JPS63255985A - Distributed reflection semiconductor laser element - Google Patents

Abstract

PURPOSE:To contrive the improvement of the coupling efficiency of an active region and an optical waveguide layer by a method wherein an impurity-doped region obtainable by doping a specified impurity to part of an active layer formed in the same growth process is used as the active region and the residual part of the active layer is used as the optical waveguide layer. CONSTITUTION:An active region 32 and an optical waveguide layer 34 are formed of the same grown layer (active layer) 26 formed in the same growth process. The region 31 is constituted of an impurity-doped region obtainable by doping an impurity to part of this layer 26 and the layer 34 is constituted of the impurity-undoped residual part of the layer 26. The impurity to be doped to the layer 26 for forming the region 32 shall be an impurity which is not absorbed in the layer 34 by doping this impurity or such an impurity that the light of a small-absorption wavelength is made to luminescence from the region 32. Accordingly, a scattering loss to generate when the emitted light is incided in the layer 34 from the region 32 and a scattering loss to generate when the feedback light is incided in the active region from the layer 34 are reduced. Thereby, the coupling efficiency of the region 32 and the layer 34 is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to the structure of a distributed reflection semiconductor laser device operating in a single longitudinal mode.

(Prior art) Conventionally, distributed reflection semiconductor laser devices (DBR lasers) have been developed that can stably oscillate in a single longitudinal mode even when high-speed modulation or temperature changes occur.
butted Bragg Reflector La5
er) has been proposed, and its research and development are being actively conducted. This DBR laser uses a buried structure (BuriedHetero) to unify the transverse mode.
structure) is often adopted.

Fabry-Perot resonator (Fabry-Perot resonator), which has the most typical configuration as a semiconductor laser.
r) type semiconductor laser device (hereinafter referred to as FP laser)
The DBR laser is equipped with a Fapley-Perot resonator consisting of a beam cut plane.
A distributed Bragg reflector (D B
R: Digtributed Bragg Refle
The purpose is to realize longitudinal mode oscillation by utilizing the wavelength dependence of the reflectance of this DBH.

In FP lasers, laser oscillation is performed at the wavelength where the gain is maximum, whereas in DBR lasers, the DBH
Since only light having the Bragg wavelength determined by the lattice spacing and the wavelength near the Bragg wavelength resonates and laser oscillation is performed, there is an advantage that the oscillation wavelength can be easily controlled. Furthermore, since the DBR laser does not necessarily require an open surface, it is suitable for use as an integrated laser, and is suitable for integration into an optical integrated circuit, for example, as a light source for an optical integrated circuit.

Below, with reference to the drawings, a conventional DBR laser (Reference: Suematsu ed. "Semiconductor Laser and Optical Integrated Circuit" (1984) pp3
41 to 389) will be explained.

FIG. 3 is a sectional view of a main part showing the basic configuration of a conventional direct coupling type DBR laser, and this figure shows a cross section taken along the laser beam emission direction.

In the figure, 10 is an F side rad layer, 12 is an active region, and 14 is an upper cladding layer. are formed sequentially. Here, the laser component region where the DBR is formed between the active region 12 and the end face of the DBR laser is referred to as a DBR region.

16 is an optical waveguide layer for extracting the optical output of the DBR region;
8 is a light guide layer, 20 is a DBR, and the light guide layer 16
is directly coupled to the laser light emitting surface of the active region 12,
The optical waveguide layer 18 and the DBR 20 are formed on the lower cladding layer 10 of the DBR region, and the optical waveguide layer 18 and the DBR 20 are sequentially formed on the optical waveguide layer 16.

In creating the main parts of this conventional DBR laser,
Although not shown, an active layer and an upper cladding layer are sequentially grown on the lower cladding layer 10, and then the active layer and upper cladding layer in the DBR region are removed by etching. As a result, a mesa-shaped active region 12 formed by etching away the active layer and a mesa-shaped upper cladding layer 14 formed by etching and removing the upper cladding layer are obtained.

Thereafter, the optical waveguide layer 16 and the optical guide layer 18 are sequentially laminated on the lower cladding layer 10 of the DBR region, and the DBR 20 is formed on the rear optical guide layer 18.

