JPH042178A - Semiconductor light emitting element - Google Patents

Abstract

PURPOSE:To sufficiently confine carrier, to prevent generation of a crystal defect due to a distortion and to provide a light emitting element having high reliability and excellent light emitting efficiency by forming an active layer and a double heterostructure of a clad layer disposed at both sides of the active layer, and specifying the material composition and the thickness of the layer. CONSTITUTION:A semiconductor light emitting element has an active layer 5 made of group II-VI semiconductor containing CdxZn1-xS or CdxZn1-xS as main as ingredients and a clad layer 3 made of group II-VI semiconductor containing CdyZn1-yS or CdyZn1-yS as main ingredients. Here, the layer 7 and the layers 3, 7 have about 2% of lattice constant difference. However, since the thickness of the layer 5 is sufficiently thin, a double heterostructure is formed in a distortion quantum well structure, and even if a lattice mismatching occurs, no defect is generated in the active layer. That is, if the relationship between a difference x of Cd components of the layers 3, 7 and 5 and the thickness d(mum) of the layer 5 satisfies d<0.02 and ¦ x.d¦<2X10<-3>, the defect of the layer 5 due to the lattice mismatching can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a current injection type semiconductor light emitting device that emits light in a wavelength range of 0.37 to 0.5 μm.

(Prior Art) At present, a short wavelength band (0.37 to 0.5 μm) semiconductor light emitting device with a double heterostructure that emits blue or green light has not been realized.

In a semiconductor light emitting device, it is desirable that the lattice constants of the substrate and the grown layer and the lattice constants of the active layer and the cladding layer of the grown layer closely match; if they do not match, crystal defects will occur due to strain.

On the other hand, for double heterostructures used in lasers and high-power light-emitting diodes, in order to effectively confine carriers, the lower end of the conduction band of the active layer is lower than that of the cladding layer, as shown in the energy band diagram in Figure 4. It is necessary that the upper end of the valence band of the active layer is below the lower end of the conduction band and above the upper end of the valence band of the cladding layer.

Currently, ZnS is used in the growth layer of semiconductors used for light-emitting devices in short wavelength bands such as blue and green due to band gap restrictions.
, Zn5e, and C:dS are considered the most promising.

However, using a grown layer of II-VI group semiconductor, ■-■
Alternatively, it is difficult to obtain a double heterostructure that is lattice-matched to the substrate of the group III bioconductor and at the same time effectively confines electrons and holes. This is the reason why semiconductor light emitting devices in short wavelength bands such as blue and green cannot be produced.

(Problems to be Solved by the Invention) As mentioned above, in a semiconductor light emitting device using an If-VI group semiconductor that emits light in a wavelength band of 0.37 to 0.5 μm as a growth layer, it is difficult to confine carriers in the active layer. In order to achieve this sufficiently, the lattice mismatch between the cladding layer and the active layer becomes large, and the effect of strain on the efficiency and durability of the device is a major problem. In addition, lattice mismatch between the substrate and the cladding layer has also been a problem, affecting efficiency and durability.

An object of the present invention is to realize a short wavelength band (0.37 to 0.5 μm) semiconductor light emitting device having a double heterostructure and emitting blue or green light. That is, by introducing a new material composition and layer structure, carrier confinement is sufficiently performed and crystal defects due to strain are prevented from occurring, thereby providing a highly reliable semiconductor light emitting device with high luminous efficiency.

(Means for Solving the Problems) The first feature of the present invention is that CdZnS or CdZnS
In a semiconductor light emitting device using a ■-VI group semiconductor whose main component is The goal is to obtain a well layer.

A second feature of the present invention is that, in addition to the structure of the first feature, Cd.
The reason is that a buffer layer of a II-VI group semiconductor whose main component is ZnS or CdZnS is provided, and the material composition and layer thickness are limited.

(Example 1) FIG. 1 shows a cross section of a semiconductor light emitting device having a layered structure according to the present invention, and is an example of an electrode stripe structure laser. 1 is n-GaAs substrate, 2 is n-CdzZn,
In the buffer layer (about 0.5 μm thick) made of −yS, Z continuously changes from 0.55 to 0.3 from the substrate 1 side. 3 is n-Cdo, aZno, ? n-cladding layer made of S (about 1.5 μm thick), 5 is Cd,
, ssZn0, active layer consisting of 48S (thickness 0.00
75 μm), 7 is a p-cladding layer (thickness approximately 1.5 μm) made of Cda, aZno, and yS, 8 is an insulating film, and 9 and 10 are electrodes.

Here, there is a difference in lattice constant of about 2% between the active layer 5 and the cladding layer 3.7. However, since the thickness of the active layer 5 is sufficiently thin, 2
The heavy heterostructure becomes a strained quantum well structure, and no defects occur in the active layer even if lattice mismatch exists. In other words, the relationship between the difference ΔX between the Cd components of the cladding layers 3 and 7 and the active layer 5 and the thickness d (μm) of the active layer 5 should be d<0.02 and ΔX−d<2×10″3. For example, the occurrence of defects in the active layer 5 due to lattice mismatch can be prevented.

Further, there is also a difference in lattice constant of about 2% between the substrate 1 and the cladding layer 3. However, because of the presence of the buffer layer 2, stress due to lattice mismatch is alleviated, and no strain occurs in the cladding layer.

That is, in the buffer layer 2, the amount of movement p(
μm) and the change in Cd component △Z is 1△z/p1〈
2, and it is necessary to select the value of the Cd component on the cladding layer 3 side of the buffer layer 2 so that the value of the Cd component of the cladding layer 3 is substantially lattice-matched, and on the substrate 1 side, the value of the Cd component is almost lattice-matched with the substrate 1. Note that when a large lattice mismatch (about 0.3%) does not occur between the substrate 1 and the cladding layer 3, the buffer layer 2
There is no need to provide

CdZnS has a smaller coefficient of linear expansion than GaAs, so if the substrate 1 is GaAs, the Cd component of the cladding layer 3 is set to 0.55 or less to change the lattice constant of CdZnS to that of GaAs.
s (if this is done, the difference in lattice constants will be smaller when the temperature is returned to room temperature than during crystal growth, and therefore the stress will be smaller, resulting in a more stable structure. In addition, CdZnS has a hexagonal structure with a composition higher than that of CdS. Cd tends to form crystals, but Cd
If the component is kept at 0.55 or less, a cubic crystal structure will be stably obtained at a thickness of about 3 μm. Therefore, cladding layers 3 and 7
A CdZnS semiconductor having a Cd content of 0.55 or less is used.

The active layer is generally CdxZn+-xS or a II-Vl group compound semiconductor mainly composed of CdxZn+-xS, and the cladding layer is generally CdyZnl-yS or a II-VI group compound semiconductor mainly composed of CdxZnl-yS.

The semiconductor layer structure was produced using metal organic vapor phase epitaxy (MOVPE). Thereafter, an insulating film, electrodes, etc. were formed using normal process steps to form a diode.

With the layered structure described above, one operating at a wavelength of 0.44 μm was obtained. Note that the Cd component in the active layer is 0.1 to 1.0.
It is possible to emit light at a wavelength of 0.37 to 0.5 μm by changing the composition of the cladding layer so that carriers and light can be confined accordingly.

(Example 2) FIG. 2 shows a cross section of a semiconductor light emitting device according to another example of the present invention. The difference from Example 1 is that an optical confinement layer 4.6 is formed between the cladding layers 3 and 7 and the active layer 5. Optical confinement layers 4 and 6 are n-Cd
Made of uZn l -uS, each with a thickness of about 0.1 μm
and U is 0.3 on the side in contact with the cladding layer 3.7 and 0.45 on the side in contact with the active layer 5, and changes continuously during this period.

Regarding the composition change of the optical confinement layers 4 and 6, the optical confinement layers 4 and 6 are made of a semiconductor having the same composition as the active layer 5 or the cladding layers 3 and 7 or an intermediate composition thereof, and the amount of movement in the thickness direction p
The relationship between (μm) and Cd component change ΔU is 1Δu/p|
If <2, the stress in the active layer 5 is relaxed and no defects occur in the optical confinement layers 4 and 6.

(Example 3) In Example 2, optical confinement layers 4 and 6 whose compositions varied monotonically were used, but a superlattice made of a multilayer ultra-thin film may be used instead. For example, Cd composition X is 0.3
and 0.35 ultra-thin films (each 100 angstroms thick);
Layers 4 and 6 are composed of three sets of superlattices (each 100 angstroms thick) and three sets of 0.4 and 0.45 ultrathin films (100 angstroms each). Of course, the superlattice made of thin films with X of 0.4 and 0.45 is in contact with the active layer. Cd in the thin film constituting the superlattice
Between the component difference ΔX and each film thickness d (μm), d<0.02 and |Δx・d|<2×10-d l <
2 If there is a relationship of XIO-3, the optical confinement layers 4, 6,
No defects occur in the active layer 5.

(Example 4) In the above-mentioned example, an example was shown in which GaAs was used as the substrate 1, but instead, Ge, GaP, Si, GaA
It is also possible to use semiconductors of the ■-V group or the IV group, such as sP, and all of the things described in Embodiments 1, 2.3 can be applied to these. Although Si cannot be said to have the same coefficient of linear expansion as GaAs as described in Example 1,
In order to obtain a stable cubic structure, the Cd content of the cladding layer is 0.
;The same can be said of setting it to 55 or less. As for the conduction type, it goes without saying that the structure may be reversed.

When GaP or Si is used, an element with a short emission wavelength can be easily manufactured. FIG. 3 shows an example in which the substrate 1 is made of GaP. In Fig. 3, 1' is an n-GaP substrate, 3 is an n-cladding layer (thickness approximately 1.5 gm) consisting of n-Cdo, +Zno, 9S, 5 is Cdo3sZno,
Active layer made of ssS (thickness 0.OIIim), 4.
6 is an optical confinement layer (each 0.1 μm thick) made of CdvZn'+-vS, and ■ is 0.1 on the side in contact with the cladding layer.
, is 0.25 on the side in contact with the active layer, and changes continuously during this period. 7 is Cdo, p consisting of +Zno9S
- cladding layer (thickness approximately 1.5 μm); 8 is an insulating film; 9.
IO is an electrode. In this example, the lattice mismatch between the cladding layer 3 and the substrate 1 is small, so no buffer layer is included. However, if the composition of the cladding layer changes and a large lattice mismatch occurs, a buffer layer similar to that in Example 1 may be added. need to be inserted. For the other configurations, the same as in Embodiment 1.2.3 can be applied.

In this example, a device operating at a wavelength of 0.39 μm was obtained.

Note that the Cd component on the substrate side of the buffer layer is approximately the same as when the substrate is Ga.
0.55 for As, 0.1 for GaP, GaA
For sP, the value is between 0.1 and 0.55 depending on its composition, for Ge it is 0.55, and for ySi it is 0.55.

In the above description, a light emitting element having an electrode stripe structure has been considered, but of course a refractive index waveguide structure such as a buried structure may also be used.

In the above example, CdZnS was used for the growth layers (active layer, cladding layer, optical confinement layer, buffer layer), but CdZnS
It may be a II-VI group compound semiconductor whose main component is xZn(-S).For example, it may be one in which part of S is replaced with Se or Te, or one in which part of cd or Zn is replaced with Hg.
It is also possible to replace it with However, it is necessary not to significantly change the energy band structure, and therefore the substitution ratio needs to be approximately 10% or less.

(Effects of the Invention) The semiconductor light emitting device of claim 1 has a short wavelength band (0.37 to 0.5μ) having a double heterostructure that emits blue or green light.
The semiconductor light emitting device of m) is realized.

In the semiconductor light emitting device of the second aspect, as compared with the first aspect, a lattice mismatch between the substrate and the cladding layer can be tolerated, so that the semiconductor light emitting device can be designed with a higher degree of freedom.

In the semiconductor light emitting device according to the third aspect, the efficiency is improved and the threshold value is low (so that continuous operation when used for laser emission becomes easier).

The semiconductor light emitting device according to the fourth aspect is easier to manufacture.

[Brief explanation of the drawing]

1, 2, and 3 are cross-sectional views of semiconductor light emitting devices according to embodiments of the present invention. FIG. 4 is an energy band diagram when a double heterostructure is obtained that effectively confines electrons and holes. 1-...-n-GaAs substrate, 1'...n-GaP substrate, 2...n-CdZnS buffer layer-13...n-
N-cladding layer made of CdZnS (thickness approximately 1.5 μm
), 4.6... Optical confinement layer made of CdZnS (thickness 0.1 μm each), 5--- Active layer made of CdZnS (thickness 0.01 μm)
m), 7... p-clad layer made of p-CdZnS (thickness approximately 1.5 μm), 8... insulating film, 9, 10... electrode. Figure Figure Figure 4 Conduction band energy diagram Figure 4

Claims (4)

[Claims] (1) A substrate made of III-V group or IV group semiconductor, and Cd_xZn_1_-_xS or Cd_xZn_1
an active layer made of a II-VI group semiconductor mainly composed of Cd_yZn_1_-_yS or Cd_yZn_1 having
a cladding layer made of a II-VI group semiconductor mainly composed of Δx=|
The relationship between x-y| and the thickness dμm of the active layer is d<0.02
A semiconductor light emitting device characterized in that |Δx·d|<2×10^−^3. (2) A substrate made of a III-V group or IV group semiconductor, and Cd_xZn_1_-_xS or Cd_xZn_1
an active layer made of a group II-IV semiconductor mainly composed of Cd_yZn_1_-_yS or Cd_yZn_1 having
a cladding layer made of a II-VI group semiconductor whose main component is _-_yS; A buffer layer made of a semiconductor whose main component is Cd_zZn_1_-_zS, and whose z value changes continuously from the substrate side from a z value that is approximately lattice matched with the substrate to a z value of the cladding layer. and the Cd component y in the cladding layer is 0.55 or less, and the difference Δx between the Cd components in the active layer and the cladding layer is |
The relationship between x-y| and the thickness dμm of the active layer is d<0.02 and |Δx・d|<2×10^-^3, and the amount of movement in the thickness direction of the buffer layer pμm A semiconductor light emitting device characterized in that the relationship between the amount of change Δz of the Cd component and the amount of change Δz of the Cd component is |Δz/p|<2. (3) A light confinement layer made of a semiconductor having the same composition as the active layer or the cladding layer or an intermediate composition thereof is formed between the active layer and the cladding layer. Item 2. The semiconductor light emitting device according to any one of Items 1 and 2. (4) The semiconductor light emitting device according to claim 3, wherein the optical confinement layer has a superlattice structure made of a multilayer ultra-thin film.