JPH0214591A - Buried semiconductor laser element - Google Patents

Abstract

PURPOSE:To form a good-quality regrowth layer by forming a buried layer in the form of a superlattice in which GaAs and AlAs thin films are alternately piled up under a condition that the top of the superlattice which is in contact with a second clad layer is a GaAs thin film. CONSTITUTION:A buried layer 4a is a superlattice (GaAs)6.(AlAs)4 which is equivalent to Al0.4Ga0.6As. In order to pile up GaAs and AlAs layers alternately, law gases trimethylgallium and trimethylaluminum are supplied alternately into a reaction chamber of the MOCVD system under the atmospheric pressure of 800 deg.C in which raw gas arsine is always supplied in a specified amount. With the top or the surface of the superlattice which contacts a second clad layer 5a being a GaAs layer which does not contain Al, a stable oxide film is never generated on the surface of the buried layer 4a which is exposed to the air when an SiO2 film on a stripe is removed by etching. As a result, since a crystal can be grown keeping a good surface condition, a semiconductor laser of stable characteristics and much longer life can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of a buried hetero type semiconductor laser device.

[Conventional technology]

A GaAs/AjGa^3-based buried heterojunction semiconductor laser device has characteristics such as a low threshold current for laser beam oscillation and stable transverse mode oscillation, and can serve as a stable point light source. It is expected that it will be used effectively as a light source for optical information transmission and optical information processing.Furthermore, in order to uniformize the characteristics and improve the yield of this type of semiconductor laser device, only the vicinity of the active layer is buried with a high-resistance layer. structure has been proposed.

FIG. 2 is a schematic cross-sectional view of this semiconductor laser device as seen from the front, and its structure includes, for example, a first cladding layer 2 of n-type A7e, *Gao, bA3 formed on an n-type GaAs substrate 1. Undoped Aj o, as Ga o,
, t As active layer 3° undoped Aj o, *G
ae, hAs high resistance buried layer 4, p-type kj @,
4Gam-&As second cladding layer5. and n-type G
It consists of aAs camps 116, and the active 1i3 is the first cladding layer 2 and the second cladding layer 115. Further embedding II
completely surrounded by 4. 7 is the p-side electrode, 8 is the n
This is the side electrode. In this structure, the carriers injected into active w3 are confined, so the electric field distribution of the device is stabilized.
Therefore, by reducing the laser oscillation threshold (tit current), it becomes stable against current changes in the oscillation mode, especially in the transverse mode, and by setting the width of the active layer 3 to an appropriate size, single-transverse mode oscillation can be prevented. It has excellent properties such as being able to

This embedded semiconductor laser device is manufactured using the MOCVD method as follows. FIG. 3 shows the order of the main manufacturing steps, and parts common to those in FIG. 2 are designated by the same reference numerals. First, on top of the 100-thick substrate 1, a thickness of 1.5
- first cladding Fi2 with thickness 0.1- active layer 3. Second
Part of the cladding layer 5 is epitaxially grown [
Figure 3 (al).

Next, 5 tat W149 was applied to the entire surface by sputtering to a thickness of 0.2 tna, resist was applied, and 2-width stripes were formed by photolithography.
FNH, SiO□ film 9 in areas other than stripes with aqueous solution
remove. Next, using a solution of H3P0t:HzOz:ethylene glycol-11:1.6, the epitaxial growth layer in areas other than the stripes was removed from the surface to a depth of lJr.
Etch approximately 100 m thick to form a striped mesa [
(in Figure 3)] Next, a high-resistance buried layer 4 is grown on both sides of the stripe portion so that its surface is flush with the upper surface of the second cladding layer, and the SlO□ film 9 on the stripe is removed. FIG. 3 fol), then again the second cladding layer 5. By growing the cap layer 6 [FIG. 3 (d13) and forming both upper and lower electrodes, an element having the structure shown in FIG. 2 is obtained.

[Problem to be solved by the invention]

However, the buried semiconductor laser device manufactured through the process shown in FIG. 3 has a problem in that its characteristics deteriorate due to the influence of oxidation.

That is, as can be seen from FIG. 3, an etching process is involved during manufacturing, and during the etching process, the element is removed from the growth reaction vessel, so the surface is exposed to the atmosphere. In particular, in order to create a difference in refractive index with the active layer 3, the buried layer 4 is made of 'y G with an M composition ratio y of 0.3 or more.
Since a+-y As is used, it is easily affected by oxidation, and since the M oxide film produced at this time is stable, it is difficult to completely remove it by etching or the like. Therefore, the second layer that is regrown on top of the buried layer 4
The crystallinity of the cladding layer 5 and the state of the bonding surface deteriorate, which increases the variation in characteristics between devices (and causes deterioration of the characteristics).

The present invention has been made in view of the above points, and its purpose is to provide a buried semiconductor laser device that can form a high-quality regrowth layer without being affected by oxidation during the manufacturing process. .

[Means to solve the problem]

As shown in FIG.
First cladding N2, Aj, Ga+-, As active layer 3. It has a reverse conductivity type Aj x Ga 1-x As second cladding layer 5 and a reverse conductivity type GaAs cap layer 6,
First cladding layer 2° active layer 3. This is a buried type semiconductor laser element having a structure in which a M, -y As buried layer 4a is provided on both sides parallel to the laser beam traveling direction of a stripe portion formed with a second cladding N5, and this buried layer 4a is formed as a superlattice in which thin films of GaAs and AjAs are deposited alternately, and the top of the superlattice in contact with the second craft layer 5 is made of a GaAs thin film.

