JPH1070342A - Surface emission semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface emission optical quantum well semiconductor laser which operates in the wavelength band of 1.3 to 1.55μm. SOLUTION: In a surface emission semiconductor laser element having a III-V compound semiconductor layer including an active layer consisting of a quantum well layer and a barrier layer on an InP substrate, the lattice constant of a quantum well layer is larger than the lattice constant of InP and the lattice constant of a barrier layer is smaller than the lattice constant of InP. Furthermore, a quantum well layer and a barrier layer are constituted of GaInAsP or AlGaInAs. Thereby, a surface emission quantum well semiconductor laser of high performance which operates in the wavelength band of 1.3 to 1.55μm can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a surface emitting semiconductor laser using a quantum well structure used as a light source for optical communication and optical information processing.

[0002]

2. Description of the Related Art Desirable characteristics of a semiconductor laser device include a low threshold current density, a small temperature dependence of the threshold current density, a high modulation frequency, and a small wavelength chirping. These characteristics are improved by a quantum well semiconductor laser device having an active layer usually made of a layer thinner than 30 nm.

An active layer of a quantum well semiconductor laser device is composed of a layer having a small energy band gap called a quantum well and a layer having a large energy band gap called a barrier layer. In such a quantum well active layer, electrons and holes are confined in the quantum well and behave according to quantum mechanics.

The characteristics of a quantum well semiconductor laser device are improved by making the lattice constant of the quantum well larger than the lattice constant of the barrier layer and introducing strain into the quantum well. The reason for this is that the heavy holes in the valence band have their effective mass lightened in the direction perpendicular to the thin film layer and form a ground quantum level in the valence band. As a result, an optical transition between electrons and heavy holes is promoted in the quantum well layer. This is because electrons and heavy holes have substantially the same effective mass, so that it is easy to form a population inversion necessary for laser oscillation. It should be noted that the magnitude of the strain and the thickness of the quantum well layer must be within a certain critical film thickness value so that no dislocation is induced by the strain.

A conventional strained quantum well semiconductor laser device
For example, the one shown in FIG. This
In the conventional strained quantum well semiconductor laser device of
On a GaAs substrate 1, an n-type GaAs buffer layer 2 and
n-type Ga_0.6Al_0.4As clad layers 3 are sequentially laminated
Then, at a thickness of 0.2 μm, the Al component is reduced from 40% to 0%.
Up and down on both sides.
4 nm thick Ga with strain _0.63In_0.37A
An active layer composed of the s quantum well layer 4 is stacked, and is further inclined.
P-type Ga on the region 6_0.6Al_0.4As clad layer 7
And a p-type GaAsP cap layer are sequentially stacked, and finally
A structure in which an n-type electrode 9 and a p-type electrode 10 are deposited
Has become.

This quantum well semiconductor laser device has an oscillation wavelength of 9.9 ppm and a threshold current density of 195 Acm ^−2.
Met. FIG. 1B shows the conduction band side of the band gap corresponding to FIG. 1A.

[0007]

However, the conventional strained quantum well semiconductor laser device cannot obtain an oscillation of 1.3 to 1.55 μm which is an important wavelength in optical fiber communication. In order to obtain an oscillation having a wavelength of 1.3 μm or longer from the active layer of Ga _1-x In _x As, from the magnitude of the energy band gap, X ≧
It must have an In composition of 0.5. However, in such a high X Ga _1-x In _x As, the lattice constant becomes large, and if it is not applied to the quantum well layer 4 of the conventional strained quantum well laser shown in FIG. There is a problem that a large strain equal to or more than the critical value is generated, and the laser characteristics are degraded due to the generation of dislocations.

In the so-called communication wavelength band of 1.3 to 1.55 μm, a surface emitting laser capable of two-dimensional arrangement is desired. It has been considered that it is more difficult to realize a surface emitting laser in this wavelength band because it is necessary to realize a high-layer quantum well structure as compared with an emission laser.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and it is an object of the present invention to provide a wavelength band of 1.3 μm to 1.55 which is an important wavelength band in optical communication.
It is an object of the present invention to provide a high-performance surface emitting semiconductor laser device that oscillates in a long wavelength band of μm.
In a surface emitting semiconductor laser device having a group III compound semiconductor layer, the quantum well layer has a lattice constant larger than the lattice constant of InP, the barrier layer has a lattice constant smaller than the lattice constant of InP, and The surface emitting semiconductor laser device is characterized in that the quantum well layer and the barrier layer are made of GaInAsP or AlGaInAs.

That is, the lattice constant of the quantum well layer is larger than that of the InP substrate, and the lattice constant of the barrier layer is InP.
GaInAsP or Al which is smaller than the lattice constant of the substrate and is used as a material for forming the quantum well layer and the barrier layer.
By employing GaInAs, the thickness of each quantum well layer is set to a thickness (2.5 to 30 nm) at which effects such as low threshold current and low chirping can be obtained, and heavy in the valence band in the quantum well. Quantum in which a compressive strain is applied to the quantum well layer so that the effective mass in the direction perpendicular to the film surface of the hole becomes small, population inversion occurs at a low carrier, and laser oscillation becomes possible with a practical injection current. It has been found that the well structure can be realized as a surface emitting laser in a wavelength band of 1.3 to 1.55 μm which is important in optical communication.

