JPS62144387A - Semiconductor light-emitting device - Google Patents

Abstract

PURPOSE:To improve threshold current density, conversion efficiency and temperature characteristics, etc. by making the difference of the energy levels of electrons and holes in each semiconductor layer having superlattice structure larger than the forbidden band width of an active layer, and performing confinement at least on one active layer of a carrier by superlattice structure. CONSTITUTION:Semiconductor layers 2-6 are grown on a PbTe substrate 1 in succession through a method such as a molecular-beam epitaxy method (an MBE method). Impurity concentration is brought to approximately 2X10<18>cm<-3> and thickness to approximately 3mum in the P-type PbTe layer 2, the superlattice structure 3 is formed in a non-doping manner and the whole thickness is brought to approximately 0.3-0.5mum, thickness is brought to approximately 10nm in Pb0.9Sn0.1Te layers 3a, and thickness is brought to approximately 5nm in Pb0.75Sn0.25Te layers 3b. The Pb0.9Sn0.1Te active layer 4 is shaped in a non-doping manner and thickness is brought to approximately 0.5mum, the superlattice structure 5 is constituted similarly in order in which the superlattice structure 3 is inverted, and impurity concentration is brought to approximately 3X10<18>cm<3> and thickness to approximately 2mum in the N-type PbTe layer 6. An electron confinement effect is acquired by the superlattice structure 3, 5, and the confinement effect of holes is obtained by the PbTe layers 2, 6, the upper ends of valence bands thereof are made lower than the Pb0.9Sn0.1Te active layer by approximately 90meV.

Description

[Detailed Description of the Invention] [Summary] The present invention provides a double heterojunction structure using a semiconductor layer that satisfies the conditions that the lower end of the conduction band is at a higher energy level and the upper end of the valence band is at a lower energy level than the active layer. In order to improve semiconductor light emitting devices, which was previously impossible or difficult to achieve, a superlattice structure is formed using a semiconductor layer that does not meet the above conditions and functions as a quantum mechanical well potential with respect to at least one carrier. at least one of making the energy level of the hole higher than the energy level of the bottom of the conduction band of the active layer, or making the highest energy level of the hole lower than the energy level of the top of the valence band of the active layer. By realizing this and making the energy level difference between electrons and holes in the superlattice structure larger than the forbidden band width of the active layer, it is possible to confine electrons and holes, and the dark value current density, temperature It improves the characteristics etc.

[Industrial application field]

The present invention relates to a semiconductor light emitting device, and particularly to a semiconductor light emitting device in which carrier confinement is achieved in an active layer in which carrier confinement using a normal double heterojunction is difficult or impossible.

For example, long-wavelength infrared light sources are required for gas detection systems, but conventional semiconductor light-emitting devices for this band still have the problem of carrier confinement, which can be solved to improve characteristics such as dark value current density. It is desired to realize this.

[Conventional technology]

Most conventional semiconductor light-emitting devices use a double heterojunction, in which an active layer with a forbidden band width corresponding to the target wavelength of light is sandwiched between cladding layers with a larger forbidden band width and a lower refractive index. The structure confines carriers and light.

In other words, for example, as illustrated in FIG.
In a semiconductor laser with a band of about 1.55 μm, the active layer A is made of indium gallium arsenide phosphorus (In+-Ja
xAsxP 1-X), indium phosphorus (
Using InP), a barrier that confines the gear in the active layer A is formed by an energy level difference at the bottom of the conduction band for electrons and an energy level difference at the top of the valence band for holes.

On the other hand, ammonia (NH:1), methane (CH
In a semiconductor light-emitting device using a light source with a wavelength band of about 8 μm corresponding to its infrared absorption spectrum for detection of Tellurium (Pbo, 9SnQ, 1T
e) Lead tellurium (PbTe) is used for the cladding layer C.

According to this configuration, the cladding layer C acts as a barrier for holes due to the energy level difference at the top of the valence band.
The lower end of the conduction band is Pb, contrary to the InGaAsP/InP system.
Te is lower than Pbo, 9sno, +Te, and no barrier is formed for electrons, resulting in no confinement effect. As a result, although it is possible to reach a laser oscillation state, there are many problems with its characteristics, such as a large reactive current, dark value current density, and a large temperature rise.

Furthermore, if active layer A contains Pbo, tssno, zsTe
,, If PbTe is used for the cladding lc, Fig. 4 (
As illustrated in bl, the upper end of the valence band of the active layer A is above the lower end of the conduction band of the cladding layer C, and no barrier is formed for both electrons and holes.

[Problems to be Solved by the Invention] For the double heterojunction structure of an active layer and a cladding layer of a semiconductor light emitting device, combinations having slightly different compositions have been generally used. This configuration is based on the crystal structure, forbidden band width,
This is the most natural method for selecting combinations of optical properties, etc., as described above (InGaAsP/InP, GaAs/A
For many I[I-V group compound semiconductor abrasive materials such as IGaAs-based materials, the desired effects such as carrier confinement have been achieved.

However, in the case of Pb5nTe/PbTe, etc., as exemplified above, in a double heterojunction structure with a combination of slightly different compositions, a barrier is not formed for at least one of the carriers, so dark value current density, conversion efficiency, temperature characteristics, etc. etc., and there is a strong demand for improvement.

Means for Solving Problem C] The above problem is that the lower end of the conduction band is at a higher energy level than the active layer, and the upper end of the valence band is at a lower energy level, and at least one carrier A superlattice structure constituted by a semiconductor layer functioning as a quantum mechanical well potential with respect to the active layer is provided above and below the active layer,
The energy level difference force q between electrons and holes in each semiconductor layer of the superlattice structure is larger than the forbidden band width of the active layer, and the superlattice structure confines at least one carrier in the active layer. This problem is solved by a semiconductor light emitting device according to the present invention.

[For production]

According to the present invention, the condition that the lower end of the conduction band is at a higher energy level than the active layer and the upper end of the valence band is at a lower energy level does not apply, and in the conventional double heterojunction structure, electrons, A quantum well type superlattice structure is formed using a semiconductor material in which it is impossible to confine both holes, and confinement is performed in the active layer of at least one gear. This superlattice structure is composed of a semiconductor layer that has a quantum well type potential at least for electrons and a semiconductor layer that has a quantum well type potential for at least holes.

In a semiconductor layer with a quantum well type potential for electrons, the lowest energy level of the electron, that is, the level of the subband of the ground state of the electron, or the level of the barrier if the thickness is extremely small and no subhand is formed. The energy level difference between the top of the electron band and the bottom of the conduction band, and the energy level difference between the highest energy level of the hole and the bottom of the conduction band in a semiconductor layer with a quantum well potential for holes, can be calculated from the forbidden band width of the active layer. to prevent carrier recombination within this superlattice structure.

If the structure is such that the lowest energy level of electrons is higher than the energy level at the bottom of the conduction band of the active layer, electrons will be confined in the active layer, and the highest energy level of holes will be at the top of the valence band of the active layer. If the structure is lower than the energy level, holes will be confined in the active layer.

〔Example〕

The present invention will be specifically explained below using examples.

FIG. 1(a) is a schematic side sectional view showing a first embodiment of the present invention, and FIG. 1(a) is a diagram showing the energy level thereof.

In the figure, 1 is a p-type PbTe substrate, 2 is an n-type PbT substrate.
e layer, 3 and 5 are PI) o, qsno, +Te layer 3
a or 5a and Pbo, tssno, 2STE1 layer 3
b or 5b, 4 is Pb0. , S
1Te active layer, 6 an n-type PbTe layer, 7 an n-type PbTe buried layer, 11 an insulating layer made of, for example, an anodic oxide film of PbTe, 12 an n-side electrode, and 13 a p-side electrode.

The semiconductor layers 2 to 6 are sequentially grown on the PbTe1 plate 1 by, for example, the molecular beam epitaxy method (MBE method), and the n-type PbTe layer 2 has an impurity temperature of about 2×10101B.
", the thickness is about 3 μm, the superlattice structure 3 is non-doped, the total thickness is about 0.3 to 0.5 μm, for example, pbo
, qsno, +Te layer 3a with a thickness of about 10 nmXPb
o, 7ssno, zsTe layer 3b has a thickness of approximately 5 nm. In addition, the Pb@, qsno, 4e active layer 4 is non-doped and has a thickness of about 0.5 μm, and the superlattice structure 5 is constructed in the same manner as the superlattice structure 3 in reverse order, and is made of n-type Pb
The Te layer 6 has an impurity temperature of about 3XIO”cm3 and a thickness of about 2
It is expressed as μm.

In contrast to the Pbo, qsno, +Te active layers of this example, the conduction band bottom of the PbTe layer is approximately 40 meν (temperature 77K).
) is low and there is no electron confinement effect as mentioned earlier, but P
bo, 7ssno.

The conduction band bottom of the z5Te layer is about 60 meV higher, and in the pb, qsno, Te quantum well layer using this as a barrier layer, the subhand energy level of the electron ground state is higher than the conduction band bottom of the active layer as shown in the figure. This superlattice structure 3.5 provides an electron confinement effect.

Moreover, the hole confinement effect of this example is as follows: Pb0. qS
No, the top of the valence band is about 90me for the 4e active layer
Obtained by a low V PbTe layer 2.6.

Note that the forbidden band width of the Pbo, tssno, z5Te layer is as narrow as about 80 meν, but for holes Pbo, , s
No. A quantum well is constructed with 1T6 layers as 17 layers, and its highest energy level is the energy level at the lower end of the conduction band of the barrier layer, and the energy level difference with the lower end of the conduction band is the upper limit of the active layer. This layer is made larger than the band width to prevent carrier recombination from occurring in this layer.

Next, FIG. 2 is a diagram showing energy levels of a second embodiment of the present invention. In the same figure, 2 is an n-type PbTe layer, 3
A and 5A are 5nTe layer 3c or 5c and PbTe layer 3d
or a superlattice structure consisting of 5d, 4 is Pbo, qsn
o, 4e active layer, and 6ban type PbTe layer.

The difference between this example and the previous example is that the semiconductor layers constituting the superlattice structure are a 5nTe layer 3c or 5c and a PbTe layer 3d or 5d. Pbo, qsno,
Compared to the forbidden band of the +Te active layer, the forbidden band of the 5nTe layer is at an extremely high level, and the forbidden band of the PbTe layer is at a slightly lower level, and due to this superlattice structure, the electrons in the PbTe layer are The energy level of the ground state sub-hand is higher than the lower end of the conduction band of the active layer, and the energy level of the hole ground state sub-band in 5nT4 is lower than the energy level of the upper end of the valence band of the active layer. An even better electron and hole confinement effect than the first embodiment is obtained.

〔Effect of the invention〕

As explained above, according to the present invention, a double heterojunction is formed using a semiconductor layer that satisfies the conditions that the lower end of the conduction band is at a higher energy level and the upper end of the valence band is at a lower energy level than the active layer. Even when it is difficult or impossible to confine electrons and holes in the active layer or its vicinity, it is possible to improve properties such as dark value current density, conversion efficiency, and temperature characteristics. .

[Brief explanation of drawings]

FIG. 1 (al is a schematic side sectional view of the first embodiment of the present invention, FIG. 1(b) is a diagram showing its energy level, and FIG. 2 is a diagram showing the energy level of the second embodiment of the present invention. Figure 3 is a diagram showing the energy levels of InGaAsP/InP lasers. Figure 4 (a) and (b) are conventional Pb5nTe/I'bT lasers.
FIG. 2 is a diagram showing energy levels of an e-based laser. In the figure, 1 is a p-type PbTe3 plate, 2 is an n-type PbTe layer,
3.3A, 5 and 5A are superlattice structures, 3a and 5a are Pbo, qSno, +Te layers, 3b
and 5b is Pbo, 7ssno, 2sTe layer, 3c
and 5c is 5nTei, 3d and 5d are PbTe layers, 4 is Pbo, Jno, +Te active layer, 6 is n-type Pb
Te layer, 7 is an n-type PbTe buried layer, 11 is an insulating layer,
12 represents an n-side electrode, and 13 represents an n-side electrode. Kaya 10Cb) Hana 2 fruit rise fl JO) Technique Lugini 4 game E/W mouth year 20

Claims (1)

[Claims] 1) Does not meet the conditions that the lower end of the conduction band is at a higher energy level and the upper end of the valence band is at a lower energy level than the active layer;
A superlattice structure composed of semiconductor layers functioning as a quantum mechanical well potential with respect to at least one carrier is provided above and below the active layer, and the energy of electrons and holes in each semiconductor layer of the superlattice structure is reduced. 1. A semiconductor light emitting device, wherein a level difference is larger than a forbidden band width of the active layer, and at least one carrier is confined in the active layer by the superlattice structure. 2) The lowest energy level of electrons in the superlattice structure is higher than the energy level of the lower end of the conduction band of the active layer, and electrons are confined in the active layer. The semiconductor light emitting device according to item 1. 3) A patent claim characterized in that the highest energy level of holes in the superlattice structure is lower than the energy level of the upper end of the valence band of the active layer, and holes are confined in the active layer. The semiconductor light emitting device according to item 1.