JPH077219A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To obtain the etching stop effect, which is equal to or more than the effect of a conventional etching stop layer having a film thickness of 5nm or more by providing a plurality of etching stop layers, and thereby compensating for the deterioration of the stop effect caused by the thinning of the etching stop layer. CONSTITUTION:A superlattice structure, wherein a plurality of etching stop layers 7 are provided, is used. The film thickness of the layer 7 is set so that the effective band-gap width of the etching stop layer 7 and an active layer 4 can be sufficiently provided by a quantum-size effect. A P-type clad layer 6 in the vicinity of the active layer 4 has a superlattice structure. Thus, the average carrier concentration is improved, and the effective difference in conduction band energy is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a short wavelength AlGaInP ridge type semiconductor laser device.

[0002]

2. Description of the Related Art An example of a conventional ridge type semiconductor laser device is shown in FIG. A conventional example of a laser device having such a structure is disclosed in Japanese Patent Laid-Open No. 90584/1990. n-AlGa
InP clad layer 2, GaInP active layer 4, p-AlG
aInP clad layer 5, p-GaInP contact layer 1
After the growth of 0, the p-type cladding layer 5 is etched halfway to form a ridge 9, and the n-GaAs layer 11 is selectively grown to fill the removed portion. The p-GaAs 12 is grown on the -GaAs embedded layer 11. At this time, in order to improve the film thickness controllability of the p-type cladding layer 5 by etching, p-AlGaI is used.
An etching stop layer 16 is provided as an nP5 intermediate layer. As the material, p-GaInP is used because of its good etching selectivity with AlGaInP, and its film thickness suppresses the reduction of the forbidden band width due to the formation of the ordered array structure peculiar to this system by impurity doping. By adding the quantum size effect, the transition emission energy of the etching stop layer is thin enough to be sufficiently larger than the band gap of the active layer, and is thick enough to effectively maintain the etching stop effect. In the case of a bulk active layer, the thickness is about 5 to 20 nm. Also,
Carrier concentration of p-AlGaInP clad layer is 7 * 1
It was about 0 to the 17th power.

[0003]

At this time, the quantum well structure is used in the active layer to shorten the wavelength of the laser, for example, the oscillation wavelength of 6
When it is attempted to achieve the order of 30 nm, the effective forbidden band width of the active layer due to the quantum size effect and the transition emission energy of the etching stop layer are substantially equal to each other, or the transition emission energy of the etching stop layer becomes lower, so that etching Carriers are recombined in the stop layer, resulting in carrier loss, which causes an increase in the threshold current of the laser and a decrease in controllability of the oscillation wavelength, making it difficult to shorten the wavelength to the 630 nm range. As the etching stop layer is made thinner, the quantum size effect increases and the effective band gap difference can be made large, but the function as an etching stop layer deteriorates, and the p-AlGaInP cladding layer other than the ridge portion is etched. There is a problem that the film thickness controllability deteriorates, the surface condition deteriorates, an interface defect occurs at the time of buried growth, and the beam shape is distorted due to insufficient etching near the ridge. Further, considering the band structure of this material system in obtaining the 630 nm band oscillation, the conduction band energy difference between the active layer and the clad layer becomes small because the oscillation wavelength becomes short, and further, the p-type carrier concentration Therefore, there is a problem in that the electron confinement in the active layer is weakened and electrons leak to the p-type cladding layer, making it difficult to obtain high-temperature operation.

[0004]

In order to solve the above problems, a GaInP etching stop layer having a thickness that allows a sufficiently large difference in effective forbidden band width between the etching stop layer and the active layer is formed as a p-AlGaInP cladding layer. Clap in 2
More layers are provided. In addition, p-AlGaInP near the active layer
The average carrier concentration was raised by periodically sandwiching p-GaInP, which can provide a carrier concentration of 1 * 10 18 or higher, in the clad layer. Further, the superlattice structure is used to reflect electrons leaked to the p-AlGaInP cladding layer and return them to the active layer.

[0005]

[Function] By reducing the thickness of the etching stop layer so that the difference in the effective forbidden band width can be sufficiently large, it is possible to suppress the recombination of carriers in the etching stop layer and reduce the loss. This layer is p-AlGaInP
By providing a plurality of clad layers sandwiched between them, the deterioration of the function as an etching stop layer was compensated, and a good surface was obtained. In addition, by sandwiching GaInP, which has a high doping efficiency of Zn, which is a p-type impurity, the average carrier concentration can be set high, so that the effective conduction band energy difference can be increased. Furthermore, the confinement of electrons in the active layer is improved by the reflection of electrons due to the superlattice structure, and the temperature characteristics are improved. Further, by introducing strain into the quantum well layer and the quantum barrier layer of the superlattice structure, the effective conduction band energy difference can be further increased, and the confinement of electrons in the active layer can be further improved.

