JPS6177383A - Buried semiconductor laser - Google Patents

Abstract

PURPOSE:to enable basic lateral mode oscillation with high efficiency and high- output action by effectively blocking the current flowing through the part except a mesa region by a method wherein the side surface of the second semiconductor layer is equipped with a semiconductor layer of the second conductivity type having a refractive index equal to or smaller than that of the second semiconductor layer, and the side surfaces of the active layer and the third and fourth semiconductor layers are equipped with semiconductor layers of the first conductivity type having a smaller refractive index than that of the active layer. CONSTITUTION:When the expose Al0.11Ga0.89As active layer 14 is etched with an etchant of H2O2+H3PO4+3CH3OH, a constriction 18 is formed. Next, a P-type Al0.4Ga0.6As buried layer 19, and an N-type Al0.4Ga0.6As buried layer 20 are successively formed by the second liquid phase epitaxial growth. Here, because of the constriction 18 on the mesa side surface, the buried layer 19 formed at the first step in the second liquid phase epitaxial growth can necessarily be located at the constriction 18. Therefore, the buried layer 19 can be selectively formed on only the mesa side surfaces of an N-type Al0.4Ga0.6As clad layer 12 and an N-type Al0.35Ga0.65As photo waveguide layer 13.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a striped buried semiconductor laser with current confinement.

(Prior art and its problems) In the structure of a buried semiconductor laser, the active layer region is surrounded by a low refractive index material, for example, in the case of a QaAa active layer, it is surrounded by an AlGaAs layer, which has a strong optical waveguide effect. Let me lean on it. However, the refractive index difference inevitably becomes larger than necessary, and therefore, although fundamental mode oscillation occurs when the stripe width is within 2 μm, higher-order mode oscillation occurs when the stripe width becomes wider than that. Also, if the stripe width is narrow, the light output will be reduced to several meters.
Only low outputs of W or less can be obtained. A striped embedded semiconductor laser has been proposed in order to improve the various drawbacks and problems of low output of the embedded semiconductor laser. In this striped buried structure, as described below, an optical waveguide layer is provided separately from the active layer, and only the active layer is surrounded by a semiconductor layer with a low refractive index, completely confining the injected carriers and allowing light to propagate to the optical waveguide layer. This aims to weaken the optical waveguide effect, prevent higher-order mode oscillation, and maintain single mode oscillation over a large current region.

Until now, the structure shown in Figure 2 has been considered as the structure of a striped buried semiconductor laser (Figure 30).
Japan Society for Applied Physics (1983) Lecture No. 7a-H-6).

That is, in FIG. 2, 1 is an n-type GaAs substrate, 2 is
is an n-type Alz Gq, y XAs cladding layer (0,3≦
X≦0.35), 3 is n-type AlyG (Ix-yAs optical waveguide layer (0,23≦y<0.26), 4 is Alg, 14G
ao, aaAs active layer, 5 is p-type AIWGa, -wA
s layer (0,4<w≦0.45), 6 is p-type A1. ), 2
Ga08As electrode layer, 7 is p-type Alo, 4cao, 6A
8 is an n-type AI0.40aO, 6A8 buried layer, 9 is a p-type electrode, and 10 is an n-type electrode.

In this structure, the p-type electrode 9. A forward voltage of 1°K was applied to the n-type electrode, and Ano, 14Ga, 86Al! active layer 4
The device enables laser operation by injecting a current into the mesa region and recombining it to emit light.Since the p-type Al(,4Gao6As buried layer 7) acts as a current confinement layer, the current flowing to areas other than the mesa region becomes effective. The laser oscillation efficiency is increased by efficiently injecting current into the mesa portion.

Furthermore, as a result of providing the n-type AAyGa, □As optical waveguide layer 3, the laser light largely seeps into the optical waveguide layer 3 side, so the effective refractive index difference in the lateral direction of active@4 is small. However, the carrier confinement is similar to the conventional embedded type.
It has a two-dimensional effect. Therefore, the original confinement effect is weakened and stable fundamental mode oscillation can be obtained over a wide current range even with a laser with a wide stripe width.

However, for reliability reasons in such a semiconductor laser, it is necessary to keep the active layer 4 away from the p-type electrode 9 ohmic layer due to structural dimensions.
This forces the AsO2 layer to be thicker.

Therefore, since the AI composition (W) is relatively large (0.4≦w<0.45) and the layer thickness is thick, the thermal resistance is low, which is disadvantageous for high-output oscillation. On the other hand, to prevent this, Kp type AA! WG & + YaAS layer 5 is thinned and p-type A
1. ), 2Gao, BAs When the electrode layer 6 is thickened, p-type AlO, 2Gao, 6As 1 formed on the mesa side surface
! Pole layer 6 and n-type A16,4 Gao6As buried layer 8
There is a drawback that the pn junction potential between the two regions becomes smaller, and leakage current flowing to areas other than the mesa region increases.

In addition, if the p-type All wG a H-WAsAsO2 is thick, the layer 5 with a high An composition will be exposed to the atmosphere before the second liquid phase epitaxial crystal growth step, so that the surface of the layer 5, which is most likely to be oxidized, will be exposed to the atmosphere. This oxide film becomes a source of growth inhibition, and greatly impairs the uniformity and reproducibility of the second □ liquid phase epitaxial crystal growth. In other words, it becomes difficult to uniformly grow the embeddings N7 and 8 on the side surfaces of the mesa.

(Object of the Invention) The object of the present invention is to eliminate the drawbacks of the conventional semiconductor laser, to have a reliable current confinement effect, to have stable fundamental transverse mode oscillation, to enable high-output operation, and to be easy to manufacture. The present invention provides an embedded semiconductor laser with good reproducibility.

(Structure of the Invention)' The semiconductor laser of the present invention includes at least a first semiconductor layer of the first conductivity type and a semiconductor laser of the first conductivity type having a higher refractive index than the first semiconductor layer, on a semiconductor substrate of a first conductivity type. a second semiconductor layer, an active layer having a higher refractive index than the second semiconductor layer, and the fourth semiconductor layer.
A striped multilayer structure formed by sequentially laminating a third semiconductor layer of a second conductivity type having a refractive index lower than that of the semiconductor layer and a fourth semiconductor layer of a second conductivity type having the same refractive index as the first semiconductor layer. a second conductivity type semiconductor layer having a refractive index the same as or lower than that of the second semiconductor layer on a side surface of the second semiconductor layer; A feature of the fourth semiconductor layer is that a first conductivity type semiconductor layer having a lower refractive index than the active layer is provided on the side surface of the fourth semiconductor layer.

(Embodiments of the invention) Examples according to the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment according to the present invention.

First, in the first liquid phase epitaxial growth step, n
On the type QaAs substrate 11, n-type Alo4Qa, ),
6As cladding layer 12. n-type Alo, 3sGao, 5s
AS original waveguide layer 13 e Alo, tlGao, a9AS
Active layer 14. p-type AJo5Gao5As layer 15. p-type A
AO,4Ga(,,6As cladding layer 16°p type Al
The polar layer 17 is sequentially formed of 15GaO, 15GaO, and 85As. The thickness of each layer is 1.5μm*o, sμm, 0.0
They were 5 μm, 0.3 μm, 1.0 μm, and 0.5 μm.

The difference from the multilayer structure that makes up conventional semiconductor lasers is that
p-type A1wGal-WAS layer 5 and p-type A7o, 2GaO
, 8AS between the p-type Alo, 4G and the electrode layer 6 (Fig. 2).
The aO,6As cladding layer 16 (Fig. 1) is formed, and the layer thickness of the p-type A/65Ga04AS layer 15 (corresponding to the p-type klWGaI-wAB layer 5 in Fig. 2) is 0.3 μm. The reason is that it is thin.

After that, H, O, + H3PO4+ 3 CH! IO
Mesa etching is performed in stripes using H etchant until reaching the n-type QaAs substrate 11, thereby forming a mesa portion having an active region. Next, etching with HF solution for 1 minute at room temperature results in p-type Ajl! o,sQa,
, only the As layer 15 is selectively etched to a depth of 0.3 μm from the side surface of the mesa. Furthermore, H,0,+HsPO
A7 exposed with ml of 4+ 3CHsOH etchant
1! Q, 11Ga(, BgAs active layer 14 at room temperature 10
When lightly etched for ~20 seconds, a constriction 18 with a depth of 0.3 μm is formed on the side surface of the mesa, as shown in FIG.

Next, in a 20th liquid phase epitaxial growth step, a p-type A10.4Gao6As buried layer 19. n-type AA! 6.4 Ga. , 6AS buried layers 20 are sequentially formed. Here, since there is a constriction 18 on the side surface of the mesa, the p-type A10.4 Gao, 6 formed first in the second liquid phase epitaxial growth step is
The As buried layer 19 does not grow above the constriction 18, but can always remain at the constriction 18. Therefore, as shown in FIG. 1, n-type Al. , 4GBo6A8 cladding layer 12 and the n-type ANo, 5sGao, a5As optical waveguide layer 13, the p-type AA! (
A 1,4 Gao, 6 As buried layer 19 can be formed. As a result of crystal growth experiments using growth solutions with various degrees of supersaturation on various mesa shapes with constrictions, it was found that crystal growth is inhibited at the constrictions, which is characteristic of the liquid phase epitaxial growth process. It was found that the properties were good and that a growth layer could be formed with good reproducibility.

