JP2002057401A - Semiconductor laser and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser and a semiconductor device, in which laser light polarization characteristics can be enhanced by relaxing stresses caused by the difference between the coefficients of thermal expansion and that of a mounting board and the reliability can be enhanced. SOLUTION: The semiconductor laser comprises a substrate 10, on which a stripe mesa protrusion 10a is formed, multilayer semiconductor body comprising a first conductivity-type first clad layer 11, active layer 12 and a second conductivity-type second clad layer 13 formed on the mesa protrusion 10a, and first conductivity-type current block layer 15 formed on the opposite side faces of the active layer 12 to touch the active layer 12 across the total thickness thereof, first electrode 20 formed on the upper layer of the multilayer semiconductor body, and second electrode 30 formed on the rear surface of the substrate wherein a level difference H caused by the height of the mesa protrusion 10a is formed on the surface of the multilayer semiconductor body and the first electrode 20 comprises a multilayer film, where two Pt layers (25, 27) sandwich a stress relax layer, i.e., Au layer 26, or an anti-alloying film of Pt layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser and a semiconductor device, and more particularly to a buried heterojunction semiconductor laser using an AlGaAs compound semiconductor and a semiconductor device having a step formed on a surface.

[0002]

2. Description of the Related Art A semiconductor laser having a low threshold current has a current blocking means for giving a refractive index difference in a lateral direction of an active layer, that is, in a direction perpendicular to a plane direction of the active layer, and for narrowing a current. It can be realized by forming.

A semiconductor laser realizing the above structure is disclosed in, for example, Japanese Patent Publication No. 30111938. FIG. 4A is a cross-sectional view of an example of the above-described semiconductor laser. It is made of GaAs or the like having a stripe-shaped (extending in a direction perpendicular to the paper surface) mesa projection 10a in which a side surface of the (100) crystal main surface has a gentle concave curved surface whose side surface is convex toward the base side. p-type compound semiconductor substrate 10
On the main surface side of the compound semiconductor substrate 10 having the mesa protrusions 10a, a p-type cladding layer 11 made of AlGaAs or the like, an active layer 12, and a first n-type cladding layer 13 made of AlGaAs or the like are entirely formed. And an epitaxial layer of a p-type current blocking layer 15 made of AlGaAs or the like, an n-type second clad layer 16 made of AlGaAs or the like, and an n-type cap layer 17 made of GaAs or the like. . Here, the above-mentioned mesa protrusion 10a
The current blocking layer 15 in the mesa groove 10b for forming the active layer 12 is formed on the side surface of the active layer 12 sandwiched between the p-type cladding layer 11 and the first n-type cladding layer 13 epitaxially grown on the mesa projection 10a. And the first n-type cladding layer 13 and the second n
It is configured to be interposed between the mold cladding layers 16.

An n-electrode 20 is formed so as to be connected to the n-type cap layer 17 of the semiconductor laminate having the above configuration. The n-electrode 20 is made of AuG, for example, as shown in FIG.
It is made of a laminate of the e layer 21, the Ni layer 22, and the Au layer 23, and the AuGe layer 21 side is the n-type cap layer 17 side. On the other hand, on the back surface of the p-type semiconductor substrate 10, a p-electrode 30 made of, for example, a Ti layer, a Pt layer, and an Au layer is formed. As described above, the buried heterojunction semiconductor laser LD is configured.

In the above structure, the active layer 1 serving as an operation region formed on the mesa protrusion 10a of the semiconductor substrate 10 is formed.
2 is a p-type cladding layer 11 and a first n-type cladding layer 13
Buried hetero (BH) surrounded by the current blocking layer 15 in the lateral direction.
) Structure. On both sides of the active layer 12, the side wall slope 1 due to the (111) B crystal plane generated in the p-type cladding layer 11
1a, and is regulated by the p-type current blocking layer 15. That is, the current block layers 15 are formed on both sides of the active layer 12 itself, which is an operation region on the stripe-shaped mesa protrusion 10a, and the mesa groove 10 is formed.
Since the pnpn structure is formed in the region b, the current is effectively narrowed, and the current can be effectively concentrated on the active layer 12 on the mesa protrusion 10a.

