JPH0722701A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To obtain element characteristics with a low resistance and improved reproducibility by providing GazIn1-zP layer between AlGaInP second clad layer and GaAs contact layer. CONSTITUTION:A lamination part for emitting light consisting of n-type (AlsGa1-s)1In1-tP (x<s<=1, 0<t<1) first clad layer 11, (Al-xGa1-x)yIn1-yP (0<=x<1, 0.3<y0.8) active layer 12, and P-type (lpGa1-xp)qIn1-qP (x<p<=1, 0<q<1) second clad layer 13 is formed on n-type GaAs substrate 1. Then. GarIn1-rP (r-0.5) layer 14 and P-type (AlpGa1-p)qIn1-qP (x<q<=1, 0<q<1)) upper second clad layer 15 are formed on it. Therefore, P-type GawIn1-wP (w=0.5) layer 16, P-type GawIn1-z0.5 (0<=z<=0.5) layer 17 and P-type GaAs contact layer 18 are formed on it, thus obtaining the title element with a small element resistance and an improved reproducibility.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is AlG which emits red light.
The present invention relates to an aInP-based semiconductor laser device.

[0002]

2. Description of the Related Art Conventionally, semiconductor laser devices composed of III-V semiconductors have been put into practical use due to the development of crystal growth techniques such as liquid phase epitaxy, molecular beam epitaxy and organometallic vapor phase epitaxy. . Such a semiconductor laser device is
It is widely used in optical data processing, optical communication, and other fields, but there is a demand for higher performance such as lower power consumption, higher output, shorter wavelength, and lower noise. In particular, attention has been paid to shortening the wavelength of a semiconductor laser element for the purpose of improving the recording density of an optical disc or the like or replacing a He—Ne laser.
In recent years, it has been put to practical use by using an AlGaInP-based crystal lattice-matched with a GaAs substrate. However, research for higher performance has been actively conducted.

In an AlGaInP-based semiconductor laser device, a light-emitting portion having an AlGaInP-based double hetero structure is generally formed on an n-type GaAs substrate, and a p-type GaAs contact layer is provided between the light-emitting portion and an electrode. Ga
The reason for forming the As contact layer is that AlGaInP
This is because good ohmic contact cannot be obtained between the system crystal and the electrode metal. However, in this case, AlGaIn
In the structure in which the GaAs contact layer is provided directly on the P clad layer, the device resistance becomes extremely high. this is,
This is because the band discontinuity in the valence band at the hetero interface between the AlGaInP layer and the GaAs layer is large, so that a potential barrier for holes is generated. Such an increase in element resistance induces heat generation during element driving, which adversely affects the reliability of the semiconductor laser element. Conventionally, in order to reduce the device resistance, a Ga _w In _{1 -w} P layer (w = 0.5) is provided between the AlGaInP clad layer and the GaAs contact layer, or the Al composition ratio of the AlGaInP layer is changed to the clad layer. A structure is provided in which layers are gradually reduced from the side toward the contact layer side or the p-type carrier concentration of each layer is increased. Further, in order to further reduce the element resistance, a semiconductor laser element as shown in FIG. 3 has been devised.

This semiconductor laser device has an n-type GaAs substrate 1 on which an n-type GaAs buffer layer 2 is formed.
Type (Al _0.7 Ga _0.3 ) _0.51 In _0.49 P first cladding layer 3
1, Ga _0.51 In _0.49 P active layer 32 and p-type (Al
_0.7 Ga _0.3 ) _0.51 In _0.49 P The light emitting laminated portion including the second cladding layer 33 is formed. Second cladding layer 33
The portion above the middle has a mesa stripe shape with a width of about 5 μm, on which the p-type Ga _0.51 In _0.49 P layer 3 is formed.
4, a p-type AlGaAs layer 35 and a p-type GaAs contact layer 36 are formed. An n-type GaAs current blocking layer 37 is formed on the upper portion of the second cladding layer 34 outside the mesa stripe. Further, on the contact layer 36 and the current narrowing layer 37, p-type GaAs is formed.
The layer 38 is formed. Further, an n-side electrode 3 is provided on the surface of the substrate 1 opposite to the semiconductor layer growth surface, and the p-type G
The p-side electrode 4 is provided on the aAs layer 38.