In this DBR laser, in order to obtain good wavelength selectivity of the DBR 20, the optical waveguide layer 16 is formed from a layer having a composition such that the forbidden bandwidth is larger than that of the active region 12. The aim was to reduce loss, especially absorption loss.

(Problems to be Solved by the Invention) However, in the conventional DBR laser described above, the active region and the optical waveguide layer, which are formed in different growth processes, are directly coupled, and therefore the active region and the optical waveguide layer are An interface is formed by the bonding of . Therefore, the loss of emitted light that enters the optical waveguide layer from the active region and the reflected light that is diffracted by the DBR and returned to the active region is large at this interface, especially scattering loss, and therefore the coupling efficiency between the active region and the optical waveguide layer is reduced. It was bad. Furthermore, since the active region and the optical waveguide layer are directly coupled, it is difficult to improve the coupling efficiency.

The purpose of this invention is to solve the above-mentioned conventional problems, and to develop a DBR that can increase the coupling efficiency between the active region and the optical waveguide layer more easily than before, and thus improve the oscillation characteristics.
The goal is to provide lasers.

(Means for Solving the Problems) In order to achieve this object, a distributed reflection type semiconductor laser device (DBR laser) of the present invention includes an active region and an optical waveguide layer for extracting optical output from the DBR region. In a distributed reflection type semiconductor laser device, an impurity doped region in which impurities are added to a part of the active layer formed in the same growth process is used as an active region, the remainder of the active layer is used as an optical waveguide layer, and an impurity is further added to the impurity. It has a structure in which the impurity is added so that the active region emits light having a wavelength that is not absorbed in the optical waveguide layer or is absorbed to a small extent.

(Function) According to the DBR laser having such a configuration, the active region and
Since the optical waveguide layer for extracting light output and the optical waveguide layer are formed from the same growth layer (active layer) formed in the same growth process, it is possible to improve the coupling efficiency between the active region and the optical waveguide layer.

In addition, the impurity added to the active layer to form the active region is an impurity that causes the active region to emit light with a wavelength that is not absorbed by the optical waveguide layer or has a small absorption. The absorption loss in the optical waveguide layer of the wavelength of the emitted light (oscillation wavelength) and the feedback light reflected by the DBR and returned to the active region among the emitted light can be reduced to almost O) or reduced.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the embodiments described below, a DBR laser having the most basic configuration to which the present invention is applied will be described.

FIG. 1 is a cross-sectional view schematically showing the structure of an embodiment of the present invention, and shows a cross section taken along the direction in which light emitted from the active region is emitted.

In the same figure, 22 is a substrate, 24, 26, 28 and 30
22J shows a lower cladding layer, an active layer, a light guide layer, and a north cladding layer that are sequentially formed on this substrate 22J, where each layer has a refractive index of 1 layer 24 > a refractive index of layer 26 and a layer 28 The refractive index of the layer 30 is smaller than the refractive index of the layer 30.

In this embodiment, the substrate 22 is an InP substrate, the lower cladding layer 24 is an n-1nP layer, and the active layer 26 is an InP substrate.
GaAsP layer, p-1nGaAs as optical guide layer 28
A p-1nP layer is formed as the P layer and the north cladding layer 30.

In addition to the p-1nGaAsP layer, for example, a p-InP layer or an InGaAsP layer may be provided as the optical guide layer 28.

Further, 32 indicates an active region and 34 indicates an optical waveguide layer for extracting optical output from the DBR region, and these active region 32 and optical waveguide layer 34 are formed from the same growth layer (active layer) 2B formed in the same growth process. do. An impurity doped region in which impurities are added to a part of the active layer 2B constitutes an active region 32, and the remaining part of the active layer 2B to which impurities are not added constitutes an optical waveguide layer 34.
Configure. The impurity added to the active layer 26 to form the active region 32 is added to the optical waveguide layer 3 due to the addition of this impurity.
The impurity is used to cause the active region 32 to emit light of a wavelength that is not absorbed by the active region 32 or has a small absorption.

38 indicates an impurity doped region, in this example, DBR
An impurity-doped region 3B is formed by diffusing zinc (Zn) from the northern cladding layer 30 to the active layer 2B except for the region. By forming this impurity doped region 3B, an active region 32 is formed from the active layer 26 in which Zn is diffused. Here, the laser component region where the DBR 40 is formed (or will be formed) between the active region 32 and the end face of the DBR laser is referred to as a DBR region. Therefore, in this example, the substrate 22, layers 24.2B, 2B and 30 in the region between the x1 and x2 lines shown in the figure,
Substrate 22, layer 24.28 in the area between the Yl line and the Y2 line
．． 28 and 30 are DBR areas.