After that, the p-type impurity diffusion layer 21. A p-type electrode 22 and an n-type electrode 23 are formed to form a buried semiconductor laser according to the present invention.

In this structure, the p-type AJo4Gao,6As buried layer 19 acts as a current confinement layer, and the p-type AJo4Gao,6As buried layer 19 acts as a current confinement layer, and
Since the Alo4Gao6A8 cladding layer 12 is formed, the p-type A16.4Ga0 formed on the mesa side surface
．． 6A8 cladding layer 12 and n-type Al (, , 4Gao, 6
Since the pn junction potential with the As buried layer 20 is large, leakage current flowing outside the mesa portion can be reduced, enabling highly efficient laser oscillation with a low oscillation threshold current, and the active layer width is 3 μm.
Even with the above, p-type Al o can maintain fundamental transverse mode oscillation over a large current region and has a large M composition and high thermal resistance.
, 5cao, , Since the As layer 15 can be made thin, the heat dissipation characteristics are also improved, and laser oscillation can be easily performed even at high output operation and at high temperatures.

In addition, since most of the layers with a low M composition are exposed on the side surfaces of the mesa, there is little oxidation and there is no problem of non-uniformity during buried growth, resulting in good reproducibility and uniformity of buried growth. Become.

(Effects of the Invention) As described above, according to the present invention, it is possible to eliminate the drawbacks of conventional semiconductor lasers, effectively block current flowing to areas other than the mesa region, achieve high efficiency and high output operation, and achieve fundamental transverse mode oscillation. In addition, it is possible to form a semiconductor laser having excellent heat dissipation characteristics, reproducibility, mass productivity, and reliability.

In the above embodiments, an example was described in which m1 is an AlGaAs-Ga, As-based semiconductor, but it goes without saying that m1 may be other compound conductors, such as InQaAsP-InP-based semiconductors.

[Brief explanation of drawings]

FIG. 1 is a structural sectional view of an embodiment according to the present invention. FIG. 2 shows structural cross-sectional views of conventional buried semiconductor lasers. In the figure, 1.11-n-type QaAs substrate, 2-n-type A
lxGa, -xAs cladding layer (0,3≦X<0.35
). 3--- n-type AlyGa4s optical waveguide layer (0,23<y
≦0.26). 4- AJo, x4Gao, 5sAS active layer, 5-p-type AIWGal-WAa layer (0,4<w<0.45)
, 6- Tl type AJ0.2GaO, 8A8 electrode layer, 7
．． 19-p-type AJo, 4Ga, ), 6Aa buried layer. 8,20-nm AJ(,,4Ga(,6As s
Inset layer, 9.22...p type electrode, 10.23...n type electrode, 12... n type Al. , 4Ga (16As cladding layer, 13...n-type AlO, 35Ga0.65All
Optical waveguide layer * 14 ”' AA! 0,11 cao8
gAs active layer, 15-p type A1.5Ga, , A8 layer,
16-p-type Allo, 4 caO, 6A 8 cladding layer, 17-...p-type Allo1s Gao, a s AS
electrode layer. 18... Constriction, 21... P-type impurity diffusion layer, 24
... sio and membrane are respectively shown. E 1 Figure 12, n-type A10, 4 Goo, 6 As cladding layer 1
3, leading wave layer 14, active layer 15, P type AfL□, 5 GOo, 5 As layer 16, P
Type Al1o, 4 Ga. , 6A5 cladding layer 17, electrode layer 18, constriction

Claims (1)

[Claims] On a semiconductor substrate of a first conductivity type, at least a first semiconductor layer of the first conductivity type, a second semiconductor layer of the first conductivity type having a higher refractive index than the first semiconductor layer, and a second semiconductor layer of the first conductivity type having a higher refractive index than the second semiconductor layer. An active layer having a high refractive index, a third semiconductor layer of a second conductivity type having a lower refractive index than the first semiconductor layer, and a fourth semiconductor layer of the second conductivity type having the same refractive index as the first semiconductor layer are sequentially formed. The active layer and the third semiconductor layer have a stripe-like multilayer structure formed by laminating them, and the width of the active layer and the third semiconductor layer is smaller than the width of the stripe-like multilayer structure, and the second semiconductor layer and the second semiconductor layer are arranged on the side surface of the second semiconductor layer. A semiconductor layer of a second conductivity type having the same or lower refractive index is provided, and a semiconductor layer of a first conductivity type having a lower refractive index than the active layer is provided on the side surfaces of the active layer and the third and fourth semiconductor layers. An embedded semiconductor laser characterized by: