JPH053375A - Semiconductor laser and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture a semiconductor laser having a highly reliable quantum well thin-wire structure at high reproducibility by constituting an active layer on the top of a layer which is epitaxially grown on a mesa projection. CONSTITUTION:After an epitaxially grown layer 10 having a triangular cross section surrounded by {111} B crystal faces is formed on a mesa projection 2 elongated in <011> crystal axis direction and the top section 10a of the layer 10 is formed, the epitaxial growth is stopped and the partial pressure of compound semiconductor layer constituting elements contained in the gaseous starting material for epitaxial growth is lowered. Thereafter, an active layer 4 is formed on the top 10a of the layer 10 by raising the partial pressure of the elements and performing epitaxial growth on the mesa projection 2. Therefore, oxidation, mixture of impurities, etc., of the active layer can be prevented and, at the same time, a precise quantum well thin-wire structure can be surely formed with high accuracy beyond the etching accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device and its manufacturing method, and more particularly to a semiconductor laser having a quantum wire structure and its manufacturing method.

[0002]

2. Description of the Related Art Quantum well structures are being applied to lower the threshold current of semiconductor lasers.

This quantum well structure is a structure in which a potential well is formed by a heterojunction by making the thickness of the active layer extremely thin to several tens of nm or less. The semiconductor laser to which this structure is applied is a bulk semiconductor laser. It is known that it exhibits unique optical characteristics as compared with, and it is possible to narrow the spectral line width and lower the threshold current, for example. In this case, the width or width and length together with the thickness of the active layer is set to a small structure of about several tens of nm to form a two-dimensional and three-dimensional potential as a quantum well wire structure or a quantum well box structure. It is desired to further improve the characteristics by forming a well.

An example of a method of manufacturing a semiconductor laser having a quantum well structure as described above is shown in schematic linear enlarged perspective views of FIGS. In this case, an example of a quantum well thin wire structure having a two-dimensional structure in which the width and thickness of the active layer are a quantum well structure is shown.

As shown in FIG. 7A, the first conductivity type, for example, n
On the semiconductor substrate 21 made of GaAs of the second type, a clad layer 22 of the first conductivity type, an active layer 23 of a quantum well structure, and a first clad layer 24 of the second conductivity type, for example, p-type, are sequentially formed, for example, by MO.
Epitaxial growth is performed by the CVD (Chemical Vapor Deposition with Organic Metal) method.

Next, as shown in FIG. 7B, this p-type first
A photoresist 25 having a desired pattern is formed on the clad layer 24 by coating the photoresist, exposing the pattern, and developing.

The pattern in this case is a stripe pattern having a required width and pitch for forming a quantum well thin wire structure. However, when forming a quantum well box structure, a rectangular pattern having a required width and length is used. And

Then, as shown in FIG. 7C, RIE (reactive ion etching) is performed using the photoresist 25 as a mask.
Is anisotropically etched to pattern the p-type first cladding layer 24 and the active layer 23.

Next, as shown in FIG. 7D, a second clad layer 26 of the second conductivity type, for example, p type, is deposited over the entire surface by MOCVD or the like, and the active layer having the quantum well thin line structure shown by the broken line is formed. A semiconductor laser having 23 can be obtained.

However, in the case of such a method, in the etching process shown in FIG. 7C, the active layer 23 is exposed, so that the active layer 23 may be oxidized or impurities may be taken in to deteriorate the characteristics. Further, in the formation of the photoresist 25 described with reference to FIG. 7B, fluctuations in the pattern occur, and due to the instability of etching, unevenness occurs in the stripe pattern of the active layer 23, for example, and the function as the quantum well thin line laser is impaired. There were cases.

In order to obtain the quantum effect as described above, the width and length of the etching pattern are set to several nm to several tens n.
It was necessary to set the thickness to about m, and it was practically difficult to form it by etching.

As a method for solving such a problem,
For example, an example thereof is reported in JP-A-63-94696. In this example, as shown in FIG. 8 as an enlarged schematic cross-sectional view of the example, the surface of a substrate 31 made of a zinc blend type crystal having a {100} plane or a crystal plane equivalent thereto has a <011> direction. The extended stripe-shaped ridge 32, a so-called mesa protrusion, is formed by appropriately selecting the dimension and shape such as the height and width thereof, and is formed on the first ridge 32, which is made of, for example, an n-type Al _x Ga _{1 -x} As layer. Clad layer 3
3 is epitaxially grown. As described above, when the size and shape of the ridge 32 and the directionality with respect to the crystal axis are appropriately selected, the grown crystal on the ridge 32 grows out on the (111) plane, so that the first cladding layer 33 has the (111) plane. It has a crystal plane and a triangular cross section. For this reason,
The crystal growth of the first cladding layer 33 is controlled by the top 35
Is stopped immediately before the formation of the barrier layer, and a barrier layer made of, for example, an undoped Al _y Ga _1-y As layer and a well layer made of Al _z Ga _1-z As are stacked on the upper surface of the first cladding layer 33. The active layer 34 having the quantum well structure is formed by, for example, x>y> z
Alternately grow to form the top 35. Then, a second layer made of, for example, p-type Al _x Ga _1-x As etc.
Of the clad layer 36 is epitaxially grown, and a cap layer 37 made of p-type GaAs or the like is further formed on the clad layer 36.
After depositing the insulating layer 38 made of iO ₂ or the like, application of photolithography or the like, that is, application of photoresist, pattern exposure, and development, and then anisotropic etching such as RIE to perform patterning into a desired pattern to form a window 38C. Is formed, and an electrode layer 39A for forming a p-side ohmic electrode is deposited so as to cover the inside of the window 38C, and n is formed on the back surface of the substrate 31.
A semiconductor laser having an active layer 34 having a quantum well wire structure can be obtained by depositing an electrode layer 39B for forming an ohmic electrode on the side.

