JP2000183458A - Semiconductor device and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To emit a beam in the vertical direction to the end surface of a substrate by varying tilt angles of two mutually facing sides of a ridge waveguide on the substrate, and proving selectively an energization easy layer on the top face of the ridge waveguide. SOLUTION: Tilting of left and right sides of a ridge waveguide 8 is asymmetrical due to formation on a tilt substrate. An energization easy layer 7 is formed selectively corresponding to the asymmetry of the ridge. That is, the left side of the ridge waveguide 8 is removed in order to allow the electric current injected via the energization easy layer 7 to spread at left and right of the ridge. In this case, the layer 7 is preferably provided so that a distance (a) from one end of the foot of the ridge and a distance (b) from the other end may be almost equal. Consequently the electrical current flows evenly left and right in the vicinity of the central part of the ridge waveguide 8. Therefore, the gain becomes symmetry left and right, and the spread of the optical mode becomes also symmetry. As a insult, beam is emitted vertically from the end face.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and a method of manufacturing the same, for example, in a ridge waveguide type semiconductor laser on an inclined substrate using an InGaAlP-based material.
The present invention relates to a semiconductor device in which an output beam is emitted perpendicular to an end face and a method for manufacturing the same.

[0002]

2. Description of the Related Art As a semiconductor laser having a wavelength of 600 nm, a ridge waveguide structure having a double heterojunction formed of an InGaAlP-based material on a GaAs substrate is often used. Usually, MOCV
A D (Metal-Organic Chemical Vapor Deposition) method is used, and is often formed on a so-called inclined substrate. In the specification of the present application, the term “inclined substrate” means that the plane orientation of the main surface of the substrate is (100) or (1).
A substrate shifted from a lower-order crystal plane such as 10) or (111) is shown. For example, a GaAs substrate having a main surface orientation deviated by several degrees from (100) is used.

The reason why such an inclined substrate is used is that the growth on the inclined substrate makes it easy to control the band gap of the active layer and the impurity concentration of the cladding layer. For example, when grown on a tilted substrate, the effect of increasing the incorporation rate of the dopant supplied during growth into the crystal and facilitating high-concentration doping can be obtained.

FIG. 4 is a schematic view showing a conventional ridge waveguide type semiconductor laser formed on an inclined substrate. That is, FIG. 2A is a cross-sectional view as viewed from a direction parallel to the laser light emitting end face, and FIG. 2B is a plan view as viewed from above the laser. This laser is, for example, (10
N) GaAs having a principal plane orientation inclined about 10 degrees from 0)
An n-type cladding layer 102, a first guide layer 103, an active layer 104, a second guide layer 10
5, the p-type cladding layer 106 and the p-type conductive layer 107 are sequentially grown, and further, the p-type conductive layer 107 and the p-type clad layer 106 are selectively etched halfway.
After forming the stripe-shaped ridge-type waveguide 108, n
GaAs current blocking layer 109 and p-type GaAs contact layer 110.

In the semiconductor laser thus formed, a current injected from an electrode (not shown) is confined by an n-type block layer 109 and passes through a p-type conductive layer 107 provided above a ridge stripe. Since the active layer 104 is implanted in the form of stripes, the injection efficiency is high and low threshold characteristics can be obtained.

[0006]

However, the conventional semiconductor laser as shown in FIG. 4 has a problem that the angle of the emitted beam deviates from a direction perpendicular to the end face of the element.

That is, the opposing side surfaces of the ridge waveguide 108 formed by the above-described steps have a {111} system plane orientation obtained by etching. That is, the left and right side surfaces have crystallographically equivalent plane orientations. Accordingly, in response to the plane orientation of the substrate 101 being inclined from (100), as shown in FIG.
The inclination angle of the side surface of the ridge waveguide 108 is also left-right asymmetric.

Here, a current injected through an electrode (not shown) flows into the ridge-type waveguide 108 through the p-type conductive layer 107, and the left and right sides of the ridge-type waveguide 108 as shown in the figure. If the spread is different, the current distribution is different on the left and right sides of the ridge. As a result, the gain differs between the left and right sides of the ridge. In addition, since the light mode spreads to the bottom, a difference occurs in the phase of the light, and the emitted beam is inclined.

