JPH06268318A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To provide an iNgAalp based semiconductor laser in which temperature characteristics are improved by setting the carrier concentration of p-clad layer sufficiently high. CONSTITUTION:The semiconductor laser has double heterostructure wherein an active layer 104 of In1-y(Ga1-zAlz)YP based material(0<=Y<1, 0<=Z<1) is formed on a semiconductor substrate 101 while being sandwiched by clad layers 103, 105. Mixed crystal composition X of GaAl is set X<=0.4 or the clad layers 103, 105 of In1-y(Ga1-zAlz)YP.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser using a compound semiconductor material, and more particularly to a semiconductor laser using an InGaAlP-based material or an InGaAs-based material in a double heterostructure portion.

[0002]

2. Description of the Related Art Recently, InGa oscillating in a 0.6 μm band
The AlP visible light semiconductor laser has been commercialized and is expected to be widely applied as a light source for optical disk devices, laser beam printers and the like.

By the way, it is very important to reduce the oscillation threshold and improve the temperature characteristic of the semiconductor laser from the viewpoint of reducing the operating current and improving the life characteristic. The laser oscillation threshold and temperature characteristics are determined by the carrier confinement performance in the active layer, and in order to lower the threshold and improve the temperature characteristics, it is an important factor to increase the carrier concentration of the p-clad layer. one of. For example, in a GaAlAs-based semiconductor laser, the band discontinuity on the conduction band side of the active layer and the p-clad layer can be sufficiently increased.
Due to this large band discontinuity, electron leakage from the active layer to the p-clad layer was effectively prevented, and there was no problem that the oscillation threshold was increased or the temperature characteristic was deteriorated.

However, the InGaAlP-based semiconductor laser has a feature that the band discontinuity on the conduction band side of the active layer and the p-clad layer is smaller than that of the GaAlAs-based material described above. Therefore, it is not possible to sufficiently prevent the leakage of electrons from the active layer to the p-clad layer side due to the small band discontinuity.
Carriers cannot be satisfactorily confined in an IP semiconductor laser. Therefore, there is a problem that the oscillation threshold becomes high and the temperature characteristic is deteriorated.

In addition, in recent years, In oscillating in the 0.9 μm band
The GaAs semiconductor laser is expected to be widely applied as a light source of a fundamental wave for generating a second harmonic and a fiber amplifier.
In the semiconductor laser using InGaAs for the active layer,
Since GaAs is used for the substrate, there is a problem that strain is introduced into the active layer and reliability deteriorates. Also, In
Even in a structure using a GaAlP layer as a cladding layer, Ga
Since it is necessary to match the As substrate and it is difficult to obtain good crystallinity, there is a problem that the device life is short.

[0006]

As described above, InGa
In a semiconductor laser using an AlP-based semiconductor material, when the Al composition of the p-cladding layer is high, for example, 0.7 to obtain a high bandgap, it is not possible to dope impurities with a high concentration due to the influence of oxygen. Since it is difficult, it is difficult to improve the temperature characteristics of the laser.

In addition, in a semiconductor laser using an InGaAs semiconductor material, strain is introduced into the active layer,
Further, since the p-clad layer has poor crystallinity, there is a problem in device life, reliability is low, and the operating environment is limited to avoid operation at high temperature and high output.

The present invention has been made in consideration of the above circumstances, and an object thereof is to increase the carrier concentration of the p-clad layer sufficiently to improve the temperature characteristics of the laser.
An object is to provide an AlP-based semiconductor laser.

Another object of the present invention is to reduce the strain of the active layer and improve the crystallinity of the p-clad layer, thereby improving reliability and enabling operation at high temperature and high output.
It is to provide a semiconductor laser using a GaAs-based semiconductor material.

[0010]

The gist of the present invention is In
_1-Y (Ga _1-Z Al _Z ) _Y 1-based material (0 ≦ Y <1, 0 ≦
Z <1), a semiconductor substrate made of GaAs _1-X P _X- based material (0 <X ≦ 1) having a lattice constant different from that of the active layer, and the semiconductor substrate having the same lattice constant I
n _1-Y (Ga _1-Z Al _Z ) _Y P-based material (0 ≦ Y <1, 0
The band discontinuity between the active layer and the p-clad layer is sufficiently increased by using the clad layer of ≦ Z <1).

