JPH05160504A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser device having a low threshold value, high efficiency, a short wavelength and high output characteristics wherein carrier overflow and thermoionic transition effect are reduced, by constituting a first conductivity type clad layer of two layers. CONSTITUTION:A first clad layer 6 constituting a first conductivity type clad layer has a large hetero barrier between the side adjacent to an active layer 5 and the active layer 5, and has a composition approximate to Al0.42In0.58P which does not lattice-match a substrate 1. The layer 6 is thinner than the critical film thickness and turns to a first carrier overflow protective film. A second clad layer 7 has large Fermi level difference and a high hetero barrier to the active layer 5, is subjected to high concentration doping, and has composition approximate to (Al0.7Ga0.3)0.5In0.5P which lattice-matches the substrate 1. The second thick clad layer 7 turns to a second carrier overflow protective layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device, and more particularly to a high power semiconductor laser device characterized by the structure of a cladding layer.

In recent years, a 0.6 μm band visible light semiconductor laser has been greatly expected as a light source capable of realizing high performance of optical information processing devices such as POS, optical disk devices and laser printers, and has a low threshold current. Characteristics such as high efficiency, short wavelength, and high output are required.

[0003]

2. Description of the Prior Art
The 6 μm band AlGaInP laser device has a high deposition rate of Al constituting the material, and it is difficult to control the composition, so that it is difficult to perform crystal growth by the liquid phase epitaxy method. Therefore, the MOVPE method or the MBE method has been conventionally used. Etc. have been manufactured by the vapor phase growth method.

Further, in this material system, the recombination rate at the crystal interface is high, and the injected carriers disappear here, so that an effective buried structure such as a BH (Buried Hetro) laser device can be formed. Difficult,
The one that has been put to practical use has a structure in which the active layer is flat and has no break.

Conventionally, (1) the band gap of the clad layer is increased as a means for improving the characteristics when manufacturing a laser device having a flat active layer as described above by the MOCVD method. (2) The band gap of the active layer is reduced. (3) Dope the cladding layer with high concentration. Etc. methods have been proposed.

All of these are means intended to prevent carrier overflow from the active layer, and (1)
(2) and (2) prevent overflow of carriers (electrons in this case) by increasing the height of the hetero barrier generated between the active layer and the cladding layer.

On the other hand, in (3), the pseudo-Fermi level in the cladding layer is brought close to the band edge by high-concentration doping in the cladding layer, and the difference between the pseudo-Fermi level and the intrinsic Fermi level is determined. It is based on the principle of increasing the built-in barrier of the pn junction. A semiconductor laser device with less carrier overflow can be obtained only by increasing the hetero barrier and performing high-concentration impurity doping as described above.

[0008]

A conventional semiconductor laser device with reduced carrier overflow will be described below.

2A and 2B are energy band explanatory diagrams of a conventional semiconductor laser device. FIG. 2A shows
FIG. 6 is an energy band diagram in the case where the clad layer lattice-matched with the substrate is heavily doped, showing a state in which a voltage is applied from the outside in order to inject carriers.

As can be seen from this figure, in this semiconductor laser device, the conditions of "(1) increase the bandgap of the cladding layer" and "(2) decrease the bandgap of the active layer". Is satisfied.

As described above, when the heterobarrier ΔE _C of the n-type cladding layer and the p-type cladding layer with respect to the active layer is increased, carriers are confined within the range of the heterobarrier, so that the heterobarrier of the cladding layer in contact with the active layer. The larger the value, the more effectively the carriers can be confined in the active layer.

However, even if this heterobarrier ΔE _C is large, for example, if the p-type cladding layer is not sufficiently doped, the pseudo-Fermi level E _{FP of the} cladding layer will be located away from the band edge E _P of the valence band. Therefore, the bottom of the conduction band drops to the position ', which causes the hetero barrier to become thin and carriers to overflow due to tunneling.

Therefore, by satisfying the condition of "(3) Dope the cladding layer with a high concentration", the pseudo-Fermi level E _FP of the cladding layer is located near the band edge E _P of the valence band. It lowers and raises the bottom of the conduction band to position 'to prevent carriers from overflowing by tunneling through the heterobarrier. In this way, a good semiconductor laser device with less carrier overflow can be obtained, but AlGaInP / GaInP
In a laser device, it is not always possible for a material capable of taking a large hetero barrier to ideally be highly doped.

FIG. 3 is a light emission characteristic diagram of AlGaInP from a deep level. The horizontal axis of this figure is (Al _0.7 G
a _0.3 ) _0.5 In _0.5 P is the ratio of the amount of Mg supplied when growing, and indirectly indicates the Mg doping concentration,
The vertical axis represents the emission intensity of photoluminescence (PL) on an arbitrary scale.

This (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P
Is formed by MOCVD at a growth temperature of 690 ° C.,
It is a material that lattice-matches the GaAs substrate. From this figure,
It can be seen that as the Mg doping concentration increases, the light emission from the deep level of the wavelength to 1 μm becomes stronger.

As described above, a high level doping of Mg causes a deep level in the crystal, and a process in which electrons oozing into the forbidden band fall to a deep level as shown by an arrow in FIG. 2B, that is, Since a thermo-ionic tunneling transition, which is a kind of interface recombination, occurs and energy is lost, the emission efficiency of the semiconductor laser device is reduced. In order to reduce this thermo-ionic transition effect, it has been conventionally considered to improve the cladding layer by adding a spacer layer having a low doping concentration.

FIG. 4 is an energy band explanatory diagram of a conventional improved semiconductor laser device. In this improved semiconductor laser device, the cladding layer is composed of the first cladding layer and the second cladding layer.
The first clad layer is composed of two layers of clad layers,
A spacer layer having a low doping concentration having a hetero barrier ΔE _{C is used,} and a second cladding layer is a high concentration cladding layer.

However, since the spacer layer, which is the first cladding layer, has a low doping concentration, it becomes thicker as shown in FIG.
The hetero barrier becomes smaller like'no '. Therefore, as shown in FIG. 4, the hetero barrier in the spacer layer portion is limited to the effect of ΔE _C , and for the thermoionic transition, the portion equal to or greater than ΔE _C becomes the same as in FIG. That is, the carrier C overflowing onto ΔE _C in FIG. 4 undergoes a thermo-ionic transition into the second cladding, and the carrier overflow and the thermo-ionic transition effect cannot be sufficiently reduced only by the spacer layer. was there.

Therefore, the present invention is used as a light source for POS, optical disk devices, laser printers, etc., and has reduced carrier overflow and thermoionic transition effect, low threshold current, high efficiency, short wavelength, and high output. An object is to provide a semiconductor laser device having characteristics.

[0020]

In a semiconductor laser device according to the present invention, a clad layer of the first conductivity type has a large hetero barrier between the clad layer of the first conductivity type and the active layer from the side close to the active layer. It has a large Fermi level difference and a high hetero-barrier between the active layer and the first clad layer, which has a composition that does not lattice match and is thinner than the critical film thickness, and serves as a first carrier overflow prevention layer. A two-layer structure, that is, a thick second clad layer that is doped and lattice-matched with the substrate and serves as a second carrier overflow prevention layer, is adopted.

In this case, the first carrier overflow prevention
The first cladding layer, which is the stop layer, is made of Al _0.42In_0.58Near P
A structure which is a crystal having a composition of was adopted.

Further, in this case, the second clad layer serving as the second carrier overflow prevention layer is a crystal having a composition in the vicinity of (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P that is lattice-matched to the substrate. ..

Further, in this case, in the second conductive type clad layer facing the first conductive type clad layer with the active layer interposed therebetween, a composition is generated which cancels the strain applied to the first conductive type clad layer. The structure in which the carrier overflow prevention layer having the above is provided is adopted.

In the above case, the first cladding layer close to the first conductivity type active layer is a crystal having a composition near Al _0.42 In _0.58 P, and the first cladding layer close to the second conductivity type active layer.
A structure in which the clad layer is a crystal having a composition near Al _0.58 In _0.42 P was adopted.

[0025]

FIG. 5 is an energy band explanatory diagram of the principle of the present invention. In the present invention, as seen in this figure,
The p-type cladding layer is a first carrier overflow prevention layer that has a large hetero barrier between the active layer and the active layer, has a composition that does not lattice match the substrate, and is thinner than the critical film thickness. Which has a large Fermi level difference and a high heterobarrier between the first clad layer and the active layer, is heavily doped and is lattice-matched to the substrate, and serves as a second carrier overflow prevention layer. It has a double structure with the clad layer.

In this case, the first cladding layer may be formed of a material that does not lattice-match with the substrate because the thickness of the first cladding layer is about the diffusion length of electrons and is not more than the critical thickness. However, it is necessary that the heavy doping does not form a high density deep level in the material itself.

Further, the second clad layer needs to be a thick film, and therefore needs to be a material that lattice-matches with the substrate. Further, even if some deep level is formed in the second cladding layer due to the high-concentration doping, it does not cause a big trouble for the reason described later.

As can be seen from FIG. 5, in the semiconductor laser device of the present invention, (1) since the first cladding layer is made to have a diffusion length of electrons or less and a critical film thickness or less, lattice matching with the substrate is required. However, since the material can be selected by paying attention to the fact that the hetero barrier ΔEc between the active layer and the active layer is large, the combination of materials having a sufficiently large built-in voltage without high-concentration doping as in the prior art. Can be formed with.

(2) Since the second cladding layer is highly doped, the built-in barrier can be increased, the overflow of carriers is small, and the carriers can be well confined.

(3) Even if a deep level is formed in the second clad layer by high-concentration doping, the first clad layer acts as a buffer layer such as a spacer layer against the deep level, so that thermo-ionic tunneling to the deep level may occur. PL does not occur.

(4) If a material that causes strain in opposite directions is selected for the p-type clad layer and the n-type clad layer, the amount of strain in the entire crystal can be reduced, and an extremely reliable laser device can be realized. it can.

(5) Further, although the above description is for the p-type clad layer, this structure can be applied to the n-type clad layer, or alternatively, it can be applied to the p-type clad layer and the n-type clad layer respectively. It can also be applied.

[0033]

EXAMPLES Examples of the present invention will be described below. Figure 1
It is a structure explanatory view of the semiconductor laser device of one example of the present invention. In this figure, 1 is an n-type GaAs substrate, 2 is an n-type GaAs buffer layer, 3 is an n-type Al _0.5 In _0.5 P second
Cladding layer, 4 is n-type Al _0.58 In _0.42 P first cladding layer, 5 is undoped Ga _0.5 In _0.5 P active layer, and 6 is p
Type Al _0.42 In _0.58 P first cladding layer, 7 is p-type (Al
_0.7 Ga _0.3 ) _0.5 In _0.5 P Second cladding layer, 8 is p
Type Ga _0.5 In _0.5 P etching stop layer, 9 is a p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P third cladding layer,
Reference numeral 10 is a p-type Ga _0.5 In _0.5 P spike prevention layer, 11 is a p-type GaAs first contact layer, 12 is an n-type GaAs current blocking layer, and 13 is a p-type GaAs second contact layer.

In the semiconductor laser device of this embodiment, the above-mentioned 2 is formed on the n-type (Si-doped) GaAs substrate 1.
Can be formed by growing each of the semiconductor layers Nos. 13 to 13 by the MOVPE method.

That is, an n-type (Si-doped) GaAs base
1 μm thick n-type on the plate 1 by MOVPE method
(Se-doped) GaAs buffer layer 2, thickness 0.8 μm
N-type (Se-doped) Al_0.5In_0.5P 2nd clad
Layer 3, 100 Å thick n-type (Se-doped) Al_0.58In
_0.42P first clad layer 4, 0.08 μm thick
Ga_0.5In_0.5P active layer 5, p type with a thickness of 100Å
(Mg-doped) Al_0.42In_0.58P first cladding layer 6,
0.2 μm thick p-type (Mg-doped) Al_0.7G
a _0.3)_0.5In_0.5P second cladding layer 7, thickness 100
Å p-type (Zn-doped) Ga_0.5In_0.5P etching
Stop layer 8, p-type (Mg-doped) with a thickness of 0.6 μm
(Al_0.7Ga_0.3)_0.5In_0.5P 3rd clad layer
9, p-type (Zn-doped) Ga having a thickness of 0.1 μm_0.5In
_0.5P spike prevention layer 10, 0.2 μm thick p-type (Z
An n-doped) GaAs first contact layer 11 was grown.

In this case, the growth temperature is 700 ° C., V / II
The I ratio was 80 for GaAs, 400 for AlGaInP, and 600 for GaInP. Then, a SiO ₂ film was formed on the entire surface by a sputtering method, and the SiO ₂ film was patterned into a mesa stripe shape by a photolithography technique.

Then, using the SiO ₂ film as an etching mask, the p-type (Zn-doped) GaAs first contact layer 11 is etched with a mixed solution of ammonia and hydrogen peroxide, and then the p-type with a hydrogen bromide solution. (Zn
(Doped) Ga _0.5 In _0.5 P spike prevention layer 10 and p-type (Mg-doped) (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P third cladding layer 9 and p-type (Zn-doped) Ga _0.5 In
_{The 0.5} P etching stop layer 8 was etched.

Next, an n-type (Se-doped) GaAs current blocking layer 12 having a thickness of 0.8 μm is selectively grown, the SiO ₂ film for selective growth is removed, and then a p-type (Zn-doped) GaAs second layer is formed. The contact layer 13 was grown.

Then, the elements are separated from each other, an n-side contact and a p-side contact are formed, cleavage is performed to form a resonator, and end faces are coated to complete a semiconductor laser device.
The n-type (substrate side) down was bonded to the heat sink.

The structure described in the claims and the first
Corresponding semiconductor layers in this embodiment when the conductivity type is p-type are as follows.

The first cladding layer, which has a large hetero barrier between the active layer, has a composition that does not lattice match with the substrate, and is thinner than the critical film thickness and serves as a first carrier overflow prevention layer. Is the “p-type (Mg-doped)” in this example.
It corresponds to the Al _0.42 In _0.58 P first cladding layer 6 ”.

According to a first aspect of the present invention, the second carrier overflow prevention layer has a large Fermi level difference with the active layer and a high hetero barrier, is heavily doped, and is lattice-matched with the substrate. The “thick second cladding layer” is the “p-type (Mg-doped) (Al _0.7 Ga _0.3 )” of the present embodiment.
_0.5 In _0.5 P second cladding layer 7 ".

The "carrier overflow prevention layer having a composition that generates a strain that cancels the strain applied to the first-conductivity-type cladding layer" described in claim 4 is the "n-type (Se-doped)" of this embodiment. Al _0.58 In _0.42 P first cladding layer 4 ".

In this case, the composition of the first conductivity type (p type) first cladding layer 6 with the active layer 5 sandwiched therebetween is Al _0.42 In _0.58.
P, the composition of the second conductivity type (n-type) first cladding layer 4 is Al _0.58 In _0.42 P, and the composition ratios of Al and In are reversed, so that the strains cancel each other out. ..

[0045]

As described above, according to the present invention, the PO
Used as a light source for S, optical disk devices, laser printers, etc., with little carrier overflow and high output,
It is possible to provide a semiconductor laser device having a low threshold current, high efficiency, short wavelength, and high output characteristics, and it makes a great contribution to this kind of technical field.

[Brief description of drawings]

FIG. 1 is a structural explanatory view of a semiconductor laser device of an embodiment of the present invention.

2A and 2B are energy band explanatory diagrams of a conventional semiconductor laser device.

FIG. 3 is a light emission characteristic diagram of AlGaInP from a deep level.

FIG. 4 is an energy band explanatory diagram of a conventional improved semiconductor laser device.

FIG. 5 is an energy band explanatory diagram of the principle of the present invention.

[Explanation of symbols]

1 n-type GaAs substrate 2 n-type GaAs buffer layer 3 n-type Al _0.5 In _0.5 P second cladding layer 4 n-type Al _0.58 In _0.42 P first cladding layer 5 undoped Ga _0.5 In _0.5 P active layer 6 p-type Al _0.42 In _0.58 P first cladding layer 7 p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second cladding layer 8 p-type Ga _0.5 In _0.5 P etching stop layer 9 p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P third cladding Layer 10 p-type Ga _0.5 In _0.5 P spike prevention layer 11 p-type GaAs first contact layer 12 n-type GaAs current blocking layer 13 p-type GaAs second contact layer

Claims (5)

[Claims] 1. A first-conductivity-type cladding layer formed on a substrate has a large hetero barrier between the active layer and a side closer to the active layer, and has a composition not lattice-matched with the substrate. It has a large Fermi level difference and a high hetero barrier between the first cladding layer, which is thinner than the critical film thickness, and serves as the first carrier overflow prevention layer, and the active layer, and is highly doped, and is highly doped. A semiconductor laser device comprising two layers of a thick second clad layer which is matched and serves as a second carrier overflow prevention layer. 2. The semiconductor laser device according to claim 1, wherein the first cladding layer serving as the first carrier overflow prevention layer is a crystal having a composition near Al _0.42 In _0.58 P. 3. A second clad layer serving as a second carrier overflow prevention layer is lattice-matched to the substrate (Al _0.7 G
2. The semiconductor laser device according to claim 1, wherein the crystal is a crystal having a composition near a _0.3 ) _0.5 In _0.5 P. 4. A carrier having a composition that generates a strain that cancels the strain applied to the first conductivity type clad layer in the second conductivity type clad layer that faces the first conductivity type clad layer with the active layer interposed therebetween. The semiconductor laser device according to claim 1, further comprising an overflow prevention layer. 5. A first cladding close to an active layer of the first conductivity type.
Layer is Al_0.42In _0.58A crystal having a composition near P
The first cladding layer close to the second conductivity type active layer is Al
_0.58In_0.42The crystal has a composition near P.
The semiconductor laser device according to claim 4, which is a characteristic of the semiconductor laser device.