In the above semiconductor laser device, a refractive index waveguide is formed based on the effective refractive index difference between the inside and outside of the mesa stripe, and the light generated in the active layer 32 is confined by the refractive index waveguide, so that single transverse mode oscillation is generated. Is obtained.
Furthermore, since the AlGaAs layer 35 is formed, G
In comparison with the case where the GaAs contact layer 36 is provided directly on the a _0.51 In _0.49 P layer 34, the Ga _0.51 In _0.49 P thin layer 3 is provided.
The band gap difference with No. 4 becomes smaller. Therefore, the hetero barrier against holes is lowered, and the device resistance can be reduced.

[0006]

However, in the above-mentioned conventional semiconductor laser device, it is necessary to switch the material of P and As immediately before growing the AlGaAs layer 35, and the growth is interrupted. Growth surface after interruption (regrowth surface)
However, surface contamination due to the adhesion of impurities and surface roughness due to oxidation are likely to occur, and it is difficult to grow a crystal containing Al thereon. Therefore, there is a possibility that the resistance of the semiconductor laser device may be increased due to the interface irregularity on the regrowth surface and the decrease of the carrier concentration, which causes a problem in the reproducibility of the device characteristics.

The present invention has been made to solve the above problems, and an object thereof is to provide a semiconductor laser device having low resistance and good reproducibility of device characteristics.

[0008]

The semiconductor laser device of the present invention comprises (Al _x Ga _1-x ) _y In _1-y P (0≤x <1, 0.
3 <y <0.8) active layer of the first conductivity type (Al _s Ga)
_1-s ) _t In _1-t P (x <s ≦ 1, 0 <t <1) first cladding layer and second conductivity type (Al _p Ga _1-p ) _q In _{1 -q} P
(X <p ≦ 1, 0 <q <1) having a light emitting laminated portion sandwiched between the second cladding layer and a second conductivity type GaAs contact layer formed on the second cladding layer. , A second conductivity type Ga _{z is provided} between the second cladding layer and the contact layer.
An In _1-z P (0 ≦ z <0.5) layer is provided, whereby the above object is achieved.

[0009]

According to the present invention, and an AlGaInP second cladding layer, between the GaAs contact layer, Ga _z In _1-z
A P (0 ≦ z <0.5) layer is provided. Ga _z In _1
-z P layer, since Ga _w an In _{1 over} w P (w = 0.5) layer having a smaller band gap than can be reduced hetero barrier for holes. Also, instead of the AlGaAs layer, G
Since the a _z In _{1 -z} P layer is grown, it is not necessary to interrupt the growth just before the growth to switch the material, and the interface irregularity on the regrowth surface and the decrease of the carrier concentration may not occur. Absent.

[0010]

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

(Embodiment 1) FIG. 1 is a sectional view showing a refractive index guided type visible light semiconductor laser device according to a first embodiment of the present invention.

This semiconductor laser device has an n-type GaAs substrate 1 on which an n-type GaAs buffer layer 2 is formed, and n
Type (Al _s Ga _1-s ) _t In _1-t P (x <s ≦ 1, 0 <t <
1) First clad layer 11, (Al _x Ga _1-x ) _y In _1-y P
(0 ≦ x <1, 0.3 <y <0.8) active layer 12 and p-type (Al _p Ga _1-p ) _q In _1-q P (x <p ≦ 1, 0 <q
<1) A light emitting laminated portion including the second cladding layer 13 is formed. _Gar In is formed on the second clad layer 13.
_1-r P ( _r- 0.5) layer 14 and p-type (Al _p G
a _1-p ) _q In _1-q P (x <p ≦ 1, 0 <q <1) The upper second cladding layer 15 is formed. A p-type Ga _w In _1-w P (w = 0.5) layer 16 and a p-type Ga _z In _1-z P (0 ≦ z <0.5) layer 17 are formed on the upper second cladding layer 15. And the p-type GaAs contact layer 18 is formed,
It has a mesa stripe shape with a width of μm. Further, n is formed on the second cladding layer 15 outside the mesa stripe.
A type GaAs current confinement layer 19 is formed. Further, an n-side electrode 3 is provided on the surface of the substrate 1 opposite to the semiconductor layer growth surface, and the contact layer 18 and the current narrowing layer 19 are provided.
A p-side electrode 4 is provided on the above. The first clad layer 11, the second clad layer 13, and the upper second clad layer 15 have t and q of 0.4 <t <0.6, 0. 4 <q
It is better to set it to <0.6. More preferably t-0.5,
It is desirable to set q to 0.5.

The growth of each semiconductor layer in this semiconductor laser device can be performed by using a liquid phase growth method, a molecular beam epitaxy method, a metal organic chemical vapor deposition method, or the like. Also,
The mesa stripe can be formed by selective etching. From the first cladding layer 11 to the Ga _z In _{1 -z} P layer 17, there is no need to interrupt the growth for switching the material between P and As, and there is no interface irregularity on the regrowth surface and a decrease in carrier concentration. It never happens.