For example, in the case of the laser shown in FIG. 4A, the ridge is wider on the right side of the ridge waveguide 108 than on the left side. Therefore, the gain on the right side of the ridge is lower than that on the left side, and the light mode is widened. As a result, as shown in FIG. 4B, the beam is emitted from the direction perpendicular to the end face of the element and inclined toward the ridge.

Usually, the laser element is mounted on a mounting member such as a stem or a chip carrier with reference to the end face. Therefore, if the emission direction of the beam is inclined with respect to the end face of the element, the direction of the beam will deviate from the design value even in a laser device obtained by mounting on a mounting member. As a result, there arise problems that a predetermined beam intensity cannot be obtained and that coupling efficiency to optical means such as an optical fiber decreases.

In order to cope with such a tilt of the beam, a method of mounting the laser device obliquely with respect to the mounting member may be considered. However, as a result of the examination of the prototype by the inventor, the inclination angle of the beam tended to vary from wafer to wafer in the manufacturing process of the laser device. This is considered to be due to the fact that the etching rates on the left and right side surfaces of the ridge when forming the ridge waveguide vary from wafer to wafer. Therefore, even when mounting the laser element obliquely with respect to the mounting member, it is necessary to evaluate the tilt angle of the beam for each wafer in advance, and the mounting process becomes extremely complicated.

Further, as shown in FIG. 4A, as a result of the left and right spreads of the ridge being different, the intensity distribution such as the far field pattern of the output beam is also asymmetric with respect to the horizontal direction. There was a potential problem.

The present invention has been made based on the recognition of such a problem. That is, an object of the present invention is to provide a semiconductor device such as a semiconductor laser formed on an inclined substrate, in which a beam is emitted in a direction perpendicular to an end face, and a method of manufacturing the same.

[0014]

In order to achieve the above object, a semiconductor device according to the present invention comprises a tilted substrate, a ridge-type waveguide provided on the tilted substrate, and an upper surface of the ridge-type waveguide. A ridge-type waveguide provided in contact with each other, wherein two opposite side surfaces of the ridge waveguide have different inclination angles with respect to the substrate, and the easiness of the ridge-type waveguide is selected on the upper surface of the ridge-type waveguide. The light beam can be emitted perpendicularly to the end face by making the current flow and the light spread in the waveguide symmetrical.

Here, the distance between one of the opposing side surfaces of the ridge-type waveguide and the energizing layer is equal to the distance between the other of the opposing side surfaces of the ridge-type waveguide and the energizing layer. If the distance is substantially the same, the distribution of current and light in the waveguide can be made more symmetrical.

Further, if each of the opposed side surfaces of the ridge-type waveguide is formed using an etchant having a plane orientation dependency so as to have a crystallographically equivalent plane orientation, it is accurate and easy. A ridge-type waveguide can be formed.

Alternatively, a semiconductor device according to the present invention includes an inclined substrate, a ridge-type waveguide provided on the inclined substrate, and a current-carrying layer provided in contact with an upper surface of the ridge-type waveguide. Wherein the inclination angles of the two opposing side surfaces of the ridge type waveguide with respect to the substrate are substantially the same, and the plane orientations of the two side surfaces are not crystallographically equivalent,
The distribution of current and light inside the ridge waveguide can be made more symmetrical.

Alternatively, in the semiconductor device according to the present invention, a ridge portion is formed on the inclined substrate, and a semiconductor layer is selectively formed so as not to cover any one corner of the upper surface of the ridge portion. The corner portion of the ridge portion not covered by the semiconductor layer is configured to be rounded by etching, so that the distribution of current and light inside the ridge waveguide can be made more symmetric. .

Here, the inclined substrate has a main surface of (10
A GaAs substrate having a plane orientation inclined at least 5 degrees from 0), wherein the ridge-type waveguide is made of InGaAlP and the current-passing layer is made of InGaP. Can be provided.