That is, the InGaAlP-based semiconductor laser according to the present invention comprises In _{1 -Y} (Ga _{1 -Z} A) on a semiconductor substrate.
l _Z ) _Y P-based material (0 ≦ Y <1, 0 ≦ Z <1) having a double heterostructure part in which an active layer is sandwiched between cladding layers, and In _1-Y (Ga _1-X Al _X ) the GaAl mixed crystal composition of the clad layer consisting of _Y P, characterized in that the X ≦ 0.4.

Another gist of the present invention is, in an InGaAs semiconductor laser, In _W Ga on a semiconductor substrate.
_1-W As-based material (0 <W ≦ 1) active layer and In
_1-Y (Ga _1-Z Al _Z ) _Y P-based material (0 ≦ Y <1, 0 ≦
A clad layer made of Z <1) is used, and the composition ratio of In _1-Y (GaAl) _{Y in} the clad layer is set to Y <0.4 to increase the amount of In to improve the crystallinity of the p-clad layer. The object is to obtain an improved and highly reliable InGaAs semiconductor laser.

That is, in the InGaAs semiconductor laser of the present invention, an active layer made of In _W Ga _1-W As material (0 <W ≦ 1) is formed on the semiconductor substrate as In _1-Y (Ga _1-Z A
l _Z ) _Y- based material (0 ≦ Y <0.4, 0 ≦ Z <1) is characterized by forming a double heterostructure portion sandwiched between clad layers.

[0014]

According to the InGaAlP semiconductor laser of the present invention, GaAs _{1-X having a} lattice constant smaller than that of GaAs is used.
When _{P X (0 <X ≦ 1} ) using the substrate, the GaAsP
The InGaAlP clad layer grown so as to be lattice-matched on the substrate is InGaA lattice-matched on the GaAs substrate.
It has a feature that the Al composition can be made smaller than that of the 1P clad layer and the carrier concentration can be made high. Also, GaA
An InGaP strained active layer can be obtained by growing the GaAs on the sP substrate so as to be lattice-matched to GaAs. Therefore, the temperature characteristics can be improved by the change in the band structure due to the introduced strain and the high concentration of the p-clad layer.

Further, according to another InGaAs semiconductor laser of the present invention, since an In _X Ga _1-X As (0 <X ≦ 1) substrate having a lattice constant close to that of InGaAs of the active layer is used, this InGaAs is used. The InGaAlP clad layer grown so as to be lattice-matched on the substrate has a larger amount of In than the InGaAlP clad layer lattice-matched on the GaAs substrate, and has good crystallinity. Therefore, InGaA
The reliability is improved by the InGaAs active layer having a low strain and configured to lattice match with InGaAs on the s substrate and the clad layer having good crystallinity.

[0016]

EXAMPLE An example according to the present invention will be described below.

FIG. 1 is a sectional view of a semiconductor laser according to this embodiment. The substrate of the semiconductor laser of this embodiment is made of GaA.
An n-type GaAsP substrate 101 having a lattice constant smaller than s is adopted. On the n-type GaAsP substrate 101, undoped In via the n-type GaAsP buffer layer 102.
A double heterostructure is formed by sandwiching the GaP active layer 104 between the n-type InGaAlP first cladding layer 103 and the p-type InGaAlP second cladding layer 105.

Second p-type InGaAlP cladding layer 105
A p-type InGaP etching stop layer 106 is stacked on top of this, and a p-type InGaAlP third cladding layer 107 having a trapezoidal cross section is formed on this etching stop layer 106. The p-type InGa is formed on the third cladding layer 107.
A P cap layer 108 is formed, and the n-type GaAsP current blocking layer 10 is formed around the third cladding layer 107.
9 is formed. The p-type GaAsP contact layer 1 is formed on the cap layer 108 and the current blocking layer 109.
The p-type electrode AuZn111 is attached via 10. In addition, an n-type electrode Au is formed on the back surface of the n-type GaAsP substrate 101.
Ge112 is attached.

Next, the composition of each of the substrate 101, the active layer 104, and the cladding layers 103, 105 and 107 will be described with reference to FIG. FIG. 2 is a diagram showing a compositional plane of a mixed crystal of InGaAlP. In FIG. 2, L1 is GaA.
s indicates the lattice matching, and L2 indicates the GaAsP lattice matching. First, the substrate 101 is represented by GaAs _1-X P _X with X =
It is composed of 0.1 to 0.2.