In this embodiment, the details of each semiconductor layer are as follows.

N-type first cladding layer 11: (Al _0.7 Ga
_0.3 ) _0.51 In _0.49 P, layer thickness 1.0 μm Active layer 12: Ga _0.51 In _0.49 P, layer thickness 0.06 μm p-type second cladding layer 13: (Al _0.7 Ga _0.3 ) _0.51 In
_0.49 P, the layer thickness 0.2μm Ga _r In _{1 over r} P layer 14: Ga _0.51 In _0.49 P, thickness 5n
mp type upper second cladding layer 15: (Al _0.7 Ga _0.3 ) _0.51
In _0.49 P, layer thickness 0.8 μm p-type Ga _w In _{1 -w} P layer 16: Ga _0.51 In _0.49 P, layer thickness 50 nm p-type Ga _z In _1-z P layer 17: Ga _0.43 In _0.57 P, layer thickness 50 nm p-type contact layer 18: layer thickness 0.5 μm The semiconductor laser device of this example was capable of continuous oscillation at room temperature in a single transverse mode of 660 nm. The voltage (Vop) of the device of this example when driven with an optical output of 5 mW was 2.
1 V and V of a device not including the Ga _z In _1-z P layer 17
Although op was 2.4 V, the element resistance could be sufficiently reduced. Furthermore, p-type Ga _w In _1-w
In the device in which the AlGaAs layer is provided on the P layer 16, Vop
Is about 2.2V, but there is lot-to-lot variation, and Vop ≧
An element having a high resistance of 2.5 V has also appeared. However, the element of this example showed no variation between lots, and had low resistance characteristics with good reproducibility.

(Embodiment 2) FIG. 2 is a sectional view showing a refractive index guided type visible light semiconductor laser device according to a second embodiment of the present invention.

This semiconductor laser device has an n-type GaAs substrate 1 on which an n-type GaAs buffer layer 2 is formed, and n
Type (Al _s Ga _1-s ) _t In _1-t P (x <s ≦ 1, 0 <t <
1) First clad layer 21, (Al _x Ga _1-x ) _y In _1-y P
(0 ≦ x <1, 0.3 <y <0.8) active layer 22 and p-type (Al _p Ga _1-p ) _q In _1-q P (x <p ≦ 1, 0 <q
<1) A light emitting laminated portion including the second cladding layer 23 is formed. _Gar In is formed on the second cladding layer 23.
_1-r P ( _r- 0.5) layer 24 and p-type (Al _p G
a _1-p ) _q In _1-q P (x <p ≦ 1, 0 <q <1) The upper second cladding layer 25 is formed. On the upper second cladding layer 25, a p-type Ga _w In _1-w P ( _{w to} 0.5) layer 26, a p-type Ga _z In _1-z P (0 ≦ z <0.5) layer 27 are formed. And the p-type GaAs contact layer 28 is formed,
It has a mesa stripe shape with a width of μm. Further, n is formed on the upper portion of the second cladding layer 25 outside the mesa stripe.
A type GaAs current confinement layer 29 is formed. Further, a p-type GaAs layer 30 is formed on the contact layer 28 and the current narrowing layer 29. An n-side electrode 3 is provided on the surface of the substrate 1 opposite to the semiconductor layer growth surface, and a p-side electrode 4 is provided on the p-type GaAs layer 30. Regarding the first clad layer 21, the second clad layer 23 and the upper second clad layer 25,
It is preferable that t and q be 0.4 <t <0.6 and 0.4 <q <0.6 in order to obtain a lattice structure in which crystal transition does not occur. More preferably, t to 0.5 and q to 0.5 are desirable.

In the manufacture of this semiconductor laser device, from the first cladding layer 21 to the Ga _z In _{1 -z} P layer 27, P
Since it is not necessary to interrupt the growth for switching the materials between As and As, neither interface irregularity on the regrowth surface nor decrease in carrier concentration occurs.

In this embodiment, the details of each semiconductor layer are as follows.

