JPH0550873B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is used in optical communication, information processing, etc.
The present invention relates to a group compound semiconductor light emitting device.

(Prior art and its problems) Light-emitting elements using InP, GaAs, or a multi-component mixed crystal thereof include semiconductor lasers and light-emitting diodes. The basic structure of these light emitting devices is a double heterostructure in which n-type and p-type cladding layers sandwich an active layer having a smaller energy gap than the cladding layers. However, in recent years, the amount of energy discontinuity at the bottom of the conduction band between the active layer and the cladding layer has changed due to the emission temperature characteristics of the generating element and the oscillation threshold current density of the semiconductor laser.
It has been found that it affects Ith. As a countermeasure to this problem, it has been proposed to insert a semiconductor layer having a larger energy gap than the cladding layer between the active layer and the cladding layer. On the other hand, research is also progressing on strained superlattices in which two semiconductor layers with different lattice constants are alternately arranged. A compound semiconductor light emitting device with a strained ultra-thin film with a larger energy gap and different lattice constant than the cladding layer was also disclosed in patent application No. 57-104756.
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FIG. 1 is an energy band diagram at the lower end of the conduction band of a light emitting device having a conventional strained ultra-thin film.
15 is an n-type cladding layer, P-type cladding layers 12 and 14 are strained ultra-thin films having different lattice constants from the cladding layers, and 13 is an active layer. Conventional strained ultra-thin films 12, 14 are disposed adjacent to active layer 13. Electrons injected into the n-type cladding layer 11 cross the low energy barrier of the strained ultra-thin film (semiconductor layer) 12 and are injected into the active layer 13. However, the electrons injected into the active layer 13
The cladding layer 15 cannot be reached due to the high barrier of the cladding layer 15. Holes injected into the p-type cladding layer 15 are also injected in the opposite direction and into the active layer 13.
The carriers injected into the active layer 13 remain in the active layer 13 and effectively contribute to light emission. However, in a conventional light emitting device having a strained ultra-thin film, the strained ultra-thin film 12
Since the film is placed adjacent to the active layer 13, the strain due to the difference in lattice constant extends to the active layer, shortening the life of the light emitting device. There was a problem in that the difference in thermal expansion coefficients promoted distortion at the interface and deteriorated the light emitting characteristics.

(Objective of the Invention) An object of the present invention is to provide a compound semiconductor light-emitting device that maintains the inherent carrier injection efficiency and luminous efficiency, and improves the device life and high-temperature operating characteristics.

(Structure of the Invention) The light emitting device of the present invention has a structure in which a single layer or multilayer active layer serving as a light emitting region is sandwiched between clad layers having a larger energy gap than the active layer, and At least one of the cladding layers has a semiconductor layer with a larger energy gap and a different lattice constant than the cladding layer.
In group compound semiconductor sending devices, the energy gap between the active layer and the semiconductor layer is larger than the energy gap of the active layer, and the lattice constant is less than the longer lattice constant of the active layer and the semiconductor layer and greater than the short lattice constant of the active layer and the semiconductor layer. The structure has a single-layer or multi-layer strain relaxation layer.

(Operation/Principle of the Invention) The present invention solves the problems of conventional light emitting elements by adopting the above-described configuration. In other words, between the strained ultra-thin film and the active layer, there is a strain relaxation layer with a lattice constant that is intermediate between the lattice constants of these semiconductor layers. I'm starting to not be able to concentrate. As a result, the lifetime and temperature characteristics of the device are improved. By making the composition of the strain relaxation layer close to that of the active layer, the thermal expansion coefficients of the strain relaxation layer and the active layer are brought close to each other, thereby suppressing the increase in strain due to temperature rise. It can also be decreased. Also,
If the strain relaxation layer has a multilayer structure in which semiconductor layers with slightly different lattice constants are laminated, the strain between the strained ultra-thin film and the active layer will be almost eliminated, and the effect will be great.

(Example) FIG. 2 is an energy band diagram for explaining an example of the present invention. The conditions tested in this example are that the n-type cladding layer 11 and the p-type cladding layer 15 are S-doped InP layer and Zn-doped layer, respectively.
The InP layer is In 0.85 Ga 0.15 P, and the strained ultra-thin films 12 and 14 are In _0.85 Ga _0.15 P.
The active layer 13 is an In _0.74 G _0.26 As _0.56 P _0.44 layer, and the strain relaxation layers 21 and 22 are S-doped InP and Zn-doped, respectively.
It was named InP. When this sample was compared with a conventional light-emitting element without a strain relaxation layer, both of which were used as stripe electrode type semiconductor lasers, the laser characteristics of this sample were that the lasing threshold current density Ith was the same as that of the conventional one.
The maximum oscillation temperature was 35°C. On the other hand, it was confirmed that the lifetime was almost the same as that of a normal double heterostructure laser without a strained ultra-thin film, and the effects of the present invention were fully confirmed.

FIG. 3 is an energy band diagram for explaining the second embodiment of the present invention. The difference from this embodiment is that the strain relaxation layers are multilayered, and the strain relaxation layers 31 and 34 are In _0.94 Ga _0.06 As _0.14 P _0.86 layers, and the strain relaxation layers 32 and 33 are In _0.87 Ga _0.13 As _0.30 P. The layer was set to _0.70 .
When this sample was made into a striped electrode type semiconductor laser similar to the first example, the maximum oscillation temperature was improved by more than 5° C. from the first example, and the effects of the present invention were fully confirmed in this example as well. In the above embodiment, an InGaAsP/InP light emitting device is used,
Although the n-type and p-type impurities are S and Zn, respectively, they are not limited to the above-mentioned compound semiconductors and impurities, and may be InGaAsP/GaAs-based, AlGaSd/GaSd-based, or other compound semiconductors, or may be other compound semiconductors such as Be or Mg. It may be an impurity.

In the above embodiments, the strained ultra-thin films were placed on both sides of the active layer, but they may be placed on one side.

In the above embodiments, the composition and the number of layers of the strain relaxation layer were made symmetrical with respect to the active layer, but the composition and the number of layers are not limited to symmetrical, and may be asymmetrical.

In this example, the active layer serving as the light emitting region is
Although the structure is made up of layers, the effects of the present invention can also be sufficiently exerted using a superlattice structure in which semiconductor layers with a smaller energy gap and semiconductor layers with a larger energy gap are alternately arranged in multiple layers.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to maintain the carrier injection efficiency and luminous efficiency, which are the characteristics of conventional light emitting elements with strained ultra-thin films, and further improve the luminous temperature characteristics and extend the lifespan. , long-term reliability can be achieved.

[Brief explanation of drawings]

FIG. 1 is an energy band diagram of a compound semiconductor light emitting device having a strained ultra-thin film, and FIGS. 2 and 3 are diagrams for explaining first and second embodiments of the present invention, respectively. 11 and 15...n-type and p-type cladding layers, 12 and 14...strained ultra-thin film, 13...active layer, 21, 22, 31, 32, 33 and 34...
...Strain relaxation layer.

Claims (1)

[Claims] 1 A structure in which a single or multilayer active layer serving as a light emitting region is sandwiched between cladding layers having a larger energy gap than the active layer, and at least one of the cladding layers is between the active layer and the cladding layer. In a / group compound semiconductor light emitting device having semiconductor layers with a large energy gap and different lattice constants, the energy gap between the active layer and the semiconductor layer is larger than that of the active layer and the lattice constant of the active layer is larger than that of the active layer. A / group compound semiconductor light emitting device, characterized in that it has a single layer or multilayer strain relaxation layer whose lattice constant is equal to or less than the longer lattice constant of the semiconductor layer and equal to or greater than the shorter lattice constant of the semiconductor layer.