JPH05343796A - Surface emission-type semiconductor laser - Google Patents

Abstract

PURPOSE:To provide a low-threshold level surface emission-type semiconductor laser wherein a reflecting plate which helps reducing the thickness of a lamination layer and producing an excellent reflection factor characteristic is used by making the ratio of a reflection factors of reflecting mirror-constituting materials large. CONSTITUTION:In a surface emission-type semiconductor laser, a II-VI compound semiconductor layer which has a smaller band gap wave length than an oscillation wave length and which has a lattice conformity with InP is used for a lower refractive index layer out of two kinds of layers which constitutes multilayer reflection films 11 and 13. Therefore, compared with the case that a III-V compound semiconductor layer is used, a refractive index can be lowered from 3.17 to 2.4 or around. In a 11-cycle lamination structure, a refractive index is 99.1% and the thickness of a lamination layer is 3mum, very much thinner than in the past, and a reflection factor is very large. Since the thickness of the lamination layer can be thinner than in the past and a reflection factor can be larger, an oscillation threshold level can be reduced more.

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.

[0002]

2. Description of the Related Art A surface emitting semiconductor laser uses a reflecting mirror having a high reflectance of 99.9% or more as a resonator, so that a driving current can be reduced as compared with a conventional edge emitting semiconductor laser.
Improvements in dimensional array, high-speed modulation, etc. can be expected. A conventional example of such a semiconductor laser is applied Physics Letters magazine, 1990, Volume 57, No. 16, 1605-16.
It is reported on page 07. This conventional semiconductor laser has a structure in which a light emitting layer and two multilayer reflecting mirrors are arranged in a cylindrical portion formed on a semiconductor substrate by photolithography and dry etching in a direction parallel to the light emission direction. Alternately, a quarter-wave plate of aluminum arsenide (AlAs) and gallium arsenide (GaAs) is alternately used for the reflecting mirror.
By using a structure in which 28 layers are stacked, a high reflectance of 99.9% or more is realized and a low threshold current is obtained. An example of a high-reflectance mirror for a surface emitting semiconductor laser in the optical communication wavelength band is given in Applied Physics Letters, 1991, 59.
Vol. 9, No. 10, pp. 1011-1012. In this conventional example, quarter-wave plates made of InGaAlAs and InAlAs are alternately laminated for 30 cycles to form a reflecting mirror, and a high reflectance of 99% or more is obtained.

[0003]

However, a conventional reflecting mirror having a structure in which quarter-wave plates of semiconductors having different refractive indexes are laminated in multiple cycles is required to obtain a high reflectance of 0.9.
It is necessary to have 20 cycles or more for the emission wavelength in the μm band, and particularly 30 cycles or more for the surface emission type semiconductor laser on the InP substrate for the communication wavelength band. As a result, the following two problems occur. First, the laminated layer thickness is 2 to 10 μm for two reflectors.
It requires a large amount of crystal growth time and lacks flatness. Secondly, absorption by charge carriers and impurities in the multilayer reflector cannot be ignored, and a high reflectance of 99.9% or more is obtained. It's difficult.

The present invention has been made in view of the conventional circumstances as described above, and has a structure in which the ratio of the refractive indexes of the materials forming the reflecting mirror can be increased, and the laminated layer has a smaller thickness and excellent reflectance characteristics. Another object of the present invention is to provide a surface-emitting type semiconductor laser having a flatter shape and a lower threshold value, which uses a reflection plate which can be expected.

[0005]

In the semiconductor laser of the present invention, the light emitting layer and the two reflecting mirrors sandwiching the light emitting layer are made of InP.
In a surface emitting semiconductor laser having a structure laminated on a substrate, at least one of the reflecting mirrors on the substrate side has a bandgap wavelength smaller than the wavelength of emitted light.
The multilayer reflective film is characterized by comprising at least one cycle of a composition III-V group compound semiconductor layer and a II-VI group compound semiconductor layer lattice-matched to nP. Particularly, as the II-VI group compound semiconductor lattice-matched to InP with the II-VI group compound semiconductor layer, CdSS is used.
The feature is that e, ZnTeS, and ZnTeSe are used.

[0006]

In general, it is known that the reflectance of a multilayer reflective film in which two types of dielectrics having a layer thickness of ¼ wavelength are multi-layered is given by the following equation.

