JPS59110186A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To manufacture easily and securely by a method wherein the surface orientation of a growing layer is selected by controlling the condition of vapor phase reaction, and a fixed bent part is formed in an active layer or a layer in the neighborhood thereof. CONSTITUTION:A groove 22 of V-shaped cross-section having the inner side surface along a [111] A crystal surface is formed in stripe through the main surface 21a of a III-V group compound semiconductor substrate 21, and a (Al, Ga) As compound, i.e., a III-V group semiconductor layer 23 is grown on the main surface 21a by an MO (metal organic) CVD method of thermal decomposition vapor growth. When the supply ratio R=CV/CIII of CV the constituent of the Vgroup element As to CIII the constituent of the III group elements Al and Ga is relatively large, the [111] A crystal surface is inherited as it is on the surface of the layer 23. When the thickness of this layer 23 is large, this groove is filled by the crystal growth from the [111] A surface on both sides, and thus flattened.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor laser, particularly a semiconductor laser using a ■-■ group compound semiconductor.

Conventional semiconductor lasers are broadly classified into index guide type and gain guide type depending on their carrier and light confinement mechanisms.

FIG. 1 shows an example of a C2S type (channeled substrate solenar type) index guide type semiconductor laser. In this case, for example, a striped recess (2) is provided on one main surface of an n-type GaAa substrate (1), and an n-type A7GaA
A cladding layer (2) of S semiconductor is formed by liquid phase epitaxial growth, and on top of this a cladding layer (2) of AtGaAs is formed.
A semiconductor n-type or p-type active layer (3) and a p-type cladding layer (4) are grown by liquid phase epitaxial growth, and furthermore, an n-type GaAs cap layer (5) is epitaxially grown thereon. A striped p-type, for example, Zn diffusion region (6) is formed across the cap layer (5) and facing the recess (2).

(7) is an insulating layer formed on the surface of the camp layer (5) to cover it, and striped windows (8) are perforated in this insulating layer.
) one electrode (9) is ohmically deposited on the region (6). αO is the other electrode provided on the back surface of the substrate (1).

In the semiconductor laser with this configuration, the distance hi between the active layer (3) on both sides of the recess (2) and the substrate (1) is the recess (
The distance h2 in 2) is selected to be sufficiently smaller than h2, so that the light from the active layer (3) is
As the substrate (1) acts as a light absorption layer in the part having the active layer (2), an effective refractive index difference occurs between the central part of the active layer (2) and its opposite sides due to the difference in light absorption, so that an index waveguide function is generated. On the other hand, as an example of a conventional gain guide type semiconductor laser, as shown in FIG.
), an n-type AtGaAs compound semiconductor cladding layer (2), an n-type or p-type active layer (3), and a p-type cladding layer (4) are grown by liquid phase epitaxial growth. A GaAs cap layer (5) is epitaxially grown. A current limiting region made of a striped p-type, for example, Zn diffusion region (6) is provided across the cap layer (5).

In this case as well, an insulating layer (7) is formed on the cap layer (5) to cover it, and the electrode (9) is passed through the stomp-shaped window (8) in the area (6). ), and the other electrode αQ1 is ohmically attached to the back surface of the substrate (1).

In this configuration, the current path is restricted to the region (6), thereby narrowing the actual width of the oscillation region. In this case, in the lateral direction, carriers and light are confined only by the stimulated emission gain generated by the injected carriers. That is, in this case, since the light confinement mechanism' is different in the direction perpendicular to the junction and in the horizontal direction, the astigmatism of the oscillation beam spot is large.

In contrast, the index type semiconductor laser mentioned above is
Although the astigmatism is small, since the longitudinal mode is a single mode, when used as a source for writing or reading, for example, an optical video disc, the influence of noise due to return light and mode pumping noise is large. There is a drawback.

The present invention is useful when obtaining index-guided or gain-guided type (IV) group compound semiconductor lasers, or by combining the above-mentioned index-guided and gain-guided waveguide mechanisms to overcome the drawbacks of both. The object of the present invention is to provide a method for manufacturing a semiconductor laser that can obtain a semiconductor laser with a special structure designed to compensate for the above.

That is, in the present invention, MOCVD (Metal Organic Chem
ical VaporDeposit) growth,
In other words, when growth by pyrolytic vapor phase growth is performed on a semiconductor substrate with unevenness, peculiar properties appear on the surface of the vapor phase grown semiconductor layer depending on the composition of the reactant gas supplied for the growth. We have discovered that the crystal planes are different, and based on this discovery, we will be able to easily and reliably manufacture various semiconductor lasers.

That is, as shown in Figure 3, the plate surface is (100)
Grooves e■ having a V-shaped cross section and having an inner surface along the (111)A crystal plane were formed in a stripe shape on one main surface (21a) of the m-■ group compound semiconductor substrate Q°C with the crystal plane direction. In this case, an (At, Ga)As compound, i.e.
- MOCVD of group compound semiconductor layer pyrolysis vapor phase growth
When grown by the method, the group V element A8 component Cv
The semiconductor layer (c) deposited and grown on the substrate e◇ when the supply ratio R-CV/Cll1 of L and Ga components CI [l of
The crystal planes appearing on the surface are different. For example, when R<10, as shown by the solid line al + azt lL3 in FIG. Above (1
13) Expose the A crystal plane, bury the (111) crystal plane that was exposed in the groove (C) as the semiconductor layer (C) grows, and make it disappear from the surface. However, ASO female R
When increasing , the broken line al' + ! in Figure 1. L2'
* As shown by a3', a1' is sequentially placed on the board (b).
→a2′→a3′ On the surface of the semiconductor layer (c), the (113) A crystal plane is not exposed, and the cross section V
The A crystal plane (111) is exposed on the inner surface of the letter-shaped groove (goods), and the Uke is continued as it is (111) The A crystal plane is exposed on the inner surface, forming a groove corresponding to the groove (A). However, if the thickness of this layer (c) is taken as a dog, then this groove is (111) on both sides.
As the crystal grows from the A-plane, it is buried and flattened.

This dependence of the growth crystal plane on the supply gas composition during MOCVD was noticeable on the groove surface formed by the V-shaped groove in cross section as explained in FIG. That is, in the vapor phase growth explained in FIG. 3, when the partial pressure PA8H of arsine As Hs is made low in the supply gas for the vapor phase growth, for example, a mixed gas of trimethyl gallium, trimethyl aluminum, and arsine 5, the process In ('
111) Although the expression of side A is seen, ultimately (31
1) Side A is exposed. In this case, the growth ratio R1, that is, the ratio of the growth rate gr (31, 1) A of the (311) A plane to the growth rate gr (100) of the (100) plane, the partial pressure of arsine PAsH When it is large, (111)
The A side is exposed, and the growth ratio R at this time is Rgr of the growth rate gr (111)A of this gr (111)A side.
≧1.

In this way, vapor phase growth on an uneven surface formed by forming grooves with a V-shaped cross section exhibits significantly different properties, depending on the amount of AsO, either a (111) plane or a (311) plane is produced. However, as shown in FIG. 4, grooves with a trapezoidal cross section are formed on the surface of the substrate (al) to form surface irregularities, or as shown in FIG. 5, protrusions with a trapezoidal cross section are provided. In the case of forming surface irregularities, or in the case of forming convexes and convexities on the surface by providing protrusions having an inverted trapezoidal cross section as shown in FIG. 6, different properties are exhibited.

In other words, in the case of the shape shown in Fig. 4, the (111) B plane appears in the growth process sH3, regardless of the magnitude of the partial pressure P of arsine, but in the end, the (311) A plane appears. The surface is visible. And its growth ratio is 1〉1 and 1 person M. When H3 becomes a dog, Rg
r〉1gr~.

In addition, when using the shape shown in Fig. 5, the partial pressure of arsine PA,
Regardless of the size of H, in its growth process (111
)A side is seen, but ultimately (311)A side is seen. And when the growth ratio is small, Rg
When r≦1 and Oshi, PA, and H3 become thick, Rgr>1.

Furthermore, in the case of the shape shown in FIG. 6, the (311)B plane is exposed regardless of the magnitude of the arsine partial pressure PAsH. And the growth ratio is Rgr > l, PAIIH75'dog'lxruto@uR=23gr and k.

In addition, FIG. 7 shows that the inner surface explained in FIG.
) surface of the substrate (1〉) with a large partial pressure P of arsine A++
In the state of H3, that is, the dashed lines a1 and a2 in Fig. 3
Grooves during growth as shown in ・・・・・・・・・
The depth of (a) is shown below.

The above-mentioned V-shaped grooves and inverted trapezoidal unevenness can be formed by crystallographic anisotropic etching.

