JPH0740620B2 - Semiconductor light emitting element - Google Patents

Description

The present invention relates to a semiconductor light emitting device which is used for optical communication, optical information processing and the like and has little temperature dependence.

[Conventional technology]

Currently, as a light source for optical communication using a quartz fiber as a transmission line, a semiconductor light emitting device having a double hetero structure having an InGaAsP quaternary mixed crystal semiconductor as an active layer and InP as a clad layer is widely used. In particular, it is experimentally known that the semiconductor laser using these materials has a large temperature dependence of the oscillation threshold current value.

In order to reduce such temperature dependence, a semiconductor light emitting device is realized in which a semiconductor ultra-thin film is used as an active layer and the temperature dependence of the carrier state is reduced so that the state in the semiconductor can be described by a two-dimensional density of states. Has been done. It has been shown that the temperature dependence of the semiconductor light emitting device using this semiconductor ultrathin film is reduced even in InGaAsP / InP materials.
For example, Sasai et al., "Journal of Applied Physics (J.Appl.Phys.)", 1986, Vol. 59, No. 1 2
Reported on page 8.

[Problems to be solved by the invention]

In the structure of this ultra-thin semiconductor film, the carrier state is changed to improve the temperature characteristics.
The suppression of carrier overflow, which is considered to be one factor that deteriorates the temperature characteristics of semiconductor light emitting devices using InP-based materials, has not been considered. This phenomenon is described by Arakawa et al. In “Applied Physics Letters (Appl.Phys
s. Lett.) ”, 1984, Vol. 45, p.

An object of the present invention is to solve such a problem, and to provide a semiconductor light emitting device in which electrons that easily overflow due to a small effective receiving amount are confined in an active layer and temperature dependence of light emitting characteristics is reduced. .

[Means for solving problems]

The structure of the present invention is such that an active layer made of a semiconductor having a narrow forbidden band width is sandwiched between clad layers made of a semiconductor having a wide forbidden band width in the stacking direction, and the semiconductors forming these clad layers are separated by the active layer. In a semiconductor light emitting device having a multi-layered heterostructure having different conductivity types, a clad layer made of a p-type semiconductor is made of a first semiconductor having a film thickness that is in contact with the active layer and electrons cannot pass by tunneling. It is characterized in that it is composed of a first layer and a second layer made of a second semiconductor in which both the energy value at the lower end of the conduction band and the energy value at the upper end of the valence band are smaller than those of the first semiconductor.

[Action]

Usually, carriers are injected into the active layer of a semiconductor light emitting device through a clad layer having a wide band gap which is sandwiched by the active layer, and electrons are activated from the n-type clad layer and holes are activated from the p-type clad layer. Injected into layers. In this active layer, light is recombined with electrons and holes to emit light. In this case, the electron has a small effective mass,
There is a case where the active layer and the cladding layer penetrate into the p-type cladding layer beyond the difference in energy value (heterobarrier) at the bottom of the conduction band of each semiconductor. In order to control this phenomenon, a part of the p-type clad layer from the active layer is made of a semiconductor material whose energy value at the lower end of the conduction band is larger than that of the semiconductor of the clad layer to increase the size of the hetero barrier for the electrons. Then, the overflow of electrons is reduced. As for holes, if the energy value at the top of the valence band of some semiconductors from the active layer is larger than that of the semiconductor in the cladding layer, holes injected from the p-type cladding layer are The holes are satisfactorily injected into the active layer without being restrained by the hetero interface.

As a film thickness of a part of the semiconductor from the active layer, if the thickness is such that electrons cannot be tunneled, it is sufficient to prevent the overflow of electrons, and because of the energy distribution of holes due to heat, To reduce the amount of holes existing in a part of the semiconductor from the active layer, it is not preferable to increase the film thickness.

〔Example〕

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

FIG. 1 is a perspective view of a semiconductor laser according to an embodiment of the present invention, and FIG. 2 is a band diagram near the active layer of the semiconductor laser of FIG. This example is a metal organic chemical vapor deposition method (MO-CVD
Method) to fabricate the substrate with the original multi-layered heterostructure, and then use the normal process and liquid phase epitaxy (LPE method) for the light emission part for lateral mode control and effective carrier injection. Is left in a stripe shape and both sides thereof are buried and grown.

First, using the MO-CVD method, on the S-doped n-type InP substrate 11,
2 μm thick n-type InP clad layer 12, 0.1 μm thick undoped In _0.6 Ga _0.4 As _0.8 P _0.2 active layer 13,5 nm thick p-type In _0.52 Al
_{A 0.48} As clad layer 14 and a 1 μm thick p-type InP clad layer 15 were sequentially grown. Next, a SiO ₂ film is formed on the growth surface to a thickness of 0.2 μm by the CVD method, and then two channels of 10 μm width are formed by an ordinary photolithography method at an interval of 1.5 μm.
It was opened to iO ₂ and the channel was etched down to the substrate 11 by wet etching. By removing this SiO ₂ over the entire surface, the p-type InP layer 16, the n-type InP layer 17, the p-type InP layer 18, p are formed by the LPE method.
A type In _0.75 Ga _0.25 As _0.53 P _0.47 cap layer 19 was sequentially grown, and electrodes 20 were formed on the upper and lower surfaces by vapor deposition. Then, a semiconductor laser was manufactured by cleaving it into a width of about 300 μm and a length of about 300 μm.

Here, the band diagram in the stacking direction near the active layer is as shown in FIG. Here, the energy value of the conduction band lower end A is p-type InAl with a forward bias of about 1 V applied.
The maximum value in As14, and the energy value at the valence band upper end B is larger in p-type InAlAs14 than in p-type InP15.

The semiconductor laser according to the present embodiment has an oscillation threshold current value at room temperature of about 25 mA, and the temperature dependence of this value is given by the following equation when the oscillation threshold current value at temperature T is I _(T). Become.

When considering this temperature characteristic, the value of the characteristic temperature T ₀ is about 90K.
Therefore, the value is 60K for a normal semiconductor laser without InAlAs14
A good value was obtained as compared with. Also, the maximum value of continuous oscillation temperature was good at 120 ° C.

In the above description, one embodiment was described, but the present invention is not limited to this embodiment, and any of semiconductor growth methods such as LPE, MO-CVD, halide vapor phase growth, and molecular beam epitaxy growth may be used. To be . In addition, the material system is InGa
Other materials such as GaAs / AlGaAs series other than AsP / InP series may be used, or a system having lattice mismatch with the substrate may be used.

〔The invention's effect〕

As described above, according to the present invention, it is possible to obtain a semiconductor light emitting element that has a small temperature dependence of oscillation and light emission characteristics such as an oscillation threshold current value and can operate up to a high temperature.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a semiconductor laser according to an embodiment of the present invention, and FIG. 2 is a band diagram near the active layer of FIG. 11 …… n-type InP substrate, 12 …… n-type InP clad layer, 13 ……
In _0.6 Ga _0.4 As _0.8 P _0.2 active layer, 14 …… In _0.52 Ga _0.48 As clad layer, 15 …… p type InP clad layer, 16,18 …… p type In
P layer, 17 ... n-type InP layer, 19 ... p-type In _0.75 Ga _0.25 As _0.53
P _0.47 Cap layer, 20 ... Electrode, A ... Lower conduction band, B
…… The top of the valence band.

Claims (1)

[Claims] 1. An active layer made of a semiconductor having a narrow bandgap is sandwiched between clad layers made of a semiconductor having a wide bandgap in the stacking direction, and the semiconductors composing these clad layers are bordered by the active layer. In a semiconductor light emitting device having a multi-layered heterostructure having different conductivity types, a clad layer made of a p-type semiconductor is in contact with the active layer and has a film thickness such that electrons cannot pass by tunneling. 1. A semiconductor light emitting device comprising one layer and a second layer made of a second semiconductor having a lower energy value at the lower end of the conduction band and a lower energy value at the upper end of the valence band than those of the first semiconductor.