JP2003037335A - Surface emission semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable surface emission semiconductor laser element by reducing strain (stress) occurring in a DBR mirror. SOLUTION: The vertical resonator type semiconductor laser element comprises a pair of upper and lower multilayer reflectors disposed on a semiconductor substrate wherein at least one multilayer reflector is formed of a pair of compound semiconductor layers having a lattice constant larger than that of the semiconductor substrate and a lattice constant lower than that of the semiconductor substrate, respectively, and the band gap wavelength of the pair of compound semiconductor layers is shorter than the laser oscillation wavelength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface emitting semiconductor laser device, and more particularly to a surface emitting semiconductor laser device having a long device life.

[0002]

2. Description of the Related Art A surface-emitting type semiconductor laser device is a semiconductor laser device that emits light in a direction orthogonal to a substrate and is different from a conventional Fabry-Perot resonator type semiconductor laser device on the same substrate. Since it is possible to arrange a large number of surface-emitting type semiconductor laser elements in a dimensional array, it is a semiconductor laser element that has been drawing attention in the field of data communication in recent years.

A surface-emitting type semiconductor laser device has a pair of semiconductor multilayer film reflecting mirrors made of, for example, Al (Ga) As / Ga (Al) As in a GaAs system formed on a semiconductor substrate such as GaAs or InP. , A laser structure having an active layer serving as a light emitting region between the pair of reflecting mirrors. In particular, in a vertical cavity surface emitting semiconductor laser device having a wavelength band of 0.6 μm to 1.6 μm, a pair of materials that can be formed on a GaAs substrate and have different refractive indices above and below the active layer. Some have a multilayer mirror (DBR mirror) formed by.

Here, the basic structure of the surface-emitting type semiconductor laser device will be described with reference to FIG. FIG. 1 is a schematic sectional view showing the basic structure of a surface-emitting type semiconductor laser device. The surface-emitting type semiconductor laser device 5 basically has the structure shown in FIG.
As shown in FIG. 1, a lower DBR mirror 2, an active layer 3 sandwiched by clad layers on the upper and lower sides, and an upper portion D on a GaAs substrate 1.
The BR mirror 4 has a laminated structure.

The lower and upper DBR mirrors 2, 4 are typically GaAs / AlAs pairs, or Al _x Ga _{1 -x.}
As (X = 0.2 to 0.4) / Al _X Ga _1-X As (X =
0.9 to 0.95), and the thickness of each is set to λ / 4n (λ is the oscillation wavelength and n is the refractive index). For example, in a surface emitting semiconductor laser device that oscillates at a wavelength of 850 nm, Al _0.2 Ga _0.8 As is generally used.
/ Al _0.9 Ga _0.1 As pair is used, and the thickness of each is about 60.7 nm / 70.8 nm. The number of pairs of the lower and upper DBR mirrors is set to an optimum number of pairs according to the application of the surface-emitting type semiconductor laser device, but generally, the lower mirror is about 35 pairs and the upper mirror is about 25 pairs. Therefore, the total number of pairs is 60 pairs. Therefore,
The total film thickness of the lower and upper DBR mirrors is (70.8 + 6)
0.7) × 60 = 7890 nm.

Further, in recent years, it has become possible to form a surface emitting semiconductor laser device having a wavelength band of 1.2 μm to 1.6 μm on a GaAs substrate by using a compound semiconductor of GaInNAs mixed crystal as an active layer. became. In the surface-emitting type semiconductor laser device of this band, the lower and upper DBs are naturally
The thickness of the R mirror increases in proportion to the wavelength. Therefore, even if the number of pairs is assumed to be the same, the total film thickness of the lower and upper DBR mirrors is about 12000 nm in the surface-emitting type semiconductor laser device with the wavelength of 1.3 μm, and the wavelength of 1.55 μm.
m surface emitting type semiconductor laser device, about 14500 nm
It also becomes.

