JPS62166583A - Distributed feedback semiconductor laser device - Google Patents

Abstract

PURPOSE:To readily manufacture, to strongly couple and to sufficiently oscillate a distributed feedback semiconductor laser device by providing an active layer and a guide layer, a substance layer distributed to present periodically in the guide layer and a clad layer. CONSTITUTION:An N-type Al0.3Ga0.7As layer 2 for forming a first clad layer, a GaAs layer 3 for forming an active layer, a P-type Al0.15Ga0.85As layer 4 for forming a guide layer and a P-type Al0.3Ga0.7As layer 5 are sequentially epitaxially grown on an N-type GaAs substrate 1. Then, the layers 5, 4 are selectively etched until the layer 4 is partly exposed and becomes in thickness the same as that of the layer 5 to form a triangular uneven surface 6. Then, a P-type Al0.15Ga0.85As layer 7 is epitaxially grown in thickness corresponding to approx. 1/2 of the depth of the surface 6, and a P-type Al0.3Ga0.7As layer 8 for forming a second clad layer is eventually epitaxially grown on the layer 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a distributed feedback semiconductor laser in which feedback occurs through a periodic structure and laser oscillation is performed.

[Summary of the invention]

The present invention provides a distributed feedback semiconductor laser as described above, in which a predetermined material layer that appears periodically along the active layer is disposed in the guide layer, and a part of the cladding layer is arranged at a period of the predetermined material layer. By correspondingly interposing the material between the predetermined material layers, it is possible to easily manufacture the material, yet to have a strong coupling with light and to perform sufficient oscillation.

[Conventional technology]

distributed feedback type
k) Semiconductor laser (hereinafter referred to as DFB laser) is a single-
It is expected to be a laser that can achieve longitudinal mode oscillation.

In this DFB laser, a first-order or second-order diffraction grating in which unevenness is uniformly formed has been conventionally used as a diffraction grating for returning light in a distributed manner by Bragg reflection.

[Problem that the invention seeks to solve]

Among these, the first-order diffraction grating has a strong coupling with light, so effective distributed feedback can be obtained, but since the pitch of the diffraction grating is small, it is difficult to fabricate it easily and with good reproducibility. is difficult.

In addition, the second-order diffraction grating shown in Figure 2 has only one coupling with light.
The absolute amount is smaller than that of the second order diffraction grating.

For this reason, it is difficult to obtain stable and sufficiently strong oscillation with a DFB laser using such a second-order diffraction grating.

[Means for solving problems]

The distributed feedback semiconductor laser according to the present invention includes an active layer, this active layer 3, and a guide layer 4 that is in contact with this active layer 3.
．． 7, and a material layer having a lower refractive index than this guide layer 4.7, which is arranged in this guide layer 4.7 so as to appear periodically along the active layer 3 in this guide layer 4.7. 5a, facing the guide layer 4.7 and the material layer 5a.
A cladding layer 8 is provided, a portion of which is interposed between the material layers 5a, corresponding to the period of .

[Effect]

The distributed feedback semiconductor laser according to the present invention has a guide N4.
A material layer 5a having a refractive index lower than 7 appears periodically along the active layer 3, and a part of the cladding layer 8 forms the material layer 5a.
Since it is interposed between the material layers 5a corresponding to the period of , a periodic structure having a period that is effectively half the period of the material layer 5a is formed.

〔Example〕

Hereinafter, an embodiment of the present invention applied to a DFB laser having an AlGaAs/GaAs heterostructure will be described with reference to FIG.

In order to manufacture the semiconductor laser of this example, the first A
As shown in the figure, first, an nAlo, 3 Gaa, As layer 2, which constitutes a first cladding layer, is formed on an n-GaAs substrate 1.
GaAs layer 3 constituting the active layer, p constituting the guide layer
-8 lo, +5 Gao, asAs layer 4 and p A
10.3 Gao,.

The As layer 5 is epitaxially grown in sequence by MBE or MOCVD. Note that p-AI. ,3Ga
,,7 The thickness of the As layer 5 is approximately half the height of the unevenness 6, which will be described later.