[0006]

EXAMPLE 1 Example 1 of the present invention is shown in FIG.
This will be described with reference to FIG. 1 is a sectional view of a laser device according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of an etching stop layer portion of FIG. 1.3 μm at a temperature of 700 ° C. on the n-GaAs substrate 1 by metalorganic vapor phase epitaxy
m n-AlGaInP first cladding layer 2, 15 nm undoped AlGaInP first optical guide layer 3, 3 nm undoped GaInP quantum well layer sandwiched by 5 nm undoped AlGaInP quantum barrier layers, and multiple quantum well active layer 4 , 15 nm undoped AlGaIn
P second optical guide layer 5, 0.2 μm p-AlGaInP second cladding layer 6, 10 nm p-AlGaInP layer 15
The superlattice etching stop layer 7 having four layers of the p-GaInP etching stop layer 16 of 1.5 nm sandwiched between
Multiple superlattice etch stop layers stacked for two periods sandwiching a 0 nm p-AlGaInP layer 8, 0.8 μm p-AlG
aInP third clad layer 9, 22 nm p-GaInP
The buffer layer 10 is sequentially grown, and p
-GaInP buffer layer 10 and p-AlGaInP third clad layer 9 are etched down to p-GaInP etching stop layer 7, and 0.8 is formed on the etching stop layer.
After the n-GaAs current blocking layer 11 having a thickness of μm is embedded by selective growth, a p-GaAs contact layer 12 having a thickness of 2 μm is grown on the ridge portion and the n-GaAs current blocking layer, and the back surface of the n-GaAs substrate and p-GaAs are grown. Metals 13 and 14 for electrodes are vapor-deposited on the upper surface of the contact layer. The photoluminescence wavelength corresponding to the multiple quantum well active layer having a quantum well layer thickness of 3 nm and a quantum barrier layer thickness of 5 nm is 625 n.
It was m. On the other hand, the photoluminescence wavelength corresponding to the etching stop layer of 1.5 nm was 585 nm, and the effective forbidden band difference from the active layer was sufficiently large. A sulfuric acid-based etching solution was used for forming the ridge. At this time, the etching stop layers of four layers having a thickness of 1.5 nm worked effectively, and etching stopped at the etching stop layers with good controllability. The laser thus obtained is
As shown in FIG. 7, continuous oscillation at room temperature was performed at a wavelength in the 630 nm range, and in the near-field image, there was no leakage of light to the outside of the ridge portion and no distortion of the beam shape was observed.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIGS. Here, FIG. 4 is an enlarged cross-sectional view of the etching stopper portion of FIG. On a (100) n-GaAs substrate 101 tilted by 7 degrees in the [011] direction at a temperature of 700 ° C. and a thickness of 1.3 μm by metalorganic vapor phase epitaxy.
N-AlGaInP first cladding layer 102, 15 nm
Undoped AlGaInP first optical guide layers 103, 7
nm undoped (Al _0.05 Ga _0.95 ) _0.5 In
Multiple quantum well active layer 10 in which 8 layers of _0.5 P quantum well layers are sandwiched by 5 nm undoped AlGaInP quantum barrier layers.
4, 15 nm undoped AlGaInP second optical guide layer 105, 22 nm p-AlGaInP second cladding layer 106, and 1.1 nm p-GaInP layer 117.
6 with a p-AlGaInP layer 118 of 6 nm
Superlattice clad structure with 0-cycle lamination 119,5 nm p-A
1.5 nm p-GaIn sandwiched by the lGaInP layer 115
Superlattice etching stop layer 107 in which seven P etching stop layers 116 are stacked, 0.8 μm p-AlG
aInP third cladding layer 109, 22 nm p-GaI
The nP buffer layer 110 is sequentially grown, and the p-GaInP buffer layer 110 and the p-AlGa layer 110 and the p-AlGa layer are left while leaving the ridge portion.
The InP third cladding layer 109 is etched to the p-GaInP etching stop layer 107, and the 0.8 μm n-GaAs current blocking layer 1 is formed on the etching stop layer.
After burying 11 by selective growth, on the ridge and n
-A 2 μm p-GaAs contact layer 112 is grown on the GaAs current blocking layer, and the back surface of the n-GaAs substrate and p-G
Metals 113 and 114 for electrodes are deposited on the upper surface of the aAs contact layer.