That is, an etching mask such as a photoresist is deposited on a substrate having an [oO] crystal plane, and an etching mask of <1.10
) axis ([110] or [110]) and etching the substrate through this window at a ratio of 1:10:1 of H3PO4, H2O2°H2O, for example.
It can be formed by etching with a mixed solution of 0. If this window is selected, the 7-shaped groove described in d can be formed as a groove with a trapezoidal cross section.

In the present invention,
- Utilizing the specificity of vapor phase growth of V group compound semiconductors.

That is, in the present invention, a plurality of growth layers are successively formed by pyrolytic vapor phase growth on the uneven surface of a -V group semiconductor substrate, and the growth layers are formed by controlling the vapor phase reaction conditions. By selecting the surface orientation of the layer and forming a predetermined bend in the active layer or a layer near it by using the fact that the bend shape of the growth layer changes continuously depending on the growth stage, index guide or dyne guide type Forms a waveguide mechanism.

First, an example of obtaining a double heterojunction index guide type semiconductor laser according to the present invention will be described with reference to FIGS. 8 to 10.

In this case, first, as shown in FIG. 8, a GaAs compound semiconductor substrate (3) of one conductivity type, for example, p-type, having a (100) crystal plane is prepared, and on one main surface of this, a substrate Q] )
A GaAs semiconductor layer ◇ of a different conductivity type, in this example an n-type, is epitaxially grown by MOCVD using a mixed gas of trimethyl gallium and arsine, for example.

Next, as shown in FIG. 9, recesses (2) with a trapezoidal cross section and a depth that crosses the entire thickness of the semiconductor layer 0 are formed in a stripe shape. This recess (a) can be formed by the crystallographic anisotropic etching described above.

Then, as shown in FIG. 10, including the inside of this recess (support), the substrate 0]) and the semiconductor layer (3[F]
) and the same conductivity type, in this example p-type AAo, 3Ggo,
a first cladding layer made of a 7As compound semiconductor layer;
An active layer (b) made of a p-type or n-type GaAs compound semiconductor layer, and an n-type ALo, 3G of a conductivity type different from that of the substrate 0.
a p, a second cladding layer 0→ made of a 7As compound semiconductor layer and a cap layer 0→ made of an n-type GaAs compound semiconductor layer of the same conductivity type are sequentially and continuously grown by vapor phase epitaxial growth using the MOCVD method. do. In MOCVD in this case, the substrate temperature is 720°C, and the supplied gas is a mixed gas of trimethylgallium and arsine, and a gas mixed with trimethylaluminum when forming the cladding layers (b) and (c). Formed by. In this case, the supply amount of A8 was R)70.

In this example, by appropriately selecting the depth of the fourth part (A) and the thickness of the cladding layer trunk, the cladding layer 0
A concave portion remains at '3', and a striped bent portion (34a) having a U-shaped cross section is formed in the active layer 04 formed thereon. In other words, in this case, the thickness of the first cladding layer 0→ is within a range where the growth thickness on the semiconductor layer 0■ is relatively small and no surface due to (1, 13) is generated. To be elected. In the semiconductor lasers 0 to 0 formed in this manner, the thickness of the active layer (b) is the same as that of the U-shaped side walls (34a 1 ) and (34a 1 ) at the bent portion (34a).
4a2), in other words, a semiconductor radar having an index guide configuration is constructed by being sandwiched between cladding layers (c) having different refractive indexes.

In the above example, the thickness h of the first cladding layer 0 [present] between the concave portion and the outside of the ring is selected to be relatively small, but as shown in FIG. Let the thickness h be relatively large, but not completely (113
) If the surface, and therefore the active layer (b), is shaped to be gently curved to the extent that no surface is formed, the structure has both a dyne guide type and an index guide type waveguide mechanism. In FIG. 11, parts corresponding to those in FIG. 10 are given the same reference numerals and redundant explanation will be omitted.
5 μm, and at this time, the ground layer 0 and the thickness h are 0.
3 μm≦h≦1 μm.

As described above, in the semiconductor laser 0 obtained by the present invention having the structure shown in FIG. 11, current confinement is performed in the width direction of the stripe portion by the semiconductor layer 0 formed inside, and the gain guide function is performed. As the active layer 0
The gentle bending of → also produces an index function to a considerable degree, and this index guide and gain guide are produced together, resulting in a laser with small astigmatism and low noise caused by the return beam.