However, it is difficult to form the first cladding layer 33 leaving a width of about 10 nm on the top portion 35 of the triangular area in the cross section as described above, and it is possible to obtain a quantum well structure having uniform characteristics with good reproducibility and high precision. In some cases, the active layer 34 cannot be formed, which may lead to deterioration in characteristics and productivity.

[0014]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for manufacturing a semiconductor laser having a highly reliable quantum well wire structure with good reproducibility, and to obtain a semiconductor laser having a large gain. And

[0015]

An example of a method for manufacturing a semiconductor laser according to the present invention is shown in the manufacturing process diagrams of FIGS. 1A to 1C and FIGS. 2A and 2B.

According to the present invention, a compound semiconductor layer is sequentially epitaxially grown on a main surface 1A of a semiconductor substrate 1 having a {100} crystal face in which a mesa protrusion 2 extending in the <011> crystal axis direction is formed, and a mesa protrusion is formed. In the method of manufacturing the semiconductor laser in which the active layer 4 is formed on the top portion 10A of the epitaxial growth layer 10 on 2, the triangular region of the cross section surrounded by the {111} B crystal plane is formed on the mesa protrusion 2 as shown in FIG. 1B. The epitaxial growth layer 10 having the above is formed, and after the top portion 10A of the epitaxial growth layer 10 is formed, the epitaxial growth is stopped, and the pressure of the elemental constituent of the compound semiconductor layer in the epitaxial growth material gas is lowered, and as shown in FIG. The component pressure is raised to perform epitaxial growth on the mesa protrusions 2 to form the epitaxial growth layer 1
The active layer 4 is formed on the top portion 10A of 0.

FIG. 3 shows a schematic enlarged cross-sectional view of an example of another semiconductor laser according to the present invention. According to another aspect of the present invention, as shown in FIG. 3, a compound semiconductor layer is formed on a main surface 1A of a semiconductor substrate 1 having a {100} crystal plane in which a mesa protrusion 2 extending in a <011> crystal axis direction is formed. In a semiconductor laser in which an epitaxial growth layer 10 having a triangular cross-sectional area surrounded by at least {111} B crystal planes on the mesa protrusions 2 is formed by sequential epitaxial growth, the top portion 10A of the triangular cross-sectional area extends from the <011> crystal axis direction. A plurality of quantum wire structure active layers 14a to 14d extending to {10.
0} crystal plane, that is, in the direction perpendicular to the main surface 1A, in this case, in the upper direction in FIG.

4 to 6 are process diagrams of another example of the method for manufacturing a semiconductor laser according to the present invention. As shown in FIG. 4A, another manufacturing method according to the present invention is performed on the main surface 1S of the semiconductor substrate 1 having the {100} crystal plane in which the mesa protrusions 2 extending in the <011> crystal axis direction are formed, and in FIG. As shown
Compound semiconductor layers are sequentially epitaxially grown to form an epitaxial growth layer 10 having at least a triangular region of a cross section surrounded by {111} B crystal planes on the mesa protrusions, and as shown in FIG. 4C, the top portion 10A of the epitaxial growth layer 10 is After the formation, the epitaxial growth is stopped, the pressure of the elemental constituent of the compound semiconductor layer in the epitaxial material gas is lowered, and as shown in FIG. 5A, the pressure of the elemental constituent is raised again to perform the epitaxial growth on the mesa protrusion 2. The active layer 4a is formed on the top portion 10A of the epitaxial growth layer 10.

Then, as shown in FIG. 5B, the compound semiconductor layer is formed while maintaining the shape so as to cover the triangular area of the cross section surrounded by the {111} B crystal planes in which the active layer 4a is formed on the top portion 10A. A step of epitaxial growth,
As shown in FIG. 5C, the step of stopping the epitaxial growth to lower the pressure of the elemental component forming the compound semiconductor layer in the epitaxial growth material gas, and as shown in FIG. 6A, increasing the pressure of the elemental component again to perform the epitaxial growth on the mesa protrusions 2. And the step of forming the active layers 4b and 4c on the top portion 10A of the cross-sectional triangular region of the epitaxial growth layer 10 is repeated at least once.