According to the present embodiment, the use of the tilted substrate partially suppresses the ordered arrangement structure of the AlGaInP material system, and as a result, the wavelength can be shortened even if the quantum well layer thickness is increased to 7 nm. The photoluminescence wavelength corresponding to this multiple quantum well active layer was 626 nm. On the other hand, 1.5
The photoluminescence wavelength corresponding to the etching stop layer of nm is 585 nm, and the effective forbidden band difference from the active layer is sufficiently large. A sulfuric acid-based etching solution was used for forming the ridge. At this time, this 1.5 nm
The 7 etching stop layers worked effectively, and etching stopped with good controllability at the etching stop layers.
The laser thus obtained continuously oscillated at room temperature at a wavelength in the 630 nm range. The carrier concentration in the p-AlGaInP clad layer near the active layer was able to be increased on average, and electron confinement in the active layer was improved due to the reflection of electrons in the superlattice clad, which made oscillation difficult conventionally. 80
An output of 3 mW was obtained up to a high temperature of ℃ or more.

(Third Embodiment) A third embodiment of the present invention will be described with reference to FIGS. Here, FIG. 6 is an enlarged cross-sectional view of the etching stopper portion of FIG. On a (100) n-GaAs substrate 201 tilted by 7 degrees in the [011] direction at a temperature of 780 ° C. and a thickness of 1.3 μm by metalorganic vapor phase epitaxy.
N-AlGaInP first cladding layer 202, 15 nm
Undoped AlGaInP first optical guide layers 203, 8
nm quantum undoped GaInP quantum well layer sandwiched by 5 nm undoped AlGaInP quantum barrier layers to form a multi-quantum well active layer 204, 15 nm undoped Al
GaInP second optical guide layer 205, 22 nm p-Al
GaInP second clad layer 206, 1.1 nm p-Ga
_{The 0.4} In _0.6 P layer 217 was formed with 1.7 nm of p- (Al _0.7 Ga).
_0.3 ) _0.6 In _0.4 P layer 218 sandwiched by 10 periods for superlattice clad structure 219, 0.15 μm p-AlGaI
nP second clad layer 220, 5 nm p-AlGaIn
Superlattice etching stop layer 207 in which seven layers of a 1.5 nm p-GaInP etching stop layer 216 are sandwiched between P layers 215, a 0.8-nm p-AlGaInP third clad layer 209, and a 22 nm p-GaInP buffer layer 210. Are sequentially grown to leave the ridge portion and p-GaI
The nP buffer layer 210 and the p-AlGaInP third clad layer 209 are formed as the p-GaInP etching stop layer 2
Etching up to 07, and etching on the etching stop layer.
After embedding the 8 μm n-GaAs current blocking layer 211 by selective growth, a 2 μm p-GaAs contact layer 21 is formed on the ridge and the n-GaAs current blocking layer.
2 is grown, and electrode metals 213 and 214 are vapor-deposited on the back surface of the n-GaAs substrate and the top surface of the p-GaAs contact layer.

According to the present embodiment, by adopting the tilted substrate and performing the high temperature growth, the ordered arrangement structure of the AlGaInP material system was completely suppressed. As a result, the quantum well layer thickness was 8 nm and the quantum barrier layer thickness was 5 nm. The photoluminescence wavelength corresponding to the multi-quantum well active layer of was 625 nm. On the other hand, the photoluminescence wavelength corresponding to the etching stop layer of 1.5 nm was 585 nm, and the effective forbidden band difference from the active layer was sufficiently large. A sulfuric acid-based etching solution was used for forming the ridge. At this time,
The 1.5 nm, 7-layer etching stop layer worked effectively, and etching was stopped with good controllability at the etching stop layer. The laser thus obtained continuously oscillated at room temperature at a wavelength in the 630 nm range. P-AlGaI near the active layer
The carrier concentration of the nP cladding layer could be increased on average and the electron confinement in the active layer was improved due to the reflection of electrons in the superlattice cladding. , The effective conduction band energy difference could be made larger. As a result, the maximum oscillation temperature at which an output of 3 mW was obtained could not be achieved in the past.
It was possible to raise the temperature to ℃ or higher.

[0011]

EFFECT OF THE INVENTION Since the effective band gap difference between the etching stop layer and the active layer is sufficiently large, carrier recombination in the etching stop layer is suppressed, so that the carriers are effectively confined in the active layer. As a result, the increase in the threshold current was suppressed, room temperature continuous oscillation in the 630 nm range was facilitated, and the controllability of the oscillation wavelength was improved. Further, the decrease in the etching stop effect due to the thinning of the etching stop layer is compensated by the plurality of stop layers,
A stop effect equal to or more than that of the etching stop layer having a thickness of 5 nm is obtained, and p-AlGaIn other than the ridge portion is obtained.
The film thickness controllability of the P clad layer was significantly improved. Furthermore, by making the p-AlGaInP clad layer near the active layer a superlattice structure, the average carrier concentration was improved and the effective conduction band energy difference was increased, resulting in improved temperature characteristics. It became possible to oscillate at 80 ° C or higher, which was not obtained in the wavelength band.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view of an etching stop layer according to the first embodiment of the present invention.