On the other hand, the method of manufacturing a semiconductor device of the present invention
Depositing a first semiconductor layer and a second semiconductor layer on a tilted substrate; and selectively etching the first semiconductor layer and the second semiconductor layer to form the first semiconductor layer. Forming a part of the ridge-type waveguide, selectively removing the second semiconductor layer on the upper surface of the ridge-type waveguide, and selectively removing the second semiconductor layer. Rounding the exposed upper edge of the ridge-type waveguide by etching and rounding the light beam by making the current flow and light spread in the waveguide symmetrical. A semiconductor device that emits light perpendicular to the end face can be manufactured.

Here, if the isotropic etching is performed as the etching in the rounding step, the rounding can be easily performed.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram illustrating a semiconductor laser according to a first embodiment of the present invention.
That is, FIG. 7A is a cross-sectional view as viewed from a direction parallel to the laser light emitting end face, and FIG. 7B is a plan view of the laser as viewed from above.

This laser is, for example, from (100) to about 1
An n-type clad layer 2, a first guide layer 3, an active layer 4, a second guide layer 5, a p-type clad layer 6, and an n-type GaAs inclined substrate 1 having a principal plane orientation inclined about 0 degrees. p ⁺ -type conducting layer 7, n-type GaAs current blocking layer 9, p-type G
It has a configuration in which aAs contact layers 10 are sequentially stacked. Here, the p-type cladding layer 6 is formed in a stripe-shaped ridge-type waveguide 8 and is buried with a current blocking layer 9. The current-carrying layer 7 has a high conductivity and has a role of injecting a current into the waveguide 8.

Also in the present embodiment, the inclination of the left and right side surfaces of the ridge waveguide 8 is asymmetric due to the formation on the inclined substrate 1. In the example shown in FIG. 1, the right slope of the ridge has a gentler slope than the left slope. In other words, the hem is wider on the right side of the ridge than on the left side.

In the present embodiment, the current-carrying layer 7 is selectively formed according to the asymmetry of the ridge. That is, as shown in FIG. 1A, the current-carrying layer 7 is not provided over the entire upper surface of the ridge, but is removed on the left side. This is to make the current injected via the current-carrying layer 7 spread evenly on the left and right sides of the ridge. Here, as shown in FIG. 1 (a), it is desirable that the conductive layer 7 is provided so that the distance from the edge of the ridge is substantially the same. For example, in FIG. 1A, it is desirable to provide the distance a and the distance b so as to be substantially the same.

According to the present embodiment, since no current flows through the portion where the easy-to-conduct layer 7 is not provided, the current flows through the ridge-type waveguide 8.
Flows almost evenly around the center of the left and right. Accordingly, the gain becomes symmetrical in the ridge waveguide 8, and the spread of the light mode becomes substantially equal in the left and right directions. As a result, FIG.
As shown in (b), the beam is emitted perpendicularly from the end face. At the same time, according to the present invention, it is possible to obtain an effect that the intensity distribution such as the far field pattern of the output beam is symmetric with respect to the horizontal direction.

When the semiconductor laser according to the present invention is used, even if the element is mounted on the mounting member with reference to the end face, the beam does not deviate, and various semiconductor lasers having a stable output beam intensity and a high coupling efficiency to a fiber or the like are provided. The device can be manufactured with high yield.

For example, in order to commercialize a relatively short-distance optical communication network for business offices and homes, it is necessary to provide a transmitter module having a stable coupling efficiency with a fiber at a low cost. It is said. According to the present invention, a semiconductor laser suitable for such a use can be provided.

A DVD (Digital Versatiel Disc)
In the optical pickup section of various optical recording systems represented by the above, the quality of the light beam determines the basic performance related to recording and reproduction. According to the present invention, a high-performance optical pickup having excellent beam characteristics can be provided at low cost.