The lattice constants of GaAs and AlAs are 5.653Å and 5.6611Å, respectively, and the lattice constants are close to each other. In a normal edge-emitting laser, a stack of compound semiconductor layers forming a waveguide structure is laminated. Structure thickness is 3
Since the thickness is as thin as about 6 μm and the Al composition is as low as 0.3 to 0.4, the strain caused by the difference in lattice constant between GaAs and AlAs is also small, and the occurrence of strain is not a big problem. However, in the surface-emitting type semiconductor laser device, as described above, since the laminated structure becomes extremely thick, even if the difference in lattice constant is small, when they are stacked, the generated strain becomes so large that it cannot be ignored, This may affect the reliability of the device. In particular, it becomes a big problem in a long wavelength region.

By the way, the problem of strain generation depends on the structure of the element, and is a particular problem in the oxide confinement type confinement structure which has been actively researched and developed in recent years. The oxide confinement type confinement structure is provided to increase the current injection efficiency and lower the threshold current value.
Attention has been paid to an oxide confinement type surface emitting semiconductor laser device in which a current constriction structure is constituted by an oxide layer.

With reference to FIG. 2, the structure of a conventional 850 nm band oxide confinement type surface emitting semiconductor laser device will be described. FIG. 2 is a schematic sectional view showing the structure of a conventional 850 nm band oxide confinement type surface emitting semiconductor laser device. First, in the conventional surface-emitting type semiconductor laser device 10, as shown in FIG. 2, each layer has a thickness of λ / 4n (λ is an oscillation wavelength and n is a refractive index) on an n-GaAs substrate 12. n-A
l _0.9 lower DBR mirror 14 consisting of 35 pairs of GaAs / n-Al _0.2 GaAs, a lower cladding layer 16, a quantum well active layer 18, upper cladding layer 20, and, the thickness of each layer is λ / 4n (λ The upper DBR mirror 22 has a laminated structure of 25 pairs of p-Al _0.9 GaAs / p-Al _0.2 GaAs having an oscillation wavelength and n is a refractive index.

In the upper DBR mirror 22, one layer on the side close to the active layer 18 is replaced with an Al _0.9 GaAs layer and replaced with AlA.
A formed in the s layer 24 and in a region other than the current injection region
Al of the lAs layer 24 is selectively oxidized to form a current confinement layer composed of an Al oxide layer 25.

The upper DBR mirror 22 of the laminated structure
Are processed into a mesa post having a diameter of 30 μm, for example, by photolithography and etching up to a layer closer to the active layer 18 below the AlAs layer 24. The laminated structure processed into a mesa post is subjected to an oxidation treatment in a steam atmosphere at a temperature of about 400 ° C. to selectively oxidize Al of the AlAs layer 24 from the outside of the mesa post, thereby forming a current constriction made of an Al oxide layer 25. Layers have been formed. For example, when the Al oxide layer 25 has a band-shaped ring with a width of 10 μm, the area of the central AlAs layer 24, that is, the area of the portion (aperture) into which current is injected is
It becomes a circle of about 80 μm ² (diameter 10 μm).

The periphery of the mesa post is filled with, for example, a polyimide layer 26. Then, a ring-shaped electrode that comes into contact with the outer periphery of the upper portion of the upper DBR mirror 22 with a width of about 5 μm to 10 μm is provided as the p-side electrode 28. Also, the back surface of the substrate is appropriately polished to reduce the substrate thickness to, for example,
After adjusting the thickness to 00 μm, the n-side electrode 30 is formed on the back surface of the n-GaAs substrate 12. Furthermore, the polyimide layer 2
On the 6 is an electrode pad 32 for connecting a wire.
Are formed so as to be in contact with the ring electrode 28.

As described above, in the oxide confinement type confinement structure, Al is used for confining lateral current and light.
Al oxide layer (Al layer formed by selectively oxidizing the As layer)
_X O _X ) is provided. This oxide layer is not crystalline but amorphous, and its volume shrinks from the original AlAs layer. For this reason, the stacking strain generated in the DBR mirror is applied to the tip end portion (the central portion side of the mesa post) of the Al oxide layer, and the problem of the distortion becomes prominent.