Furthermore, the thickness h of the first cladding layer 03 is increased to
As shown in Figure 2, if the surface, and therefore the active layer (b), is made almost flat, a gain guide type semiconductor laser with zero power can be obtained due to the effect of current confinement only due to the internal semiconductor layer. .

Then, in the first cladding layer 0) in FIG. 12, the first
As shown in Figure 3, at a certain thickness t, an intermediate layer (3
3'), at the bent part (3) in this layer (33'), between this layer (3:\) and the above-mentioned At, 3Ga o, 7As parts, for example, above and below it. It is also possible to form a refractive index difference in the lateral direction to produce a semiconductor laser that has both the effects of an index guide and a gain guide.

In this example, cladding layer 0 → middle layer (3
In the case where only 3') has a high At content composition, that is, when layers with the same composition are formed above and below this layer (33'), the cladding layer 0'3
For example, in the middle layer (3J), AA, 4Ga
The composition of the cladding layer below this is Ato, 3Ga o,, As, and the intermediate layer (33'
) The active layer (b) side above the active layer (b) may have a composition with a lower p ht, such as Ato, 1Ga, .

In the past, as shown in FIG. 14, the active layer (
For example, the bending width W of the bending portion (34a) in (b) is set to 1 μm.
By making it less than m, the center of the optical field can be shifted from the active layer to achieve high output operation.

In the above example, the recess (A) has a trapezoidal cross section, but as shown in FIG. 15, the recess (G) has an inverted trapezoidal shape, and the first It is also possible to perform MOCVD on the cladding layer 03 and fill the recess (1). 14 of this figure 15
Portions corresponding to those in the figures are given the same reference numerals and redundant explanations will be omitted. In this case, the curved surface of the intermediate layer (33') is (11
1) Easy to clean.

Furthermore, the four parts (2) are not limited to the inverted trapezoidal shape, but may also have a V-shaped cross section.

The above-mentioned case is a case where the buried semiconductor layer 02 restricts the current path, that is, narrows the current on each side, but it is not limited to this structure, and the current in a conventional general striped structure There are various ways to limit the path, for example, by forming a current path region by reverse Zn diffusion, by implanting a high resistance region by proton implantation, or by forming a current limiting region by an insulating layer on the surface or inside the stripe. It is also possible to adopt an embodiment in which the material is embedded in the material.

Furthermore, in the above example, the concave portion (A) is formed, but as shown in FIG. The first cladding layer 0, the active layer (b),
The second cladding layer (c) and the cap layer OQ are sequentially formed by MOCVD as described above, and the convex portion (8) is formed on the active layer (b).
) is formed, and on both sides above this a high resistance layer (/4
1) may be formed so that stripe-like current concentration occurs between them.

As described above, according to the manufacturing method of the present invention, various semiconductor lasers can be manufactured depending on the purpose.

It should be noted that the present invention is not limited to the above-mentioned example, and can be modified in various ways, including the case where the conductivity type of each part shown in the drawings is reverse conductivity type.

[Brief explanation of the drawing]

1 and 2 are enlarged linear cross-sectional views of each side of a conventional semiconductor laser. FIG. Figures 4 to 6 are enlarged cross-sectional views showing each side of the irregularities on the surface of the substrate, and Figure 7 shows the groove depth and growth ratio when As supply is used to explain the manufacturing method of the present invention. Figures 8 to 10 are manufacturing process diagrams of an example of the manufacturing method of the present invention, and Figures 11 to 16 are linear enlarged cross-sections of each side of the semiconductor laser obtained by the manufacturing method of the present invention, respectively. It is a diagram. 0■ is the substrate, 0→ and 0→ are the first and second cladding layers, (b) is the active layer, (c) is the cap layer, □□□ and O
Q is a concave portion and a convex portion. Figure 1 10 Figure 2 Figure 3 Figure 5 Figure 6 Figure 7 Figure 8 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14

Claims (1)

[Claims] A plurality of growth layers are successively formed by pyrolytic vapor phase growth on the uneven surface of a group m −=·■ group semiconductor substrate, and the plane orientation of the growth layers is selected by controlling the vapor phase reaction conditions. A method for manufacturing a semiconductor laser, characterized in that a predetermined bent portion is formed in an active layer or a layer near the active layer by using the fact that the bent shape of the grown layer changes continuously depending on the growth stage.