N-type first cladding layer 21: Al _0.51 In _0.49 P, layer thickness 1.0 μm active layer 22: (Al _0.2 Ga _0.8 ) _0.51 In _0.49 P, layer thickness 0.08 μm p-type second cladding layer 23: al _0.51 In _0.49 P, the layer thickness 0.2μm Ga _r In _{1 over r} P layer 24: Ga _0.51 In _0.49 P, thickness 3n
m p type second upper cladding layer 25: Al _0.51 In _0.49 P, thickness 0.6 .mu.m p-type Ga _w an In _{1 over w} P layer 26: Ga _0.51 In _0.49 P, thickness 50 nm p-type Ga _z In _1-z P layer 27: Ga _0.35 In _0.65 P, layer thickness 3 nm p-type contact layer 28: layer thickness 0.3 μm p-type GaAs layer 30: layer thickness 0.5 μm The semiconductor laser device of this embodiment has a single transverse mode of 620 nm. It was possible to oscillate continuously at room temperature. Further, the Vop of the element of this example is 2.5 V, and the Vop of the element not including the Ga _z In _{1 -z} P layer 27 is 2.9 V,
The element resistance could be reduced sufficiently. Further, lot-to-lot variation was not observed, and low resistance characteristics were obtained with good reproducibility.

In this embodiment, the p-type Ga _z In _{1 -z} P layer 2 is used.
In order to reduce the band gap difference between the p-type GaAs contact layer 28 and the p-type GaAs contact layer 28, the Ga mixed crystal ratio z was reduced to 0.35. However, if the mixed crystal ratio z is too small, Ga
The lattice constant of InP increases and the lattice mismatch rate with GaAs increases. If this lattice mismatch rate becomes too large, dislocations will occur at the interface between the GaInP layer and the GaAs layer, and conversely the element resistance will increase. To prevent this, the thickness of the Ga _z In _1-z P layer, it is desirable not to exceed significantly the critical thickness for the occurrence of dislocation. However, if the layer thickness of the Ga _z In _{1 -z} P layer is too thin, the effect of reducing the hetero barrier against holes is lost.
Since there is a limit to preventing the transition by reducing the layer thickness as described above, the mixed crystal ratio z of Ga is preferably 0.2 or more.

In the first and second embodiments, the light emitting portion having the DH (double heterostructure) structure as described above is formed as the light emitting portion, but the present invention is not limited to this, and AlG is used.
The same effect can be obtained when light emitting parts of various structures using aInP-based crystals are adopted. For example, a layer having a lattice strain such as Ga _0.4 In _0.6 P or Ga _0.6 In _0.4 P can be used as the active layer, or a quantum well structure can be used.
In addition, SCH (separated confiment heterostructur
Even if the structure e) or the superlattice structure is adopted, a practical index-guided semiconductor laser device with a low driving voltage can be obtained with good reproducibility.

[0023]

As is apparent from the above description, according to the present invention, in the AlGaInP-based red semiconductor laser device, between the second cladding layer and the GaAs contact layer, Ga _z In _{1 -z} P (0 By providing the ≦ z <0.5) layer, the potential barrier against holes can be reduced. Further, this Ga _z In _1-z P (0 ≦ z <0.
5) Since it is not necessary to interrupt the growth immediately before growing the layer, the interface resistance and the increase in the resistance due to the decrease in the carrier concentration do not occur. Therefore, a semiconductor laser device having a small device resistance can be obtained with good reproducibility.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a semiconductor laser device of Example 1.

FIG. 2 is a sectional view showing a semiconductor laser device of Example 2.

FIG. 3 is a cross-sectional view showing a conventional semiconductor laser device.

[Explanation of symbols]

1 n-type GaAs substrate 2 n-type GaAs buffer layer 3 n-type electrode 4 p-type electrode 11 and 21 n-type first cladding layer 12, 22 an active layer 13, 23 p-type second cladding layer 14, 24 Ga _r an In _{1 over r} P layer 15, 25 p-type second upper clad layer 16, 26 p-type Ga _w an In _{1 over w} P layer 17 and 27 p-type Ga _z In _1-z P layers 18, 28 p-type contact layer 19 and 29 p Type current narrowing layer 30 p-type GaAs layer

Claims (1)

[Claims] 1. (Al _x Ga _1-x ) _y In _1-y P (0 ≦ x <
1, 0.3 <y <0.8) active layer of the first conductivity type (A
_{l s Ga 1-s) t} In 1-t P (x <s ≦ 1,0 <t <1) and the first cladding layer, a second conductivity type _{(Al p Ga 1-p)} q In
_1-q P (x <p ≦ 1, 0 <q <1) Light emitting laminated portion sandwiched by a second cladding layer, and a second conductivity type GaAs contact layer formed on the second cladding layer And a second conductivity type Ga _z In _{1 -z} P (0 ≦ z <0.5) layer is provided between the second cladding layer and the contact layer.