A specific example of the manufacturing process of the semiconductor laser according to the present embodiment is as follows. First, (10
N-type GaAs having a principal plane orientation inclined 10 degrees from 0)
On the inclined substrate 1, n-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5
P cladding layer _{2, In 0.5 (Ga 0 .4} Al 0.6) 0.5 P guiding layer 3, In _0.5 Ga _0.5 P layer / In _0.5 (Ga _0.5 Al
_0.5) layer _0.5 consisting of P MQW (Multiple Quantum Wel
l: multiple quantum well) active layer 4, In _0.5 (Ga _0.4 A)
l _0.6 ) _0.5 P guide layer 5, p-type In _0.5 (Ga _0.3 Al
_0.7) are sequentially grown _{0 .5} P cladding layer 6, p ⁺ -type In _0.5 Ga _0.5 P current easily layer 7. As a crystal growth method, for example, an MOCVD method can be used. Here, in particular, when fabricating an InGaAlP-based semiconductor laser, a G laser having a principal plane direction shifted from (100) by 5 degrees or more is used.
When an aAs substrate is used, a sufficiently high carrier concentration is obtained, which is effective.

Next, a part of the p ⁺ -type conducting layer 7 and the p-type cladding layer 6 is selectively etched to form a striped ridge waveguide 8. As the etching method, for example, a wet etching method using an etching solution having a dependence of a plane orientation on an etching rate can be mentioned. Specifically, for example,
A phosphoric acid etching solution or the like can be used. The dimensions of the waveguide 8 are, for example, the width W at the upper end thereof.
1 is 2.5 μm and the height H is 1.0 μm.

Next, the easy conducting layer 7 remaining on the ridge waveguide 8 is selectively removed by etching. The size of the portion to be removed by etching can be appropriately determined according to the asymmetry of the left and right side surfaces of the waveguide 8. Specifically, for example, the etching is performed so that the width W2 of the current-carrying layer 7 is 2.0 μm.

Next, n-type GaAs is formed by MOCVD.
A current blocking layer 9 and a p-type GaAs contact layer 10 are grown and the waveguide 8 is buried. Further, electrodes (not shown) are formed on the p-side and the n-side, and the wafer is divided by a method such as scribe or cleavage to complete the semiconductor laser device.

As a result of measuring the angle of the outgoing beam with respect to the end face of the semiconductor laser device prototyped as described above, it was found that the "deviation" from the vertical was suppressed to within 0.5 degrees. On the other hand, as illustrated in FIG. 3, an element in which the current-carrying layer 7 is provided over the entire upper surface of the waveguide 8 was prototyped in the same process, and the angle of the output beam was evaluated. It was found that the direction was shifted by about 2 degrees.

According to the present invention, as described above, it is possible to eliminate the “deviation” of the angle of the emitted beam for the semiconductor laser device formed on the inclined substrate. As a result, various effects as described above can be obtained.

Next, a second embodiment of the present invention will be described.

FIG. 2 is a schematic diagram showing a semiconductor laser according to a second embodiment of the present invention. That is, the drawing is a cross-sectional view as seen from a direction parallel to the emission end face of the laser light. In FIG. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description is omitted.

The semiconductor laser of this embodiment is a further improvement of the semiconductor laser of the first embodiment. That is, in the semiconductor laser of this embodiment, the ridge waveguide 8 has a substantially symmetrical cross-sectional shape. this is,
After selectively removing the conductive layer 7 by etching, it can be formed by etching the exposed corner C of the ridge waveguide 8.

Therefore, the semiconductor laser of this embodiment is characterized in that the plane orientation of the left side surface and the plane direction of the right side surface of the waveguide 8 are not crystallographically equivalent. Specifically, in FIG. 2, the right side surface of the waveguide 8 is # 1.
The side surface on the left side has a higher-order plane orientation, while a relatively lower-order plane orientation such as 11 °.

FIG. 3 is a schematic process sectional view showing a main part of a method of manufacturing a semiconductor laser according to this embodiment.

First, a predetermined laminated structure is formed on an inclined substrate by a method such as the MOCVD method.