FIG. 3 is a sectional view showing a second embodiment of the present invention.

FIG. 4 is a sectional view of the vicinity of a p-AlGaInP second cladding layer according to a second embodiment of the present invention.

FIG. 5 is a sectional view showing a third embodiment of the present invention.

FIG. 6 is a sectional view of the vicinity of a p-AlGaInP second cladding layer according to a third embodiment of the present invention.

FIG. 7 is a longitudinal mode spectrum diagram of the laser according to the first embodiment of the present invention.

FIG. 8 is a sectional view showing the structure of a conventional ridge type semiconductor laser.

[Explanation of symbols]

1 ... n-GaAs substrate, 2 ... n-AlGaInP first cladding layer, 3 ... undoped AlGaInP first optical guide layer, 4 ... multiple quantum well active layer, 5 ... undoped AlGa
InP second optical guide layer, 6 ... p-AlGaInP second cladding layer, 7 ... Superlattice etching stop layer, 9 ... p-
AlGaInP third clad layer, 10 ... p-GaInP
Buffer layer, 11 ... n-GaAs buried layer, 12 ... p-
GaAs buried layer, 13 ... N-side electrode.

Claims (7)

[Claims] 1. A first conductive type A on a first conductive type GaAs substrate.
lGaInP first clad layer, active layer, second conductivity type Al
It has a GaInP second clad layer, a second conductive type GaInP etching stop layer, and a second conductive type AlGaInP third clad layer, and the active layer is (Al _x1 Ga _{1 -x1} ) _y1 In.
_1-y1 P (0 ≦ x ₁ <0.7, 0 <y ₁ <1) or (Al _x2
Ga _1-x2 ) _y2 In _1-y2 P / (Al _x3 Ga _1-x3 ) _y3 In _1-y3
AlGaInP-based ridge having a P (0 ≦ x ₂ <x ₃ <0.7, 0 <y ₂ , y ₃ <1) multiple quantum well structure and having a ridge portion in the second conductivity type AlGaInP third cladding layer. In the semiconductor laser device of the type, the GaInP etching stop layer has a thickness such that the transition emission energy due to the quantum size effect thereof is sufficiently larger than the forbidden band width of the active layer, and is the same as the second conductivity type AlGaInP second cladding layer. A semiconductor laser device having a superlattice structure in which a plurality of layers are sandwiched between second conductive type barrier layers having substantially the same composition. 2. The second conductivity type Ga according to claim 1.
The InP etching stop layer is the second conductive type AlG.
A plurality of sets of semiconductor laser devices are provided which are sandwiched by a second conductive clad layer having a composition substantially equal to that of the aInP second clad layer and having a film thickness larger than that of the second conductive barrier layer. 3. The method according to claim 1 or 2, wherein a part or all of the second conduction type AlGaInP second cladding layer is
(Al _x4 Ga _1-x4 ) _y4 In _1-y4 P / (Al _x5 Ga _1-x5 ) _y5 In _1-y5
P (0 ≦ x ₄ <x ₅ ≦ 0.7, 0 <y ₄ , y ₅ <1) Conductor laser device having a multiple quantum well structure. 4. The In composition y ₄ of part or all of the quantum well layer of the second conductive type second cladding layer of the second conductive type second cladding layer, wherein the quantum well layer is 0 <y ₄ or less. <
A semiconductor laser device in which 0.5 or 0.5 <y ₄ <1. 5. The In composition y ₅ according to claim 3 or 4, wherein the In composition y ₅ of part or all of the quantum barrier layer of the second conductive type second clad layer, the quantum barrier layer being a portion having the multiple quantum well structure is 0 <. A semiconductor laser device in which y ₅ <0.5 or 0.5 <y ₅ <1. 6. The method according to claim 1, 2, 3, 4 or 5.
A semiconductor laser device in which the plane orientation of the GaAs substrate is tilted in the [011] direction from 2 degrees to 25.3 degrees from the (100) plane. 7. A semiconductor laser device according to claim 1, 2, 3, 4, 5 or 6, wherein a crystal growth temperature is 650 ° C. or higher and 780 ° C. or lower.