[0020]

As described above, according to the method of manufacturing a semiconductor laser of the present invention, the mesa protrusion 2 extending in the <011> crystal axis direction.
The compound semiconductor layer is epitaxially grown on the main surface 1S of the semiconductor substrate 1 having the {100} crystal plane in which the mesa protrusions 2 are once grown. When a {111} B crystal plane is generated from the
Since methyl-based epitaxial growth does not easily occur on the crystal plane, the compound semiconductor on the mesa protrusion 2 spontaneously forms a triangular region of a cross section surrounded by the {111} B crystal plane, and is separated from the compound semiconductor in the mesa groove. Formed.

In the present invention, the epitaxial growth layer 10 having the {111} B crystal plane is thus formed on the mesa protrusion 2 and the epitaxial growth layer 10 is formed.
The epitaxial growth is temporarily stopped after the top portion 10A of the film is formed, and the pressure of the elemental component forming the compound semiconductor layer in the epitaxial growth material gas is lowered. Thus, the pressure of a certain elemental component in the epitaxial growth material gas is lowered. Then, this component element evaporates to the outside, that is, an annealing effect occurs, and the portion constituted by this component element is scraped.

Therefore, when the compound semiconductor layer surrounded by the {111} B crystal planes is epitaxially grown and then the pressure of the elemental constituents of the crystal planes is lowered, the surface of the epitaxial growth layer 10, that is, the {111} B crystal planes are removed. As shown in FIG. 1C, in the region where the {111} B crystal planes intersect, this element is evaporated particularly from both sides, and the top portion 10A of the epitaxial growth layer 10 is scraped off.
0S is formed.

The width of the top surface 10S can be accurately controlled with a fine width of, for example, about 10 nm by adjusting the time for reducing the component pressure, that is, the annealing time and the pressure at this time. The active layer 4 having a quantum well structure is epitaxially grown on the top surface 10S by increasing the elemental component pressure to form the active layer 4 sandwiched by {111} B planes, and the thickness thereof is, for example, about 10 nm. As a result, the active layer 4 having a quantum well thin wire structure having a width and a thickness of, for example, about 10 nm can be formed.

The semiconductor laser of the present invention, as shown in FIG. 3, has a major surface 1 of a semiconductor substrate 1 having a {100} crystal plane in which a mesa protrusion 2 extending in the <011> crystal axis direction is formed.
A compound semiconductor layer is sequentially epitaxially grown on A, and an epitaxial growth layer 1 having at least a triangular region of a cross section surrounded by {111} B crystal planes on the mesa protrusion 2 is formed.
In the semiconductor laser in which 0 is formed, the active layers 14a to 14d having a plurality of quantum wire structures extending in the <011> crystal axis direction from the apex 10A of the triangular region of the cross section are {100}.
Since the layers are formed in a direction perpendicular to the crystal plane and have a multilayer quantum wire structure, the gain can be increased.

Further, in the case of such a structure, the active layers 14a to 14d have good crystallinity because their lateral end faces are constituted by {111} B crystal planes which spontaneously occur during growth. Since it has, reliability can be improved.

According to another manufacturing method of the present invention, as shown in FIG. 4A, on the main surface 1S of the semiconductor substrate 1 having the {100} crystal plane in which the mesa protrusion 2 extending in the <011> crystal axis direction is formed. 4B, a compound semiconductor layer is sequentially epitaxially grown to form an epitaxial growth layer 10 having at least a triangular region of a cross section surrounded by {111} B crystal planes on the mesa protrusion, and as shown in FIG. 4C. Then, after the top portion 10A of the epitaxial growth layer 10 is formed, the epitaxial growth is stopped, the pressure of the elemental constituents of the compound semiconductor layer in the epitaxial material gas is lowered, and the pressure of the elemental constituents is raised again as shown in FIG. 5A. The active layer 4a is formed on the top portion 10A of the epitaxial growth layer 10 by performing the epitaxial growth on the mesa protrusion 2 to form one book. Like the bright manufacturing method, the width and thickness of time lowering the elemental component pressure i.e. annealing time and the active layer 4a formed in the top portion 10A under the control of the pressure 10
Since it can be precisely controlled as a fine structure of about nm, the active layer 4a having the quantum wire structure extending in the <011> crystal axis direction can be reliably obtained with good reproducibility.

After that, as shown in FIG. 5B, the compound semiconductor layer is formed while maintaining the shape so as to cover the triangular area of the cross section surrounded by the {111} B crystal plane in which the active layer 4a is formed on the top portion 10A. Although it has a step of performing epitaxial growth, the epitaxial growth on {111} B can be performed by the MOCVD method using an ethyl-based raw material such as triethylgallium and triethylaluminum.

