JPH0373586A - Quantum well laser - Google Patents

Abstract

PURPOSE:To shorten carrier life without loss of characteristics of a quantum well laser and to perform an extremely abrupt optical pulse response even at the time of high speed pulse modulation by using a first quantum well structure as an active layer and a second quantum well structure having larger bottom state energy of the first structure and an impurity added to a well layer. CONSTITUTION:A quantum well active layer 40 is formed of a first quantum well structure 50, second quantum well structures 70, 71 at both sides, and barrier layers 60, 6 for isolating the first and second structures. The structure 50 is formed of an InGaAsP barrier 57, 6 layers of InGaAs well 55, and energy gap has quantum levels 51, 52. The structure 70 has barrier 77 of the same composition as that of the structure 50 and InGaAsP wells 75, 76, zinc is doped as an impurity in the wells 75, 76, and the well 76 is doped with silicon. Thus, an impurity can be added to a semiconductor layer having a small diffusion speed without diffusion of the impurity into the first quantum well structure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a quantum well laser used as a light source for optical communications, optical calculations, optical measurement devices, and the like.

[Conventional technology]

Semiconductor lasers have the characteristic of being capable of high-speed modulation up to several GHz by changing the applied current, so-called direct modulation, and are being developed as light sources for high-speed and long-distance optical communications. Particularly in recent years, distributed feedback semiconductor lasers (Distributed Fe semiconductor lasers) that operate in a single-axis mode have been developed.
edback La5er Diode:hereinafter referred to as DFB
-LD), or Distributed Bragg Ref.
tectorlB6rDiode: Hereinafter referred to as DBR-LD
) is expected to be used as a light source for ultra-high-speed, long-distance optical fiber communications, as well as for optical measuring instruments that incorporate coherent optical systems, due to its extremely excellent monochromaticity of oscillation wavelength. Development is proceeding at a rapid pace. DFB-LD using InGaAsP/InP material
It has been used as a light source in an experiment for an optical fiber communication system with an ultra-high speed of 10 Gb/s and a transmission distance of over 80 km, and good results have been obtained.

In addition to the capacitance of the device itself, the frequency response characteristics of semiconductor lasers are determined by relaxation oscillations (resonance oscillations that occur at a specific modulation frequency and significantly increase modulation sensitivity) caused by mutual interaction between photons and carriers in the active layer. phenomenon), and carrier lifetime. In particular, in recent years, quantum well structure semiconductor lasers with a quantum well layer as the active layer have been developed, and as the relaxation oscillation frequency increases compared to conventional double heterojunction (bulk structure) semiconductor lasers, faster semiconductor lasers have been realized. There is a possibility that it can be done.

[Problem to be solved by the invention]

However, even in a semiconductor laser with a small element capacitance and a high relaxation oscillation frequency, during pulse modulation, the optical output pulse has a tail depending on the carrier lifetime at the falling edge of the drive current pulse. Similarly to the bulk structure semiconductor laser, the carrier lifetime in the quantum well structure semiconductor laser described above is several ns (1ns=IX10-' seconds).
Therefore, when the pulse modulation rate exceeds several Gb/s, there is a problem that the transmission characteristics deteriorate.

In conventional bulk structure semiconductor lasers, the carrier lifetime can be shortened by adding impurities to the active layer, but in quantum well structure semiconductor lasers, adding impurities directly to the quantum well structure causes drooping at the heterojunction interface and the quantum level. This has the disadvantage that the quantum effect is lost due to the broadening of .

[Means to solve the problem]

Means provided by the present invention to solve the above problems are as follows:
In a quantum well laser in which a semiconductor layer having an active layer having a quantum well structure is laminated on a semiconductor substrate, the active layer has a first quantum well structure and the ground state energy is equal to or greater than the ground state energy of the first quantum well structure. larger than
In addition, a second quantum well structure in which impurities are added to the well layer is used.

[Effect]

The operation of the present invention will be explained below. In general, a semiconductor with a long wavelength composition has a lower diffusion rate of impurities, and in the case of a quantum well structure, the optical transition energy is larger than that of a bulk with the same composition. Therefore, if the method of adding impurities to the well of the second quantum well structure as described above is used,
Impurities can be added to a semiconductor layer with a low diffusion rate without causing impurity diffusion into the first quantum well structure. Further, since the second quantum well structure doped with impurities can be placed between the well layers of the first quantum well structure or very close to it, great effects can be obtained.