Then, as shown in FIG. 3A, the ridge waveguide 8 is formed by an etching method having a plane orientation dependency. The specific method can be the same as that described above with respect to the first embodiment. At this stage, the left and right side surfaces of the waveguide 8 have the same crystallographic plane orientation. For example, the left and right side surfaces each have a relatively low-order plane orientation such as {111}.

Next, as shown in FIG. 3B, the current-carrying layer 7 is selectively removed. At this time, it is desirable to etch away the easy conducting layer 7 so that the distances a and b from the lower end of the waveguide 8 are the same.

Next, as shown in FIG. 3C, the projected corner C of the waveguide 8 is rounded by etching. At this time, an etching mask (not shown) may be formed so that only the left side of the waveguide 8 is exposed. However, at this time, it is not easy to round the corner C of the waveguide 8 by using an etching method having a strong plane orientation dependency used when forming the waveguide 8, and is indicated by a broken line in FIG. 3B. As described above, the right side surface of the waveguide 8 retreats uniformly, and it becomes difficult to eliminate the asymmetry.

In this embodiment, an isotropic etching method is used as the etching method at this time. That is, an etching method that does not have a very strong dependence of the plane orientation on the etching rate is used.

When such isotropic etching is performed, a protruding portion of the object tends to be preferentially etched. As a result, the corner C of the waveguide 8 is rounded, and as shown in FIG.
The waveguide 8 can be made closer to a symmetrical shape on the left and right.
The etched left side surface can be substantially smooth and has a relatively higher plane orientation.

The present inventor has studied various etching methods. As a result, when a hydrobromic acid-based or bromine-methanol-based etching solution is used as such an etching solution, extremely good results are obtained. I knew that I could get it. If isotropic etching is realized, a dry etching method in which these are introduced in a gaseous state can also be used.

As shown in FIG. 3C, after the corners of the waveguide 8 are rounded, the block layer 9 and the contact layer 10 are buried, and predetermined electrodes are formed and separated into elements. The semiconductor laser is completed.

According to the present embodiment, the cross-sectional shape of the waveguide 8 can be made almost symmetrical by etching and then rounding off the corners of the waveguide 8 which are exposed after selectively removing the conductive layer 7 by etching. it can. As a result,
The current spreads left and right uniformly inside the waveguide 8, and the gain can be made symmetrical. Further, the problem that the spread of light becomes symmetrical and the phase becomes asymmetric can also be solved. As a result, an output beam that is exactly perpendicular to the end face can be obtained, and the light intensity distribution can be made exactly symmetrical.

The embodiment of the invention has been described with reference to examples. However, the present invention is not limited to these specific examples. For example, the present invention relates to I
The present invention is not limited to the nGaAlP-based semiconductor laser, but can be similarly applied to all semiconductor devices having a ridge-type waveguide formed on an inclined substrate to obtain the same effect. For example, the present invention can be similarly applied to a semiconductor laser made of a material system other than the InGaAlP system. Further, the present invention can be similarly applied to not only a semiconductor laser but also an optical amplifying element, an optical modulating element, a light receiving element, or the like having a ridge structure.

[0051]

The present invention is embodied in the form described above, and has the following effects.

First, according to the present invention, a current flows approximately uniformly in the vicinity of the center of the ridge-type waveguide by selectively providing an easy conducting layer on the ridge-type waveguide.
The gain becomes bilaterally symmetric, and the spread of the light mode becomes almost equal between the left and right. As a result, the beam is emitted vertically from the end face. At the same time, according to the present invention, it is possible to obtain an effect that the intensity distribution of the output beam, such as a far field pattern, becomes symmetric with respect to the horizontal direction.

Furthermore, according to the present invention, the cross-sectional shape can be made closer to left-right symmetric by selectively removing the current-conducting easy layer and then rounding the corner of the waveguide by etching. As a result, the current distribution and the spread of the light mode are made more uniform, and a beam perpendicular to the end face and symmetric in intensity distribution can be obtained more accurately.

When the semiconductor laser according to the present invention is used, even if the element is mounted on the mounting member on the basis of the end face, the beam does not shift, and various semiconductor lasers having a stable output beam intensity and a high coupling efficiency to a fiber or the like are provided. The device can be manufactured with high yield.

For example, in order to commercialize a relatively short-distance optical communication network for business establishments and homes, it is necessary to provide a transmitter module with stable coupling efficiency with a fiber at low cost. It is said. According to the present invention, a semiconductor laser suitable for such a use can be provided.

Also, a DVD (Digital Versatiel Disc)
In the optical pickup section of various optical recording systems represented by the above, the quality of the light beam determines the basic performance related to recording and reproduction. According to the present invention, a high-performance optical pickup having excellent beam characteristics can be provided at low cost.

As described in detail above, according to the present invention, various semiconductor devices such as a semiconductor laser having good beam characteristics can be provided, and industrial advantages are great.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a semiconductor laser according to a first embodiment of the present invention. That is, FIG. 7A is a cross-sectional view as viewed from a direction parallel to the laser light emitting end face, and FIG. 7B is a plan view of the laser as viewed from above.

FIG. 2 is a schematic diagram illustrating a semiconductor laser according to a second embodiment of the present invention.

FIG. 3 is a schematic process sectional view illustrating a main part of a method for manufacturing a semiconductor laser according to the present invention.

FIG. 4 is a schematic view showing a conventional ridge waveguide type semiconductor laser formed on an inclined substrate. That is, FIG.
FIG. 2 is a cross-sectional view as viewed from a direction parallel to an emission end face of the laser light, and FIG. 2B is a plan view as viewed from above the laser.

[Explanation of symbols]

1, 101 n-type GaAs tilted substrate 2, 102 n-type cladding layer 3, 103 n-type guiding layer 4, 104 active layer 5, 105 p-type guiding layer 6, 106 p-type cladding layer 7, 107 p ⁺ -type current-carrying easy layer 9,109 n-type GaAs current blocking layer 10,110 p-type GaAs contact layer

Claims (8)

[Claims] 1. A ridge waveguide provided on an inclined substrate, a ridge waveguide provided on the inclined substrate, and an energization easy layer provided in contact with an upper surface of the ridge waveguide. The semiconductor element, wherein two opposite side surfaces have different inclination angles with respect to the substrate, and the current-carrying layer is selectively provided on the upper surface of the ridge waveguide. 2. A distance between one of the opposing side surfaces of the ridge-type waveguide and the current-carrying layer, the distance between the other of the opposite side surfaces of the ridge-type waveguide and the current-carrying layer. 2. The semiconductor device according to claim 1, wherein the distance is substantially the same as the distance. 3. The semiconductor device according to claim 1, wherein each of the opposed side faces of the ridge waveguide has a crystallographically equivalent plane orientation. 4. A ridge-type waveguide provided on an inclined substrate, a ridge-type waveguide provided on the tilt-type substrate, and a current-carrying layer provided in contact with an upper surface of the ridge-type waveguide. A semiconductor element, wherein two opposing side surfaces have substantially the same inclination angle with respect to the substrate, and the plane orientations of the two side surfaces are not crystallographically equivalent. 5. A ridge portion is formed on an inclined substrate, and a semiconductor layer is selectively formed so as not to cover one corner of an upper surface of the ridge portion, and is not covered by the semiconductor layer. A semiconductor element, wherein the corner of the ridge is rounded by etching. 6. The inclined substrate has a principal surface of (100) to 5
6. A GaAs substrate having a plane orientation inclined at an angle of not less than degrees, wherein the ridge-type waveguide is made of InGaAlP, and the current-carrying layer is made of InGaP. Semiconductor element. 7. A step of depositing a first semiconductor layer and a second semiconductor layer on an inclined substrate, and selectively etching the first semiconductor layer and the second semiconductor layer, Forming a part of the first semiconductor layer into a ridge-type waveguide; selectively removing the second semiconductor layer on the upper surface of the ridge-type waveguide; and selectively forming the second semiconductor layer. A step of rounding the corner of the upper end of the ridge-type waveguide exposed by the removal by etching, the method comprising: 8. The method according to claim 7, wherein the etching in the rounding step is an isotropic etching.