Further, as shown in FIG. 5C, the step of stopping the epitaxial growth to lower the pressure of the elemental component constituting the compound semiconductor layer in the epitaxially grown material gas, and as shown in FIG. Protrusion 2
By performing the above epitaxial growth, the active layer 4b is formed on the top portion 10A of the cross-sectional triangular region of the epitaxial growth layer 10.
By repeating the step of forming 4c at least once, a plurality of active layers 4b, 4 having a fine structure with a width and thickness of about 10 nm are formed in the same manner as the above-mentioned active layer 4a.
It is possible to reliably form c ... Reproducibly.

According to such a manufacturing method, since etching is not performed across the active layer as in the conventional method, it is possible to avoid oxidation of the active layer, contamination of impurities, etc., and to exceed the etching accuracy. It is possible to accurately and reliably form a fine quantum well thin wire structure.

[0030]

EXAMPLES Example 1 Hereinafter, referring to FIGS. 1A to 1C and FIGS. 2A to 2B,
An example of the method for manufacturing the semiconductor laser of the present invention will be described in detail.

In this case, when obtaining an AlGaAs III-V compound semiconductor laser, first, a semiconductor substrate 1 made of GaAs of the first conductivity type, for example, n-type, is prepared. This semiconductor substrate 1 has, for example, (1
00) having a crystal plane, and having a width W of, for example, about 3 μm on the main surface 1A in the <011> direction, for example, [011].
1] forming a mesa protrusion 2 extending in a direction, that is, a direction orthogonal to the paper surface in FIG.

The method of forming the mesa protrusions 2 is not illustrated, but an etching mask having a required width W and extending in the [011] direction is formed by anisotropic coating such as RIE after photoresist coating, pattern exposure, and development. formed by gender etching, which H ₂ SO ₄ from the main surface 1A side for example sulfuric acid etchant as a mask and H ₂ O ₂ and H ₂ O 3:
It is formed by performing crystallographic etching with an etching solution mixed at a ratio of 1: 1.

As shown in FIG. 1B, the entire surface including the mesa protrusion 2 is of the first conductivity type, for example, n type Al _x G.
The cladding layer 3 made of a _1-x As is, for example, x = 0.45.
As a result, epitaxial growth is performed by the methyl-based MOCVD method. In this case, the main surface 1A and the 55
When a slope (10C) composed of a (111) B crystal face, that is, a (111) As crystal plane, which occurs at an angle of 0 °, occurs spontaneously,
Since epitaxial growth does not easily occur on the B crystal plane, the first conductivity type cladding layer 3 is selectively formed in the mesa groove 2A of the semiconductor substrate 1 and on the mesa protrusion 2 so as to be separated from each other. Becomes When the epitaxial growth layer 10 formed of the first conductivity type cladding layer 3 on the mesa protrusion 2 continues to grow epitaxially until both slopes 10C thereof intersect, the intersecting portion, that is, the plane perpendicular to the plane of FIG. 1 [011]. The ridge line extending in the direction is formed into a triangular shape with a top portion 10A.

After the epitaxial growth is once stopped, the pressure of the elemental constituents of the compound semiconductor layer in the epitaxial growth material gas, that is, the pressure of, for example, the group V element As in this case, is lowered. Since As atoms are exposed on the surface of the slope 10C composed of crystal faces, and since the vapor pressure of As is higher than that of Ga, As gradually evaporates to the outside including the top 10A. Therefore, as shown in FIG. 1C, the top portion 10A of the epitaxial growth layer 10 is removed and the top surface 10S is removed.
Is formed. This has the same effect as annealing by lowering the As pressure. In this case, the width of the top surface 10S is set to about 10 nm by adjusting the lowered As pressure, the holding time thereof, and the like.

Then, the group V element component pressure, that is, the As pressure is raised again, and as shown in FIG. 2A, the epitaxial growth layer 10 is formed.
The active layer 4 is formed on the top surface 10S. This active layer 4
Is a quantum well structure formed by stacking, for example, GaAs and Al _y Ga _1-y As, and is continuously epitaxially grown with y <x. Even in this case, since the epitaxial growth does not easily occur on the (111) B crystal plane, the active layer 4 is formed on the mesa protrusion 2 and the mesa groove 2A so as to be separated from each other.

With this structure, it is possible to obtain the active layer 4 having a so-called quantum well thin wire structure having a quantum well structure in the width direction and the thickness direction.

Then, as shown in FIG. 2B, the first clad layer 5 of the second conductivity type, for example, p-type Al _x Ga _1-x As or the like, and the n-type Al _x Ga _1-x As, for example, are used. A current blocking layer 6 made of, for example, a second conductivity type, for example, p type Al _x
The second cladding layer 7 made of Ga _1-x As or the like, p-type G
The cap layer 8 made of aAs or the like is sequentially formed into a methyl-based MOCV.
Epitaxial growth is performed by the D method or the like. At this time, by appropriately selecting the thicknesses of the first conductivity type first cladding layer 5 and the current blocking layer 6, both ends of the second conductivity type second cladding layer 7 facing the sloped surface 10C of the active layer 4. The p-type cladding layer 7 is formed so as to be in contact with the surface, that is, the p-type cladding layer 7 entirely covers the active layer 4. Further, on the slope 10C of the epitaxial growth layer 10 on the mesa protrusion 2, no epitaxial growth occurs in the initial stage, but as the growth progresses, (111) B on the top 10A of the epitaxial growth layer 10.
When a crystal plane other than the crystal plane is generated, the entire surface including the slope 10C is grown. Therefore, each of these layers 7 and 8 is entirely grown.

Thereafter, although not shown, electrodes are ohmic-deposited on the cap layer 8 and on the back surface of the semiconductor substrate 1, respectively, to obtain a semiconductor laser having a quantum well thin wire structure.

Here, each of the layers 3, 4, 5, 6, 7 and 8 can be formed by one operation, that is, one-time crystal growth by switching the source gas to be supplied by a series of MOCVD methods. As described above, a semiconductor laser having an active layer having a quantum wire structure can be obtained without causing contamination or deterioration of the end face of the active layer. Further, the quantum wire structure can be easily and accurately obtained by controlling the element component pressure, that is, the annealing time, etc., and the reliability of the semiconductor laser can be improved.

Embodiment 2 Next, an example of another semiconductor laser according to the present invention will be described in detail with reference to FIG. In FIG. 3, parts corresponding to those in FIG. 2B are designated by the same reference numerals. 1 is, for example, n-type A
In a semiconductor substrate made of 1Ga, a {100} crystal plane, for example, a main surface 1A made of a (100) crystal plane,
1) A mesa protrusion 2 extending in the [011] crystal axis direction in the crystal axis direction is formed, and a buffer layer 12 made of n type GaAs or the like, and an n type Al _x Ga layer are formed on the mesa protrusion 2.
_First conductivity type first cladding layer 3a made of _1-x As or the like
However, it is epitaxially grown with x = 0.45, for example, and the epitaxial growth layer 10 having a triangular region in cross section is formed on the mesa protrusion 2. An active layer 4a of, for example, GaAs having a quantum wire structure with a width of about 30 nm and a thickness of about 10 nm is provided on the top portion 10A so as to extend in the [011] crystal axis direction, and is further laminated on the active layer 4a. , The second clad layer 3b of the first conductivity type is epitaxially grown so as to entirely cover the epitaxial growth layer 10 in the triangular region in cross section, and the active layer 4b made of GaAs or the like having the quantum wire structure is also formed on the top thereof. The third clad layer 3c of the first conductivity type is also provided.
And an active layer 4c having a quantum wire structure, a fourth clad layer 3d of the first conductivity type, and an active layer 4d having a quantum wire structure. In this way, the active layers 14a, 14b, 14c and 14 extending in the [011] crystal axis direction of the plurality of quantum wire structures in the direction perpendicular to the (100) crystal plane from the top 10A of the epitaxial growth layer 10 in the triangular region in cross section.
d are formed side by side.

The outermost clad layer thus laminated, in this case, a second conductivity type made of p-type Al _x Ga _{1 -x} As or the like reaching the middle of both slopes of the fourth clad layer 3d. The first cladding layer 5 is epitaxially grown only inside the mesa groove 2A, that is, without maintaining the shape of the epitaxial growth layer 10 having a triangular cross section,
Further, a current blocking layer 6 made of n-type Al _x Ga _{1 -x} As or the like is further sandwiched on both sides of the plurality of active layers 14a to 14d formed on the epitaxial growth layer 10, that is, the left and right sides in FIG. It is provided. Then, a second conductivity type second cladding layer 7 made of p-type Al _x Ga _{1 -x} As or the like is laminated on each of the compound semiconductor layers on the mesa protrusions 2, that is, on the epitaxial growth layer 10. The semiconductor laser of the present invention is constructed by epitaxially growing the entire surface so as to cover the triangular region, and further forming a cap layer 8 made of p-type GaAs or the like on the epitaxial layer.

As described above, the gain can be increased by providing the active layers 14a to 14d having a plurality of quantum wire structures. Moreover, each active layer 14a-1
As will be described later in 4d, similarly to the semiconductor laser described in the above-described first embodiment, since it can be formed without using the conventional manufacturing method, that is, without performing etching across the active layer, oxidation of the active layer or It is possible to avoid mixing of impurities and the like, and it is possible to obtain a plurality of active layers having a fine quantum well fine wire structure that exceeds etching accuracy, and it is possible to obtain high reliability.