The semiconductor laser having the above structure can be manufactured by one-time epitaxial growth. As a method of manufacturing the semiconductor laser, for example, (10
On the main surface of the p-type compound semiconductor substrate 10 made of GaAs or the like whose main surface is the 0) surface, a mask layer made of a photoresist is formed and a sulfuric acid-based crystallographic etching is performed, and the side surface protrudes toward the base side. A mesa projection 10a having a gentle concave curved surface (extending in a direction perpendicular to the paper surface) is formed. Here, the stripe direction of the mesa projection 10a is formed so as to extend in a direction perpendicular to the (011) plane with the cross section in FIG. Next, after a p-type buffer layer is formed as necessary by MOCVD (metal organic chemical vapor deposition) or the like, AlGaAs
The p-type cladding layer 11 made of s is epitaxially grown. In this case, as the epitaxial growth proceeds, an inclined surface 10b composed of a (111) B crystal plane which forms an angle of about 55 degrees with the (100) plane on the upper surface of the mesa protrusion 10a naturally occurs on both sides of the mesa protrusion 10a. . The growth of the p-type cladding layer 11 is stopped in a state where the inclined surface 10b composed of the (111) B crystal plane exists, and the continuous MOC is performed.
When the active layer 12 is epitaxially grown by the VD process, the growth rate on the slope 10b composed of the (111) B crystal plane is very slow, and the active layer 12 does not substantially grow.
Are formed separately on the mesa protrusion 10a and the mesa groove 10b.

Next, a first n-type cladding layer 13 made of AlGaAs is epitaxially grown on the active layer 12 by a continuous MOCVD process. The above active layer 12
Similarly to the growth of the crystal, the slope 10 made of the (111) B crystal plane is formed.
Since growth on b is not substantially performed, it is formed separately on the mesa protrusion 10a and the mesa groove 10b. Here, the p-type cladding layer 11 is formed on the mesa protrusion 10a to a position where two inclined surfaces formed of (111) B crystal planes on both sides of the mesa protrusion 10a cross each other, and in the mesa groove 10b.
Is grown to a film thickness up to the middle position of the inclined surface 11a. By the above-mentioned epitaxial growth, on the mesa protrusion 10a,
The active region 12 is formed by the active layer 12 sandwiched between the p-type cladding layer 11 and the first n-type cladding layer 13, and has a substantially triangular cross section.

Next, a current block layer 15 made of AlGaAs is epitaxially grown on the first n-type clad layer 13 by a continuous MOCVD process. here,
The current blocking layer 15 is formed on the side of the active layer 12 sandwiched between the p-type cladding layer 11 and the first n-type cladding layer 13 epitaxially grown on the mesa protrusion 10a.
2 is formed in the region of the mesa groove 10b so as to be in contact with the entire thickness of the substrate. Next, the second n-type cladding layer 16 made of AlGaAs is epitaxially grown on the entire surface of the first n-type cladding layer 13 and the current blocking layer 15 by a continuous MOCVD process. Next, continuous MOCV
In step D, an n-type cap layer 16 made of GaAs is epitaxially grown on the entire surface of the second n-type clad layer 16. As described above, the semiconductor laminate having the above configuration can be formed on the semiconductor substrate 10 by one continuous epitaxial growth. Further, the AuGe layer 21,
N electrode 2 composed of a laminate of Ni layer 22 and Au layer 23
0 is connected to the n-type cap layer 17, while the p-electrode 30 is formed of, for example, a Ti layer, a Pt layer, and an Au layer.
Is formed on the back surface of the p-type semiconductor substrate 10, and through a pelletizing step or the like, the semiconductor shown in FIG. 4A can be obtained.

[0009]

However, when the semiconductor laser having the above structure is mounted using solder or the like from the n-electrode side, the p-type cladding layer 11 is formed as follows.
And the active layer 12 sandwiched between the first n-type cladding layers 13, and a stress is applied to the operating region 14 having a substantially triangular cross section from the bonding surface between the n-electrode and the solder, and the laser light oscillated. There has been a problem that the polarization direction may be unintentionally rotated or a defect may occur.

FIG. 5 is a schematic diagram when the semiconductor laser LD having the above-mentioned conventional structure is mounted on a submount substrate 40 made of AlN or the like from the n-electrode 20 side by using a solder layer 41. A wiring portion 42 connected to the solder layer 41 is formed on the submount substrate 40, and furthermore, a lead 42
a are connected to each other. On the other hand, a semiconductor laser LD
The lead 30a is also connected to the p-electrode 30 formed on the p-type semiconductor substrate constituting the above. When a predetermined voltage is applied to both the leads (30a, 42a), laser light oscillates from the active layer 12 in the operation region 14.

In the semiconductor laser having the above structure, a step is left on the surface of the semiconductor laminate on the n-electrode side by the height of the mesa protrusion formed on the semiconductor substrate. The stress ST caused by the difference in the thermal expansion coefficient of the semiconductor laser has a structure in which the cross section is concentrated and applied to a substantially triangular structure inside the semiconductor laminate, and affects the laser characteristics such as the polarization direction of the oscillating laser light. Or a defect is caused to cause a problem that reliability is reduced.

