JPS60140777A - Buried type semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a positive current constriction effect easily by formin striped stepped sections on both sides of a mesa section. CONSTITUTION:An n type Al0.4Ga0.6As layer 2, an Al0.05Ga0.95As active layer 3, a p type Al0.4Ga0.6As layer 4 and a p type Al0.5Ga0.5As layer 14 are formed on an n type GaAs substrate 1 in succession. A mesa section with an active region is formed through mesa etching to a striped shape up to reaching to the substrate 1. Only the layer 14 is etched selectively to shape a layer 14 in width narrower than the striped width of the layer 4, and a striped stepped section 15 is formed between the layer 4 and the layer 14. An n type Al0.6Ga0.4As buried layer 11, a p<-> type Al0.35Ga0.65 high-resistance layer 12 and an n type Al0.35Ga0.65 As buried layer 13 are shaped in succession so as to surround the mesa section. A p type impurity diffusion layer 7 is formed in the layer 14 and the layer 13. According to the constitution, a current component flowing from the layer 7 except the mesa section is stopped completely by a p-n reverse bias of the layer 13 and the layer 12.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a buried semiconductor laser with current confinement.

This is the first structure of an embedded semiconductor laser to date.
The structure shown in the figure has been considered. That is, in FIG. 1, l is n! ! ! ! GaAs substrate, 2 is n-type Ato, Ga0. As layer, 3 digits Ajoo5Ga0.
, As active layer, 4 a P-type At04Gao6As layer, 5 a P-type GaAs layer, 6 Ato3. Ga, 6. 7 is a P-type impurity diffusion layer, 8 is a 5i02 film, 9 is a P-type electrode, and 10 is an n-type electrode.

In this structure, the P-type electrode 9. A voltage in the direction of 10 KM is applied to the n-type electrode, and a current is injected into the Atoo, Gao, 5As active layer 3 to cause light emission recombination to enable laser operation. The As high resistance layer 6 blocks current flowing outside the mesa region and efficiently injects the current into the mesa region to increase the efficiency of laser oscillation.

However, Ato or Ga065A, which becomes the current blocking layer,
s6 high resistance layers, usually undoped n-type layers with 050
Even if the P- type layer has a low concentration of about -6n, a resistivity of only a few Ω-m can be obtained. Therefore, as shown in FIG. 1, the P-type impurity diffusion layer 7 is made of AI. 350a, 6. Since As is also formed on the side of the high resistance layer 6, current tends to flow in areas other than the mesa region, resulting in a high oscillation threshold current.
Alternatively, there was a drawback that laser oscillation became difficult. Furthermore, since the oscillation threshold current depends on the width of the P-type impurity diffusion layer 7, it has been difficult to obtain highly efficient laser oscillation with a low oscillation threshold current with good reproducibility. Therefore, in order to improve this, a structure as shown in FIG. 2 has been proposed, in which the current blocking layer is an n-type At06Gao4As buried layer 11, a P-
Type Ato, a5 Ga o65 A S high resistance layer 12
(usually low concentration on the order of 1o16t7n1), n-type At
o3. 3 in which Gao65As buried layers 13 are sequentially laminated
As shown in FIG.
o, 5 Gao, A, s buried layer 13 and P-type ALo,
s 5Ga065A s n-P reverse bias junction with high resistance layer 12 and P-type AtO, 35GaO, 66
As high resistance layer 12 and n-type Ato6Ga with large forbidden band width
This is attempted to be prevented by forming a junction surface with a large diffusion potential difference with the o4As buried layer 11.

However, P-type Ato3. It is difficult to completely prevent the current component flowing from the P-type impurity diffusion layer 7 portion formed in the Gao65As high-resistance layer 12 by the diffusion potential difference at the P-n junction. The higher the voltage applied to the region, the more the current blocking effect is impaired. Furthermore, in the second crystal growth step, the n-type Ato35Gao65As buried layer 13
As shown in FIG. 2, it is difficult to grow the surface of the growth layer in a shape that is in contact with the side surface of the mesa portion of the P-type GaAs layer 5 with good reproducibility. There are many things. This is F type A,
To350ao6', when growing the As high J ash resistant layer 12, generally kt, Ga,
-8 In order to improve wetting of the side surface of the mesa part of the As layer with the growth solution of the high-resistance layer 12 and achieve good buried growth, it is necessary to use a growth solution with a high degree of supersaturation. This is because it becomes difficult to form the growth layer thickness with good controllability, and the embedded shape of the P-type Ato35Gao, As high resistance layer 12 cannot be formed with good reproducibility as shown in FIG.

Therefore, the region of the P-type impurity diffusion layer 7 formed in the P-type Ato, Gao, A, s high-resistance layer 12 is widened, and there is no large current component flowing outside the mesa region, and the laser The drawback was that oscillation was difficult.