Embodiment 3 Next, an example of another manufacturing method according to the present invention will be described in detail with reference to FIGS. 4 to 6, parts corresponding to those in FIGS. 1 and 2 are denoted by the same reference numerals, and also in this case, the case of obtaining an AlGaAs III-V group semiconductor laser has been described in the second embodiment. The case of obtaining the semiconductor laser of the present invention will be described.

First, as shown in FIG. 4A, a semiconductor substrate 1 made of a first conductivity type, for example, n-type GaAs or the like is prepared.
The main surface 1A of the semiconductor substrate 1 is, for example, a (100) crystal plane of a {100} crystal plane, and the main surface 1A has a width W of, for example, about 3 μm on the <011> crystal axis direction. 011] Form the mesa protrusions 2 extending in the crystal axis direction, that is, in the direction orthogonal to the paper surface of FIG.

The method of forming the mesa protrusion 2 is similar to the manufacturing method described in the first embodiment, by applying photolithography or the like, anisotropic etching such as crystallographic etching or RIE (reactive ion etching) is performed. Go and form.

Then, as shown in FIG. 4B, a buffer layer 12 made of, for example, n-type GaAs or the like, and a first cladding layer 3a made of Al _x Ga _{1 -x} As of the first conductivity type, for example, n-type, are formed thereon. And x are made to be, for example, x = 0.45, and are epitaxially grown by a usual or methyl-based MOCVD method. At this time, similarly to the example described in the first embodiment,
Once the inclined surface 10C composed of {111} B crystal planes grows from the edge of the mesa protrusion 2, the growth by the methyl-based MOCVD method is hard to occur in this portion, so the mesa protrusion 2
Above, the groove 2A is sandwiched between these slopes 10C.
It is formed separately from the compound semiconductor layer inside. Then, the growth is performed to a position where both slopes 10C intersect, and the epitaxial growth layer 1 having a triangular area in cross section is formed on the mesa protrusion 2.
Form 0. 10A is this epitaxial growth layer 10
Of the ridge line, that is, the apex extending in the [011] crystal axis direction.

Next, after the epitaxial growth is once stopped, the pressure of the elemental constituent of the compound semiconductor layer in the epitaxial growth material gas, that is, the pressure of As in this case, is lowered. As atoms forming the surface of the inclined surface 10C gradually evaporate to the outside including the top 10A, that is, an annealing effect occurs, and the top 10A of the epitaxial growth layer 10 is removed as shown in FIG. 4C. The surface 10S is formed. In this example, as in Example 1, the vapor pressure of As is higher than that of Ga. And this reduction is not the As pressure, by adjusting the retention time i.e. the annealing time and the like, 30n width w _a of the top surface 10S
It is formed as about m.

Then, the group V element component pressure, that is, the As pressure is raised again, and as shown in FIG.
The first active layer 4a is formed on the top surface 10S of the. The first active layer 4a is made of, for example, GaAs and Al _y Ga _1-y A.
As a quantum well structure by stacking with s, y <x, that is, y <0.45 in this case, is continuously provided by a methyl-based MOCVD.
Epitaxially grown by the method. Even in this case, since the epitaxial growth does not easily occur on the slope 10C composed of the (111) B crystal plane, this active layer is formed separately from the other on the mesa protrusion 2 and the mesa groove 2A. Are grown until they intersect, and the thickness h is formed to be about 10 nm. In this case, the width w _a and the thickness h can be controlled by the above-described element component pressure reduction time, that is, the annealing time.

Next, as shown in FIG. 5B, a second conductivity type Al _x Ga _{1 -x} As of the second conductivity type, for example, p type Al _x Ga _{1 -x} As is entirely covered so as to cover the epitaxial growth layer 10 on which the first active layer 4a is formed.
The second clad layer 3b made of, for example, a thickness t of 10 n
Epitaxial growth is performed with a thickness of about m. The second cladding layer 3b is epitaxially grown by an ethyl-based MOCVD method using an ethyl-based material such as triethylgallium, triethylaluminum, and arsine. If an ethyl-based material is used, epitaxial growth also occurs on the {111} B crystal plane, so that the second cladding layer 3b is formed by (1
11) Epitaxial growth can be performed on the inclined surface 10C composed of the B crystal plane in the same manner as other portions. That is, the p-type second cladding layer 3b grows while maintaining the shape of the epitaxial growth layer 10 having a triangular cross section, that is, forming the slope 10C composed of the (111) B crystal plane.

Then, after the epitaxial growth of the second cladding layer 3b is once stopped, the pressure of the elemental constituents of the compound semiconductor layer in the epitaxial growth material gas, that is, the pressure of As in this case, is lowered to form the (111) B crystal plane. As atoms forming the surface of the inclined surface 10C are gradually evaporated to the outside, that is, an annealing effect is generated, and as shown in FIG. 5C, the top surface of the second conductivity type second clad layer is ground to remove the top surface 10S. Form. As pressure is also reduced its in this case, by adjusting the retention time i.e. the annealing time and the like, to form the width w _a of the top surface 10S as about 30 nm.