[0011]

A feature of the present invention lies in an active layer structure forming a vertical cavity formed on an InP substrate, for example, a reflecting mirror structure provided at both ends of the vertical cavity and a laser driving structure for driving a laser. Since the structure other than the active layer structure such as the electrode structure can be the same as that of a well-known surface emitting laser, the active layer structure which is the main point of the present invention will be described in detail.

In the present invention, the active layer has a thickness of 2.5
Each layer is composed of n-thick quantum well layers having a thickness of 2.5 to 30 nm and alternately separated by (n-1) barrier layers having a thickness of 〜30 nm. In this case, both sides of the active layer are quantum well layers, but (n + 1) barrier layers are arranged.
Both sides of the active layer may be barrier layers. The composition of the quantum well layer is on the equiband gap line C corresponding to the oscillation wavelength of 1.3 μm in FIG. 2, and the lattice constant is I
A composition close to T between PTs larger than the nP substrate, Ga _X1 I
n _{1 -X1} As _Y1 P _{1 -Y1} .

The thickness of each quantum well layer has an upper limit, which is determined by the occurrence of strain-induced dislocations.
Is 20 to 30 nm.

The composition of the barrier layer is selected so that the band gap is larger than the band gap of the quantum well layer and the lattice constant is larger than the lattice constant of InP.
That is, in the region where no oblique line is shown in FIG.

In this case, the oscillation wavelength is 1.3 μm because the wavelength is increased by the narrowing of the band gap due to the strain and the wavelength is shortened by the quantum confinement of electrons.
Will be slightly off. In order to make the oscillation wavelength exactly coincide with 1.3 μm, the composition is slightly shifted from the line C in FIG. 2 in consideration of the effect of band gap reduction due to the above-described strain and the effect of band gap expansion due to the quantum confinement effect. Adjust it.

With this configuration, an active layer structure that oscillates in the 1.3 μm band, which is important as a communication wavelength, and can realize low threshold density and low chirping, has several quantum well layers and barrier layers. It is possible to grow up to a hundred without strain-induced dislocations,
A surface emitting laser having a vertical cavity can be realized in the 1.3 μm band.

The average lattice constant of the active layer can be adjusted by adjusting the thickness and composition of the quantum well layer and the barrier layer.
It can be equal to the lattice constant of P. In the surface emitting semiconductor laser of the present invention, the quantum well layer and the barrier layer are made of Al.
It can also be composed of GaInAs. Here, when the quantum well layer is made of AlGaInAs, the composition having a band gap wavelength of 1.3 μm from the region of InAs rather than the L ′ line (lattice constant line with InP) in FIG. 3, that is, the shaded region in FIG. And the barrier layer is made of AlG
In the case of aInAs, GaAs of the L ′ line in FIG.
A composition having a band gap wavelength of 1.3 μm or less may be selected from a region of s or AlAs, that is, a region without oblique lines in FIG.

Thus, the quantum well layer and the barrier layer are made of GaInAsP, and the quantum well is made of GaInAs.
P, a barrier layer of AlGaInAs, a quantum well of AlGaInAs, and a barrier layer of GaInA.
The type of the sP, the quantum well, and the barrier layer are AlGa.
Four types of surface emitting lasers of the type of InAs can be realized.

In the above embodiment, 1.3 μm
Although the surface emitting semiconductor laser device oscillating in the band has been described, it is apparent to those skilled in the art that the configuration of the present invention can be obtained in the 1.3 to 1.55 μm band in the same manner as described above.

[0020]

As described above, according to the present invention,
There is an excellent effect that a high performance quantum well semiconductor laser having an oscillation wavelength in the 1.3 to 1.55 μm band can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a conventional example (a) and a view showing a conduction band side of a band gap thereof (b).

FIG. 2 is a diagram of GaInAsP.

FIG. 3 is a diagram of AlGaInAs.

[Explanation of symbols]

 1 is an n-type GaAs substrate 2 is an n-type GaAs buffer layer 3 is an n-type GaAlAs cladding layer 4 is a GaInAs quantum well layer 5, 6 is an inclined region 7 is a p-type GaAlAs cladding layer 8 is a p-type GaAs cap layer 9 is an n-type Electrode 10 is a p-type electrode

Claims (1)

[Claims] In a surface emitting semiconductor laser device having a group III-V compound semiconductor layer including an active layer comprising a quantum well layer and a barrier layer on an InP substrate, the quantum well layer has a lattice constant of InP. A surface emitting semiconductor laser device characterized in that the barrier layer has a lattice constant smaller than that of InP, and the quantum well layer and the barrier layer are composed of GaInAsP or AlGaInAs. .