JPH0449689A - Strain quantum well semiconductor laser - Google Patents

Abstract

PURPOSE:To eliminate the overflow of electrons, to execute a uniform carrier injection operation and to obtain a strain quantum well laser whose gain spectrum is sharp and whose threshold value is low by a method wherein the lattice constant of a semiconductor forming a well layer is made larger than the lattice constant of a substrate. CONSTITUTION:A strain quantum well semiconductor laser where a semiconductor forming a well layer is composed of InXGa1-XAsYP1-Y or InAsZP1-Z and its lattice constant is larger than the lattice constant of a substrate is formed. X, Y and Z are set as 0<=X,Y, and Z<=1. Its manufacturing method is as follows: an n-InP buffer layer 14 is grown in 0.1mum on an n-InP substrate 15 by an MOVPE method; then, an InGaAsP barrier 12 is grown in 1.3mum; and an In0.8 Ga0.2As0.6P0.4 well 13 is grown in 40Angstrom on it. The growth operation of the well and the barrier is repeated five times; and a five-layer multiple quantum well structure is manufactured. In addition, a p-InP clad layer 11 is grown in about 11mum on it. A strain quantum well wafer manufactured in this manner is buried in a DC-PBH structure. Lastly, a p-side electrode and an n-side electrode are vapor-deposited.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a strained quantum well semiconductor laser.

(Prior art) Quantum well semiconductor lasers have steeper gain spectra than normal semiconductor lasers with a bulk active layer, so they are expected to reduce the oscillation threshold and improve high-speed modulation characteristics. It is seen as promising as a high-performance light source for communications, etc. In recent years, strained quantum well lasers have been proposed as a method to further improve this performance, and are attracting attention. This strained quantum well laser applies biaxial compressive stress to the well to deform the band structure of the valence band within the well (~, with the aim of improving device characteristics such as lowering the threshold even further). It is something.

In conventional 1.3-1.6/im band long-wavelength strained quantum well lasers, a ternary mixed crystal of InGa and xAs is used in the well, but in this strained well using nxGa1-xAs, the In composition By doing so, a large compressive strain can be applied. However, as the In composition increases, the well energy gap also decreases, so in order to obtain the desired oscillation wavelength, the well width must be increased by /h. For example, when a strain of about 1.5% is applied using a 1.55 μm band strained quantum well valve, the In composition X becomes x=0.75, and the well width becomes very small at this time by 25 people. When the width of the well becomes extremely small in this way, the gain spectrum is broadened and the peak gain is reduced because the well is significantly influenced by the atomic layer step at the hetero interface between the well and the barrier.

In addition, in conventional strained quantum well lasers with strained InGaAs wells/InGaAsP barriers, the confinement potential AEc for electrons is smaller than the confinement potential ΔEv for holes, resulting in the problem of electrons leaking out of the well (overflow) during high injection. A problem has arisen in which hole confinement is too strong and hole injection becomes non-uniform between different wells. See the band diagram in FIG. 3(a).

(Problems to be Solved by the Invention) The purpose of the present invention is to eliminate the drawbacks of the conventional strained quantum well semiconductor laser, and to provide a laser with a sharp gain spectrum, less electron overflow, and uniform carrier injection. The object of the present invention is to provide a strained quantum well semiconductor laser that can realize the following states.

(Means for Solving the Problems) In a strained quantum well semiconductor laser according to the present invention using InP as a substrate and InGaAsP as a barrier layer, the semiconductor forming the well layer may be In, Ga, -XAs, Pne,
Alternatively, the above problem can be solved by a strained quantum well semiconductor laser made of InAs P and characterized in that its lattice constant is larger than the lattice 1-z constant of the substrate. X.

Y and Z are 0≦X, Y, z≦1.

(Function) The present invention will be explained in detail using FIG. 2 and FIG. 3 (aXb). FIG. 2 is a diagram showing the relationship between lattice constant and band gap, and FIG. 3 (aXb) is a band diagram of the conventional example and the present invention, respectively.

The structure according to the present invention can be expected to improve device characteristics due to the effects described below.

One is to add P to a conventional InGaAs strained well to
When nGaAsP or InAsP is used, as can be seen from Fig. 2, it becomes strained InGa with a similar amount of strain.
It can have a larger energy gap than As. Therefore, even when applying a large strain of about 2%, I
no7゜Gao28Aso6Po4 Barrier InAso
If a 6P, 4-well composition is used, a gain peak can be obtained in the 1.55 □m band even with a large well width of about 50 people. If the well width is as thick as about 50, the broadening of the gain spectrum due to the atomic layer step described above becomes negligible.

