelength selectivity, an N-InGaAsP optical waveguide layer 4, an InGaAsP active layer 5, a P-InP clad layer 6 and a P-InP cap layer 8 are grown onto an N-InP substrate 2 in an epitaxial manner, and structure in which N-InGaAsp current constriction layers 7 to which striped windows are bored are buried at approximately the center of the clad layer 6 is formed. Accordingly, injection currents concentrate to stripes and flow because they are blocked by the current constriction layer, gain waveguide is conducted while beams are confined owing to an effective refractive-index difference generated by the presence of the current constriction layer, and a change into a single mode and the control of a transverse mode are enabled by properly setting the width of stripes.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to the structure of a distributed feedback semiconductor radar.

[Prior art]

Distributed feedback semiconductor lasers form a wavelength-selective, constant-pitch diffraction grating along the region where laser light is confined, including the active region, and generate light based on the principle of black diffraction reflection of electromagnetic waves by this diffraction grating. This is a semiconductor laser that uses a resonator.

This type of Rade element does not have a structure in which the crystal bone plane is the optical resonant plane like the Fabry 40-type, so it is easy to apply to optical integrated circuits and has many features such as excellent mode selectivity. have.

Up until now, the structures of distributed feedback semiconductor radars, especially waveguide structures for the purpose of transverse mode control, have been the dual channel solena buried hetero (DC-PBH) type or the buried hetero (BH) type. Embedded structures such as these are the mainstream.

FIG. 3 is a diagram of this BH type laser seen from the light emitting surface, in which an optical waveguide layer (for example, n-I
nGaAsP) 37, active layer (e.g. InGaAsP)
) 39, cladding layer (for example, p-InP) 35, etc. are grown, and both sides are covered with a first buried layer (for example, p-InP) 34, a second buried layer (for example, n-I
nP)40. Second cladding layer (e.g. n-InGaAs)
P) 36 etc.

A diffraction grating with a constant pitch is formed on one side of the optical waveguide layer 37 and the active layer 39, which are mainly light-confined regions surrounded by heterojunctions. Therefore, stable single-longitudinal mode and fundamental transverse mode oscillation can be realized.

[Problem that the invention seeks to solve]

By the way, when manufacturing the above-mentioned BH structure distributed feedback semiconductor laser, the following two points have become major problems.

(1) A submicron periodic diffraction grating is formed on a compound semiconductor substrate using a photo-phosphorography method such as a direct two-beam interference exposure method, and a diffraction grating with a desired depth is formed on the grating, and the light guide is sequentially placed on the diffraction grating. The waveguide layer, active layer, cladding layer, etc. are grown epitaxially, but in this process it is extremely difficult to control the manufacturing conditions to produce a wafer with a layer thickness that satisfies the design value, and it is difficult to achieve good reproducibility. It was not possible to manufacture the laser element.

(2) After the laminated semiconductor elements are formed, side etching is performed on both sides of the active layer to form a buried structure, and then the first buried layer, second buried layer, etc. are sequentially epitaxially buried. The process of forming the diffraction grating plane mentioned above is to adjust the thickness of the grown layer, the width of the active layer, etc. while controlling the force of growing the buried layer so that the end of the buried layer is near the active layer. ) was also more difficult, and it was difficult to achieve reproducibility.

Therefore, the BH structure laser of the distributed feedback type is an element with a structure that has a very poor yield in terms of industrial production because the above-mentioned individual difficulties in manufacturing appear as a synergistic effect.

[Purpose of the invention]

This invention has been made in view of the above-mentioned problems, and its purpose is to provide a distributed feedback semiconductor laser structure that has excellent reproducibility and high yield. .

[Means to solve the problem]

The distributed feedback semiconductor laser according to the present invention includes a cladding layer formed on a region where light is mainly confined.
This is formed by forming a current confinement layer having striped windows.

〔Example〕

FIG. 1 is an overall side view showing an embodiment of a distributed feedback semiconductor laser according to the present invention. In other words, n-In
On a P substrate 2, a constant pitch diffraction grating surface 3 having wavelength selectivity, an n-InGaAsP optical waveguide layer 4, and an InGaAs
A P active layer 5, a p-InP cladding layer 6, and a p-InP casso layer 8 are epitaxially grown, and a stripe-shaped window is opened approximately in the center of the cladding layer 6.
It has a structure in which an IylGaAs+P current confinement layer 7 is embedded. Therefore, the injected current is in this current confinement layer! Since the current is locked, the flow is concentrated in the stripe and gain waveguide is performed, and the effective refractive index difference caused by the presence or absence of the current confinement layer acts to confine light. Mode conversion and lateral mode control are possible.

A semiconductor radar having such a structure is formed by the following process.

First, as shown in Figure 2), a diffraction grating surface 3 with a constant pitch is formed on an n-InP semiconductor substrate 2 by the photo-phosphorographic method (or a diffraction grating surface 3 with a constant pitch is formed on an n-InP semiconductor substrate 2).
You may also use one that has grown layers. ).

Next, as shown in FIG. 2(B), an n-InGaAsP optical waveguide layer 4, an InGaAsP active layer 5, a p-InP layer 6, and an n-InGaAsP optical waveguide layer 4 are formed on the diffraction grating surface.
The current confinement layer 7 is epitaxially grown in sequence, and a resistive and anti-etching film having striped windows is formed thereon, and etched until the cladding layer 6 is reached (see FIG. 2).
Q).

Then, a p-InP 2-rad layer is epitaxially grown again to form a structure in which the current confinement layer 7 is buried in the cladding layer.

Finally, after lapping both sides of the element, metal electrodes are deposited and diffused to complete the Rade element. In the above embodiment, the region in which light is mainly confined is composed of two layers: an active layer and an optical waveguide layer, and a diffraction grating surface is formed on one side of the optical waveguide layer. The structure of the region is arbitrary. For example, the region may have a structure in which an intermediate layer is provided between the active layer and the optical waveguide layer, and a diffraction grating surface is formed on one side of the intermediate layer.

In addition, P-type compound semiconductor substrates, short wavelength GaAs/G
It goes without saying that the present invention can also be implemented with an aA/As-based substrate.

〔Effect of the invention〕

As described above in detail, the present invention has a structure in which a current confinement layer having a striped window is embedded in a cladding layer epitaxially formed on a region where light is mainly confined. Gain waveguiding is performed by the current confinement layer, and radar light is emitted in correspondence to the striped window.

Therefore, unlike a buried structure, it does not have a complicated structure and there is no difficulty in controlling manufacturing conditions, so it is possible to easily realize stable fundamental transverse mode oscillation with good reproducibility, and a distribution distribution with excellent yield. This has the effect of making it possible to manufacture a feedback type semiconductor radar.

[Brief explanation of the drawing]

FIG. 1 is an overall perspective view showing an embodiment of the present invention, FIG. 2 is a perspective view showing one manufacturing process of the present invention, and FIG. 3 is a conventional embedded structure. A cross-sectional view when viewed from the light emitting surface.In the figure, 2...semiconductor substrate, 3...diffraction grating surface, 4...
... optical waveguide layer, 5 ... active layer, 6 ... cladding layer, 7 ... current confinement layer.

Claims (1)

[Claims] 1. It has a cladding layer formed on a region where light is mainly confined, which is composed of at least an active layer and an optical waveguide layer, and a current confinement layer having a striped window embedded in the cladding layer. Distributed feedback semiconductor laser featuring: