JPH02263491A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To manufacture a semiconductor laser for dynamic-single-longitudinal mode oscillations having optical wave guides of low loss which are suitable for integration by providing two channels of optical waveguide layers which are combined optically by diffraction gratings and performing current injection from a transverse direction to an active layer. CONSTITUTION:At least the 1st and 2nd optical waveguides 2 and 5 which are used for emitting light and for combining optically with an active layer 4 respectively are provided and both of them are combined optically by diffraction gratings 21 and 22 in which their degree are high, i.e., more than second order. In a dynamic-single-longitudinal mode oscillation laser that is manufactured in this way, carriers are injected horizontally from a transverse direction to the active layer 4 and then the carriers combine each other again in an active waveguide to emit light. Distributed feedback of light emitted is performed by the diffraction gratings of the 2nd optical waveguides 5 and its light combines optically with the 1st optical waveguide 2. Then it is induced and emitted in an active region by being reflected in the form of distribution. The waveguides of oscillating light become uniform and even when amplitude modulation takes place, they may oscillate at a stable, dynamic-single-mode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser device that oscillates in a dynamic single longitudinal mode and is suitable for integration, useful for optical communication, optical applied measurement, etc.

[Background Art] In technical fields such as optical communication, optical recording, and optical measurement, there is a need for a small and lightweight semiconductor laser device that is capable of high-speed modulation. Semiconductor lasers used for this type of application include distributed feedback semiconductor lasers (DFB-1,0), which stably excavate a single longitudinal mode even during high-speed modulation, and distributed Bragg reflection semiconductor lasers (DBR-LDl, etc.). It is seen as a promising light source for long-distance, large-capacity optical fiber communications.

On the other hand, similar to the field of electronics, in the field of optoelectronics, research has begun on integration in order to achieve small size, light weight, high functionality, and high speed. Advanced integration such as switch waveguides is being considered. Suematsu et al. of Tokyo Institute of Technology are
Guide AlGaAs La5erWith M
ultimate structure E
EEE J, Quant.

Elecl, Vol, QE-11, No, 7. July
, Integrated Twin in 1975
-Guide (ITG) structure is proposed, which uses two optical waveguide layers that form a directional coupler in the film thickness direction, allowing for separate integration of the active region and optical waveguide region. It is a structure.

[Problem 1 to be Solved by the Invention] However, there are not many examples of structures suitable for integrating F-dynamic single mode lasers.

- 1.5-1.6 am Ga1nAsP # as an example
nPD Dynamic-5ingle-Mode (DS
M) La5ers with Distributed
BraggReflector” IEEE J,
Quantt: Iect, Vol, QE-19, No.
6. DBR with ITG type structure described in JUNE 1988
There's a laser. This is a dynamic single longitudinal mode oscillation laser structure suitable for integration, but in actual fabrication, two
It has been difficult to control the temple constant of light between two optical waveguides, and it has been difficult to manufacture a semiconductor laser with good characteristics.

[Means for Solving the Problems] The present invention provides at least a first optical waveguide layer, a first cladding layer, an active layer, a second optical waveguide layer, and a second cladding layer in this order on a semiconductor or semi-insulating substrate. grown epitaxially,
In a semiconductor laser device configured to allow current to be injected into the active layer, the first optical waveguide layer and the second optical waveguide layer have high-order or higher order light emitted from the active layer. A semiconductor characterized in that a diffraction grating is formed, the first optical waveguide layer and the second optical waveguide layer are optically coupled to each other, and the first optical waveguide layer is an optical output waveguide. It is a laser device.

In particular, the present invention is characterized in that p-wall regions and n-type regions are formed on both sides of the active waveguide, so that current injection into the active layer is carried out laterally in the active layer. The semiconductor laser device described above is characterized in that the electrode connected to the region is provided on the upper surface, that is, the surface opposite to the substrate, and further, the active layer has a superlattice structure, and the p-type impurity The semiconductor described above, characterized in that the superlattice of the impurity region is disordered by heat treatment such as impurity diffusion during the fabrication of the region and the n-type impurity region, and current and light in the active waveguide are confined. It is a laser device.

According to the present invention, a first optical waveguide used for emitting light;
By providing at least a second optical waveguide that is optically coupled to the active layer and optically coupling the two using a high-order diffraction grating north of the second order, stable oscillation is achieved in a dynamic single longitudinal mode. This makes it possible to create a semiconductor laser suitable for integration.

Current is injected into the active layer from the lateral direction horizontal to the film, so layers other than the active layer can be made high in resistance by not adding impurities, and the parasitic capacitance of the laser can be reduced. , Moreover, by reducing the number of free carriers, an optical waveguide layer and a crat layer with less light absorption loss can be realized.
It has become possible to reduce optical loss, which is the biggest problem with integrated optoelectronic devices made of compound semiconductors.

In addition, the first optical waveguide layer can be used as the main leading waveguide for integration, and can not only be formed by one film formation over the entire integrated device, but also can be used as a leading waveguide with low optical loss as described above. I was able to realize this.

Furthermore, since the active layer and the second guiding waveguide are configured to exist within the same electric field distribution of light, the reflected light that contributes to stimulated emission is reflected by the diffraction gratings of both the first guiding waveguide and the second guiding waveguide. Because the light is coupled by the laser beam, it has strong monochromaticity, making it possible to oscillate more stably than conventional dynamic single longitudinal mode oscillation lasers, and the diffraction grating of the second optical waveguide also uses distributed reflection. Because it acts as a vessel, the element length of the semiconductor laser can be shortened.

In order to inject current into the active layer, impurities are diffused on both sides of the active waveguide, but this method allows the top surface to be flat and both electrodes to be taken out from the top surface, and the metal electrodes do not face each other. It has become possible to extremely reduce the electrostatic capacitance parasitic to the laser, and electrical wiring has become easier.

When a superlattice is used in the active layer, the superstructure becomes disordered during heat treatment such as diffusion of impurities, making it easy and effective to create an index-guided laser with strong current and light confinement in the active waveguide. realizable.

[Embodiment 1] FIG. 1 shows a cross-sectional view (a) in the co-iron direction and a vertical cross-sectional view (b) in the resonance direction of a semiconductor laser that best represents the features of the present invention.

This semiconductor laser has a diffraction grating 21 consisting of periodic concavities and convexities.
A first optical waveguide layer t is formed on a semi-insulating 1nP substrate 1 formed with
-1no, 72GaO, 21SAS0.6IP0.3
92 + first cladding layer 1-InP 3, active layer P-1
no, 5gGa6.41ASo, 9OPO10 layer 4
, second optical waveguide layer 1-Ink, ? 2GaO2A embryo. 6,
5 are stacked one after another. The first optical waveguide layer 2 had a thickness of 0.15 μm, the active layer 4 had a thickness of 0.1 μm, the second optical waveguide layer 5 had a thickness of 0.1 μm, and the first cladding layer 3 had a thickness of 1 to 2 μm. Thereafter, a diffraction grating 22 having periodic irregularities is created on the second optical waveguide layer 5 by a photolithography process such as a three-beam interference exposure method or a mask exposure method, and etching, and the second cladding layer 1- Stack rnP6. The diffraction grating 21 and the diffraction grating 22 are designed to be diffraction gratings having the same Bragg wavelength of higher order than second order for the emission wavelength of 1.55 μm. It was shaped.

After the second cladding layer 6 is grown, the insulating layer 5i
A film of 027 was formed by CVD, and as shown in FIG. 1(b), an 8μ
form a stripe of m. Sj is diffused into the n-type impurity region 11 and Zn is diffused into the p-type impurity region 10, and as a result, the width of the active waveguide is about 2 μm. Then, Au is placed on the top surface of each as an n-type electrode.
Ge/Au and Au/Zn/Au were vapor-deposited and alloyed as a p-type electrode.

Finally, if necessary, it is possible to cut into the first cladding layer as shown in FIG. 1(a).

The advantage of this is that after the epitaxial growth is completed, it is possible to cut into the first cladding layer and form another light receiving element, light modulating element, etc. thereon, which facilitates integration. Moreover, if the depth of this cut is made different between the front and the front, the equipolarized refractive index changes in each region, so that the reflectance differs between the front and rear surfaces, making it easy to control the efficiency.

In the dynamic single longitudinal mode oscillation laser fabricated as described above, carriers are injected horizontally into the active layer from the lateral direction, recombine in the active waveguide, and emit light. The generated light is distributed back by the diffraction grating of the second guide waveguide 5, optically coupled to the first optical waveguide 2, reflected distributed, and stimulated to be emitted in the active region. As a result, the oscillated light has the same wavelength and oscillates in a stable dynamic single mode even during modulation, and the laser light propagates within the first optical waveguide and is emitted.

The thickness and composition of each layer are controlled so that only the fundamental mode of the waveguide modes of the first optical waveguide layer, the second optical waveguide layer, and the active layer propagates, and the Bragg wavelength of the diffraction grating on both of the optical waveguide layers is controlled. must be the same.

In addition, the layer thickness of the first cladding layer and the second cladding layer is 1 μm so that the electric field distribution of light propagating through the optical waveguide layer is independent.
It is good if it is above a certain level.

In this embodiment, the waveguide of the first optical waveguide layer-1 confines light by diffusing impurities until it reaches the first optical waveguide layer. There is no problem as long as the refractive index changes with equal polarization and there is a light confinement effect.

FIG. 2 shows a semiconductor laser device which is another embodiment of the present invention.

Similar to the first embodiment, the semi-insulating 1 on which the diffraction grating is formed
On the nP substrate 1, first optical waveguide layers 14no, 72Gao,
2FIASO6+Po, 392, first cladding layer 1
-1nP3, active layer P-1nn, s! 1cao, 4
1ASQ, 90P0. +04, second crust layer 1-
After laminating 1nP 6, the active layer except for [11] in Figure 2 was removed by selective wet etching, [I]
and the sixth-order second optical waveguide layer 1-In that creates diffraction grating irregularities on the distributed reflector of the [rV] section. , ,2G80.2FI
AS0.61PO395, 2nd cladding layer 1-1nP6
The epitaxial growth is completed by stacking the layers. Next [I],
[11], [III], active waveguide 4 by diffusing p-type impurities and n-type impurities in the region corresponding to the [rV] part.
, current is injected into the second leading waveguide 5 from the lateral direction horizontally into the film, and electrodes are deposited on each film.

Furthermore, the [I] and [rV] sections in Fig. 2 are electrically separated so that the injection currents do not interfere with each other.
[1 to [IV] portions are distributed reflection regions, [m1 portion is a phase adjustment region, and [In portion is an active region.

The light generated in the active region passes through the distributed reflector [1
and [Distributed reflection at the IVJ section, part of which is optically coupled to the first optical waveguide, distributed reflection, and oscillation in a dynamic single longitudinal mode. Also, in FIG. 2, the end of the trapezoid on the right side was cut deeper than that on the left side, but this apparently increased the reflectance on the platform side and increased the output to the left side.

In this embodiment, it is possible to change the oscillation wavelength by controlling the currents injected into the [I], [rV] and [+1] parts.

In this embodiment, the distributed reflection regions are provided at the front and rear, but they may be located at either the front or rear, and the wavelength can be varied within a certain range even without the phase adjustment region.

The impurity region can be formed by diffusion or ion implantation of Si, Sn, etc. for n-type and Zn, Be, etc. for p-type.

When a superlattice is used in the active layer in the present invention, for example,
In the case of AlGaAs/GaAs-based materials, diffusion of Si or the like into n-type and Zn or the like into p-type causes disorder in the superlattice of impurity tilting. As a result, the current and light in the active waveguide are confined, and a highly efficient semiconductor laser can be realized.In this example, the active region is made to have refractive index waveguiding properties, and as a method to facilitate current injection, the p-type , the diffusion of n-type impurities has been described, but lateral implantation may be performed using a buried structure. In that case,
P-type and n-type implants must be performed separately.

The present invention is applicable only to InGaAsP/InP based semiconductor materials.
Of course, other semiconductor materials such as AlAs may also be used.

[Effects of the Invention] As explained above, by providing two optical waveguide layers optically coupled by a diffraction grating and injecting current into the active layer from the lateral direction, a low-loss optical waveguide suitable for integration can be achieved. It has become possible to fabricate a dynamic single longitudinal mode oscillation semiconductor laser with a wave path.

[Brief explanation of drawings]

FIG. 1 shows (a) a sectional view in the resonance direction, (b) a vertical sectional view in the resonance direction, and FIG. 2 shows a wavelength tunable distributed reflection type laser in which the present invention is implemented. FIG. 2 is a cross-sectional view in the resonance direction of a type semiconductor laser. 1... Semi-insulating substrate 2... First optical waveguide layer 3...
-First cladding layer 4...Active layer 5...Second optical waveguide layer 6.6'...Second cladding layer 7...Insulating layer 8-P type electrode 9...N type electrode 10 ... ρ-type conductive region 11 --- n-type conductive region 21 --- Diffraction grating 22 on the first optical waveguide layer --- Diffraction grating [1] [TV] on the second optical waveguide layer --- Distributed reflection region [f[I... Active region [I11] -... Phase adjustment region

Claims (1)

[Claims] 1. At least a first optical waveguide layer, a first cladding layer, an active layer, a second optical waveguide layer, a second optical waveguide layer, and a second optical waveguide layer are formed on a semiconductor or semi-insulating substrate.
In a semiconductor laser device configured such that cladding layers are epitaxially grown in this order and current can be injected into the active layer, the first optical waveguide layer and the second optical waveguide layer have a A high-order diffraction grating of second order or higher is formed, and the first optical waveguide layer and the second optical waveguide layer are optically coupled to each other, and the first optical waveguide layer serves as an optical output waveguide. A semiconductor laser device characterized by: 2. A p-type region and an n-type region are formed on both sides of the active waveguide, and electrodes connected to each region are formed on both sides of the active waveguide so that current injection into the active layer is carried out laterally parallel to the active layer. 2. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is provided on an upper surface, that is, on a surface opposite to the substrate. 3. The active layer has a superlattice structure, and the superlattice of the impurity region is disordered due to heat treatment such as impurity diffusion during the formation of the p-type impurity region and the n-type impurity region, and the current in the active waveguide is 3. The semiconductor laser device according to claim 2, wherein light is confined.