JPH0621572A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser wherein heat generation due to contact resistance does not occur, by forming junction layers capable of reducing contact resistance, between a clad layer and an electrode. CONSTITUTION:In order to reduce contact resistance, a first junction layer 17 (nitrogen-doped Zn0.25Cd0.75S, thickness 0.1mum) and a second junction layer 18 (nitrogen doped Zn0.25Hg0.75S, thickness 0.1mum) are formed between a second clad layer 13 and a second conductivity type electrode 15. Thereby the forbidden bandwidth can be narrowed. Further contact resistance can be reduced by forming the junction layers of material wherein defect due to mismatching with lattice constants of a substrate 10 is not generated. Since the forbidden bandwidth of the second junction layer 18 is small to be nearly equal to that of gallium aarsenide of a substrate 10, low contact resistance can be expected by doping concentration of about 10<18>cm<-3>. In the above case, a composition matched in lattice with the substrate 10 can be obtained in the first junction layer 17 and the second junction layer 18, by about 25% zinc ratio of group II component composition. Thereby dislocation defect due to lattice distortion is not generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a II-VI compound semiconductor laser.

[0002]

2. Description of the Related Art A II-VI group compound semiconductor laser emits light of short wavelength green-blue because of a wider band gap of a material than a III-V group compound semiconductor laser, which emits red light only at a limit. It is useful from the application. A conventional example of such a semiconductor laser is the Applied Physics Letters magazine, 1991, Volume 59, No. 11, 1272-1274.
Reported on the page. This semiconductor laser is composed of chlorine (Cl) -doped ZnSe, ZnSS on a gallium arsenide substrate.
n-type clad layer in which e and ZnSe are laminated, CdZn
Se emitting layer and nitrogen-doped ZnSe, Z
The p-type cladding layer is formed by stacking nSSe and ZnSe, and a gold electrode is formed on the p-type ZnSe forming the upper p-type cladding layer. In this conventional example, pulse oscillation is reported at room temperature.

[0003]

However, the conventional semiconductor laser has not been able to obtain continuous oscillation at room temperature. One of the main causes of this is a high contact resistance between the p-type cladding layer and the p-type electrode. Due to this high contact resistance, a large amount of heat is generated, which causes problems such as a decrease in luminous efficiency due to a rise in the temperature of the light emitting layer and element destruction.

The present invention has been made in view of the conventional circumstances as described above, and has a bonding layer between the p-type clad layer and the electrode, which can reduce the contact resistance. The purpose is to provide a semiconductor laser that does not have the above.

[0005]

In a semiconductor laser according to the present invention, a light emitting layer, a lower first conductivity type clad layer and an upper second conductivity type clad layer sandwiching the light emitting layer are cadmium, zinc, sulfur and II consisting of 4 elements of selenium
In the group VI compound semiconductor laser, a first bonding layer made of zinc, cadmium and sulfur and a second bonding layer made of zinc, mercury and sulfur are provided between the second conductivity type clad layer and the electrode. There is. Further, between the first bonding layer and the second bonding layer, the composition of zinc and sulfur is kept constant, and the remaining composition is cadmium at a portion in contact with the first bonding layer and mercury at the second bonding layer. Is characterized by having a graded composition bonding layer in which the compositions of cadmium and mercury are gradually changed. Further, it is characterized by having a mercury sulfide layer having a layer thickness of 10 nm or less between the second bonding layer and the electrode.

[0006]

In general, in order to reduce the contact resistance between the semiconductor layer and the electrode, it is effective to increase the doping concentration of the semiconductor layer or decrease the forbidden band width to increase the tunnel current. The former method is not effective in II-VI group compound semiconductors in which high-concentration doping is difficult.
In the semiconductor laser of the present invention, as the latter method, the forbidden band width can be reduced, and the contact resistance can be reduced by using a material that does not cause a defect due to a mismatch with the lattice constant of the substrate as the bonding layer. First, Z with almost the same forbidden band width as the clad layer
A first bonding layer made of an nCdS layer is provided, a second bonding layer made of ZnHgS having a smaller forbidden band width is stacked on the first bonding layer, and an electrode is formed on the second bonding layer. 10 ¹⁸ cm because the forbidden band width of the second bonding layer is close to the gallium arsenide of the substrate
^{Even with} a doping concentration of about ^-3, a contact resistance of about 10 ^-4 Ωcm can be expected. In this case, since the composition of the group II component zinc in the first bonding layer and the second bonding layer is approximately 25% and lattice-matched to the substrate, dislocation defects due to lattice strain do not occur. In addition, the composition of zinc and sulfur is kept constant between the first bonding layer and the second bonding layer, and the remaining composition is cadmium at the portion in contact with the first bonding layer and cadmium at the portion bonding to the second bonding layer so as to be mercury. By providing a graded composition bonding layer in which the composition of mercury is gradually changed,
Since the resistance increase due to the heterojunction barrier between the junction layer and the second junction layer can be suppressed, the contact resistance can be further reduced. Further, between the second bonding layer and the electrode, 10
The contact resistance can be made extremely small by providing the mercury sulfide layer having a layer thickness of nm or less. This is because the forbidden band width of the mercury sulfide layer is a semimetal having a negative value, and by using a layer thickness of 10 nm or less, it is possible to suppress the generation of defects due to a lattice mismatch of about 4%.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram for explaining a first embodiment of the present invention. Substrate 10 is Si-doped (100) plane GaAs
A substrate is used. The double heterostructure has a first conductivity type clad layer 11 made of chlorine-doped ZnS _0.05 Se _0.95 having a thickness of 2 μm and a light emitting layer 1 made of CdZnSe having a thickness of 50 nm.
0, and a second conductivity type cladding layer 13 made of nitrogen doped ZnS _0.05 Se _{0. 95} having a thickness of 2 [mu] m. In order to reduce the contact resistance with the second conductivity type electrode 15, the first bonding layer 17
(Nitrogen-doped Zn _0.25 Cd _0.75 S, thickness 0.1 μm) and the second bonding layer 18 (nitrogen-doped Zn _0.25 Hg _0.75 S, thickness 0.1 μm) are provided. The hole current is confined from the electrode 15 by the insulating layer (SiO ₂ ) 14 and the second bonding layer 18,
It is injected into the light emitting layer 12 through the first bonding layer 17 and the second conductivity type cladding layer 13. The electron current is injected into the light emitting layer 12 through the first conductivity type electrode 16, the substrate 10, and the first conductivity type clad layer 11. Since the forbidden band width of the second bonding layer 18 is close to that of gallium arsenide of the substrate 10, a contact resistance of about 10 ⁻⁴ Ωcm can be expected even at a doping concentration of about 10 ¹⁸ cm ⁻³ . In addition, both the first bonding layer 17 and the second bonding layer 18 are II
Since the composition in which the zinc content of the group component composition is approximately 25% is lattice-matched to the substrate 10, dislocation defects due to lattice strain do not occur. Furthermore, the first bonding layer 17 and the second bonding layer 1
In No. 8, since the group VI element is only S, the composition can be easily controlled and the lattice matching can be more accurately obtained. As a result, it is possible to obtain a semiconductor laser in which heat generation is small because the contact resistance is reduced, and there are no problems such as a decrease in light emission efficiency due to a rise in the temperature of the light emitting layer and element destruction.

FIG. 2 is a schematic diagram for explaining the second embodiment of the present invention. For calculation 10, a Si-doped (100) plane GaAs substrate is used. Double hetero structure has a thickness of 2 μm
Chlorine doped ZnS _0.05 Se _0.95, first conductivity-type cladding layer 11 made of, light emitting layer 10, a thickness of 2μm nitrogen-doped ZnS _0.05 Se _{0. 95} consisting of CdZnSe thickness 50nm
The second conductivity type cladding layer 13 is formed of. In order to reduce contact resistance with the second conductivity type electrode 15, the first bonding layer 17 (nitrogen-doped Zn _0.25 Cd _0.75 S, thickness 0.1 μm).
m) and the second bonding layer 18 (nitrogen-doped Zn _0.25 Hg _0.75
S, thickness 0.1 μm), and further the first bonding layer 17
The composition of zinc and sulfur is kept constant between the second bonding layer 18 and the second bonding layer 18, and the composition of cadmium and mercury is adjusted so that the remaining composition becomes cadmium at the portion in contact with the first bonding layer 17 and mercury at the second bonding layer 18. Gradient composition graded bonding layer 19
(Zn _0.25 Hg _0.75x Cd _{0.75 (1-x)} S, x = 0 to 1) is provided. As a result, the first bonding layer 17 and the second bonding layer 1
Since the increase in resistance due to the heterojunction barrier between 8 can be suppressed, the contact resistance can be further reduced. Since the first bonding layer 17, the second bonding layer 18, and the graded composition bonding layer 19 can have a composition in which the proportion of the group II component zinc is approximately 25% and which is lattice-matched to the substrate, dislocation defects due to lattice strain occur. Absent. Further, also in the first bonding layer 17, the second bonding layer 18, and the graded composition bonding layer 19, the composition of the VI group element is only S, and the composition can be easily controlled and the lattice matching can be more accurately obtained. As a result, it is possible to obtain a semiconductor laser in which the contact resistance is further reduced, the heat generation is small, the luminous efficiency is lowered due to the temperature rise of the light emitting layer, and the element is not destroyed.

FIG. 3 is a schematic diagram for explaining a third embodiment of the present invention. As the substrate 10, a Si-doped (100) plane GaAs substrate is used. Double hetero structure has a thickness of 2 μm
Chlorine doped ZnS _0.05 Se _0.95, first conductivity-type cladding layer 11 made of, light emitting layer 10, a thickness of 2μm nitrogen-doped ZnS _0.05 Se _{0. 95} consisting of CdZnSe thickness 50nm
The second conductivity type cladding layer 13 is formed of. In order to reduce contact resistance with the second conductivity type electrode 15, the first bonding layer 17 (nitrogen-doped Zn _0.25 Cd _0.75 S, thickness 0.1 μm).
m) and the second bonding layer 18 (nitrogen-doped Zn _0.25 Hg _0.75
S, thickness 0.1 μm), and further the second bonding layer 18
A mercury sulfide layer 20 having a layer thickness of 10 nm or less is provided between the second conductivity type electrode 15 and the second conductivity type electrode 15. As a result, the contact resistance can be made extremely small. This is because the forbidden band width of mercury sulfide is a semimetal having a negative value. The mercury sulfide layer 20 has a lattice mismatch of about 4% with respect to the substrate 10, but by using an extremely thin layer thickness of 10 nm or less, generation of dislocation defects due to the lattice mismatch can be suppressed.

The epitaxial growth layer of the semiconductor laser of the above-mentioned embodiment according to the present invention is a molecular beam epitaxial growth method in which sulfur, selenium, zinc, cadmium, and mercury are evaporated in a Knudsen cell, and the composition of each layer is adjusted to the molecular beam shutter and Knudsen. It was formed by controlling the cell temperature. In addition, chlorine and nitrogen radicals used chlorine and nitrogen radicals.

In the above embodiment, the insulating layer was used as the current confinement method, but other current confinement methods using buried growth or the like may be used, and the present invention is not limited to this.

[0012]

The semiconductor laser according to the present invention has a bonding layer between the clad layer and the electrode, which can reduce the contact resistance, and therefore it is an object of the present invention to provide a semiconductor laser free from the problem of heat generation due to the contact resistance.

[Brief description of drawings]

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

FIG. 2 is a schematic cross-sectional view for explaining a second embodiment of the semiconductor laser of the present invention.

FIG. 3 is a schematic cross-sectional view for explaining a third embodiment of the semiconductor laser of the present invention.

[Explanation of symbols]

 Reference Signs List 10 substrate 11 first conductivity type clad layer 12 light emitting layer 13 second conductivity type cladding layer 14 insulating layer 15 second conductivity type electrode 16 first conductivity type electrode 17 first bonding layer 18 second bonding layer 19 gradient composition bonding layer 20 Mercury sulfide layer

Claims (3)

[Claims] 1. A light emitting layer, a lower first conductivity type cladding layer and an upper second conductivity type cladding layer sandwiching the light emitting layer, the group II-VI comprising four kinds of elements of cadmium, zinc, sulfur and selenium. A compound semiconductor laser comprising a first bonding layer made of zinc, cadmium and sulfur and a second bonding layer made of zinc, mercury and sulfur between the second conductivity type clad layer and the electrode. . 2. The composition of zinc and sulfur is kept constant between the first bonding layer and the second bonding layer, and the remaining composition is cadmium and the second composition at a portion in contact with the first bonding layer.
2. The semiconductor laser according to claim 1, further comprising a graded composition junction layer in which the composition of cadmium and mercury is gradually changed so that the portion in contact with the junction layer becomes mercury. 3. A gap between the second bonding layer and the electrode is 10 nm.
The semiconductor laser according to claim 1, further comprising a mercury sulfide layer having the following layer thickness.