[Example 1] A first example of the quantum well laser according to the present invention will be described in detail with reference to FIG. Metal organic chemical vapor deposition (MOCVD) was used as the growth method for the quantum well structure.

As shown in the energy band diagram of the conduction band in FIG. 1(a), the quantum well active layer 40 consists of a first quantum well structure 50, a second quantum well structure 70. Paris 7 layer separating the second quantum well structure 80.61
It is composed of.

The first quantum well structure 50 is made of 1.1 μm InGaAs.
Consisting of a P barrier 57 (thickness 100A) and a 6-layer InGaAs well 55 (thickness 80mm), the energy gear and beam are 0.8 eV (λ = 1.55 μm) and 0.92, respectively.
It has a quantum level of 51.52 eV (λ=1.35 μm). The second quantum well structure 70 has a barrier 77 (thickness 70A) having the same composition as the first quantum well structure 50, and 1
．． It consists of 4μm composition 1nGaAsP wells 75 and 76 (each layer has a thickness of 60 layers), and the wells 75 and 76 contain 4×10 ``an-'' of zinc (Zn) as an impurity, and the well 76 contains silicon (Si). 6 x 10”cm
-'Doped. The thickness of the Paris 7 layer 60,61 separating the first and second quantum well structures is 300 and 200, respectively.

Using the quantum well active layer described above, as shown in the perspective view of FIG. 1(b), a diffraction grating 15 consisting of periodic irregularities is
InGaAsP is formed on the InP substrate IO formed on the surface.
A double channel buried structure (DC-PBH) distributed feedback (DFB) semiconductor laser with a multilayer structure including a guide N20 and a quantum well active layer 40 is formed. The characteristics of a device cleaved with a cavity length of 300 μm include an oscillation threshold of about 15 mA and an external differential quantum efficiency of 0.1.
Approximately 8W/A/facet, carrier life is 0.3n
s ~0.6 ns (ns=IX10-' seconds), and a sufficiently steep fall of the optical pulse is expected to not cause deterioration of transmission characteristics even during 10 Gb/s pulse modulation. Furthermore, further improvement in pulse response characteristics can be expected by optimizing the doping amount, dopant, and the thickness of the Paris layer and the number of wells.

The above embodiments are based on dual channel embedding (DC-P B
Although the description has been given using an example of a semiconductor laser having the H) structure, it is naturally effective for other buried structures, ridge waveguide structures, and the like.

[Embodiment N2] A second embodiment of the quantum well laser according to the present invention will be described with reference to FIG.

The first quantum well structure 150 is made of 1.3 μm composition InGa
It consists of an A s P barrier 57 (thickness: 100 mm) and 10 layers of InGaAs wells 155 (thickness: 65 Å). The second quantum well structure 170 is made of 1.3 μm composition InGaAs.
P barrier 77 (thickness 60 people), and 1.4 p m
Composition InGaAsP well 175 (thickness 50, 6 layers)
The well 175 contains zinc (Zn) as an impurity.
6 >10"cm-" doped. First,
and a Paris 7 layer 180 separating the second quantum well structure,
The thickness of 161 is 400 and 100A, respectively.

It is expected that such a quantum well laser will also have excellent characteristics similar to those of the first embodiment.

Furthermore, although the above two embodiments have been explained using an InP-based quantum well structure as an example, the present invention is also effective in a general semiconductor quantum well structure such as a GaAs-based quantum well structure.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to shorten the carrier lifetime without impairing the characteristics of a quantum well laser, and to realize a quantum well laser that can obtain an extremely steep optical pulse response even during high-speed pulse modulation. can.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the invention, and FIG. 2 is an explanatory diagram of a second embodiment of the invention. In the figure, 10 is an n-InP substrate, 15 is a diffraction grating, 20 is an n-InGaAsP guide layer, 40 is a quantum well active layer,
50,150 is the first quantum well structure, 51.52 is the quantum level of the conduction band, 55,155 is the InGaAs well, 5
7, 1'57 is an InGaAsP barrier layer, 60, 61,
160 and 161 are the first. A barrier layer separating the second quantum well structure, To, 71° 170 is the second quantum well structure,
75, 77.175°177 are the well and barrier layer of the second quantum well structure, respectively.

Claims (1)

[Claims] In a quantum well laser in which a semiconductor layer having an active layer having a quantum well structure is laminated on a semiconductor substrate, the active layer has a first quantum well structure and the ground state energy has a ground state of the first quantum well structure. 1. A quantum well laser comprising a second quantum well structure having an energy larger than that of the quantum well and having a well doped with impurities.