JPH0395983A - Semiconductor laser element and its manufacture - Google Patents

Abstract

PURPOSE:To reduce element resistance than conventional by constituting it out of the first to third light wave guide layers which consists of Al, Ga, In, and P and whose composition ratios are restricted respectively, and forming the third light wave guide layer into the ride stripe shape in the longitudinal direction of a resonator, and setting the refractive index of the third light wave guide layer below the refractive index of a second light wave guide layer. CONSTITUTION:This has a semiconductor substrate, a first light wave guide layer 3, consisting of n-type (AlyGa1-y)0.51In0.49P (0<y<=1, y>x), a double hetero junction structure, consisting of an active layer 4 comprised of (AlxGa1-x)0.51In0.49 P (0<=x<0.4) and a second light wave guide layer 5 comprised of P-type (AlyGa1-y)0.51In0.49P (0<y<=1, y>x), and a third light wave guide layer, consisting of p-type AlalphaGa1-alphaAs (0.35<=alpha<=1) being formed on the second light wave guide layer, and which are formed in order on this semiconductor substrate. Element resistance can be reduced by putting the structure of the p-type light wave guide layer into the laminate of (AlyGa1-y)0.51In0.49P (0<y<=1) and AlalphaGa1-alphaAs layers, and putting it in the structure that the AlGaAs layer is formed in stripe shape on the surface on the side opposite to the active layer of AlGaInP layer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser device, and particularly to a short wavelength semiconductor laser device suitable as a light source for an optical disc. [Prior Art] Conventionally, the element structure of an AfiGalnP semiconductor laser is based on, for example, Abride Physics Letter 4 7 (1
985) Pages 1027 to 1028 (App
l. Phys. Lett 4 7 (Sat 985)pp
l027 -1028) or Electronics Letter 2
3 (1987), pages 938 to 939 (1
:electronLett23 (King 987) pp938
-939).

[All issues to be solved by the invention] The above conventional technology does not give sufficient consideration to the transverse mode control structure of the AQGaInP semiconductor laser, and the element resistance is high or the threshold current is high, and the saturation of the optical output due to heat generation occurs. The problem was that it was difficult to obtain high output. An object of the present invention is to provide an element that performs highly efficient laser oscillation with a low threshold current by reducing element resistance and creating an optimal transverse mode control structure.

[Means to solve the problem]

The above objective is achieved as follows. Conventionally, it has been revealed that when the level of impurity is low, even if the flow rate of the added impurity gas is increased, the impurity is not activated sufficiently and does not have an effective carrier concentration. Therefore, p-AQGalnP
In an AQGaInP semiconductor laser using a mixed crystal for the optical waveguide layer, when the thickness of the film is increased, a problem arises in that the element resistance increases depending on the thickness of the film.

Therefore, in the present invention, the p-type impurity doping concentration is set to AQG.
A that can be achieved to a higher level than in the case of aInl' mixed crystal
Q a Gax- a As layer (0.3 5-≦α≦
By using 1) in the optical waveguide layer, we attempted to reduce the element resistance. That is, the structure of the p-type optical waveguide layer is (A Q
yGax-y)o. sz I no. +aP (0
<3'< 1) and A Q a Ga1-a As
The above object was achieved by forming a stack of layers and forming a structure in which an AQGaAs layer was formed in a ridge stripe shape on the surface of the AnGaInF layer opposite to the active layer. here. The refractive index of the AQαGas-αAs layer is (A Q yGa
ty)o. Ist I no. It is less than the refractive index of the ael' layer. Further, an optical waveguide layer having a ridge portion is formed using an etching solution that etches the AQGalnF mixed crystal and the AQGaAS mixed crystal at greatly different etching rates.

At this time. The etching stop layer inserted between the AQGaAs optical waveguide layer and the AQGalnt' optical waveguide layer has a structure that is the same as or close to that of the active layer, which reduces the OJ ability of the laser light in the active layer to be absorbed by the etching stop layer. There is a sex.
This problem can be solved by making the etching stop layer thinner and utilizing the quantum size effect, and by creating a mixed crystal composition due to impurity diffusion, which makes the band gap larger than that of the active layer and greatly reduces light absorption. do.

[Effect]

AQαGa s - aAs layer has a doping concentration of AQ
It is easier to adjust than GaInP mixed crystal, and the carrier concentration is also lower than I.
It can be set high in the range of XIO18 to IX10 "cn-". Therefore, the resistance can be lowered than that of AQGaInP mixed crystal. In addition, the AQ composition of A Q a Gal-ct As was set to 0.
．． 35 If α<1, then the bandgap is the active layer G
ao. δs L no. It can be made larger than the bandgap of asP, and furthermore, when α is about 0.6 to 0.7, it has a bandgap and refractive index comparable to that of the AQGalnP optical waveguide layer. Therefore, A Q a G
The at-tx As layer can be used as an optical waveguide layer instead of the AQGalnl' layer.

In order to realize an accurate and appropriate transverse moat control structure using the AQαG a 1-aAs layer as an optical waveguide layer, for example, as shown in Figs. 1 and 2, etching with a high etching selectivity with respect to the AQGaAs layer is required. A stop pair 6 is provided. Since this etching stop layer 6 has a composition similar to that of the active layer, there is a possibility that the laser light is absorbed by the etching stop layer. In order to avoid this, the etching stop layer is made into a thin film and the bandgap thereof is increased by making it a mixed crystal with the optical waveguide layer having the AQ composition above and below it. For example, the etching stop layer is doped with impurities at a commercial concentration as shown in FIG.
As shown in the figure, this is done by doping a region close to the etching stop layer with impurities at a high concentration, and causing the impurities to diffuse through a subsequent heat treatment process. [Example] Example 1 Example 1 of the present invention will be explained using the first construction drawing.

In Fig. 1, first the n-GaAs (001) substrate fabrication (
n − Ga As buffer layer 2 (thickness 0.5 μm, no=IX1056O-δ
), n - (A Q yGat-y) o. sz I n
o. asP cladding layer (optical waveguide layer) 3 (thickness 0.8
~l. O /j m + n. o = 5 ~
7XIO”aa-δt O − 4 < y≦1 engineering),
Undoped (A QxGax-x) o. atIn0.4
9P active layer 4 (thickness 0.04-0.08 μm, O≦1X
≦-0.2). p-(A Q yGaz-y)o. sx
InO@4S P clad layer (optical waveguide k!)) 5(
Thickness 0.2~0.4μm, n^:=3~5X1057c
m-”, 0.4 < y≦-1), high concentration impurity (Zn) doped p-(AlyGa1-βGaz-β)o
．． 8z I no. asP etching stop layer 6 (thickness O.002~0.01μm, n^=5X10
” ~ I X 1 0”car-8, O≦-β strain 0.
2) (or p-AQγGai-γAs etching stop layer (thickness 0.002-0.0 1pm.n^=sxio
”~I
6)). p - A Q a Gas- a As cladding layer (optical waveguide layer) 7? Thickness 0.5-1.0 pm, n
＾=7
a<0.7), PGaAs layer 8 (thickness 0.2-0.4
μm, n^ = ↓ ~ 2 × 1016 dl-8) are sequentially grown by gold organic vapor phase epitaxy (MOCVL) method. After this, an insulating film SiZ mask (not shown, thickness 0.1~0.
3 μm) is formed in a stripe shape, and layers 7 and 8 are etched using a phosphoric acid solution or a sulfuric acid solution to produce a ridge stripe (width 3 to 6 μm). Next, with the absolute IMrm mask left in place, the sample was placed in a long furnace (MOCVL again) to a crystallization temperature of 8°C, which was lower than the normal long temperature of 600-700℃.
The temperature is raised to 00 to 850°C, and heat treatment is performed for about 10 to 30 minutes. At this time, impurities diffuse into the surrounding area from the heavily doped layer 6, and a mixed crystal region 9 (shaded area in FIG. The AOi111 formation becomes larger than that at the time of the Bochu. After this, the temperature is lowered to 600-700℃, and n Ga
A s light absorption and current block J*10 (thickness 0.6 ~
Select or lengthen 1.0μms no=3~6×↓O"(!m-'). Next, take out the sample from a long furnace and remove the insulating liIS i 02 mask. A sample is placed in the p-GaAs cap layer 11.
(Thickness 2 ~ 4 μm, n^ = 5 x 10" ~
A p-side electrode 12 and an n{111 electrode 13 are then deposited and cleaved and scribed to cut into an element shape.

According to this example, the conventional element resistance could be reduced to 3 to 5 Ω. This increases the maximum oscillation temperature of the laser to 100°C.
I was able to improve it to. Stripe width 3-6
By setting it in the range of μm, the threshold value #1 flow is 30 to 5
0 mA, and it oscillated stably in the fundamental transverse mode up to an optical output of 30 mW. In addition, the differential quantum efficiency is 60~ higher than before.
I was able to get 70%. In this device, no significant deterioration was observed even after 2000 hours at a constant light output of 10 mW at a temperature of 50°C. Example 2 Example 2 of the present invention will be described using FIG. 2.

In FIG. 2, an element is manufactured in the same manner as in Example 1, but
In this embodiment, in order to cause mixed crystal formation of the etching stop layer 6, a highly concentrated impurity doped layer (with a thickness of 0.05 to 0.5 mm) is applied only to the region of the slide 7 near the interface with the etching stop layer.
2μm, n^=5X1018~5X10E11
Country-8) is formed. Temperature 800-8 as in Example 1
By performing heat treatment at 50° C. (10 to 30 minutes), mixed crystal composition is caused between the etching stop layer 6 and the layer 7 to form a disordered region 9 (hatched area in FIG. 2). . The other steps are exactly the same as in Example 1. In this example, the device characteristics were similar to those in Example 1.

Example 3 Example 3 of the present invention will be described using FIG. 3.

In FIG. 3, a crystal layer is grown in the same manner as in Example 1, but after growing layer 5, a p-AQαGai-αAs cladding layer 7 (thickness 0.5 to 1.0 μm, n^=7×1017
~1X1018 Kokuichi 8, 0.5-≦, α distortion 0.7),
p-GaAs layer 8 (thickness 0.2-0.4 pm, n^=
The film is sequentially grown using the MOCVD method using 1 to 2 x 10 m-")*. After this, a SiOz mask (not shown) is formed into a stripe shape, and layers 7 and 8 are etched to form a ridge stripe. In this case, p − (A
Q y Gax-y) o. 5t I n0.49 P cladding layer 5 acts as an etching stop layer. next. Si
P doped with impurities at a high concentration while leaving the ns mask
GaAs layer 14 (thickness 0.1 to 0.3 μm + n^
= 5 x 10'' to 5 x 10''cs-3) at a certain temperature of 600 to 700°C. After that, the temperature is raised to 800 to 850°C and heat treatment is performed for 10 to 30 minutes to diffuse the impurities in the layer 14.
Impurity diffusion regions 9 shown in the shaded areas in the figure are formed. Thereafter, the temperature is lowered to a growth temperature of 600 to 700° C. to selectively lengthen the n-GaAs light absorption/current confinement layer 10. The subsequent steps are exactly the same as in Example 1.

According to this embodiment, since impurity diffusion is performed on both sides of the active layer 4 except for the central part of the active layer facing the edge stripe part, so-called AQGaInP mixed crystal is used.
The expected ordered structure collapses and becomes a disordered structure. As a result, the central part of the active layer maintains an undoped and ordered structure, and its band gap is 1.85.
eV, and its flesh side becomes a disordered structure with a bandgap of 1.90eV. Therefore, a band barrier of about 0.05 eV is formed in the lateral direction of the active layer against carriers injected into the non-diffused region at the center of the active layer, so carrier confinement is improved compared to the conventional method. It turns out.