Next, p
Alo, +5Gao, esAS layer 4 is partially exposed and further p-AI. ,, Ga, , p-A1. until the depth becomes approximately the same as the thickness of the As layer 5. ,, Gao,t
As layer 5 and p-AI. , +5Gao, esAs
Selectively etch layer 4.

Then, as shown in Figure 1B, p -AIo, 3 Ga
o, tAs layer 5 and p AIo, +5Gao, os8S
Triangular wave-like unevenness 6 is formed with the center line at the interface with layer 4.

Note that the second-order diffraction lattice as shown in Figure 2 is based on the anisotropy (crystal plane dependence) that the semiconductor substrate and the etching solution have.
Therefore, if the exposure intensity distribution is to a certain extent, it can be produced in a self-aligned manner with good reproducibility.

Next, as shown in Fig. 1C, p-810.1sGao,
858SN7 is epitaxially grown to a thickness that is approximately half the depth of the unevenness 6 to cover the unevenness 6. At this time,
By using the MBE method or the MOCVD method, the pAlo, +5Gao, and asAs layers 7 can be epitaxially grown while preserving the shape of the unevenness 6.

Then, pAlo, +5Gao, esAS layers 4 and 7 become new guide layers 4.7, and 1o, 3Gao, 7As layer 5 is added to p-, which has a triangular cross section left during the etching described above.
a are arranged in this new guide layer 4.7 in such a way that they appear periodically along the GaAs layer 3 in the new guide layer 4.7.

Finally, as shown in FIG.
. , 3Ga, , As layer 8 is epitaxially grown.

Then, since the shape of the unevenness 6 is preserved in the pAlo, +5Gao, and BsAS layers 7, it is p-AI. ,3Gao
, 7 A part of the As layer 8 is p-^IQ, 3 Gao, t corresponding to the period of the pAlo, 3 Gao, 7 As layer 5a.
It is interposed between the As layers 5a.

In the DFB laser of this embodiment as described above, although the same method as that of the second-order diffraction grating shown in FIG. 2 is used, as is clear from FIG. 1C, the effective A periodic structure having a period half the period of the first-order diffraction grating, that is, the period of the second-order diffraction grating, is formed.

The height of the triangular wave-like unevenness 6 is p-^10.3 Gao, A
The thickness of the ss layer 5 can be controlled by the thickness of the ss layer 5, but the manufacturing method of the above embodiment is based on the MBE method or the MO method, which allows precise control of the film thickness.
Since the CVD method is used, the controllability of the periodic structure is good. Therefore, the DFB laser of the above embodiment has good shape uniformity and reproducibility.

In addition, in the above-mentioned embodiment, pA constituting the guide layer
lo, +5 Gao, p -AIo, 3 on asAS layer 4
Gao,.

Although the ^S layer 5 was formed, another material layer could be used in place of this pAIo, 3 Gao, t Ass layer 5 if it was made of a material that could form the triangular wave-like unevenness 6 as shown in FIG. 1B by etching. For example, AlGaAs layers having different At compositions may be used.

Moreover, the above-mentioned embodiments also demonstrate the present invention in AlGaAs/Ga
Although the present invention is applied to a DFB laser having an As heterostructure, the present invention can also be applied to DFB lasers having other structures.

〔Effect of the invention〕

In the distributed feedback semiconductor laser according to the present invention, a periodic structure having a period that is effectively half the period of the material layer is formed, so although it is easy to manufacture, the coupling with light is strong and sufficient oscillation is achieved. can be done.

[Brief explanation of drawings]

FIGS. 1A to 1C are cross-sectional views showing step by step a method for manufacturing a DFB laser according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of a second-order diffraction grating. In addition, in the symbols used in the drawings,
Layer 4, 7-------・-p Alo, +5
Gao, 15As layer 5a, 8-=-p Al
o, 3 Gao, TAS layer.

Claims (1)

[Claims] An active layer, a guide layer in contact with the active layer, and a guide layer arranged in the guide layer so as to appear periodically along the active layer in the guide layer. A distributed feedback semiconductor comprising: a material layer having a refractive index lower than that of the material layer; and a cladding layer that is in contact with the guide layer and that is partially interposed between the material layers in a manner corresponding to the period of the material layer. laser.