JPS6316690A - Semiconductor light emitting device - Google Patents

Abstract

PURPOSE:To improve the oscillation characteristic of a semiconductor light emitting device by forming a semiconductor layer having a large band gap by an energy level difference between electrons and holes with respect to the laser oscillation of an active region to prevent the generation of a light absorption loss. CONSTITUTION:A corrugation 7 of a diffraction grating is formed on a part of an AlGaAs guide layer 4, and an impurity, such as a zinc is diffused in a range 8 which arrives at an N-type AlGaAe clad layer 2 from the surface of a GaAs contact layer 6. Then, the width of an optical guide is mesa etched to approx. 3mum, a P-type AlGaAs layer and an N-type AlGaAs layer are buried and grown, and a P-type electrode 9 is disposed on the layer 6 of a part held with a quantum well structure 3 and an N-type side electrode 10 is disposed on the rear surface of a substrate without forming the corrugation 7 of a semiconductor substrate. In this case, the energy level difference between the sub band ends of electrons and holes of a base level with respect to a laser oscillation of the structure 3 for forming an active region is 1.53eV, and an oscillation wavelength is 0.82mum, while the band gap of the semiconductor layer disordered by diffusing Zn is approx. 1.5eV, and does not absorb the light of the oscillation wavelength.

Description

[Detailed Description of the Invention] [1] The present invention relates to a distributed reflection type semiconductor laser, in which the active region has a quantum well structure, the feedback region by a diffraction grating does not have a quantum well structure, and the active region By forming a semiconductor layer with a band gap larger than the energy level difference between electrons and holes involved in laser oscillation, light absorption loss in the feedback region is prevented and oscillation characteristics are improved.

[Industrial application field]

The present invention relates to improvements in the structure of semiconductor lasers, particularly distributed Bragg reflection type semiconductor lasers, for reducing optical absorption loss and improving oscillation characteristics.

In order to advance the sophistication of optical communication systems that use light as a medium for information signals, distributed Bragg reflection (DBR) lasers, which are suitable for longitudinal mode control, and distributed feedback (DBR) lasers are being developed.
FB) There are expectations equal to or higher than lasers, but
Traditional DBI? As will be described later, lasers have problems such as difficulty in obtaining good oscillation characteristics because feedback is weakened by light absorption, and there is a strong demand for improvement.

[Conventional technology]

The Fapley-Perot type resonator, which is commonly used in semiconductor lasers, has a standing wave between a pair of folds, that is, a longitudinal mode with a large mode order of, for example, about 2000, and the energy band gear changes as the temperature changes. It is not possible to control the longitudinal mode due to factors such as changing the knob and changing the oscillation wavelength.

On the other hand, DBR lasers and DFB lasers, which are equipped with a resonator that performs feedback using a diffraction grating provided at the interface of an optical waveguide, achieve a single wavelength by controlling the longitudinal mode to provide wavelength selectivity for feedback. It becomes possible to do so.

That is, as shown in a schematic side sectional view of a conventional example in FIG. 2, a DBR laser epitaxially grows an n-type cladding layer 22, an n-type active layer 23, and a p-type guide layer 24 on an n-type semiconductor substrate 21, for example. A corrugation 27 of a diffraction grating is formed on the surface of this guide layer 24, and a p-type cladding layer 25 and a p-type contact layer 26 are epitaxially grown. 24, where the corrugation 27 of the leading wavepath is formed, and the region where the p-side electrode 29 and n(jQl electrode 30
The region sandwiched between the region and the region where current injection is performed are separated and adjacent to each other.

In this way, a DBR laser in which the carrier injection region of the active layer 23 that amplifies light and the region in which light is returned by the corrugation 27 are spatially separated is compared to a DFB laser in which both functions are performed in the same region. There are many degrees of freedom in design, and it is expected that even better lasers will be realized.

[Problem that the invention seeks to solve]

As explained above, DBR lasers are suitable for single-wavelength oscillation, and are being developed as light sources for optical communications that maintain single-wavelength oscillation even during high-speed modulation. In lasers, there is a problem in that the amount of feedback is weakened because the light is absorbed by the active layer 23 in the region where the light is returned, making it difficult to achieve good oscillation characteristics, and a solution to this problem is desired.

[Means for solving problems]

The problem is that a part of the guide waveguide is sandwiched between opposing electrodes and includes an active region having a quantum well structure and a light guide layer, and a part of the guide wavepath that is not sandwiched between the electrodes selectively transmits light. A semiconductor light emitting device according to the present invention comprising a semiconductor layer that is equipped with a feedback diffraction grating, does not have a quantum well structure, and has a band gap larger than the energy level difference between electrons and holes that are involved in laser oscillation in the active region. Solved by the device.

[For production]

According to the present invention, the active region of the DBR laser has a quantum well structure, and the portion where carriers are not injected by forming the diffraction grating of the guiding waveguide is diffused with impurities to disorder the extended portion of the active region, thereby forming a quantum well structure. Assume that no well structure exists.