In particular, the problem of affecting the laser characteristics such as the direction of polarization of the oscillating laser light becomes significant in the case of a two-beam laser in which two semiconductor laser elements are mounted on one chip. FIG. 6 (a) shows the above 1
Two semiconductor laser elements (LD1, LD2) on a chip
FIG. 2 is a cross-sectional view of a two-beam laser equipped with a laser beam. The structure of each of the semiconductor laser devices (LD1, LD2) is substantially the same as the case where the semiconductor laser device is configured alone as shown in FIG. The boundary region of each semiconductor laser element (LD1, LD2)
Are formed, and the elements are separated. FIG. 6B shows the above 2
It is a schematic diagram when a beam laser is mounted on a submount substrate 40 of AlN or the like from the n-electrode 20 side using solder layers (41, 43). On the submount substrate 40, wiring portions (42, 4) connected to the solder layers (41, 43) are provided.
4) are formed, and leads (42a, 44) are further formed.
a) are connected to each other. On the other hand, the semiconductor laser L
The lead 30a is also connected to the p-electrode 30 formed on the p-type semiconductor substrate constituting D. When a predetermined voltage is applied to each of the leads (30a, 42a, 44a), laser light oscillates from the active layer 12 in the operation region 14 of each laser diode (LD1, LD2).

In the two-beam laser having the above structure, the stress ST caused by the difference in the coefficient of thermal expansion between the sub-mount substrate 40 and the two-beam laser causes each laser diode (LD1, L
D2), the rotation direction (P1, P2) of the polarization of the laser light oscillated by each laser diode (LD1, LD2) is reversed, and the difference between the rotation angles is different. May reach 30 °. Further, when the submount substrate is made of a less expensive silicon substrate or the like, the stress ST caused by the difference in the coefficient of thermal expansion between the submount substrate 40 and the two-beam laser is further increased, and the difference in the rotation angle reaches 45 °. Would. If there is a difference in the polarization rotation angle as described above, even if a non-polarization optical system is used, there will be a difference in reflectance and the like, which is a non-negligible amount.

[0014] The above-mentioned problem is caused by the fact that stress is applied to the semiconductor similarly to the above in a semiconductor device generally provided with an electrode on a semiconductor having a step on the surface and mounted from the electrode side. There is a problem in reliability, such as promotion.

The present invention has been made in view of the above-described circumstances. Therefore, the present invention provides a semiconductor substrate in which a mesa projection is formed and a step corresponding to the height is left on the surface of the semiconductor laminate. In semiconductor lasers, the stress caused by the difference in the coefficient of thermal expansion between the mounting substrate and the semiconductor laser is alleviated to reduce the influence on the laser characteristics such as the polarization direction of the oscillating laser light and the decrease in reliability such as the occurrence of defects. It is an object of the present invention to provide a semiconductor laser that can prevent the occurrence of stress and a semiconductor device that can reduce stress applied to the semiconductor even when an electrode is provided on the semiconductor having a step on the surface.

[0016]

In order to achieve the above object, a semiconductor laser according to the present invention comprises a substrate on which stripe-shaped mesa protrusions are formed, and a first substrate formed on the mesa protrusions.
In the first cladding layer of the conductivity type, the active layer and the second cladding layer of the second conductivity type, and in the mesa grooves on both sides of the mesa projection, both sides of the active layer are laid over the entire thickness of the active layer. A semiconductor laminate including a first conductivity type current blocking layer formed so as to be in contact with the first laminate, a first electrode formed on an upper layer of the semiconductor laminate, and a second electrode formed on a back surface of the substrate. Wherein a step due to the height of the mesa protrusion is formed on the surface of the semiconductor laminate, and the first electrode includes an alloying prevention film.

The semiconductor laser of the present invention is preferably used by being mounted from the first electrode side toward a mounting surface on which the semiconductor laser is mounted.

Preferably, in the semiconductor laser according to the present invention, the first electrode is formed of a two-layered alloying prevention film and a two-layered alloying prevention film formed between the two-layered alloying prevention film. A stress relaxation layer made of a material softer than the oxidation prevention film.

In the above-described semiconductor laser according to the present invention, more preferably, the alloying prevention film contains platinum.

In the above-described semiconductor laser of the present invention, more preferably, the stress relaxation layer contains at least gold or indium.

In the above-described semiconductor laser according to the present invention, more preferably, the first electrode has a layer which alloys with the semiconductor laminate on the semiconductor laminate side of the two-layer alloying prevention film.

More preferably, the semiconductor laser of the present invention is used by being mounted via solder from the first electrode side toward a mounting surface on which the semiconductor laser is mounted. A layer that alloys with the solder is provided on the solder side of the two-layer alloying prevention film.

In the above-described semiconductor laser of the present invention, preferably, the main surface of the substrate is a (100) plane, and the side surfaces of the stripe-shaped mesa projections are gently convex toward the base side of the substrate. It is a curved surface.