Reference numeral 38 indicates a current injection region, and in this embodiment, the current injection region 38 is formed from the north cladding layer 30 and the optical guide layer 28 of the region in which Zn is diffused by forming the impurity doped region 3B.

Further, 40 indicates a distributed Bragg reflector (DBR),
In this embodiment, the DBR 40 is formed at the interface between the L-side rat layer 30 and the light guide layer 28 in the DBR region, and is formed on both sides of the active region 32 .

The DBR 40 is formed so that the Bragg wavelength matches the oscillation wavelength, so that the wavelength of the feedback light reflected by the DBR 40 and returned to the active region 32 matches the wavelength of the emitted light (oscillation wavelength).

In the DBR laser of this embodiment configured as described above, carriers are injected into the active region 32 through the current injection region 38, and as a result, the emitted light emitted from the active region 32 is guided through the optical waveguide layer 34. Of the zero emitted light that is waved and output to the next stage optical circuit element, the light from the optical waveguide layer 34 to the optical power layer 28
The light that leaks into the active region 32 is reflected by the DBR 40 and
to return to. In the active region 32, the returned light causes stimulated emission, thereby realizing longitudinal single mode oscillation.

Next, in order to deepen the understanding of this invention, Figures 1 and 2 (
The first stage of manufacturing of this example will be explained with reference to A) to (C).

First, as shown in FIG. 2(A), the substrate 22 is made of In.
For example, liquid phase epitaxial growth (LPE) is performed using a P substrate.
) method or metal organic chemical vapor deposition (MOCVD) method,
A lower layer of n-InP 24 is sequentially formed on the substrate 22.
An InGaAsP active layer 26 and a p-InGaAsP optical guide layer 28 are grown in layers.

Next, as shown in FIG. 2(B), the optical waveguide layer 28 in the DBR region is patterned by, for example, a laser interference exposure method, and then chemically etched to form the DBR 20.
form.

In order to replace the vertical moat, DBR40 is
It is designed and formed so that the Bragg wavelength of the laser beam matches the oscillation wavelength, that is, the wavelengths of the emitted light and the feedback light match.

Next, as shown in FIG. 2(C), the above-mentioned layers 24, 26
．． Similarly to step 28, a p-1nPt side cladding layer 30 is laminated and grown on the optical guide layer 28h by, for example, the LPE method or the MOCVD method.

Next, as shown in FIG. 1, an impurity is added by diffusing Zn, for example, from the north cladding layer 30 in the region excluding the DBR region to the active layer 26 to form an impurity-doped region 36. An optical waveguide layer 34 and an active region 32 are formed from the grown layer (active layer) 26, and a current injection region 38 is formed in the upper cladding layer 30 and the optical guide layer 28.

The impurity is added so that the oscillation wavelength is longer than the bandgap wavelength of the optical waveguide layer.

Therefore, since the DBR 40 is formed so that the wavelengths of the emitted light and the feedback light match as described above, the wavelengths of the emitted light and the feedback light are longer than the bandgap wavelength of the optical waveguide layer 34.

According to the DBR laser of the present invention configured as described above, since the active region 32 and the optical waveguide layer 34 are configured from the same growth layer (active layer) 32, emitted light is transmitted from the active region 32 to the optical waveguide layer 34. The scattering loss when the feedback light enters the active region from the optical waveguide layer 34 is reduced, and the coupling efficiency between the active region 32 and the optical waveguide layer 34 can be improved compared to the conventional method. .

At the same time, since the wavelengths of the emitted light and the feedback light are longer than the bandgap wavelength of the optical waveguide layer 34, it is necessary to reduce or reduce the absorption loss of the emitted light and the feedback light in the optical waveguide layer 34. I can do it.

As a result, the oscillation characteristics can be improved compared to conventional DBR lasers, and in particular, the oscillation current can be reduced.

