JPS60133780A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To improve the reproducibility of element characteristics by improving the phase interference of active layers by a method wherein the gaps of the buried active layers arranged in a lateral direction are filled with semiconductor layers having a larger refractive index than clad layers sandwitching the top and bottom of the active layers. CONSTITUTION:An N-InP buffer layer 2, the active layers 3, and the P-InP clad layers 4 are laminated on an N-InP substrate 1. Next, mesa stripes 5, etching grooves 6 and 7, and current block layers 8 and 9 are formed by etching a wafer of such a double hetero structure. Then, except the upper surfaces of the layers 5, a P-InP buries layer 10 and an electrode layer 11 are laminated. Excellent phase synchronization can be obtained by forming the layer 8 of a semiconductor having a refractive index larger than InP.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a buried heterostructure phase-locked semiconductor laser capable of high-output operation, and in particular, to a buried heterostructure phase-locked semiconductor laser which is capable of high output operation. By embedding the active layer with a semiconductor layer with a high refractive index, the phase interference between the individual active layers improves, thereby improving the reproducibility of device characteristics.

The present invention relates to a phase-locked buried structure semiconductor laser with significantly improved manufacturing yield.

Recently, interest in phase-locked semiconductor lasers has rapidly increased. This operates by phase-coupling spatially independent coherent light sources using external resonators, optical overlap, introduction of coupling stripes, etc. Since coherent light sources that are originally independent in the lateral direction are phase-synchronized, it is possible to emit an extremely large optical output compared to ordinary semiconductor lasers, and at the same time, when operating with a 00 phase displacement, the beam oscillates at a very narrow beam radiation angle, making it possible to focus light. It is easy to use and is expected to be used not only in the field of optical information processing but also as a light source for long-distance optical communications. As an example of such a phase-locked semiconductor laser, T. R. Chen et al.
ed Physics Lettsrs) Pragmatics Volume 43, No. 2.

From pages 136 to 137, a phase-locked InGaAsP/InP semiconductor laser using diffraction coupling is reported. This semiconductor laser has an n-InP buffer layer, an InGaAsP active layer, and a p-InP substrate on an n-InP substrate.
After sequentially stacking the InP cladding layer and the p+-InP electrode layer, etching is performed up to the P-InP layer, and by taking advantage of the high electrode resistance at that part, a width of 3 μm1 is formed.
The central part of the element (length 100 μm) has a striped laser of 2 μm in width, and the output region (length 50 μm) where individual laser beams diffract each other and cause light wave mixing.
Chen et al. developed a phase-locked semiconductor laser with such a structure, and the element length was 2.
Laser array of 50 μm, 50 μm width, and 10 lasers has an oscillation threshold current of 200 at room temperature pulses.
mA, lateral beam radiation angle 3°, maximum pulse power 210
A characteristic of mW was obtained. However, in Chen et al.'s phase-locked laser, the active layer has a flat and spread structure, so there is a large carrier leakage in the active layer in the lateral direction, and the launch threshold current is -1 It doesn't work, and it's not efficient. Therefore, there was a drawback that a relatively large light output could not be obtained. Moreover, the output area is basically 5 in width.
Since it is a laser with a 0μm stripe electrode structure,
The phase conditions in the output region and the phase conditions in the medium heat region consisting of 10 laser arrays were affected by the device length, film thickness parameters, etc., resulting in poor reproducibility of device characteristics and poor manufacturing yield.

In order to eliminate the above-mentioned drawbacks, it is possible to construct a phase-locked semiconductor laser array composed of buried structure lasers (BH-LDs) with less carrier leakage and effective current confinement. Good phase synchronization cannot be obtained unless the spacing between the active layers of the LD is made sufficiently narrow.

SUMMARY OF THE INVENTION An object of the present invention is to provide a phase-locked BH-LD array that eliminates the drawbacks of the conventional example, can obtain a large output, and has significantly improved reproducibility of device characteristics and manufacturing yield.

The structure of the semiconductor laser according to the present invention includes a plurality of buried heterostructures on a semiconductor substrate surrounding an active layer covered with a semiconductor layer having a large energy gap and a small refractive index compared to the active layer. The semiconductor device is characterized in that a semiconductor layer having a higher refractive index than the semiconductor layers sandwiching the active layer above and below is formed between the active layers that meet each other. As described above, the present invention has the advantage that good phase synchronization can be obtained without reducing the active layer spacing because the refractive index difference between the active layer and the buried layer is small.

The present invention will be explained in detail below using drawings showing embodiments.

The figure shows a perspective view of a phase-locked BH-LD array that is an embodiment of the present invention. To obtain such a device, first, an n-InP buffer layer 2 is formed to a thickness of 5 μm on an n-InP substrate 1 having a (100) plane orientation.

Non-doped In (1,71G) with an emission wavelength of 1.3μm
ao, BA%61PO180 active layer 3 with a thickness of 015 μm
, pInP cladding layers 4 are sequentially stacked to a thickness of 1 μm. In such a double heterostructure (DH) semiconductor wafer, the etching groove 6 in the middle of the etching stripe 5 has a width of 3.
μm.