Preferably, in the semiconductor laser according to the present invention, the current blocking layer is formed such that a contact surface between the current blocking layer and the active layer is linear along a longitudinal direction of the mesa protrusion. Is filmed. More preferably, the linear film-forming portion of the current block layer has a {311} crystal plane.

In the above-described semiconductor laser of the present invention, preferably, a plurality of the above-mentioned semiconductor laminated bodies separated from each other are formed on the above-mentioned substrate, and a plurality of laser elements are mounted.

In the above-described semiconductor laser of the present invention, the first electrode formed on the surface of the semiconductor laminated body having a step due to the height of the mesa projection includes an alloying prevention film such as Pt, It is possible to prevent the alloying of the interface between the electrode and the semiconductor or the progress of alloying of the interface between the electrode and the solder over the alloying prevention film. Therefore, by arranging a stress relaxation layer softer than the alloying prevention film such as an Au layer at a position where the progress of alloying is prevented, stress caused by a difference in thermal expansion coefficient between the mounting substrate and the semiconductor laser is reduced. Accordingly, it is possible to prevent the influence on the laser characteristics such as the polarization direction of the oscillating laser light and the decrease in reliability such as occurrence of defects. The above alloying is the electrode
In the case of proceeding at both the semiconductor laminate interface portion and the electrode-solder interface portion, a structure in which a stress relaxation layer softer than an alloying prevention film such as an Au layer is disposed between two alloying prevention films. As a result, the alloying of the stress relaxation layer between the two alloying prevention films is prevented, so that the stress caused by the difference in the coefficient of thermal expansion between the mounting substrate and the semiconductor laser is reduced as described above. Thus, it is possible to prevent the polarization direction of the oscillating laser light from affecting the laser characteristics and from lowering the reliability such as the occurrence of defects.

In order to achieve the above object, a semiconductor device according to the present invention comprises a semiconductor layer having a step formed on a surface thereof;
A semiconductor device having an electrode formed on an upper layer of the semiconductor layer, wherein the semiconductor device is mounted from the electrode side toward a mounting surface on which the semiconductor device is mounted, and the electrode is used.
Including an alloying prevention film.

The semiconductor device of the present invention is preferably
The electrode includes a two-layered alloying prevention film and a stress relaxation layer formed between the two-layered alloying prevention film and made of a material softer than the two-layered alloying prevention film.

In the above-described semiconductor device of the present invention, the electrode formed on the surface of the semiconductor laminate having a step formed on the surface is formed of P
t, etc., alloying of the electrode-semiconductor laminate interface portion over the alloying prevention film,
Alternatively, the progress of alloying at the electrode-solder interface can be prevented. Therefore, the stress applied to the semiconductor can be reduced by disposing a stress relaxation layer such as an Au layer that is softer than the alloying prevention film at a position where the progress of alloying is prevented.

[0030]

Embodiments of the present invention will be described below with reference to the drawings.

First Embodiment FIG. 1A is a sectional view of a semiconductor laser according to the present embodiment. Mesa projection 10a (extending in a direction perpendicular to the paper surface) in which a main surface formed of a (100) crystal surface has a gentle concave curved surface whose side surface is convex toward the base side.
-Type compound semiconductor substrate 1 made of GaAs or the like having
On the main surface of the compound semiconductor substrate 10 having the mesa protrusions 10a, a p-layer made of AlGaAs or the like is entirely formed.
Type cladding layer 11, an active layer 12, a first n-type cladding layer 13 made of AlGaAs or the like, a p-type current blocking layer 15 made of AlGaAs or the like, and an AlGaAs
The respective epitaxial layers of an n-type second cladding layer 16 made of, for example, and an n-type cap layer 17 made of GaAs or the like are sequentially laminated. Here, the above-mentioned mesa protrusion 10
a, the current blocking layer 15 in the mesa groove 10b
A side surface of the active layer 12 sandwiched between the p-type clad layer 11 and the first n-type clad layer 13 epitaxially grown on the mesa protrusion 10a so as to be in contact with the active layer 12 over the entire thickness thereof; , The first n-type cladding layer 13 and the second n-type cladding layer 16. Further, in the semiconductor laser having the above configuration, the surface of the semiconductor laminated body obtained by laminating each layer such as the clad layer and the active layer on the upper layer so as to correspond to the height of the mesa protrusion 10 a formed on the semiconductor substrate 10. Also, a step having a height H occurs.

In the semiconductor laminate having the above-described structure, the p-type current blocking layer 15 is formed such that the contact surface between the p-type current blocking layer 15 and the active layer 12 becomes linear along the longitudinal direction of the mesa protrusion 10a. Is formed, and the linear film-forming portion is composed of a {311} crystal plane.