(Modification) FIG. 3 is a sectional view similar to FIG. 1 showing the structure of a modification of the above-described embodiment. Components that are the same as those shown in FIG. 1 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

In FIG. 3, 42 is a light guide layer made of, for example, n-InGa.
The AsP layer is shown.

As shown in FIG. 3, in this modification, the F-side rad layer 24, the optical guide layer 42, and the active layer 26 are sequentially formed on the substrate 22H.
and an upper cladding layer 30, and further a DBR 40 is provided at the interface between the north cladding layer 24 and the light guide layer 28 in the DBR region.

Furthermore, in this modification, the impurity doped region 36 is formed from the L-side clad layer 30 in the region excluding the DBR region to the active layer 26, and therefore the current injection region 38 is formed in the -L-side clad layer 30. The structure is as follows.

Even with this modified example configured in this way, the same effects as in the above-mentioned embodiment can be expected.

The present invention is not limited to the above-described embodiments, and therefore, the forming force/method of each component, forming material, conductivity type, and other design conditions can be arbitrarily and suitably set according to the design.

For example, the material for forming each component is not limited to the above-mentioned embodiments, and any suitable semiconductor material such as InP/InGaAsP semiconductor material, GaAs/AlGaAs semiconductor material, etc. can be used.

Further, Zn, silicon (Si), or the like may be used as the impurity, and diffusion, ion implantation, or other methods for adding the impurity may be used. Further, it is sufficient that the impurity is added to at least the active layer in the region where the active region is to be formed, and therefore, the region to which the impurity is added can be changed as desired. The impurity added to form the active region can be made of any material, method, and method as long as the addition of this impurity eliminates or reduces the absorption of the optical waveguide layer for the oscillation wavelength of light emitted from the active region. It may be added in an additional amount.

In addition, with current technology, DBR is applied to the very thin active layer.
However, if such technical problems are solved in the future, problems such as separation of the active layer will occur, making it extremely difficult to provide a DBR in the active layer itself. A DBR may be provided in itself.

Furthermore, in the embodiment described above, the optical waveguide layer and the DBR are formed on both sides of the active region, but the optical waveguide layer may be provided only on one side of the active region, and/or the DBR is formed only on one side of the active region. It may also be provided.

The manufacturing process can be changed arbitrarily and suitably according to changes in the design. For example, the current injection region and the active region may be formed continuously in the same process, or the current injection region and the active region may be formed separately. They may be formed in different steps.

(Effects of the Invention) As is clear from the above description, according to the distributed reflection semiconductor laser device of the present invention, when emitted light enters the optical waveguide layer from the active region, and when the feedback light enters the optical waveguide layer, By reducing the scattering loss when the light enters the active region, the coupling efficiency between the active region and the optical waveguide layer can be improved more than before.

At the same time, absorption loss of emitted light and feedback light in the optical waveguide layer can be eliminated or eliminated.

For this reason, it is possible to provide a distributed reflection type semiconductor laser that has superior oscillation characteristics than conventional ones, and in particular can reduce the oscillation dark value current.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of an embodiment of the distributed reflection type semiconductor laser device of the present invention, FIG. 2 is a process diagram showing the manufacturing process steps of the embodiment shown in FIG. 1, and FIG. FIG. 3 is a cross-sectional view showing a configuration of a modification of the embodiment shown in the figure. FIG. 4 is a sectional view of a main part showing the structure of a conventional distributed reflection type semiconductor laser device. 22... Substrate, 24.30... Clad layer 26... Active layer, 28.42... Optical guide layer 32... Active region, 34... Optical waveguide layer 3
6...Impurity doped region, 38...Current-human region 4
0...Distributed Bragg reflector (DBR). Patent Applicant: Oki Denki Gyokugyo Co., Ltd. 224 Nuclear 34 Kyushu Kuzu 211, 30 Kura Shitoko, yg7r
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Claims (1)

[Claims] (1) In a distributed reflection semiconductor laser device comprising an active region and an optical waveguide layer for extracting optical output from a DBR region, an impurity-doped region in which an impurity is added to a part of the active layer formed in the same growth process as described above. an active region, the remainder of the active layer is the optical waveguide layer, and the impurity is an impurity that causes the active region to emit light at a wavelength that is not absorbed or is absorbed in the optical waveguide layer by adding the impurity. What is claimed is: 1. A distributed reflection type semiconductor laser device characterized by comprising: