JPH06275919A - Optical semiconductor device - Google Patents

Abstract

(57) [Abstract] [Purpose] An optical semiconductor device having excellent characteristics by reducing both the disorder of atoms at the interface and the thermal interdiffusion of atoms in the growth of strained quantum wells. I try to realize the device. [Constitution] The P composition of the well layer in the quantum well structure made of InGaAsP mixed crystal formed on the InP substrate 1 is larger than the P composition of the barrier layer, for example, In _0.61 Ga
_0.39 As _0.52 P _0.45 Barrier layer 3 / In _0.91 Ga _0.09 As
_0.42 P _0.56 Well layer 4 / In _0.61 Ga _0.39 As _0.52 P _0.45
It consists of a barrier layer 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor device using a strained quantum well such as a laser using a strained quantum well for an active layer or a photo diode using a strained quantum well for a light absorption layer. Regarding improvement.

At present, for example, as a light source in a large-capacity optical communication system, it is required to realize a semiconductor laser capable of high-speed operation with a narrow spectrum line width.

Quantum well lasers have a remarkable improvement effect especially in narrowing the spectral line width because the quantum density effect changes the density of states function and the dipole moment increases the differential gain and oscillation. This is due to the reduction of line width.

In the strained quantum well laser, in addition to the quantum size effect in the quantum well laser, the strain effect causes
It is a device that can operate at a low threshold carrier density by increasing the transition probability or reducing the effective mass of holes, and it is necessary to further improve these characteristics in the future.

[0005]

2. Description of the Related Art Generally, in a strained quantum well structure, whether the strain of the well layer is a compressive stress or a tensile stress,
Further, depending on whether the strain of the barrier layer is the compressive stress or the tensile stress, and whether the strain is not applied to either the well layer or the barrier layer, there are 6 types in total. .

In order to properly use these six types of strained quantum well structures for strained quantum well lasers, any of various characteristics such as low oscillation threshold current, high output, increased strain amount, and long life is required. It is selected depending on whether to give priority. For example, a structure in which the well layer has in-plane compressive strain and the barrier layer has in-plane tensile strain is advantageous in terms of improving output and increasing strain amount.

Meanwhile, the strained quantum well structure made of a compound semiconductor has a peculiar problem of mixing constituent atoms at the interface between the barrier layer and the well layer.

This mixing is a disturbance of the interface that occurs during vapor phase growth of crystals, that is, unevenness caused by the intermingling of atoms, or the formation of an optical confinement layer after the formation of a strained quantum well structure. Caused by thermal mutual diffusion in the strained quantum well laser, the characteristics are greatly deteriorated, such as changing the oscillation wavelength in the strained quantum well laser or inhibiting the unity of the oscillation wavelength.

As a means for solving this problem, for example, in a strained quantum well laser using an InGaAsP mixed crystal semiconductor, among the mixed crystals constituting the barrier layer and the well layer, a Group 5 atom ( As and P) are made common, that is, As and P
It has been proposed that the strains be the same and the strain is generated only by the composition of the group III atoms.

This is because when the crystal is grown, the characteristic of this semiconductor system that the interdiffusion of only the Group 5 atoms occurs at an appropriate growth temperature is used to suppress the mixing caused by the interdiffusion. It is a technology.

[0011]

In the technique for suppressing the mixing caused by the mutual diffusion described above, in order to sufficiently bring out the effect of the strain in the strained quantum well, when the strain amount is increased, the barrier There is a problem that mixing at the interface between the layers and the well layer is increased during the growth of the crystal due to the force for relaxing the strain applied near the interface. An extreme example is the phenomenon that crystals grow in islands.

In the present invention, it is intended to realize an optical semiconductor device having excellent characteristics by reducing both the disorder of atoms at the interface and the thermal interdiffusion of atoms at the time of growing a strained quantum well. .

[0013]

In the present invention, when a strained quantum well is composed of a quaternary mixed crystal semiconductor, it is basically necessary to appropriately control the composition of P in the barrier layer and the well layer. ing.

FIG. 1 is a diagram showing the depthwise distribution of P composition in a strained quantum well in order to explain the principle of the present invention in comparison with the strained quantum well according to the prior art. In the figure,
(A) is a depth distribution of P composition in the present invention, (B)
Shows the depth distribution of the P composition in the first conventional example, and (C) shows the depth distribution of the P composition in the second conventional example.

As is clear from the figure, in the strained quantum well of the present invention, the P composition is larger in the well layer than in the barrier layer. On the other hand, in the strained quantum well according to the conventional technology, the P composition is the same in the barrier layer and the well layer (group 5 composition is common), or the well layer is smaller. The reason why the present invention is applied to the P composition is as follows.
This can be better understood by explaining with reference to FIG.

FIG. 2 is a diagram showing the relationship among the composition of the quaternary mixed crystal, the energy band gap, and the lattice constant for explaining the principle of the present invention. In the figure, the solid line is energy
A band gap, a broken line indicates a lattice constant, a square indicates a barrier layer, a circle indicates a well layer, and A to D indicate sample identification symbols. The thick solid line shows the case where lattice matching with InP is performed.

In the present invention, the strained quantum well is prepared by using the compositions shown by □ A and ○ A shown in FIG. 2, and the advantage thereof is that other samples are explained. Will be revealed in.

As shown by the thick solid line in the figure, InP
When a strained quantum well is formed by adopting a composition that is lattice-matched to, that is, when the composition is designated by □ D and ○ D, good results can be obtained in forming a steep interface, but it depends on mutual diffusion. The composition shifts in the direction indicated by the arrow. However, in this case, since the distortion caused by the progress of the mutual diffusion suppresses the mutual diffusion itself, the mutual diffusion does not proceed beyond a certain level.

Further, in the case of the compositions indicated by □ C and ◯ C, that is, when the Group 5 composition is made common, mutual diffusion can be suppressed, but it is known that the steepness of the interface deteriorates. .

On the other hand, in the compositions indicated by □ A and ◯ A, it is possible to take into account only the advantages of the compositions of □ D and □ D and the compositions of □ C and □ C in a well-balanced manner. You can do it.

Incidentally, in the compositions shown by □ A and ○ A, in-plane tensile strain is generated in the barrier layer with respect to the InP substrate, and in-plane compressive strain is generated with respect to the InP substrate in the well layer. .

Conventionally, in order to realize the relationship between the in-plane tensile strain and the in-plane compressive strain, as shown by □ B and □ B, the composition is shifted based on the composition of the quantum well of the lattice matching system. Is being done. However, in the composition, the composition changes in the direction in which the strain is relaxed due to the mutual diffusion, so that the structure is likely to cause the mutual diffusion.

From the above, in the optical semiconductor device according to the present invention, (1) a quantum well structure made of an InGaAsP mixed crystal formed on a compound semiconductor substrate of GaAs or InP (eg, substrate 1) is provided. The P composition of the well layer (for example, the well layer 4) is larger than the P composition of the barrier layer (for example, the barrier layers 3 and 4), or

(2) In the above (1), the well layer in the quantum well structure has in-plane compressive strain and the barrier layer has in-plane tensile strain.

[0025]

By adopting the above-mentioned means, mutual diffusion does not occur between the barrier layer and the well layer in the strained quantum well structure, so that the semiconductor strained quantum well laser has a stable oscillation wavelength. In addition, it is possible to improve monochromaticity, and it is possible to improve the characteristics in terms of narrowing the spectral line width, high-speed operability, operability at low threshold carrier density, and the like.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 is a side sectional view showing a main part of a semiconductor laminated structure in an optical semiconductor device for explaining an embodiment of the present invention. In the figure, 1 is a substrate, 2 is a buffer layer, 3 is a barrier layer, 4 is a well layer, 5 is a barrier layer, and 6 is a cap layer.

The main data regarding the substrate 1 and each semiconductor layer shown here will be illustrated as follows. Substrate 1 Material: InP Buffer layer 2 Material: InP Thickness: 500 [nm]

About the barrier layer 3 Material: In _0.61 Ga _0.39 As _0.52 P _0.45 Thickness: 8 [nm] About the well layer 4 Material: In _0.91 Ga _0.09 As _0.42 P _0.56 Thickness: 6 [nm]

About Barrier Layer 5 Same as Barrier Layer 3 About Cap Layer 6 Material: InP Thickness: 50 [nm]

In order to obtain this semiconductor laminated structure, it is possible to easily form it by using a technique which has been widely used conventionally. The conditions are, for example, applied technology: metalorganic vapor phase epitaxy (metalorgani)
c vapor phase epitaxy: MOV
PE) source gas: trimethylindium (TMIn: In (C
H _{3) 3)} triethyl gallium _{(TEGa: Ga (C 2 H} 5) 3) arsine (AsH _3), phosphine (PH ₃₎ Growth Temperature: 650 [℃] Growth rate: 1 [[mu] m / Time] (for all semiconductor layers ). After the growth of each semiconductor layer, annealing was performed at a temperature of 680 [° C.] for 2 hours.

The above-mentioned examples correspond to □ A and □ A in terms of the composition described with reference to FIG. 2, and for comparison, □ B and □ B, □ C and □ C, □ D and □. Since the strained quantum wells having the respective compositions of D were prepared, the explanation will be given below. For □ B and ○ B, barrier layers: In _0.78 Ga _0.22 As _0.30 P _0.70 well layers: In _0.74 Ga _0.26 As _0.79 P _0.21 □ C and About ○ C Barrier layer: In _0.62 Ga _0.38 As _0.47 P _0.53 Well layer: In _0.89 Ga _0.11 As _0.47 P _0.53 □ D and About ○ D Barrier layer: In _0.88 Ga _0.12 As _0.28 P _0.72 Well layer: In _0.70 Ga _0.30 As _0.68 P _0.32 , and other growth conditions were exactly the same as in the present invention.

FIG. 4 shows the photoluminescence of the embodiment of the present invention and the conventional example.
It is a diagram showing the result of e: PL) measurement. The data collection was performed while the sample was immersed in liquid helium, that is, 4.2 [K].

In the figure, (A) is a strained quantum well according to the present invention, (B) is a strained quantum well having a composition of □ B and ◯ B,
(C) is a strained quantum well having a composition of □ C and ○ C, (D)
Shows the photoluminescence peaks for the strained quantum wells having the compositions of □ D and ◯ D, respectively.

The full width at half maximum of the photoluminescence peak immediately after growth shown in this figure serves as an index showing the steepness at the interface, and the movement of the photoluminescence peak observed after annealing is thermal. It is an indicator of stability.

From the above-mentioned index, when the strained quantum well laser is constructed according to the present invention, the wavelength is stable and the monochromaticity is high as compared with the case where the strained quantum well laser according to the prior art is used. It will be taken care of.

[0036]

In the optical semiconductor device according to the present invention,
It is characterized in that the P composition of the well layer in the quantum well structure made of InGaAsP mixed crystal formed on the compound semiconductor substrate of GaAs or InP is larger than that of the barrier layer.

By adopting the above structure, mutual diffusion does not occur between the barrier layer and the well layer in the strained quantum well structure. Therefore, for example, in the case of a semiconductor strained quantum well laser,
The oscillation wavelength is stable and monochromaticity can be improved, and the characteristics can be improved in terms of narrowing the spectral line width, high-speed operability, and operability at low threshold carrier density.

[Brief description of drawings]

FIG. 1 is a diagram showing the distribution of P composition in the depth direction in a strained quantum well in comparison with a strained quantum well according to a conventional technique for explaining the principle of the present invention.

FIG. 2 is a diagram showing a relationship among a composition of a quaternary mixed crystal, an energy band gap, and a lattice constant for explaining the principle of the present invention.

FIG. 3 is a cross-sectional side view of essential parts showing a semiconductor laminated structure in an optical semiconductor element for explaining an embodiment of the present invention.

FIG. 4 is a diagram showing the results of photoluminescence measurement regarding an example of the present invention and a conventional example.

[Explanation of symbols]

 1 substrate 2 buffer layer 3 barrier layer 4 well layer 5 barrier layer 6 cap layer

Claims (2)

[Claims] 1. An optical semiconductor, wherein the P composition of a well layer in a quantum well structure made of an InGaAsP mixed crystal formed on a compound semiconductor substrate of GaAs or InP is larger than that of a barrier layer. element. 2. The optical semiconductor device according to claim 1, wherein the well layer in the quantum well structure has in-plane compressive strain and the barrier layer has in-plane tensile strain.