[0014]

However, in the conventional technique, it is difficult to reduce the above-mentioned strain generated in the surface-emitting type semiconductor laser device and improve the reliability. Therefore, an object of the present invention is to provide a surface-emitting type semiconductor laser device having good reliability by reducing the strain (stress) generated in the DBR mirror.

[0015]

In order to reduce the strain (stress) generated in the DBR mirror, the present inventor has, for example, used Al.
In a semiconductor multi-layered film reflecting mirror having (Ga) As as one of the pairs, a compound semiconductor having a strain opposite to that of Al (Ga) As with respect to GaAs is used for the other of the pair, and the strains are offset each other. The idea was to reduce the distortion of the mirror. Further, the same effect can be obtained by combining materials having opposite strains with respect to the GaAs substrate.
Further, in order to function as a semiconductor multilayer film reflecting mirror, the bandgap wavelength of the compound semiconductor layers forming the pair is
It must be smaller than the oscillation wavelength of the laser. Under the above conditions, pairs of DBR mirrors were produced by combining various compound semiconductor layers, the generated strain was measured, and the idea was confirmed to be correct, and the present invention was accomplished.

In order to achieve the above object, in a vertical cavity surface emitting semiconductor laser device having a pair of lower multilayer film reflecting mirrors and an upper multilayer film reflecting mirror on a semiconductor substrate, at least one of the multilayer film reflecting mirrors is provided. The mirror is formed by a pair of a compound semiconductor layer having a lattice constant larger than that of the semiconductor substrate and a compound semiconductor layer having a lattice constant smaller than that of the semiconductor substrate, and the bandgap wavelength of the compound semiconductor layers forming the pair is The wavelength is smaller than the laser oscillation wavelength.

In a preferred embodiment of the present invention, a compound semiconductor layer having a bandgap energy intermediate between one and the other of the pair is interposed between each pair of the multilayer mirrors. As a result, even when the band gap difference between the pair is large, a hetero spike is generated, and the operating voltage of the surface-emitting type semiconductor laser device may rise,
It is possible to suppress the generation of hetero spikes.

The present invention can be applied to the structure of the current confinement structure without any limitation, but is particularly suitable for a surface emitting semiconductor laser device having an oxide confinement type confinement structure. In addition, the thickness of the semiconductor multilayer film reflecting mirror is large, 1.2 to 1.6.
The effect of the present invention is great in a surface-emitting type semiconductor laser device having a long wavelength region of μm.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described concretely and in detail with reference to the drawings and examples of embodiments. Embodiment 1 In this embodiment, the semiconductor substrate is 650 n in which GaAs is used.
It is an example of an embodiment in which the surface-emitting type semiconductor laser device according to the present invention is applied to an m-band surface-emitting type semiconductor laser device. In the present embodiment, at least one of the multilayer film reflecting mirrors, for example, the pair of upper DBR mirrors, is composed of InGaP / InGaP, AlGaInP / InGaP, Al _X Ga _{1 -X} AsP (0 ≦ X ≦ 1) / InGaP, Al _X Ga. _1-X AsP (0 ≦ X ≦ 1) / Al _X Ga _1-X As
(0 ≦ X ≦ 1), AlGaInP / Al _X Ga _1-X As
(0 ≦ X ≦ 1) and InGaP / Al _X Ga _1-X As (0 ≦ X ≦ 1).

Instead of the upper DBR mirror, a pair of lower DBR mirrors may be formed by the above combination. Preferably, a pair of upper and lower DBR mirrors are formed from the above combination.