Therefore, laser oscillation is effective at a low threshold current, and in this example, a threshold current of 20 to 30 mA was obtained. The longitudinal mode was a single mode, and the King generation light output was 40 to 50 mW, while the destructive level was 60 to 70 mW. [Effects of the Invention] According to the present invention, AnG having a ridge stripe structure
In the aInP semiconductor laser, not only can the thickness of the optical waveguide layer be manufactured to the desired thickness with good controllability and reproducibility,
We were able to reduce the element resistance to 3 to 5 Ω compared to conventional models. This increases the maximum oscillation temperature of the laser to 100°C.
Therefore, it was possible to modify the temperature characteristics compared to the conventional one. In addition, by introducing a layer doped with highly concentrated impurities and creating mixed crystals through impurity diffusion, it became possible to sufficiently avoid light absorption loss due to the etching stop layer introduced to control the thickness of the optical waveguide layer. In the device of the present invention, the threshold Y4 current 20
Highly efficient laser oscillation with a differential quantum efficiency of 60-70% was possible at ~50 mA. Furthermore, the kink generation light output is 40
~50mW. An end face destruction level of 60 to 70 mW was obtained.

[Brief explanation of drawings]

Figures 1 to 3 are cross-sectional views of embodiments 1 to 3 of the present invention, respectively. 1-n-GaAs substrate, 2-n-
G a As buffer layer, 3 − n − (A
Q yGat-y) o. Ist I no. is P cladding layer, 4... undoped (A 11 xGax-
x)o. sx1n0.49P activity M, 5-p-
(A Q yGaz-y) o. sx I no. +oP
Cladding layer. 6=・p−(lβGaz−β)o. szI
no. asP etch stop layer or . p-AQγGa1
-γAg layer, 7...p-AQαGa 1-αAs cladding layer, 8...p-GaAs layer, 9...Z
n diffused disordered region, 10...n-GaAs light absorption and current confinement layer, l1=-p-GaAs\(Nl"Q\P

Claims (1)

[Claims] 1. A semiconductor substrate, and n-type semiconductors sequentially formed on the semiconductor substrate.
Type (Al_yGa_1_-_y)_0_. _5_1In
＿0＿． A first optical waveguide layer consisting of _4_9P (0<y<1, y>x), (Al_xGa_1_-_x)_0_. _5_1In_
0__. An active layer consisting of _4_9P (0≦x<0.4) and p-type (Al_yGa_1_-_y)_0_. ＿５＿
1In_0_. A double heterojunction structure consisting of a second optical waveguide layer consisting of _4_9P (0<y≦1, y>x) and a p-type Al_αGa_1_−_αAs (0.35 ≦α≦1), wherein the third optical waveguide layer is formed in the shape of a ridge stripe in the direction of the resonance skirt length, and A semiconductor laser device characterized in that the refractive index of the optical waveguide layer is less than or equal to the refractive index of the second optical waveguide layer. 2. In the semiconductor laser device according to claim 1, a current blocking and light absorption layer made of n-type GaAs is formed on the second optical waveguide layer on the side surface of the third optical waveguide layer. Semiconductor laser element. 3. When manufacturing the semiconductor laser device according to claim 1, in the step of sequentially forming the constituent layers of the double heterojunction structure and the third optical waveguide layer on the semiconductor substrate, Before forming the constituent layers of the optical waveguide layer No. 3, a p-type (AlPGa_1_-
＿β)＿0＿. _5_1in_0_. _4_9P(0<
β<1) or Al_γGa_1_−_γAs(0≦γ≦
After forming the etching stop layer consisting of 1), the third optical waveguide layer in the shape of a ridge stripe is formed by etching, and then heat treatment is performed to form the etching stop layer and the second and third optical waveguide layers. A method for manufacturing a semiconductor laser device, characterized in that the etching stop layer is made disordered by mixed crystal composition between the etching stop layer and the etching stop layer. 4. In the method for manufacturing a semiconductor laser device according to claim 3, the thickness of the etching stop layer is 1 to 2.
It is in the range of 0 nm, and the impurity concentration is 3 × 10^1^8 ~
A method for manufacturing a semiconductor laser element in the range of 1×10^1^9cm^-^3. 5. When manufacturing the semiconductor laser device according to claim 1, in the step of sequentially forming the constituent layers of the double heterojunction structure and the third optical waveguide layer on the semiconductor substrate, Before forming the constituent layers of the optical waveguide layer in step 3, p
of type (Al_βGa_1_−_β)_0_. _5_1In_
0__. _4_9P (0≦β<1) or Al_γGa_1
An etching stop layer made of ____γAs (0≦γ≦1) is formed, and the impurity concentration near the etching layer of the constituent layers of the third optical waveguide layer is adjusted to The impurity concentration is made higher than that of the other parts, the etching layer and the second optical waveguide layer, and then etching is performed to form the third optical waveguide layer in the shape of a ridge stripe, followed by heat treatment. A method for manufacturing a semiconductor laser device, characterized in that the etching stop layer is disordered by mixing the composition between the high impurity concentration layer in the wave layer and the etching stop layer. 6. In the method for manufacturing a semiconductor laser device according to claim 5, the film thickness of the high impurity concentration layer is 0.05.
It is in the range of ~0.2 μm, and the impurity concentration is 5 × 10^1
A method for manufacturing a semiconductor laser device having a size in the range of ^8 to 5 x 10^1^9 cm^-^3. 7. When manufacturing the semiconductor laser device according to claim 1, after sequentially forming the constituent layers of the double heterojunction structure and the third optical waveguide layer on the semiconductor substrate, the above-mentioned layer is formed by etching. forming a third optical waveguide layer in the shape of a ridge stripe, and then forming a ridge side surface portion of the third optical waveguide layer and a portion of the surface of the second optical waveguide layer that is not covered with the third optical waveguide layer; A semiconductor layer having an impurity concentration higher than the impurity concentration of the active layer, the second optical waveguide layer, and the third optical waveguide layer and having a p-type conductivity is formed thereon, and then heat treatment is performed to The composition is mixed between the semiconductor layer, the third optical waveguide layer, the second semiconductor layer, and the active layer, so that both sides of the active layer except for the central portion facing the third optical waveguide layer are mixed. 1. A method for manufacturing a semiconductor laser device, characterized by disordering the semiconductor laser device. 8. In the method for manufacturing a semiconductor laser device according to claim 7, the thickness of the upper semiconductor layer is 0.05 to 0.05.
It is in the range of 2 μm, and the impurity concentration is 5 × 10^1^8 ~
5x10^1^9cm^-^3 and the thickness of the second optical waveguide layer is in the range of 0.1 to 0.5 μm. 9. A double heterojunction structure consisting of a semiconductor substrate, a first optical waveguide layer, an active layer, and a second optical waveguide layer sequentially formed on the semiconductor substrate, and a resonance structure on the second optical waveguide layer. a third optical waveguide layer having the same conductivity type as the second optical waveguide layer formed extending in the longitudinal direction and having a refractive index lower than the refractive index of the second optical waveguide layer; In the semiconductor laser device in which a current is injected into the active layer through the optical waveguide layer No. 3, the non-emissive region of the active layer is disordered and has a bandgap width larger than the bandgap width of the emissive region. A semiconductor laser device characterized by: 10. In the semiconductor laser device according to claim 9, the first optical waveguide layer is of n-type (Al_yGa_1
＿−＿y)＿０＿. _5_1In_0_. ＿４＿９P(
0<y≦1, y>x), and the active layer is (Al_
xGa_1_−_x)_0_. _5_1In_0_. ＿
4_9P (0≦x<0.4), and the second optical waveguide layer is p-type (Al_yGa_1_-_y)_0_. ＿５
_1In_0_. _4_9P (0<y≦1, y>x), and the third optical waveguide layer is Al_αGa_1_-_
A semiconductor laser device made of αAs (0.35≦α≦1).