Then, the group V element component pressure, that is, As pressure is increased again to form the second active layer 4b on the top surface 10S of the second conductivity type second cladding layer 3b as shown in FIG. 6A. . The second active layer 4b is epitaxially grown again by the methyl MOCVD method, similarly to the first active layer 4a, with a quantum well structure by stacking GaAs and Al _y Ga _1-y As, for example, y <0.45. To do. At this time, since the active layer 4b is formed by the methyl MOCVD method, like the above-described active layer 4a, the active layer 4b is formed on the mesa protrusion 2 and the mesa groove 2A so as to be separated from each other.
Are grown until they intersect, and the thickness h is formed to be about 10 nm. Also in this case, the width w _a and the thickness h can be controlled by adjusting the time for lowering the above-mentioned elemental component pressure, that is, the annealing time.

After this, the above-mentioned FIGS.
By repeating the epitaxial growth step described in A, the third clad layer 3c of the second conductivity type having a triangular cross section and the third clad layer 3c on the top thereof are formed on the second active layer 4b.
It is possible to form the active layer 4a having the quantum wire structure, and further to form the second conductive type fourth clad layer 3d having a triangular cross-section on it and the fourth active layer 4d on the top thereof. In this case, four clad layers 3a to 3d and (1
00) Four layers are laminated in the direction perpendicular to the crystal plane [01
1] Active layer 4a having a quantum wire structure extending in the crystal axis direction
It is possible to obtain the epitaxial growth layer 40 in which 4d are formed side by side.

At this time, the width and thickness of each active layer 4c and 4d can be controlled by adjusting the time for lowering the element component pressure, that is, the annealing time, as in the case of the above-mentioned active layers 4a and 4b.

As shown in FIG. 6B, the first clad layer 5 of the second conductivity type, eg, p-type Al _x Ga _1-x As, and the current of, eg, n-type Al _x Ga _1-x As. Block layer 6, second conductivity type, eg p-type Al _x Ga _1-x
The second clad layer 7 made of As and the cap layer 8 made of p-type GaAs or the like are sequentially epitaxially grown by, for example, x = 0.45 by the methyl MOCVD method or the like. At this time, by appropriately selecting the thicknesses of the first conductivity type first cladding layer 5 and the current blocking layer 6,
The conductive second clad layer 7 is formed so as to be in contact with both end surfaces of the fourth active layer 4d facing the slope 10C, that is, to cover the entire surface. At this time, the epitaxial growth does not occur on the slope 10C of the epitaxial growth layer 40 in the initial stage, but if a crystal plane other than the (111) B crystal plane occurs on the top of the epitaxial growth layer 40 due to the progress of the growth, the slope 10C Grown all over, including the top. Therefore, the second clad layer 7 and the cap layer 8 of the second conductivity type are entirely grown.

Then, although not shown, electrodes are ohmic-deposited on the cap layer 8 and on the back surface of the semiconductor substrate 1, respectively, to obtain a semiconductor laser having a plurality of quantum wire structures.

Also in this case, each of the layers 3a to 3d, 4a to 4
d, 5, 6, 7 and 8 can be formed by one operation, that is, one-time crystal growth by switching the source gas to be supplied by a series of MOCVD methods. A semiconductor laser having an active layer having a quantum wire structure can be obtained without being accompanied by the above. Further, a plurality of quantum wire structures can be easily and accurately formed by controlling the element component pressure, that is, annealing, and the reliability of such a semiconductor laser can be improved.

In the third embodiment described above, the case where four active layers having a quantum wire structure are provided has been described, but the present invention is not limited to this, and a quantum wire structure having, for example, five layers or more may be used.

Further, the device and the manufacturing method of the present invention are not limited to the above-mentioned embodiments, and it is possible to use, for example, an InGaAsP-based material, and the conductivity type of each layer may be a conductivity type opposite to that shown in the drawings, and it is also necessary. Accordingly, various configurations and manufacturing methods can be adopted, such as forming a guide layer and the like in the vicinity of the active layer 4 by a continuous MOCVD method.

[0059]

As described above, according to the method for manufacturing a semiconductor laser of the present invention, at the top portion 10A of the epitaxial growth layer 10 on the mesa protrusion 2, the pressure of the elemental component forming the compound semiconductor layer in the epitaxial growth material gas is adjusted. By lowering it, it is possible to evaporate the elements in this portion and to reliably form the narrow top surface 10S having a width of, for example, about 10 nm, and the activity of the quantum well structure can be accurately formed on the top surface 10S with a fine width. By epitaxially growing the layer 4, a semiconductor laser having the active layer 4 having a quantum well thin wire structure can be reliably formed with high accuracy.

According to such a manufacturing method, since etching is not performed across the active layer as in the conventional method, it is possible to avoid oxidation of the active layer, mixing of impurities, etc., and to exceed the etching accuracy. It is possible to accurately and reliably form a fine quantum well thin wire structure, and it is possible to improve the reliability and productivity of the semiconductor laser.

Further, according to the semiconductor laser of the present invention, since the active layers having a plurality of quantum wire structures are provided, the gain can be increased, and each active layer is formed by the spontaneously generated {111} B crystal planes. Since the structure in which the end face in the lateral direction is configured is adopted, the reliability can be improved.

In still another semiconductor laser manufacturing method according to the present invention, similarly to the above-described manufacturing method, the active layer having the quantum wire structure can be formed with high accuracy and reliability by reducing the elemental component pressure. By providing a plurality of active layers, a semiconductor laser having a larger gain can be obtained.

[Brief description of drawings]

FIG. 1 is a manufacturing process chart showing an example of a method for manufacturing a semiconductor laser of the present invention.

FIG. 2 is a manufacturing process diagram showing an example of a method for manufacturing a semiconductor laser of the present invention.

FIG. 3 is a schematic enlarged cross-sectional view of an example of a semiconductor laser of the present invention.

FIG. 4 is a manufacturing process chart showing an example of a method for manufacturing a semiconductor laser of the present invention.

FIG. 5 is a manufacturing process diagram showing an example of a method for manufacturing a semiconductor laser of the present invention.

FIG. 6 is a manufacturing process diagram showing an example of a method for manufacturing a semiconductor laser of the present invention.

FIG. 7 is a process chart showing a method of manufacturing a conventional quantum well wire structure semiconductor laser.

FIG. 8 is a schematic linear enlarged sectional view of an example of a conventional semiconductor laser.

[Explanation of symbols]

1 Semiconductor substrate 2 Mesa protrusion 3 First conductivity type cladding layer 3a First clad layer of first conductivity type 3b Second clad layer of first conductivity type 3c Third clad layer of first conductivity type 3d Fourth clad layer of first conductivity type 4 Active layer 4a First active layer 4b Second active layer 4c Third active layer 4d Fourth active layer 5 First conductivity type first cladding layer 6 Current blocking layer 7 Second clad layer of the second conductivity type 8 Cap layer 10 Epitaxial growth layer 10A top 10C slope 10S top surface 40 Epitaxial growth layer

Claims (3)

[Claims] 1. A compound semiconductor layer is sequentially epitaxially grown on a main surface of a semiconductor substrate having a {100} crystal plane in which a mesa protrusion extending in the <011> crystal axis direction is formed,
In the method of manufacturing a semiconductor laser in which an active layer is formed on the top of an epitaxial growth layer on the mesa protrusion, an epitaxial growth layer having a triangular region cross section surrounded by {111} B crystal planes is formed on the mesa protrusion, and the epitaxial growth is performed. After the top of the layer is formed, the epitaxial growth is stopped, the pressure of the elemental constituent of the compound semiconductor layer in the epitaxial growth material gas is lowered, and the pressure of the elemental constituent is raised again to carry out the epitaxial growth on the mesa protrusion to perform the epitaxial growth. A method for manufacturing a semiconductor laser, comprising forming an active layer on the top of the layer. 2. A compound semiconductor layer is sequentially epitaxially grown on a main surface of a semiconductor substrate having a {100} crystal plane in which a mesa protrusion extending in the <011> crystal axis direction is formed. In a semiconductor laser in which an epitaxial growth layer having a triangular region having a cross section surrounded by 111} B crystal planes is formed, a plurality of quantum wire active layers extending in the <011> crystal axis direction from the top of the triangular region having the cross section are {100}. A semiconductor laser characterized by being formed side by side in a direction perpendicular to a crystal plane. 3. A compound semiconductor layer is sequentially epitaxially grown on a main surface of a semiconductor substrate having a {100} crystal plane in which a mesa protrusion extending in a <011> crystal axis direction is formed,
An epitaxial growth layer having at least a triangular region of a cross section surrounded by {111} B crystal planes on the mesa protrusions is formed, epitaxial growth is stopped after the top of the epitaxial growth layer is formed, and the compound semiconductor in the epitaxial material gas is formed. The pressure of the elemental constituents of the layers is lowered,
The elemental component pressure is increased again to perform epitaxial growth on the mesa protrusions to form an active layer on the top of the epitaxial growth layer, and then the active layer is formed on the top and surrounded by a {111} B crystal plane. A step of epitaxially growing the compound semiconductor layer while maintaining the shape so as to cover the triangular area in the cross section; a step of stopping the epitaxial growth and lowering the elemental component pressure of the compound semiconductor layer in the epitaxial growth material gas; And a step of performing epitaxial growth on the mesa protrusion to form an active layer on the top of the triangular region of the cross section of the epitaxial growth layer are repeated at least one or more times.