[0007]

In the formula, R, n ₀ , n _s , n ₁ , n ₂ and N are the reflectance of the multilayer reflective film, the refractive index of the medium on the incident side, the refractive index of the substrate and the first dielectric. The refractive index, the refractive index of the second dielectric material, and the number of stacked periods are shown.

In the surface emitting semiconductor laser according to the present invention,
A group III-V compound semiconductor layer and a group II-V compound semiconductor layer having a composition having a bandgap wavelength smaller than the oscillation wavelength and having a layer thickness of a quarter wavelength, lattice-matched to InP, in two types of layers constituting the reflecting mirror, and II- A Group VI compound semiconductor layer is used. The refractive index n ₂ of the II-VI group compound semiconductor layer is 3. When the oscillation wavelength is 1.55 μm, as compared with the case where the conventional III-V group compound semiconductor layer (for example, InP) is used.
Since it is as small as 17 to 2.4 to 2.6, a high reflectance can be obtained with a small number of lamination cycles. For example, oscillation wavelength 1.5
In the case of 5 μm, the reflectance using InP and CdSSe is 9
A multilayer reflection film of 9,9% requires a total thickness of 4 μm for 14 periods, which is much thinner than the conventional one. Therefore, a flat shape that is easier to integrate than the conventional one can be formed, and the reflectance can be increased, so that the oscillation threshold value can be further reduced.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view for explaining an embodiment of the present invention. The emitted light 20 is emitted from the back surface of the substrate 10 in a direction perpendicular to the substrate surface. The substrate 10 was a (100) plane S-doped n-type InP substrate. Double hetero structure 1
Reference numeral 2 is a structure in which an n-type InP layer, an InGaAs light emitting layer 16, and a p-type InP layer are sequentially stacked, and the emission wavelength is 1.55 μm.
It is a quantum well structure having a light emitting layer thickness of m. An n-type multilayer reflective film 11 and a p-type multilayer reflective film 13 were formed at positions sandwiching the double hetero structure 12 from above and below. The n-type multilayer reflective film 11 is an n-type InGaAsP layer 18 having a thickness of 112 nm.
(Bandgap wavelength 1.45 μm) and thickness 164 nm
The n-type CdSSe layers 19 are alternately laminated for 11 periods. The p-type multilayer reflective film 13 is a p-type I having a thickness of 112 nm.
After stacking the nAsP layer (bandgap wavelength 1.45 μm) and the p-type CdSSe layer having a thickness of 164 nm for 15 cycles,
It is shaped into a 10 μm square to limit the oscillation region. Regarding current injection, among the carriers injected into the InGaAs light emitting layer 16, electrons are transferred from the n-type electrode 14 on the back surface of the substrate to the substrate 10.
Then, it is injected through the n-type multilayer reflective film 11. On the other hand, holes are injected from the p-type electrode 15 on the multilayer reflective film 13 through the p-type multilayer reflective film 13. The recombination of electrons and holes mainly occurs in the light emitting region 17, and since the resonator is formed only in the p-type multilayer reflective film 13, the injection current after the oscillation flows only in the light emitting region 17. It enables low drive current and high efficiency oscillation.

The surface emitting semiconductor laser of the present invention is as follows.
On the n-type InP substrate 10 having a (100) plane, In
112nm thick n-type InGaAsP lattice-matched to P
Layer 18 (bandgap wavelength 1,45 μm) and thickness 16
The n-type CdSSe layers 19 having a thickness of 4 nm are alternately laminated for 11 cycles. For the stacking, an MBE growth apparatus having a structure in which an independent growth chamber for III-V compound semiconductor and a growth chamber for II-VI compound semiconductor are connected by a vacuum transfer chamber is used, and the InP substrate 10 is provided in each growth chamber. And reciprocate to stack. Next, the n-type InP layer, the InGaAs light emitting layer, and the p-type In
The P layers are sequentially stacked to grow the double heterostructure 12 having a light emitting layer thickness with an emission wavelength of 1.55 μm. Further, the p-type multilayer reflective film 13 is a p-type InG film having a thickness of 112 nm.
An aAsP layer (bandgap wavelength 1.45 μm) and a p-type CdSSe layer having a thickness of 164 nm are stacked for 15 periods. I
In the MBE growth method of II-V group compound semiconductor, 950 ° C.
Gases of arsine and phosphine are introduced into the high vacuum chamber through the cracking cell heated above, and In and Ga metals are heated by the Knudsen cell and irradiated with the InP substrate 10 under the control of a shutter to grow the InP substrate 10. In the MBE growth method for II-VI compound semiconductors, the K cell is heated to C
The InP substrate 10 is irradiated with d, S, and Se to grow. After stacking the p-type multilayer reflective film 13, the p-type multilayer reflective film 13 is shaped into a 10 μm square by dry etching using a resist formed by ordinary photolithography as a mask.
When the SiO ₂ layer 21, the n-type electrode 14 and the p-type electrode 15 are formed, the semiconductor laser of FIG. 1 is completed.