In addition, by selecting the configuration of the quantum well structure in advance and making the band gap of this disordered semi-m-layer larger than the energy level difference between the electron and hole subbands involved in laser oscillation in the active region, , the light at the oscillation wavelength is not absorbed in the feedback region formed by the diffraction grating of the optical waveguide, resulting in a large feedback rate and improved oscillation characteristics.

〔Example〕

The present invention will be described in detail below with reference to Examples.10 FIG. 1 is a schematic side sectional view taken longitudinally of an optical waveguide according to an example of the present invention, which is manufactured, for example, in the following manner.

That is, first, a cladding layer 2 is formed on an n-type GaAs semiconductor substrate using a molecular beam epitaxial growth (MBE) method or the like.
, a multi-quantum well structure 3 serving as an active region, and a guide layer 4 are grown, for example, as follows.

4 A1. Ga+-, As (x=0.15) p
-lXl0Il'30Qnm3 Multiple quantum well: 3aX
6 layers + 3b x 5 layers 3b AlxGal-MAs (xJ
, 3) Non-doped 7nm3a AlXGa+
-, As (x=0.05) non-doped 7nm2
81. Ga, -XAs (x=0.4)
n-2X101a 3-On a part of the surface of this AlGaAs guide layer 4, a corrugation 7 of a diffraction grating is formed with a period of 245 nm and a depth of about 5 nm, for example.

The pattern of this corrugation 7 is formed by applying a two-beam interference method using a conventional technique.

The cladding layer 5 and the contact layer 6 are formed again by the MB2 method etc.
For example, grow as shown below.

Code Composition Impurity Thickness cm
-”6 GaAs p-7X10”
300nm5 AlxGa+-x^5 (x=0.
4) p-lXl0'' 3-In the portion of this semiconductor substrate where the corrugations 7 are formed, an impurity such as zinc (Zn) is diffused into a range 8 extending from the surface of the GaAs contact layer 6 to the n-type AlGaAs cladding layer 2.

This diffusion uses, for example, zinc arsenide (ZnAs) as a source,
At a temperature of about 700°C, the surface concentration is
degree. Note that this disordering of the quantum well structure by impurity diffusion may be performed before the formation of the corrugations 7.

Next, mesa etching is performed to make the width of the optical waveguide about 3 μm, and a p-type AlGaAs layer and an n-type AlGaAs layer (none of which are shown) with x = 0.4, for example, are buried and grown, and the corrugation 7 of this semiconductor substrate is grown. A p-side electrode 9 is provided on the contact layer 6 in a portion where the quantum well structure 3 is preserved without being formed, and an n-side electrode IO is provided on the back surface of the substrate.

Furthermore, the quantum well structure 3 of the active region and the corrugated thin 7 of the diffraction grating are provided with folds at positions where the lengths are, for example, about 200 μl each, and an antireflection coating 11 is applied to the end face between the folds.

In this example, the one unit energy difference between the subband edges of electrons and holes at the ground level involved in laser oscillation in the quantum well structure 3 constituting the active region is 1.53 eV, and the oscillation wavelength is 0.
．． 82 μIn, while the quantum well structure 3 is made of Zn.
The band gap of the thick layer disordered by diffusion is about 1.6 eV, and it does not absorb light at the oscillation wavelength.

In the above-mentioned embodiment, the dark value current is reduced from, for example, about 50 mA in the conventional example to about 100 mA, and the gain difference between the main oscillation mode and other oscillation modes increases, resulting in high-speed modulation of the rated output. The mode stability is significantly improved.

Although the embodiments described above use GaAs/AlGaAs-based semiconductor materials, for example, indium phosphorous/indium gallium arsenide phosphorus (InP/InGaAsP)-based materials, etc.
Similar effects can be obtained by the present invention for semiconductor light emitting devices using other semiconductor materials.

〔Effect of the invention〕

As explained above, according to the present invention, the optical absorption loss of the DBrl laser is prevented and the oscillation characteristics are improved, and the laser has a great effect on optical communication systems, etc. as a laser that maintains single wavelength oscillation well even during high-speed modulation. give.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side sectional view of an embodiment of the present invention, and FIG. 2 is a schematic side sectional view of a conventional example. In the figure, l is n-type GaAs14, 2 is n-type AlGaAs cladding layer, 3 is the active region of quantum well structure, 3a is the AlGaAs well layer, 3b is the AlGaAs barrier layer, 4 is the p-type AlGaAs guide layer, 5 is a p-type AlGaAs cladding layer, 6 is a p-type ^lGaAs contact layer, 7 is a corrugation of a diffraction grating, 8 is a region in which impurities are diffused, 9 is a p (uII electrode, 10 is an n-side electrode, 11 is an antireflection coating) shows.

Claims (1)

[Claims] A portion of the optical waveguide is sandwiched between opposing electrodes and includes an active region having a quantum well structure and a light guide layer, and a portion of the optical waveguide that is not sandwiched between the electrodes selectively transmits light. 1. A semiconductor comprising a semiconductor layer that is equipped with a diffraction grating for feedback, does not have a quantum well structure, and has a band gap larger than the energy level difference between electrons and holes involved in laser oscillation in the active region. Light emitting device.