Etched grooves 7 on both sides of the 9 phase synchronized array with a depth of 3 μm
The width is 10 μm to prevent light from seeping out to the outside of the phase-locked BH-LD array and suffering absorption loss there. Each mesa stripe 5 had a width of 1.5 μm in the active layer 30 portion. For simplicity, a phase-locked laser composed of five BH-LDs is shown here, but the number can be further increased in order to achieve high output. Even in this case, a sufficiently good device can be obtained by slightly selecting the epitaxial growth conditions in the buried growth step after etching. In the second LPE growth on the DH wafer subjected to mesa etching as described above, p-In196"0.04A80.10PO with a composition close to InP corresponding to an emission wavelength of approximately 0.97 μm was grown.
, 90 current blocking layer 8. n-InP current current plug 2
The two layers 9 are also shifted except for only the top surface of the mesa stripe 5, and the p-InP buried layer 101 has p"0.78Ga0.22"0.48P0.5 corresponding to the emission wavelength of 1.2 μm.
Two electrode layers 11 are laminated over the entire surface. P”0.
96"0.04"Q, 10PO, 9G current blocking layer 8
Both the n-InP current layer and the n-InP current layer are grown by a two-phase solution method in which small InP crystal pieces are suspended in the growth melt, and conditions such as growth temperature are appropriately set to prevent growth on the top surface of the mesa. This allowed crystal growth to be performed with good reproducibility. A p-type ohmic electrode 12. An n-type ohmic electrode 13 is formed and a desired phase-locked BH-
An LD array was obtained.

Such a phase synchronized BI (BH in -LD array)
The device has 8 active layers and a cavity length of 250 μm, and the temperature at room temperature C
Oscillation threshold current at W 150mA, differential quantum efficiency 50
-60%, a device with a maximum CW output of about 300 mW at room temperature was obtained with good reproducibility. InP on the top and bottom of the buried active layer
clad with p-”0.96”O,04AI on the left and right
By embedding with a semiconductor layer of I0.10PO,90, which has a slightly higher refractive index than InP, the active layer width can be reduced to 1.5
μm, even if the distance between the active layers is 311 m, the mutual phase coupling is sufficiently good, and 00 phase shift operation can be obtained with a high yield, and the beam expansion of the emission far-field pattern at that time is υ The angle was a single lobe of 4° to 5° full width at half maximum.

In the embodiment of the present invention, in order to increase the effectiveness of current confinement and to arrange a plurality of LDs in the lateral direction and to reduce the difference in refractive index in the lateral direction, the upper and lower portions of the buried active layer are
Cladding with P layer, and at the same time P layer with composition close to InP on the side.
Clad with "0.96" 0.04A80.10PO,90 current blocking layer 8. As a result, good phase synchronization was obtained, and a phase-synchronized BH-LD array with significantly improved characteristic reproducibility and manufacturing yield compared to the conventional example was obtained.

In the examples of the present invention, elements having five to eight light emitting active layers are shown, but of course the number is 20.
It doesn't matter if it is larger than one piece. As for the buried structure, in the embodiment, a structure in which etched grooves are sandwiched between both sides of a mesa stripe is shown, but of course the structure is not limited to this, and any structure in which an active layer is formed buried inside the groove is acceptable. . The semiconductor material used is a material with a wavelength band of 1 μm using InP as a substrate and InGaAgP as an active layer, but is not limited to this.
tAs/GaAs, InGaAaP/Ga
There is no problem in using other semi-credible materials such as AsP.

Furthermore, in addition to the simple Fapre-Perot type B H-LD, it is also possible to use a DFB/DBR-LD or the like.

The feature of the present invention is that in a phase-locked semiconductor laser array in which a plurality of active layers oscillate in phase synchronization, a BH-LD is adopted for each laser, and at the same time, the side of the buried active layer is
This is done by using a semiconductor material with a higher refractive index than the cladding layers sandwiching the top and bottom. As a result, good phase synchronization is obtained, and not only excellent characteristics such as low oscillation threshold current, high differential quantum efficiency, and high power CW operation are obtained, but also the reproducibility of characteristics and manufacturing yield are significantly improved compared to conventional examples. An improved phase-locked BH-LD array was obtained.

[Brief explanation of drawings]

The figure is a perspective view of a phase-locked BH-LD which is an embodiment of the present invention. In the figure, 1 is an n-InP substrate, 2 is an n-I
nP buffer layer, 3 is If'+1.71 Gm6.2B
Aso, t3@Po, 3g active layer, 4 is p-InP cladding layer, 5 is mesa stripe, 6 and 7 are etching grooves, 8 is p-InO, 96Ga 6,64 As 646
P 0,90 current blocking layer, 9 is n-InP current blocking layer, 10 is p-1nP buried layer, 11 is p
-1n6. qB Gao, 2. , A-so, 4BP6
．． 52 electrode layers, 12 a p-type ohmic electrode and 13 an n-type ohmic electrode.

Claims (1)

[Claims] A semiconductor substrate is provided with a plurality of buried heterostructures in which the periphery of an active layer is covered with a semiconductor layer having a larger energy gap and a smaller refractive index than the active layer; A semiconductor laser characterized in that a semiconductor layer having a higher refractive index than the semiconductor layers sandwiching the active layer above and below is formed between the active layer and the active layer.