Embodiment 2 In this embodiment, the semiconductor substrate is GaAs, 850
It is an embodiment example in which the surface-emitting type semiconductor laser device according to the present invention is applied to the surface-emitting type semiconductor laser device of the nm band and the 980 nm band. In the present embodiment example, at least one multilayer film reflecting mirror, for example, a pair of upper DBR mirrors, in addition to the combination of the first embodiment example, AlGaInAs / Al _X Ga _1-X As (0 ≦ X ≦ 1), AlGaInAs / InGaP, InGaP / InGaAsP, AlGaInP / InGaAsP, AlGaInAs / InGaAsP, Al _X Ga _1-X AsP (0 ≦ X ≦ 1) / InGaAsP, AlGaInP / AlGaAsSb, Al _X Ga _1-X AsP (0 ≦ X ≦ 1) / AlGaAsS
b, InGaP / AlGaAsSb, and AlGaInAs / AlGaAsSb.

Instead of the upper DBR mirror, a pair of lower DBR mirrors may be formed by the above combination. Preferably, a pair of upper and lower DBR mirrors are formed from the above combination.

Embodiment 3 In this embodiment, the semiconductor substrate is GaAs, 1.2.
For surface-emitting type semiconductor laser devices in the μm to 1.65 μm band,
It is an embodiment example to which the surface emitting semiconductor laser device according to the present invention is applied. In the present exemplary embodiment, at least one multilayer film reflecting mirror, for example, a pair of upper DBR mirrors, in addition to the combination of the first and second exemplary embodiments, Al _X Ga _1-X AsP (0 ≦ X ≦ 1 ) / GaAsSb, AlGaInP / GaAsSb, InGaP / GaAsSb, and AlGaInAs / GaAsSb.

Instead of the upper DBR mirror, a pair of lower DBR mirrors may be formed by the above combination. Preferably, a pair of upper and lower DBR mirrors are formed from the above combination.

Further, in each of the above-mentioned combinations, when the band gap difference between the pair is large, a hetero spike may be generated and the operating voltage of the surface-emitting type semiconductor laser device may increase. Therefore, one intermediate layer having an intermediate band gap between the two layers forming the pair is formed at the interface of the pair of two layers.
It is desirable to suppress the generation of hetero spikes by inserting more layers. For example, InGaP / InG
InGaP having an intermediate bandgap energy between aP and AlGaInAs / Al _X G
Between a _1-X As (0 ≦ X ≦ 1), AlGaAs having a band gap energy intermediate between the two is
_{Between X} Ga _{1 -X} AsP (0 ≦ X ≦ 1) / GaAsSb, AlGaAs having a band gap energy intermediate between the two is interposed.

The compound semiconductor layers mentioned in the first to third embodiments are MOCVD, MBE, gas source MBE,
Crystal growth can be performed by applying the CBE method or the like.
DBRs of the pair of combinations listed in the first to third embodiments
After forming the mirror, a confinement structure by ion implantation or an oxide confinement type confinement structure is formed to fabricate a surface emitting semiconductor laser device or a surface emitting laser array. In the surface-emitting type semiconductor laser device manufactured in this way,
Since the strain (stress) generated by the difference in the lattice constants of the upper and lower DBR mirrors can be reduced, it is possible to prevent the life of the element from being shortened due to the influence of this strain. In particular, DBR
The effect of the present invention is great in the surface-emitting type semiconductor laser device in the long wavelength region of 1.2 to 1.6 μm in which the thickness of the mirror is large. It is also effective when an oxide layer confinement structure that is weak against strain is used.

[0027]

According to the present invention, a pair of a compound semiconductor layer having a lattice constant larger than that of a semiconductor substrate and a compound semiconductor layer having a lattice constant smaller than that of the semiconductor substrate is used as a pair, and at least one of the multilayer film reflecting mirrors. By forming the, the strains generated in the multi-layered film reflection mirror are mutually offset, and the DBR
It is possible to reduce distortion of the mirror and realize a surface-emitting type semiconductor laser device having a long life and high reliability.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the basic structure of a surface-emitting type semiconductor laser device.

FIG. 2 is a schematic cross-sectional view showing the structure of a conventional 850 nm band oxide confinement type surface emitting semiconductor laser device.

[Explanation of symbols]

5 Layered structure of surface-emitting type semiconductor laser device 1 GaAs substrate 2 Lower DBR mirror 3 Active layer 4 Upper DBR mirror 10 Conventional oxide confinement type surface emitting semiconductor laser device 12 n-GaAs substrate 14 Lower DBR mirror 16 Lower clad layer 18 Quantum well active layer 20 Upper clad layer 22 Upper DBR mirror 24 AlAs layer 25 Al oxide layer 26 Polyimide layer 28 p-side electrode 30 n side electrode 32 electrode pad

Continued front page    (72) Inventor Noriyuki Yokouchi             2-6-1, Marunouchi, Chiyoda-ku, Tokyo             Kawa Electric Industry Co., Ltd. F term (reference) 5F073 AA65 AB17 CA14 CA19 CB02                       EA06 EA07 EA28

Claims (6)

[Claims] 1. In a vertical cavity surface emitting semiconductor laser device having a pair of lower multilayer film reflecting mirrors and upper multilayer film reflecting mirrors on a semiconductor substrate, at least one of the multilayer film reflecting mirrors of the semiconductor substrate. A compound semiconductor layer having a lattice constant larger than the lattice constant and a compound semiconductor layer having a lattice constant smaller than the semiconductor substrate have a band gap wavelength smaller than the laser oscillation wavelength. A surface-emitting type semiconductor laser device characterized by the above. 2. The semiconductor substrate is GaAs and the oscillation wavelength is 6
In the surface-emitting type semiconductor laser device with a wavelength of 30 nm or more and less than 700 nm, at least one of the multilayer film reflection mirror pairs is InGaP / InGaP, AlGaInP / InGaP, Al _X Ga _{1 -X} AsP (0 ≦ X ≦ 1) / InGaP, Al _X Ga _1-X AsP (0 ≦ X ≦ 1) / Al _X Ga _1-X As
(0 ≦ X ≦ 1), AlGaInP / Al _X Ga _1-X As
2. The surface emitting semiconductor according to claim 1, wherein the surface emitting semiconductor is formed of any combination of (0 ≦ X ≦ 1) and InGaP / Al _X Ga _1-X As (0 ≦ X ≦ 1). Laser device. 3. The semiconductor substrate is GaAs and the oscillation wavelength is 7
In the surface-emitting type semiconductor laser device of 00 nm or more and less than 1100 nm, in addition to the combination according to claim 2, the pair of multilayer film reflection mirrors further comprises AlGaInAs / Al _X Ga _1-X As (0 ≦ X ≦ 1). , AlGaInAs / InGaP, InGaP / InGaAsP, AlGaInP / InGaAsP, AlGaInAs / InGaAsP, Al _X Ga _1-X AsP (0 ≦ X ≦ 1) / InGaAsP, AlGaInP / AlGaAsSb, Al _X Ga ≦ _1-X AsP 1) / AlGaAsS
2. The surface emitting semiconductor laser device according to claim 1, wherein the surface emitting semiconductor laser device is formed of any combination of b, InGaP / AlGaAsSb, and AlGaInAs / AlGaAsSb. 4. The semiconductor substrate is GaAs and the oscillation wavelength is 1
In the surface-emitting type semiconductor laser device having a wavelength of 100 nm or more and 1650 nm or less, in addition to the combination described in claim 2 and 3, the pair of multilayer film reflecting mirrors further comprises Al _X Ga _1-X AsP (0 ≦ X ≦ 1) / 2. The surface emitting semiconductor laser device according to claim 1, wherein the surface emitting semiconductor laser device is formed of any combination of GaAsSb, AlGaInP / GaAsSb, InGaP / GaAsSb, and AlGaInAs / GaAsSb. 5. A compound semiconductor layer having a band gap energy intermediate between one of the pair and the other of the pair is interposed between each pair of the multilayer-film reflective mirrors. The surface-emitting type semiconductor laser device according to any one of items. 6. The surface-emitting type semiconductor laser device according to claim 1, which has an oxide confinement type confinement structure.