Furthermore, when InAsP or InGaAsP is used for the well, the difference in energy gap between the well and the barrier is caused by the compositional difference between group III In and Ga rather than light elements such as As and P, which are group V elements. Become. Group III + V compound semiconductors are formed by covalent bonding of these elements through SP hybrid orbitals, and among these, group III elements mainly have S orbitals, and group V elements mainly have P orbitals. is in charge of On the other hand, according to the -p perturbation theory, the bottom of the conduction band is formed by the S orbit, and the vicinity of the top of the valence band is formed by the electrons of the P orbit. Therefore, in a semiconductor heterojunction, if the difference in composition due to group III elements is large, the energy difference ΔEc in the conduction band will be large, and conversely, if the difference in composition due to group II elements is large, the energy difference ΔEv in the valence band will be large. is formed. InAsP or InGaA
When using an sP strain well, for the reasons mentioned above, the confinement potential ΔEc for electrons can be increased and confinement potential ΔEv for holes can be decreased, as shown in FIG. 3(b).
The above-mentioned problem of electron overflow and non-uniformity of hole injection can be solved at the same time. By the way, Tsuru Ino,
-t Gao 3As well/Ino7□Gao28A
In the case of the so6Po4 barrier, ΔEc has a value of about 0.3 eV, but in the case of the strained InAso6Po4 well/InO, 72
In the case of Ga0.2B""0.6"0.4 barrier, △Ec is about 0.5eV (see Figure 3 (aXb)) Furthermore, from the viewpoint of crystal growth, InGaAs/In
InAsP/InGaA than GaAsP heterojunction
In the sP heterojunction, a steeper change in composition at the hetero interface is obtained, and a quantum well with a better potential structure can be obtained.

(Example) An embodiment of the present invention will be described with reference to FIG.

FIG. 1 shows a cross-sectional view of the active region of a buried strained superlattice semiconductor laser. The manufacturing method begins with an n-InP substrate 15.
An n-InP buffer layer 14 is formed on top by the MOVPE method.
．． 1. zm grow, then 1.3. um composition InGaAs
Grow 150 P barrier 12 and add InO, 8G on top of it.
40 aO,2""0.6"0.4 wells 13 are grown. This well and barrier growth is repeated five times to produce a five-layer multi-quantum well structure.

On top of that, a p-InP cladding layer 11 of approximately 11□m
grow up. At this point, a compressive stress of about 1.5% is applied to the well. The strained quantum well wafer thus produced is embedded in a DC-PBH structure, and finally electrodes are deposited on the p-side and n-side.

When this laser was evaluated, the oscillation threshold Ith=5
mA, efficiency 1. = 0.28W/A, maximum optical output Pma
It showed good static characteristics with x=about 50 mW. Furthermore, when the internal quantum well efficiency was measured, a very high value of 0.95 was obtained. Furthermore, we prototyped a laser with a DFB structure and evaluated it through transmission experiments. As a result, good low chirp performance was obtained due to the reduction of the linewidth increase coefficient (α parameter) due to the effect of distortion, and a speed of 2.5 Gbit/see-100 km was obtained.
transmission has also been successful.

In this example, the In composition of the strained well layer was set to 0.8, but by increasing the In composition to form a strained InAsP well, the effect becomes even more remarkable.
, W. Matthews et al. in the Journal of Crystal Growth.
Growth) Vol, 27. On the contrary, it gets worse as it approaches the condition given by the critical layer thickness calculated at pH 8. In addition to this, 1.1
A similar trial production was conducted using a barrier layer having a composition of 5 μm, and a device with similarly good characteristics was obtained.

(Effects of the Invention) According to the present invention, it is possible to obtain a low threshold strain quantum well laser that eliminates electron overflow, enables uniform carrier injection, and has a sharp gain spectrum.

In the strained quantum well semiconductor laser of the present invention, the characteristics of the conventional strained quantum well laser become much lower than logically predicted values as the strain increases, and the characteristics are not improved as much as expected. This provides a solution to the problem, and is expected to find wide application as a high-performance light source for large-capacity direct detection systems and coherent detection systems in trunk optical communications.

[Brief explanation of drawings]

FIG. 1 is a structural diagram showing one embodiment of the present invention, FIGS. 2 and 3 are diagrams showing the principle of the present invention, FIG. 2 is a diagram showing the relationship between lattice constant and band gap, and FIG. FIG. 3(a) is a band diagram of a conventional example, and FIG. 3(b) is a band diagram of an embodiment of the present invention. In the figure, 11...p-InP cladding layer, 12...
...1.3 μm composition InGaAsP barrier layer, 13...
・Ino8Gao2Aso6Po4n8Gao4n-
InP buffer layer, 15·n-InP substrate.

Claims (1)

[Claims] In a strained quantum well semiconductor laser using InP as a substrate and InGaAsP as a barrier layer, the semiconductor forming the well layer is In_xGa_1_-_XAs_yP_1_-
A strained quantum well semiconductor laser made of _y or InAs_zP_1_-_z, characterized in that its lattice constant is larger than the lattice constant of the substrate.