The surface-emitting type semiconductor laser of the present invention comprises a multi-layered reflective film with InGaAsP as a high refractive index layer and a low refractive index layer.
(Bandgap wavelength 1.45 μm) and CdSSe
(S composition 80%) is used, and the refractive index at the oscillation wavelength is 3.466 and 2.357, respectively, which is a large difference in refractive index from each other.
A high reflectance of 9% is obtained. As a result, the layer thickness of the n-type multilayer reflective film 11 is 3 μm, which is a remarkably reduced layer thickness as compared with the prior art. Also, a very high refractive index of 99.99% or more can be obtained with a multilayer reflective film of 15 periods, and the oscillation threshold can be reduced.

In the above embodiment, CdSS is used as the low refractive index layer.
Although e was used, ZnTeS (Te composition about 67%), ZnTeSe (T
e composition about 46%) may be used.

In the above-mentioned embodiment, the multilayer reflective film consisting of the III-V group compound semiconductor layer and the II-VI group compound semiconductor layer is used on the upper and lower sides, but the multilayer reflective film of the above structure is used for the lower reflecting mirror (adjacent to the substrate. However, the upper reflecting mirror may be formed of a dielectric multilayer reflective film by vapor deposition or the like. In particular, when it is difficult to form one of the high-concentration p-type and n-type II-VI compound semiconductors due to the nature of the crystal, a conductivity type that is easy to form may be used for the lower multilayer reflective film.

In the above embodiment, the lower multilayer reflective film is of n type, but if a p type substrate is used, the same effect can be obtained even if the p type and n type are changed.

In the above embodiment, the epitaxial growth method is used.
Although the MBE method having a growth chamber was used, the present invention is not limited to this.

[0018]

Since the semiconductor laser according to the present invention has a structure capable of increasing the refractive index ratio of the material forming the reflecting mirror, excellent reflectance characteristics can be obtained with a smaller laminated layer thickness. It is possible to obtain a flat surface emitting semiconductor laser having a low threshold value.

[Brief description of drawings]

FIG. 1 is a schematic sectional view for explaining an embodiment of a semiconductor laser of the present invention.

[Explanation of symbols]

10 substrate 11 n-type multilayer reflective film 12 double heterostructure 13 p-type multilayer reflective film 14 n-type electrode 15 p-type electrode 16 InGaAs light-emitting layer 17 light-emitting region 18 n-type InGaAsP layer 19 n-type CdSSe layer 20 emitted light 21 SiO ₂ layer

Claims (4)

[Claims] 1. In a surface emitting semiconductor laser having a structure in which a light emitting layer and two reflecting mirrors sandwiching the light emitting layer are laminated on an InP substrate, at least the reflecting mirror on the substrate side of the reflecting mirrors is exposed. A multi-layered reflective film comprising a composition III-V compound semiconductor layer and a II-VI compound semiconductor layer having a bandgap wavelength smaller than the wavelength of emitted light and lattice-matched to InP, and comprising at least one cycle. Surface emitting semiconductor laser. 2. The group II-VI compound semiconductor layer containing In
The surface emitting semiconductor laser according to claim 1, wherein CdSSe having a composition lattice-matched to P is used. 3. The II-VI group compound semiconductor layer is formed of In.
The surface emitting semiconductor laser according to claim 1, wherein ZnTeS having a composition lattice-matched with P is used. 4. The II-VI compound semiconductor layer is formed of In.
A ZnTeSe having a composition lattice-matched to P is used.
The surface emitting semiconductor laser described.