[Operation] As described above, in the present invention, the embedded l14a is
GaAs and klAs thin films are alternately deposited so that they are optically equivalent to a+-y As, and the top layer is deposited with GaAs.
By forming the s-thin film, the surface of the buried N4a becomes GaAs even in the etching process during device manufacturing, so an oxide film such as uGaAs is not generated.

Therefore, the buried layer 4a is bonded to the second cladding layer 5 in a good crystalline state and acts as a current confinement layer without causing any disadvantages due to oxidation.

〔Example〕

The present invention will be explained below based on examples.

FIG. 1 is a schematic cross-sectional view of a buried semiconductor laser device according to the present invention as seen from the front, and shows a buried N4a according to the present invention.
The other parts are exactly the same as those shown in FIG. Therefore, the same reference numerals are used for parts common to those in FIG. The difference between Figure 1 and Figure 2 is that in Figure 2, the buried layer 4 is made of AZyGa+-As mixed crystal, whereas in Figure 1, GaAs and klAs thin films are alternately laminated. The reason for this is that the buried layer 4a is formed using the same method.

(GaAs)m (Aj As)n is optically A7 −
It is equivalent to a Ga-As ring +n +s+n, and there is no problem in confining the laser light emitted from the active layer 3 in the lateral direction. A large barrier exists and plays the role of blocking current, and it is also possible to form a deep energy level by introducing oxygen or the like into these layers.
It has the same current confinement function as the I- and As buried layers.

The method for manufacturing the device of the present invention is basically the same as the process shown in FIG. 2, that is, FIG. 3, so only the method for forming the buried layer 4a in FIG. 3 (c+) will be described here. Layer 4a is u*, *Gao, hA
The superlattice is (GaAs) h(Aj
As)*. That is, GaAs is a 6 atomic layer 2M^3
is 4 atomic layers. Niha deposits each of these layers alternately,
In the MOCVD equipment system, a predetermined amount of arsine (A383), which is a raw material gas, is constantly flowed into a reaction vessel maintained at a normal pressure of 800 °C, and trimethyl gallium (Ga (OH) co, hereinafter referred to as TMG), which is also a raw material gas, and trimethyl Aluminum (Aj (OH) s , hereinafter referred to as TMA) is supplied by switching these lines, and the flow rates of TMG and TMA are 15e, c, and 15c, respectively.
/■1n, and each atomic layer with different growth rate and number of atoms can be controlled by time, TMG is 2 sec,
The above superlattice can be formed as the buried layer 4a by alternately supplying TMA for 2.5 seconds.

Furthermore, an important point in the present invention is that the top of the superlattice, that is, the position where the surface contacts the second kraft layer 5a, is made of M-free GaAs. In this way, as shown in Fig. 3 (Sio on the stripe in the process of C1, the embedded eyebrow 4a exposed to the atmosphere during etching for film removal).
The three surfaces that do not produce a stable oxide film on the surface of M
The influence of oxidation caused by the presence of is removed, and subsequent epitaxial growth can be continued while maintaining a good crystalline state.

The buried semiconductor laser device of the present invention obtained as described above has a buried layer of AJ o, *Ga*, iAs
The initial characteristics are the same as those of the conventional structure, and the 5-APC (Auto Power Control)
As a result of an aging test of 25 tons and 1000 hours in operation, the defective rate was 5% for the device of the present invention, compared to 20% for the conventional device, indicating a significant improvement in life.

〔Effect of the invention〕

A buried semiconductor laser device, in which the active layer is completely surrounded by two craft layers (top and bottom) and a high-resistance layer buried on the sides, exhibits excellent characteristics, but when manufactured,
y The formation of the As buried layer involves an etching process carried out in the atmosphere, which is affected by surface oxidation and has instability factors such as variation in characteristics between devices and deterioration of characteristics. As mentioned in the example, Ga is used as a buried layer equivalent to M a Ga1-y^3.
Since a superlattice is formed by alternately stacking As and AjAs thin films, and the M-free GaAs\II film is located at the top, an oxide film is not formed on the surface during the etching process during manufacturing. As a result, the embedded semiconductor laser device of the present invention has stable characteristics,
It was possible to significantly increase the lifespan compared to a structure having an Aj, GaI-yAs buried layer.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of the embedded semiconductor laser device of the present invention as seen from the front, FIG. 2 is a schematic sectional view of the conventional embedded semiconductor laser device as seen from the front, and FIG. 3 is the main structure of the device in FIG. This is a structural process diagram. 1: Substrate (GaAs) 2: First craft ITJ
(AJXGa+-++ As), 3: Active layer (
A7. Ga, -, A5) 4: Buried layer (
AZ y GaI-y As), 4a: Buried layer (GaAs/kl As) 5: Second cladding layer (AI.Gap-@As), 6: Q+7 layer (GaAs
) 7, 8: Figure 2 Figure 3

Claims (1)

[Claims] 1) One conductivity type Al_xGa_1_-_xAs first cladding layer, Al_mGa_1_-mAs active layer, and opposite conductivity type Al_
xGa_1_-_xAs second cladding layer and opposite conductivity type GaAs cap layer, laser beam traveling direction of a stripe portion formed in the thickness direction by the first cladding layer, the active layer, and the second cladding layer A on both sides parallel to
In a buried semiconductor laser device having a l_yGa_1_-_yAs buried layer, the buried layer is made of Ga.
The thin films of As and AlAs are alternately deposited to form a superlattice, and the top layer in contact with the second cladding layer is made of GaA.
An embedded semiconductor laser device characterized in that it is made of a thin film.