An object of the present invention is to provide a buried semiconductor laser which eliminates the drawbacks of the conventional buried semiconductor laser, has a reliable current confinement effect, is easy to manufacture, and has good reproducibility.

The semiconductor laser of the present invention has at least one first semiconductor layer of the first conductivity type on a semiconductor substrate of the first conductivity type, and an active layer having a narrow bandgap width than the first semiconductor layer; The stripe-shaped multilayer structure is formed by sequentially laminating a second conductivity type second semiconductor layer having a large band width and a second conductivity type third semiconductor layer, and the stripe width of the third semiconductor layer is the same as that of the second semiconductor layer. a second conductivity type semiconductor layer having a width smaller than the stripe width of the active layer and having a larger forbidden band width than the active layer on at least the side surfaces of the active layer and the first and second semiconductor layers; A feature is that a semiconductor layer of the first conductivity type is provided on the side surface of the semiconductor layer.

Hereinafter, in the embodiments according to the present invention, the same parts as those in the drawings are indicated by the same symbols.

First, in the first liquid phase epitaxial growth step, n
Type G a As substrate! Sequentially on top, n-type AtGa04
06 As layer 2, Ato, , Gao, 5As active layer 3. P type,
klα4Gao.

An As layer 4 and a P-type Ato, Gao5As layer 14 are formed.

The thickness of each layer is 1.5 μm%, 0.1 μm, 1.5 μr, respectively.
n was set to 1.0 μm. The difference from the conventional multilayer structure is that
On the P-type 11o4 Ga 06As layer 4, a P-type k10. The GaoBAs layer 14 is laminated.

That is, the P-type At, Ga, -, As layer 14 stacked on the P-type AttGa, -tAs layer 4 is grown such that the composition ratio y satisfies y>x.

After that, H20□+H, PO4+30H, OHj-y
Mesa etching is performed in a stripe pattern using an f-layer 7 until it reaches the n-type GaAs substrate 1, thereby forming a mesa portion having an active region. Next, by etching for a few seconds using HFfi, P-type Ato5Gao, As /i
Only tI4 is selectively etched to form P-type At0. Ga0. P-type Ato whose width is about 0.6 μm narrower than the stripe width of the As layer 4,
Ga0. As layer 14 is formed. That is, as shown in FIG. 3, striped step portions 15 having a width of about 0.3 μm are formed on both sides of the mesa portion between the layer 4 and the layer 14. Next, in a second liquid phase epitaxial growth step, an n-type Ato6Gao4As buried layer 11, a P-type Ato35Gao6. As high resistance layer 1
2. Sequentially form n-type Ato35Ga and 65As buried layers 13. Here, the de-type Ato3. The GaO,,As high resistance layer 12 contains 0.01 Ge as a P-type impurity, as in the conventional case.
By using a growth solution doped with at% 0.5
A material having a specific resistance of approximately Ω-m is formed.

In addition, since there is a step part 15 in the mesa part, the i-type AZos 5 formed in the second step of the second liquid phase epitaxial growth process is
G3o, 6. The AS high resistance layer 12 does not grow above the step portion 15 and can always be stopped at the step portion 15 portion. Therefore, as shown in Figure 3, the n
Type At0. , Gao, , the As buried layer 13 is P-type At
o50ao, the As layer 14 can be formed in a shape that is in contact with the side surface of the mesa portion.

As a result of crystal growth experiments using growth solutions with various degrees of supersaturation on various mesa shapes with stepped portions, it was found that the characteristic surface properties of the liquid-phase epitaxial growth process, in which crystal growth is inhibited in the stepped portions, were observed. It was found that it was possible to perform implantation growth with good reproducibility.

After that, the P-type impurity diffusion layer 7 is made of P-type AL05Ggo,
sAs layer 14 and n-type Ata, Ga06. The embedded semiconductor laser according to the present invention is formed by forming As in the buried layer 13, and forming the P-type electrode 11 and the n-type electrode io.
´Reru. In this structure, the current component flowing from the P-type impurity diffusion layer 7 portion other than the mesa region is n-type At0BS.
Ga6. s5 A S buried layer 13 and P-type Ato3
5Ga o6. Since this is completely blocked by the n-P reverse bias junction with the As high resistance layer 12, highly efficient laser oscillation can be achieved with a low oscillation threshold current.

FIG. 4 shows a second embodiment of the invention. The difference from the above embodiment is that the KP type Ato, as shown in FIG.
The P-type GaAs layer 5 is laminated on the Ga05As layer 14. This was etched into P-type Alo, a Ga as As
Only the layer 14 portion is selectively etched to form a stepped portion 15. Next, by a second liquid phase epitaxial growth process, each layer 11, 12, 13 is grown so as to surround the mesa part.
[Next formation. Therefore, n-type A4+3. Ga o65A
, S layer 13 is P-type AZo5 Ga o, B As layer 14
The P-type GaAs layer 5 is formed in a shape that is in contact with the side surface of the mesa portion.

After that, P type impurity diffusion layer 7, P type! M1t.