An n-electrode 20 is formed on the surface of the semiconductor laminate having the above-described structure where a step having a height H is generated, connected to the n-type cap layer 17. FIG. 1B is an enlarged sectional view of the n-electrode 20 portion. n electrode 20
Is, for example, an AuGe layer 21 having a thickness of 160 nm and a thickness of 5
0 nm Ni layer 22, 500 nm thick Au layer 23, 50 nm thick Ti layer 24, 100 nm thick Pt layer 2
5. Au layer 26 with a thickness of 500 nm, P with a thickness of 100 nm
It is made of a laminate of a t layer 27 and a 500 nm thick Au layer 28, and the AuGe layer 21 side is the n-type cap layer 17 side. In the n-electrode having the above configuration, the Pt layer 25
The Pt layer 27 is an alloying prevention film that hardly forms an alloy with a semiconductor layer or solder, and the Au layer 26 between them is a position protected by the Pt layer 25 and the Pt layer 27 from the progress of alloying. The stress relaxation layer is softer than the Pt layer 25 and the Pt layer 27. The AuGe layer 21, the Ni layer 22, and the Au layer have a layer configuration conventionally used as an n-electrode, and the Ti layer 24 functions as an adhesion layer. The lower side of the Pt layer 25, that is, the AuGe layer 21, the Ni layer 22, the Au layer 23, and the Ti layer 24
It becomes a region where alloying proceeds from the mold cap layer 17 side, and the alloying can form an ohmic contact with the n-type cap layer 17. Further, the upper layer side of the Pt layer 27, that is, the Au layer 28 becomes a region where the alloying with the solder layer progresses when it is mounted via the solder layer, and makes an ohmic contact with the solder layer by alloying. be able to.

On the other hand, on the back surface of the p-type semiconductor substrate 10, for example, a p-electrode 30 made of a Ti layer, a Pt layer and an Au layer is formed.
Are formed. As described above, the buried heterojunction semiconductor laser LD is configured.

In the above structure, the active layer 1 serving as an operation region formed on the mesa protrusion 10a of the semiconductor substrate 10 is formed.
2 is a p-type cladding layer 11 and a first n-type cladding layer 13
Buried hetero (BH) surrounded by the current blocking layer 15 in the lateral direction.
) Structure. On both sides of the active layer 12, the side wall slope 1 due to the (111) B crystal plane generated in the p-type cladding layer 11
1a, and is regulated by the p-type current blocking layer 15. That is, the current block layers 15 are formed on both sides of the active layer 12 itself, which is an operation region on the stripe-shaped mesa protrusion 10a, and the mesa groove 10 is formed.
Since the pnpn structure is formed in the region b, the current is effectively narrowed, and the current can be effectively concentrated on the active layer 12 on the mesa protrusion 10a.

The semiconductor laser according to the present embodiment is
It is mounted on a submount substrate or the like using solder or the like from the n-electrode side. FIG. 2A shows the above semiconductor laser LD.
From the n-electrode 20 side to a submount substrate 4 such as AlN.
FIG. 4 is a cross-sectional view when mounting is performed on a solder layer 41 using a solder layer 41. A wiring portion 42 connected to the solder layer 41 is formed on the submount substrate 40, and a lead 42a is further formed by connection. On the other hand, the lead 30a is also connected to the p-electrode 30 formed on the p-type semiconductor substrate constituting the semiconductor laser LD. When a predetermined voltage is applied to both the leads (30a, 42a), laser light oscillates from the active layer 12 in the operation region 14.

FIG. 2B is an enlarged cross-sectional view of the junction between the n-electrode 20 and the solder layer 41. The laminated film A on the n-type cap layer 17 side of the Pt layer 25, that is, AuG
e layer 21, Ni layer 22, Au layer 23 and Ti layer 24
Is a region where alloying proceeds from the n-type cap layer 17 side, and an ohmic contact can be made with the n-type cap layer 17 by forming the n-type cap layer 17 and the alloying film a. Further, the film B on the solder layer 41 side with respect to the Pt layer 27, that is, the Au layer 28 becomes a region where alloying with the solder layer 41 proceeds, and by forming the solder layer 41 and the alloyed film b, the solder layer is formed. Ohmic contact can be made with 41. The Pt layer 25 and the Pt layer 27 are made of an alloying prevention film C which hardly forms an alloy with a semiconductor layer or solder.
The alloying from the n-type cap layer 17 side or from the solder layer 41 side stops at this layer. Further, the Au layer 26 between the two alloying prevention films C is protected from the progress of alloying from the n-type cap layer 17 side or the solder layer 41 side by the two alloying prevention films C. And a stress relaxation layer D made of a material softer than the two-layered alloying prevention film C and capable of relaxing the stress when the stress is applied via the Au layer 26. Has become.