The active layer 104 has a thickness of 150 A (angstrom) and is L1 so as to match GaAs.
With the composition of point A above, that is, the composition of X = 0, Y = 0, 5,
It is composed of In _0.5 Ga _0.5 P. Therefore, the active layer 104 is formed as a strained active layer by introducing strain into the n-type GaAsP substrate 101, and the bandgap at this time is 1.9 eV.

On the other hand, the first to third cladding layers 103, 1
The compositions of 05 and 107 are the same for both p-type and n-type, and n-type G
The composition of point B on L2, that is, In _1-Y (Ga _1-Z Al _Z ) _Y P is represented by Y in order to obtain a lattice constant with respect to the substrate 101 of aAsP and obtain a band gap of 2.33 eV. = 0.5 to 0.7 and Z ≦ 0.4. As described above, the Al composition ratio is reduced to 0.4 or less from the conventional value of 0.7 shown at the point D in FIG. 2. Therefore, the impurity concentration is increased to sufficiently increase the carrier concentration, thereby increasing the band gap. You can Here, each clad layer 103, 1
Impurity doping of 05 and 107 is performed by using Zn for p-type as an impurity and about 8 × 10 ¹⁷ cm ⁻³ for n-type, and Si as an impurity for n-type with a concentration of about 2 × 10 ¹⁷ cm ⁻³ .

In the semiconductor laser having such a structure and composition, the band discontinuity difference between the active layer and the p-clad layer can be increased by about 100 meV as compared with the conventional case, and high temperature operation of 150 C and 50 mW can be realized. Further, InGaP lattice-matched on the substrate 101 has a wavelength of 670 nm or less in the active layer of Al.
It can be realized without introducing.

As described above, according to this embodiment, an n-type GaAsP substrate having a lattice constant smaller than that of GaAs is used, and the active layer is composed of In _0.5 Ga _0.5 P so as to match GaAs. By forming a strained active layer having strain, and by increasing the Al concentration in the cladding layer to X ≦ 0.4 to increase the impurity concentration and carrier concentration, the active layer and the p-clad layer on the conduction band side are formed. Band discontinuity can be increased. Therefore,
It is possible to provide an InGaAlP-based semiconductor laser having improved temperature characteristics. Next, a second embodiment will be described. FIG. 3 is a sectional view of the semiconductor laser according to the present embodiment. The substrate 201 of the semiconductor laser of this embodiment has an n-type I
Adopt nGaAs.

On this substrate 201, a double hetero structure is formed in which an undoped InGaAs active layer 204 is sandwiched between an n-type InGaAlP first clad layer 203 and a p-type InGaAlP second clad layer 205 via an n-type InGaP buffer layer 202. To be done.

On the second cladding layer 205, p-type InG is formed.
An aP etching stop layer 206 is laminated, and p-type InGa having a trapezoidal cross section is formed on the etching stop layer 206.
The AlP third cladding layer 207 is formed. A p-type InGaP cap layer 208 is formed on the third clad layer 207.
And an n-type InGaAs current blocking layer 209 is formed around the third cladding layer 207.
Then, the cap layer 208 and the current blocking layer 209
A p-type InGaP contact layer 210 is formed on the
A p-type electrode AuZn211 is formed on the contact layer 210.
Is installed. Further, on the back surface of the substrate 201, the n-type electrode A
uGe212 is attached. Next, the substrate 201 and the active layer 2
04, the cladding layers 203, 205, and 207, the composition of each layer will be described with reference to FIG. The active layer 204 is In
_In the notation _W Ga _1-W As, 0 <W ≦ 1, for example W = 0.1
It is formed with a composition of 5 to a thickness of 80 to 200 A (angstrom).

On the other hand, the substrate 201 is made of In of the active layer 204.
It is formed to have a composition of 0 <X ≦ 1, for example, X = 0.1 by the expression of In _X Ga _1-X As, which is close to the lattice constant of GaAs. Therefore, the active layer 204 can be grown on the substrate 201 so as to be lattice-matched with InGaAs, and strain can be reduced.

Further, the cladding layers 203, 205, 207
Have the same composition for both p-type and n-type In _1-Y (Ga _{1 -Z} A
l _Z ) _Y P, where 0 ≦ Y <0.4 and 0 ≦ Z <1,
Impurity doping of each clad layer 203, 205, 207 is about 8 × 10 ¹⁷ cm ⁻³ with p-type Zn as an impurity,
The n-type has Si as an impurity and has a concentration of about 2 × 10 ¹⁷ cm ⁻³ . Therefore, the cladding layers 203, 205, 2 grown on the substrate 201 so as to be lattice-matched to InGaAs.
07 is a lattice-matched I on a GaAs substrate as in the conventional case.
Depending on the composition ratio Y, the In content may be higher than that of the nGaAlP cladding layer.
The amount of is increased, and good crystallinity can be obtained.

Thus, according to this embodiment, InGaA
In _X Ga close to the lattice constant of InGaAs in the s active layer
_{Since the 1-X} As substrate (0 <X ≦ 1) is adopted, an active layer with less strain can be formed, and an InGaAlP clad layer having good crystallinity can be obtained by increasing the amount of In. Therefore, it is possible to provide an InGaAs semiconductor laser having improved reliability and capable of operating at high temperature and high output. 1000 in the structure using the conventional GaAs substrate
While a lifetime of only about 10 hours was obtained, the semiconductor laser of the above-described structure according to this example could secure a lifetime of 10,000 hours or more. The present invention is not limited to the above-described embodiments, but can be implemented with various modifications.

[0029]

As described above in detail, the present invention is based on GaAs
GaAs with smaller lattice constant _1-X P _X (0 <X ≦ 1)
Since the substrate is used, the InGaAlP clad layer grown so as to be lattice-matched on this GaAsP substrate is made of Ga.
The Al composition can be made smaller and the carrier concentration can be made higher than that of the InGaAlP clad layer lattice-matched on the As substrate, and as a result, an InGaP strained active layer grown so as to be lattice-matched to GaAs on the GaAsP substrate can be obtained.
It is possible to provide an InGaAlP-based semiconductor laser capable of improving the temperature characteristics by sufficiently increasing the band discontinuity between the active layer and the p-clad layer.

Further, according to the present invention, by using an In _X Ga _1-X As (0 <X ≦ 1) substrate having a lattice constant close to that of InGaAs of the active layer, the growth is performed so as to be lattice-matched on this InGaAs substrate. The InGaAlP clad layer is
It is possible to provide an InGaAs-based semiconductor laser in which the amount of In is larger than that of the InGaAlP clad layer lattice-matched on the GaAs substrate, the crystallinity is improved, and the reliability of light emission operation is improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic configuration of a semiconductor laser according to an embodiment of the present invention.

FIG. 2 is a diagram showing a composition plane of a mixed crystal of InGaAlP.

FIG. 3 is a sectional view showing a schematic configuration of a semiconductor laser according to another embodiment of the present invention.

FIG. 4 is a diagram for explaining lattice matching of a substrate, an active layer and a cladding layer of a semiconductor laser according to another embodiment of the present invention.

[Explanation of symbols]

 101 ... n-type GaAsP substrate, 102 ... n-type GaAsP buffer layer, 103 ... n-type InGaAlP first cladding layer, 104 ... undoped InGaP active layer, 105 ... p-type InGaAlP second cladding layer, 106 ... p-type InGaP etching stop layer , 107 ... p-type InGaAlP third cladding layer, 108 ... p-type InGaP cap layer, 109 ... n-type GaAsP current blocking layer, 110 ... p-type GaAsP contact layer, 111 ... p-type electrode AuZn, 112 ... n-type electrode AuGe.

Claims (2)

[Claims] 1. An In _{1 -Y} (Ga _{1 -Z} Al) layer on a semiconductor substrate.
_{Z) Y} P type material (having a 0 ≦ Y <1,0 ≦ Z < 1) double heterostructure section for sandwiching the active layer in the cladding layer made of,
A semiconductor laser, wherein the GaAl mixed crystal composition of the clad layer made of In _{1 -Y} (Ga _{1 -X} Al _X ) _Y P is X ≦ 0.4. 2. An active layer made of In _W Ga _1-W As based material (0 ≦ W <1) is formed on a semiconductor substrate as In _1-Y (Ga _1-X).
Al _{X) Y} P type material (having a 0 ≦ Y <1,0 ≦ Z < 1) double heterostructure section sandwiched between cladding layers formed of, In
In of the clad layer of _1-Y (Ga _1-X Al _X ) _Y P
A semiconductor laser having a (GaAl) mixed crystal composition of Y <0.4.