An n-type electrode 10 is formed. This structure enables highly efficient laser oscillation with a low oscillation threshold current as in the above-mentioned embodiments, and furthermore, since the KP-type GaAs layer 5 is used as a cap layer, the electrode resistance can be reduced. Type At
Since the o5Ga, 5As layer 14 can be made thinner, thermal resistance can also be reduced, and laser oscillation can be achieved with sufficient efficiency even at high temperatures.

FIG. 5 shows a third embodiment of the invention. In this structure, after sequentially forming the same layer structure as the multilayer structure shown in Fig. 2, this is
Using an etchant, mesa etching is performed in a stripe pattern until reaching the n-type GaAs substrate 1, thereby forming a mesa portion having an active region. Next, 1NI (40H+2
0H20 □ Engineering 2 Chi? When etching is performed for 10 seconds using an etching agent, only the P-type GaAs layer 5 and the n-type 0aAs substrate 1 are selectively etched, resulting in a pattern as shown in FIG.
CP type GaAs layer 5 and P mkl-o4Gao6
A step portion 15 is formed between the As layer 4 and the As layer 4 . Further, a step portion 15 is also formed between the n-type GaAs substrate 1 and the n-type Ato, Ga06As layer 2. Therefore, when layers 11, 12, and 13 are sequentially formed to surround the mesa portion in the next liquid phase epitaxial growth step, the first
The n-type Ato6Gao,4As buried layer 11, which grows second, has a stepped portion 15, so the n-type GaAs substrate 1
It is reliably formed only in the area. Similarly, since the second do type AZo, 35 Gacis5 A S high resistance layer 12 can be stopped at the stepped portion 15, the Kn type Ato, Gao, As shown in FIG. The buried layer 13 can be formed in such a shape that it is in direct contact with the side surface of the mesa portion of the P-type GaAs layer 5.

Thereafter, a P-type impurity diffusion layer 7, a P-type electrode 9, and an n-type electrode 10 are formed. In this structure, even if it is a multilayer structure similar to the conventional one, P-type GaAs serves as the cap layer.
N-type Ato, 5sGa (
16. Since the As m embedded layer 13 can be formed, embedded growth can be performed more easily and with better reproducibility than in the above two embodiments, and highly efficient laser oscillation can be achieved with a low oscillation threshold current.

Furthermore, as shown in the first to third embodiments, in the structure of the present invention, the current confinement effect is not impaired even if the P-type impurity diffusion layer and the P-type electrode width are made wider than in the conventional structure. Therefore, the heat dissipation characteristics are also improved, and laser oscillation can be performed satisfactorily even at high temperatures.

As described above, according to the present invention, the drawbacks of conventional semiconductor lasers can be eliminated, current flowing to areas other than the mesa region can be effectively blocked, and low oscillation threshold current and high efficiency laser oscillation can be achieved. In addition, it is possible to form a semiconductor laser with excellent heat dissipation characteristics, reproducibility, and mass productivity.

In addition, - in the above embodiments, At, Ga, -fAs -G
Although nine examples have been described using an aAs-based semiconductor, it goes without saying that other compound semiconductors, such as InGaAsP-In-based semiconductors, may also be used.

[Brief explanation of drawings]

1 and 2 are structural sectional views of a conventional buried semiconductor laser, and FIGS. 3, 4, and 5 are structural sectional views of embodiments of the present invention, respectively. In the figure, 1... n-type OaAs substrate, 2...
・N-type A2o4Ga o, As layer, 3...Atoo
5Gao1. As active layer, 4-P type Ato4Gao,
a As layer, 5...P-type GaAs layer, 6''' At
0.5Ga0. l, As high resistance layer, 7 - P type impurity diffusion layer, 8...5in2 film, 9... P type electrode, 10
... n-type electrode, 11 ・-n-type Ato, 6 (Ja6
．． 4 As buried layer, 12 ・P' type Ato ss
GaO, 65A s high resistance layer, 13-n type At0
．． , Gaoj5As m inset layer, 14-P type At0゜O 1 Figure 72 Figure O 3 Figure; + 4 Figure

Claims (1)

[Claims] on a semiconductor substrate of a first conductivity type, at least a first semiconductor layer of a first conductivity type and a band gap smaller than that of the first conductor layer;
a striped multilayer structure formed by sequentially stacking a thin active layer, a second semiconductor layer of a second conductivity type having a larger forbidden band width than the active layer, and a third semiconductor layer of the second conductivity type; The stripe width of the semiconductor layer is smaller than the stripe width of the second semiconductor layer, and at least the active layer and the first and second semiconductor layers have a stripe width smaller than that of the second semiconductor layer.
A semiconductor layer of a second conductivity type having a larger forbidden band width than the active layer is provided on a side surface of the semiconductor layer, and a semiconductor layer of a first conductivity type is provided on a side surface of the third semiconductor layer. Embedded semiconductor laser.