Since the step of the height H of the semiconductor laminate having the above-described structure remains, the stress caused by the difference in the coefficient of thermal expansion between the submount substrate 40 and the semiconductor laser LD is reduced by the p-type cladding layer 11. The active layer 12 is sandwiched between the first n-type cladding layers 13 and has a structure in which the cross section concentrates on the operation region 14 having a substantially triangular shape. Since the structure has the stress relaxation layer D sandwiched between the alloying prevention films C of the layers, the above-mentioned stress can be relaxed, whereby the laser characteristics such as the polarization direction of the oscillating laser light can be reduced. It is possible to prevent a decrease in reliability such as influence or occurrence of defects.

The semiconductor laser having the above structure can be manufactured by one epitaxial growth, as in the conventional example shown in FIG. As a method of manufacturing the above-described semiconductor laser, for example, GaAs having a (100) plane as a main surface is used.
A mask layer made of a photoresist is formed on the main surface of the p-type compound semiconductor substrate 10 made of, for example, and a sulfuric acid-based crystallographic etching is performed to form a gentle concave curved surface whose side surface is convex toward the base side. A striped mesa protrusion 10a (extending in a direction perpendicular to the paper surface) is formed. Here, the stripe direction of the mesa protrusion 10a is the same as that shown in FIG.
The cross section is defined as a (011) plane and is formed so as to extend in a direction perpendicular to this plane. Next, a p-type buffer layer is formed as required by MOCVD (metal organic chemical vapor deposition) or the like, and then a p-type cladding layer 11 made of AlGaAs is formed.
Is epitaxially grown. In this case, as the epitaxial growth proceeds, (10
An inclined surface 10b composed of a (111) B crystal plane having an angle of about 55 degrees with respect to the 0) plane naturally occurs on both sides of the mesa protrusion 10a. When the growth of the p-type cladding layer 11 is stopped in a state where the inclined surface 10b composed of the (111) B crystal plane is present and the active layer 12 is epitaxially grown by a continuous MOCVD process, the (111) B crystal plane is formed. Since the growth rate on the slope 10b is very slow, the growth does not substantially occur, and the active layer 12 is formed on the mesa protrusion 10a and the mesa groove 1a.
0b.

Next, a first n-type cladding layer 13 made of AlGaAs is epitaxially grown on the active layer 12 by a continuous MOCVD process. The above active layer 12
Similarly to the growth of the crystal, the slope 10 made of the (111) B crystal plane is formed.
Since growth on b is not substantially performed, it is formed separately on the mesa protrusion 10a and the mesa groove 10b. Here, the p-type cladding layer 11 is formed on the mesa protrusion 10a to a position where two inclined surfaces formed of (111) B crystal planes on both sides of the mesa protrusion 10a cross each other, and in the mesa groove 10b.
Is grown to a film thickness up to the middle position of the inclined surface 11a. By the above-mentioned epitaxial growth, on the mesa protrusion 10a,
The active region 12 is formed by the active layer 12 sandwiched between the p-type cladding layer 11 and the first n-type cladding layer 13, and has a substantially triangular cross section.

Next, a current block layer 15 made of AlGaAs is epitaxially grown on the first n-type clad layer 13 by a continuous MOCVD process. here,
The current blocking layer 15 is formed on the side of the active layer 12 sandwiched between the p-type cladding layer 11 and the first n-type cladding layer 13 epitaxially grown on the mesa protrusion 10a.
2 is formed in the region of the mesa groove 10b so as to be in contact with the entire thickness of the substrate. At this time, the mesa protrusion 10a formed above is formed in a stripe shape (extending in a direction perpendicular to the paper surface) having a gentle concave curved surface whose side surface is convex toward the base side. As a main surface of the block layer 15, the (311) plane can be ensured to emerge, whereby the contact surface between the p-type current block layer 15 and the active layer 12 extends along the longitudinal direction of the mesa protrusion 10a. , {311} crystal planes, and the current blocking layer 15 can be easily formed so as to be in contact with the entire thickness of the active layer 12.

Next, a second n-type cladding layer 16 made of AlGaAs is epitaxially grown on the entire surface of the first n-type cladding layer 13 and the current blocking layer 15 by a continuous MOCVD process. Next, continuous MOCV
In step D, an n-type cap layer 16 made of GaAs is epitaxially grown on the entire surface of the second n-type clad layer 16. As described above, the semiconductor laminate having the above configuration can be formed on the semiconductor substrate 10 by one continuous epitaxial growth. Further, the n-electrode 20 having the above configuration is formed by connecting to the n-type cap layer 17.
For example, a p-electrode 3 composed of a Ti layer, a Pt layer, and an Au layer
1 is formed on the back surface of the p-type semiconductor substrate 10, and through a pelletizing step or the like, the semiconductor shown in FIG. 1A can be obtained.

Second Embodiment FIG. 3A is a sectional view of a two-beam laser according to the present embodiment in which two semiconductor laser elements (LD1 and LD2) are mounted on one chip. Each semiconductor laser element (LD1,
The structure of the LD 2) is substantially the same as the semiconductor laser according to the first embodiment shown in FIG. A separation groove I is formed in a boundary region between the semiconductor laser elements (LD1, LD2), and the semiconductor laser elements (LD1, LD2) are separated. That is, a step caused by the mesa protrusion 10a formed on the substrate 10 is left on the surface of the semiconductor laminated body constituting each of the semiconductor laser elements (LD1, LD2), and two layers are formed on the surface. An n-electrode 20 having a structure having a stress relaxation layer sandwiched between alloying prevention films is formed.

FIG. 3B shows that the two-beam laser is n
FIG. 4 is a cross-sectional view when the semiconductor device is mounted on a submount substrate 40 made of AlN or the like from the side of an electrode 20 using solder layers (41, 43). On the submount substrate 40, a solder layer (41,
43), a wiring portion (42, 44) is formed, and a lead (42a, 44a) is further connected to the wiring portion. On the other hand, the lead 30a is also connected to the p-electrode 30 formed on the p-type semiconductor substrate constituting the semiconductor laser LD. Each of the above leads (30a, 42
When a predetermined voltage is applied to the semiconductor laser elements (LD1, LD2), laser light oscillates from the active layer 12 in the operation region 14 of each semiconductor laser element (LD1, LD2).

In the two-beam laser having the above-described structure, the stress caused by the difference in the thermal expansion coefficient between the submount substrate 40 and the two-beam laser causes each semiconductor laser element (LD1, LD
2), the polarization of the laser light oscillated by each of the semiconductor laser elements (LD1, LD2) is rotated in the opposite direction. In the two-beam laser according to the present embodiment, As described above, since the n-electrode 20 has the structure having the stress relaxation layer sandwiched between the two alloying prevention films, the above-mentioned stress can be relaxed, and thereby the polarization direction of the oscillating laser light can be reduced. It is possible to suppress the influence on the laser characteristics, for example, by suppressing the rotation, and to prevent a decrease in reliability such as the occurrence of a defect. Further, since the stress can be reduced as described above, it is also possible to reduce the cost by using a silicon substrate having a large difference in thermal expansion coefficient with the two-beam laser as the submount substrate.

Although the present invention has been described with reference to the two embodiments, the present invention is not limited to these embodiments. For example, the shape of the mesa protrusion may be a so-called inverted mesa protrusion having a reverse trapezoidal cross section in addition to a stripe shape having a gentle concave curved surface whose side surface is convex toward the base side. Further, a semiconductor material and a metal material constituting the semiconductor laser and their thicknesses can be appropriately selected. Further, as the plurality of semiconductor lasers mounted monolithically in the second embodiment, elements having different emission wavelengths, elements having the same emission wavelength but different emission intensities, or elements having the same element characteristics can be used. It is. Further, the present invention is also applicable to a semiconductor light emitting device having three or more semiconductor laser elements. Furthermore, the present invention is applicable not only to a semiconductor laser, but also to a semiconductor device in which an electrode is provided on a semiconductor having a step on the surface and mounted from the electrode side, and the stress applied to the semiconductor can be reduced as described above. it can. In addition, various changes can be made without departing from the spirit of the present invention.

[0047]

According to the semiconductor laser of the present invention, the first electrode formed on the surface of the semiconductor laminate having the step formed due to the height of the mesa projection includes the alloying prevention film such as Pt. Thus, the alloying of the interface between the electrode and the semiconductor layer or the progress of the alloying of the interface between the electrode and the solder over the alloying prevention film can be prevented. Therefore, by arranging a stress relaxation layer softer than the alloying prevention film such as an Au layer at a position where the progress of alloying is prevented, stress caused by a difference in thermal expansion coefficient between the mounting substrate and the semiconductor laser is reduced. Accordingly, it is possible to prevent the influence on the laser characteristics such as the polarization direction of the oscillating laser light and the decrease in reliability such as occurrence of defects.

According to the semiconductor device of the present invention, the electrode formed on the surface of the semiconductor laminate having the step formed on the surface is formed of P
t, etc., alloying of the electrode-semiconductor laminate interface portion over the alloying prevention film,
Alternatively, the progress of alloying at the electrode-solder interface can be prevented. Therefore, the stress applied to the semiconductor can be reduced by disposing a stress relaxation layer such as an Au layer that is softer than the alloying prevention film at a position where the progress of alloying is prevented.

[Brief description of the drawings]

FIG. 1A is a sectional view of a semiconductor laser according to a first embodiment, and FIG. 1B is an enlarged sectional view of an n-electrode portion.

FIG. 2A is a cross-sectional view when the semiconductor laser shown in FIG. 1 is mounted, and FIG. 2B is an enlarged cross-sectional view of a bonding portion between the n-electrode and a solder layer. is there.

FIG. 3A is a sectional view of a semiconductor light emitting device according to a second embodiment, and FIG. 3B is a sectional view when the semiconductor light emitting device shown in FIG. 3A is mounted. .

FIG. 4A is a sectional view of a semiconductor laser according to a first conventional example, and FIG. 4B is an enlarged sectional view of an n-electrode portion.

FIG. 5 is a schematic diagram showing a problem when the semiconductor laser shown in FIG. 4 is mounted.

6A is a sectional view of a semiconductor light emitting device according to a second conventional example, and FIG. 6B shows a problem when the semiconductor light emitting device shown in FIG. 6A is mounted. It is a schematic diagram.

[Explanation of symbols]

Reference Signs List 10: semiconductor substrate, 10a: mesa protrusion, 10b: mesa groove, 11: p-type cladding layer, 11a: slope of side wall by (111) B crystal plane, 12: active layer, 13: first n-type cladding layer, 14 ... operating area, 15 ... current block layer,
16 ... second n-type cladding layer, 17 ... n-type cap layer,
20 ... n electrode, 21 ... AuGe layer, 22 ... Ni layer, 23
... Au layer, 24 ... Ti layer, 25 ... Pt layer, 26 ... Au
Layer, 27: Pt layer, 28: Au layer, 30: p-electrode, 40
... Submount substrate, 41, 43 ... Solder layer, 42, 4
4: Wiring part, 30a, 42a, 44a: Lead, A: P
a laminated film on the n-type cap layer side from the t layer, a ... alloyed film, B ... a film on the solder layer side from the Pt layer, b ... alloyed film,
C: alloying prevention film, D: stress relaxation layer, H: height of step,
I: Element isolation groove.

Claims (13)

[Claims] A substrate having a stripe-shaped mesa projection formed thereon; a first cladding layer of a first conductivity type, an active layer, and a second cladding layer of a second conductivity type formed on the mesa projection; A semiconductor laminate including a first conductivity type current blocking layer formed so as to be in contact with both side surfaces of the active layer across the entire thickness of the active layer in the mesa grooves on both sides of the mesa protrusion; A first electrode formed on an upper layer of the semiconductor laminate; and a second electrode formed on a back surface of the substrate, wherein a step caused by a height of the mesa protrusion is formed on a surface of the semiconductor laminate. Wherein the first electrode includes an alloying prevention film. 2. The semiconductor device according to claim 1, wherein the semiconductor laser is mounted from a side of the first electrode toward a mounting surface on which the semiconductor laser is mounted.
4. The semiconductor laser according to claim 1. 3. The method according to claim 1, wherein the first electrode comprises a two-layer alloying prevention film,
2. The semiconductor laser according to claim 1, further comprising: a stress relaxation layer formed between the two layers of the alloying prevention film and made of a material softer than the two layers of the alloying prevention film. 4. The semiconductor laser according to claim 3, wherein said alloying prevention film contains platinum. 5. The semiconductor laser according to claim 3, wherein said stress relaxation layer contains at least gold or indium. 6. The semiconductor laser according to claim 3, wherein the first electrode has a layer that alloys with the semiconductor laminate on the semiconductor laminate side of the two-layer alloying prevention film. 7. The semiconductor device is used by being mounted via solder from the first electrode side toward a mounting surface on which the semiconductor laser is mounted, wherein the first electrode is provided on the solder side of the two-layer alloying prevention film. 4. The semiconductor laser according to claim 3, further comprising a layer alloyed with the solder. 8. The substrate according to claim 1, wherein a main surface of the substrate is a (100) plane, and a side surface of the stripe-shaped mesa projection is a gentle curved surface convex toward a base side of the substrate. Semiconductor laser. 9. The semiconductor according to claim 1, wherein the current block layer is formed such that a contact surface between the current block layer and the active layer is linear along a longitudinal direction of the mesa protrusion. laser. 10. The semiconductor laser according to claim 9, wherein said linear film-forming portion of said current block layer comprises a {311} crystal plane. 11. The semiconductor laser according to claim 1, wherein a plurality of semiconductor laminations separated from each other are formed on said substrate, and a plurality of laser elements are mounted. 12. A semiconductor device, comprising: a semiconductor layer having a step formed on a surface thereof; and an electrode formed on an upper layer of the semiconductor layer, wherein the semiconductor device is mounted on the surface of the semiconductor device. A semiconductor device which is mounted and used, wherein the electrode includes an alloying prevention film. 13. An electrode according to claim 13, wherein said electrode comprises a two-layered alloying prevention film and a stress relaxation layer formed between said two-layered alloying prevention film and made of a material softer than said two-layered alloying prevention film. 13. The semiconductor device according to claim 12, comprising: