Semiconductor laser element and semiconductor laser device

A semiconductor laser element is provided which includes a first semiconductor layer, an active layer having a current injection region, a second semiconductor layer, a third semiconductor layer, and an electrode for injecting a current into the active layer. In the semiconductor laser element, the first semiconductor layer, the active layer, the second semiconductor layer, and the third semiconductor layer are laminated in that order on a substrate, the first semiconductor layer has a current constriction layer which constricts the current injection region of the active layer, the third semiconductor layer is formed on an upper surface of the second semiconductor layer in a region corresponding to the current injection region of the active layer, and the electrode is formed on the upper surface of the second semiconductor layer in a region other than that of the third semiconductor layer.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. JP 2009-011989 filed in the Japanese Patent Office on Jan. 22, 2009, the entire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor laser element and a semiconductor laser device which includes a support member and the semiconductor laser element mounted thereon.

2. Description of the Related Art

Heretofore, in a semiconductor laser, a ridge for current constriction is formed at an upper portion of a p-type semiconductor layer to increase a current injection efficiency into an active layer.

SUMMARY OF THE INVENTION

However, since the p-side electrode and the p-type semiconductor layer are in contact with each other in a limited area of only an upper portion of the ridge, there has been a problem in that an operation voltage is increased due to an increase in series resistance.

Accordingly, a technique has been proposed in which in a nitride semiconductor laser, a current constriction layer is provided in an n-type semiconductor layer without forming a ridge, and thereby the contact area between a p-side electrode and a p-type semiconductor layer is increased (for example, see Japanese Unexamined Patent Application Publication No. 2003-8145). However, according to the structure of the nitride semiconductor laser described above, penetration of the optical field into the p-type semiconductor layer, which causes free carrier absorption, disadvantageously occurs, and in order to reduce the light absorption loss, the above technique is preferably further improved.

In consideration of the above problems, it is desirable to provide a semiconductor laser element which can reduce the series resistance and a semiconductor laser device including the above semiconductor laser element.

According to an embodiment of the present invention, there is provided a semiconductor laser element which includes: a first semiconductor layer; an active layer having a current injection region; a second semiconductor layer; a third semiconductor layer; and an electrode for injecting a current into the active layer. In the semiconductor laser element described above, the first semiconductor layer, the active layer, the second semiconductor layer, and the third semiconductor layer are laminated in that order on a substrate, the first semiconductor layer has a current constriction layer which constricts the current injection region of the active layer, the third semiconductor layer is formed on an upper surface of the second semiconductor layer in a region corresponding to the current injection region of the active layer, and the electrode is formed on the upper surface of the second semiconductor layer in a region other than that of the third semiconductor layer.

According to an embodiment of the present invention, there is provided a semiconductor laser device which includes a semiconductor laser element and a support member, and this semiconductor laser element is the above-described semiconductor laser element according to an embodiment of the present invention.

In the semiconductor laser element or the semiconductor laser device according to an embodiment of the present invention, since the current constriction layer is provided in the first semiconductor layer, when a predetermined voltage is applied between a pair of electrodes, the current constriction occurs by the current constriction layer, and current is injected into the current injection region of the active layer, so that light emission occurs by electron-hole recombination. Since the third semiconductor layer is formed on the upper surface of the second semiconductor layer in the region corresponding to the current injection region of the active layer, and the electrode is formed in the region other than that described above, the contact area between the electrode and the second semiconductor layer is increased, and as a result, the series resistance can be reduced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The description will be made in the following order.

1. First embodiment (example in which a third semiconductor layer is directly bonded to a submount).

2. Second embodiment (example in which a metal film is formed on the third semiconductor layer).

3. Third embodiment (example in which the third semiconductor layer has a laminate structure including an n-type layer and a non-doped layer).

4. Fourth embodiment (example in which a dielectric multilayer film is formed on the third semiconductor layer).

6. Application example

FIG. 1is a cross-sectional view showing the structure of a semiconductor laser element1according to a first embodiment of the present invention. This semiconductor laser element1is used for a laser display or a laser irradiation apparatus, such as a laser machining apparatus, and has a first semiconductor layer20, an active layer30, a second semiconductor layer40, and a third semiconductor layer50, which are provided in that order on a substrate10made of n-type GaAs.

The first semiconductor layer20has, for example, a current constriction layer21, an n-type clad layer22, and an n-side guide layer23in that order from a side of the substrate10.

The current constriction layer21is a layer to constrict a current injection region30A of the active layer30, has a thickness of approximately 0.1 μm, and is formed of p-type GaAs doped with a p-type impurity such as zinc (Zn). The current constriction layer21has an opening portion21A corresponding to the current injection region30A and is configured so that a current passing through the opening portion21A is injected into the current injection region30A. In addition, this semiconductor laser element1is a so-called broad-area semiconductor laser in which the width of the opening portion21A is, for example, 10 μm or more and is typically 20 to 400 μm.

The n-type clad layer22has a thickness, for example, of 1 μm and is formed of an n-type AlInP mixed crystal doped with an n-type impurity, such as silicon (Si). The n-side guide layer23has a thickness, for example, of 0.1 μm and is formed of a non-doped AlGaInP mixed crystal.

The active layer30has a thickness, for example, of 10 nm and is formed of a non-doped GaInP mixed crystal. In this active layer30, a region facing the opening portion21A of the current constriction layer21is used as the current injection region (light emission region)30A.

The second semiconductor layer40has, for example, a p-side guide layer41, a p-type clad layer42, and a p-side contact layer43in that order from the substrate10side.

The p-side guide layer41has a thickness, for example, of 0.1 μm and is formed of a non-doped AlGaInP mixed crystal. The p-type clad layer42has a thickness, for example, of 0.3 μm and is formed of a p-type AlInP mixed crystal doped with a p-type impurity such as magnesium (Mg). The p-side contact layer43has a thickness, for example, of 0.1 μm and is formed of p-type GaAs heavily doped with a p-type impurity such as zinc (Zn). In addition, between the p-type clad layer42and the p-side contact layer43, an etching stopper layer (not shown) and an interlayer (not shown) may be provided. The etching stopper layer may be formed, for example, of a GaInP mixed crystal doped with a p-type impurity such as magnesium (Mg). The interlayer may be formed, for example, of a p-type GaInP mixed crystal doped with a p-type impurity such as magnesium (Mg).

The third semiconductor layer50has a belt shape and is formed on an upper surface of the second semiconductor layer40in a region corresponding to the current injection region30A of the active layer30. In a region on the upper surface of the second semiconductor layer40other than that of the third semiconductor layer50, a p-side electrode61for injecting a current into the active layer30is formed. Accordingly, in this semiconductor laser element1, the series resistance can be reduced.

The third semiconductor layer50has a thickness, for example, of 0.7 μm and is formed of an AlInp mixed crystal. In addition, the p-side contact layer43described above is formed on an upper surface of the p-type clad layer in a region other than that of the third semiconductor layer50.

The conduction type of the third semiconductor layer50may be a p type by addition of a p-type impurity, such as magnesium (Mg), may be an n type by addition of an n-type impurity, such as silicon (Si), or may be a non-doped type. The reason for this is that current is not injected into the third semiconductor layer50, but only light is confined therein. In particular, the conduction type of the third semiconductor layer50is preferably a non-doped type. The reason for this is that since the free carrier absorption caused by carriers of the p-type clad layer is reduced, and the optical loss is reduced, the energy conversion efficiency of laser can be improved, and in particular, the output of a high output laser can be significantly effectively increased.

The p-side electrode61is formed by lamination, for example, of titanium (Ti), platinum (Pt), and gold (Au) in that order from a side of the second semiconductor layer40and is electrically connected to the p-side contact layer43.

On the other hand, on the rear surface of the substrate10, an n-side electrode62for injecting a current into the active layer30is formed. The n-side electrode62has a lamination structure formed, for example, of an alloy of gold (Au) and germanium (Ge), nickel (Ni), and gold (Au) in that order from the substrate10side and is electrically connected thereto.

Furthermore, in this semiconductor laser element1, for example, two side surfaces of the third semiconductor layer50located in a longitudinal direction face each other and are used as a pair of resonator end surfaces, and a pair of reflection mirror films (not shown) is formed on the pair of resonator end surfaces. The reflectance of one reflection mirror film is adjusted to decrease, and the reflectance of the other reflection mirror film is adjusted to increase. Accordingly, it is configured that light generated in the active layer30is amplified when reciprocating between the pair of reflection mirror films and is then emitted as laser beams from one reflection mirror film. That is, this semiconductor laser element1is an edge emitting laser in which light generated from the active layer30is emitted in a direction perpendicular to the lamination direction of the first semiconductor layer20, the active layer30, the second semiconductor layer40, and the third semiconductor layer50.

FIG. 2is a schematic perspective view showing the structure of a semiconductor laser array2including a plurality of semiconductor laser elements1. In this semiconductor laser array2, the semiconductor laser elements1are monolithically formed on a common substrate10so as to obtain an optical output on the order of watt.

In the semiconductor laser array2, a thermal interaction is liable to occur between adjacent emitters (each corresponding to one semiconductor laser element1), and hence the emitter distance is preferably set to approximately 400 μm. Accordingly, when the optical output from one emitter increases, the number of emitters can be reduced, and as a result, an optical element which is optically coupled with the semiconductor laser array2can be miniaturized, and/or the number of optical elements can be reduced.

FIG. 3is a schematic perspective view sowing the structure of a semiconductor laser device3including the semiconductor laser array2. This semiconductor laser device3is used, for example, for laser display, laser machining, or medical application. The semiconductor laser array2is bonded, for example, to a submount70made of SiC or the like having a high thermal conductivity with a solder layer71interposed therebetween. The submount70is bonded to a metal-made heat sink80with a solder layer72(not shown inFIG. 3, and seeFIG. 4) interposed therebetween. The semiconductor laser array2may also be directly bonded to the heat sink80with the solder layer71without using the submount70. In this embodiment, the submount70or the heat sink80corresponds to one particular example of a “support member” according to an embodiment of the present invention.

An electrode member81electrically connected to the n-side electrodes62with wires85interposed therebetween is provided at a side opposite to a light emission side of the semiconductor laser array2. This electrode member81is fixed on an insulating plate83with screws82, and this insulating plate83separates the heat sink80from the electrode member81for the insulation purpose. A protective member84protecting the wires85from the outside is fixed on the electrode member81with a screw82.

The semiconductor laser array2is bonded, for example, to the submount70in a junction down manner as shown inFIG. 4. The third semiconductor layers50of the individual semiconductor laser elements1are bonded to the submount70with the solder layer71interposed therebetween. Accordingly, heat from the p-type clad layer42and the third semiconductor layer50can be efficiently removed, and a decrease in energy conversion efficiency caused by heat can be suppressed.

For example, this semiconductor laser element1can be manufactured as described below.

First, as shown inFIG. 5, the substrate10which is formed from the aforementioned material is prepared, and the current constriction layer21is formed in an upper surface of this substrate10, for example, by diffusion or ion implantation of zinc (Zn). In particular, ion implantation is preferable since the current constriction layer21can be easily formed.

Next, as shown inFIG. 6, the n-type clad layer22, the n-side guide layer23, the active layer30, the p-side guide layer41, the p-type clad layer42, and a solid third semiconductor layer film50, each of which is formed of the aforementioned material and has the aforementioned thickness, are laminated in that order, for example, by a metal organic chemical vapor deposition (MOCVD) method. In this step, as starting materials for compound semiconductors, for example, trimethylaluminum (TMAl), trimethylgallium (TMGa), trimethylindium (TMIn), phosphine (PH3), and arsine (AsH3) are used; as starting materials for donor impurities, for example, monosilane (SiN4) is used; and as starting materials for acceptor impurities, for example, bis(cyclopentadienyl) magnesium (Cp2Mg) and dimethylzinc (DMZn) are used.

Subsequently, as shown inFIG. 7, the solid third semiconductor layer film50is processed by etching or the like to form the third semiconductor layer150having a belt shape on the upper surface of the second semiconductor layer40in the region corresponding to the current injection region30A of the active layer30. Next, also as shown inFIG. 7, a selective growth mask91made of SiO2is formed on an upper surface and side surfaces of the third semiconductor layer50, for example, by a CVD method, and the p-side contact layer43made of the aforementioned material and having the aforementioned thickness is formed.

After the p-side contact layer43is formed, as shown inFIG. 8, the selective growth mask91is etched off, and for example, by deposition, the p-side electrode61made of the aforementioned material is formed on the upper surface of the second semiconductor layer40in the region other than that of the third semiconductor layer50.

In addition, after the rear surface side of the substrate10is processed, for example, by lapping and polishing to decrease the thickness of the substrate10to approximately 100 μm, the n-side electrode62is formed on the rear surface of the substrate10. Subsequently, the substrate10is shaped to have a predetermined size, and the reflection mirror films (not shown) are then formed on the pair of resonator end surfaces which face each other. As a result, the semiconductor laser element1shown inFIG. 1is obtained.

In this semiconductor laser element1, when a predetermined voltage is applied between the n-side electrode62and the p-side electrode61, a current is injected into the active layer30, and light emission occurs by electron-hole recombination. The light thus emitted reflects between the pair of reflection mirror films and reciprocates therebetween to generate laser oscillation, and as a result, laser beams are emitted outside. In this embodiment, since the current constriction layer21is provided in the first semiconductor layer20, the current constriction is performed by this current constriction layer21, and hence a current is injected into the current injection region30A of the active layer30. In addition, since the third semiconductor layer50is formed on the upper surface of the second semiconductor layer40in the region corresponding to the current injection region30A of the active layer30, and the p-side electrode61is formed in the region other than that described above, the contact area between the p-side electrode61and the second semiconductor layer40is increased, and hence the series resistance can be reduced.

In this embodiment, as described above, the current constriction layer21is provided in the first semiconductor layer20, the third semiconductor layer50is formed on the upper surface of the second semiconductor layer40in the region corresponding to the current injection region30A of the active layer30, and the p-side electrode61is formed in the region other than that described above; hence, the series resistance can be reduced, and an increase in operation voltage can be suppressed. In addition, since the energy conversion efficiency of laser can be improved, the reliability can be improved, the control range of operation temperature can be increased, and a high temperature operation can be performed.

FIG. 9is a cross-sectional view showing the structure of a semiconductor laser element1A according to a second embodiment of the present invention. In this embodiment, except that a metal film51is formed on the third semiconductor layer50, this semiconductor laser element1A can be formed in a manner similar to that of the first embodiment so as to have similar structure, performances, and advantages to those of the first embodiment.

The metal film51is formed of the same material as that of the p-side electrode61and can be formed by the same process as that for the p-side electrode61. Since the metal film51is formed on the third semiconductor layer50, bonding characteristics to the solder layer71are improved, and hence heat can be effectively removed.

In this case, the conduction type of the third semiconductor layer50is preferably an n type or a non-doped type. The reason for this is that a Schottky barrier between the p-side electrode61and the third semiconductor layer50can be increased so as to prevent a current from flowing into the third semiconductor layer50. In particular, the conduction type of the third semiconductor layer50is preferably a non-doped type. The reason for this is that since the free carrier absorption caused by carriers of the p-type clad layer is reduced, and the optical loss is reduced, the energy conversion efficiency of laser can be improved, and in particular, the output of a high output laser can be significantly effectively increased.

FIG. 10is a cross-sectional view showing the structure of a semiconductor laser element1B according to a third embodiment of the present invention. In this embodiment, except that the third semiconductor layer50is formed to have a lamination structure of an n-type layer52A and a non-doped layer52B, this semiconductor laser element1B can be formed in a manner similar to that of the first embodiment so as to have similar structure, performances, and advantages to those of the first embodiment.

The n-type layer52A forms a pn junction with the p-type clad layer42and suppresses diffusion of carriers to the non-doped layer52B. In addition, the n-type layer52A is formed, for example, of an AlInP mixed crystal doped with an n-type impurity, such as silicon (Si), and has a thickness of 0.1 μm. The non-doped layer52B is formed, for example, of a non-doped AlInP mixed crystal having a thickness of 0.6 μm. When the third semiconductor layer50is formed to have a lamination structure of the n-type layer52A and the non-doped layer52B, the free carrier absorption in the non-doped layer52B can be reliably suppressed.

FIG. 11is a schematic cross-sectional view showing the structure of a semiconductor laser element1C according to a fourth embodiment of the present invention. In this embodiment, except that light absorption caused at the solder layer71is reduced by forming a dielectric multilayer film53on the third semiconductor layer50, this semiconductor laser element1C can be formed in a manner similar to that of the first embodiment so as to have similar structure, performances, and advantages to those of the first embodiment.

FIG. 12is a schematic cross-sectional view showing the structure of a semiconductor laser element1D according to a fifth embodiment of the present invention. This semiconductor laser element1D is a surface emitting laser which includes a first semiconductor layer120, an active layer130, a second semiconductor layer140, and a third semiconductor layer150provided in that order on a substrate110made of n-type GaAs.

The first semiconductor layer120has an n-side distributed Bragg reflector (DBR) layer121, a current constriction layer122, and an n-side guide layer123. The n-side DBR layer121has a multilayer structure formed, for example, of an n-type AlGaAs mixed crystal. The current constriction layer122has a low resistance region122A of aluminum arsenide (AlAs) and a high resistance region122B of oxidized aluminum arsenide provided around the low resistance region122A and is configured so that a current is constricted only by the low resistance region122A. The n-side guide layer123is formed, for example, of an n-type AlGaAs mixed crystal.

The active layer130is formed, for example, of GaAs doped with no impurity, and a region of the active layer130corresponding to the low resistance region122A is a light emission region (current injection region)130A.

The second semiconductor layer140has a p-side guide layer141. The p-side guide layer141is formed, for example, of a p-type AlGaAs mixed crystal.

The third semiconductor layer150is a DBR layer having a multilayer structure formed, for example, of an AlGaAs mixed crystal. The third semiconductor layer150is formed on an upper surface of the second semiconductor layer140in a region corresponding to the current injection region130A of the active layer130to have a cylindrical shape and is configured so that light generated in the active layer130is emitted in a direction perpendicular to an upper surface of the third semiconductor layer150. A p-side electrode161for injecting a current into the active layer130is formed on the upper surface of the second semiconductor layer140in a region other than that of the third semiconductor layer150. Accordingly, in this semiconductor laser element1D, the series resistance can be reduced.

The conduction type of the third semiconductor layer150may be a p type by addition of a p-type impurity, such as magnesium (Mg), may be an n type by addition of an n-type impurity, such as silicon (Si), or may be a non-doped type. The reason for this is that current is not injected into the third semiconductor layer150, but only light is reflected thereby. In particular, the conduction type of the third semiconductor layer150is preferably a non-doped type. The reason for this is that since the free carrier absorption caused by carriers of a p-type DBR layer is reduced, and the optical loss is reduced, the energy conversion efficiency of laser can be improved, and in particular, the output of a high output laser can be significantly effectively increased.

The p-side electrode161is formed by lamination, for example, of titanium (Ti), platinum (Pt), and gold (Au) in that order from a side of the second semiconductor layer140and is electrically connected to the p-side guide layer141.

On the rear surface of the substrate110, an n-side electrode162for injecting a current into the active layer130is formed. The n-side electrode162has a lamination structure formed, for example, of an alloy of gold (Au) and germanium (Ge), nickel (Ni), and gold (Au) in that order from a side of the substrate110and is electrically connected thereto.

For example, this semiconductor laser element1D can be formed as described below.

First, the n-side DBR layer121, an aluminum arsenide layer122C to be formed into the current constriction layer122, the n-side guide layer123, the active layer130, the p-side guide layer141, and a solid third semiconductor layer film150are formed in that order on the substrate110made of the aforementioned material by crystal growth or the like.

Next, the solid third semiconductor layer film150is processed by etching or the like to form the third semiconductor layer150having a cylindrical shape on the upper surface of the second semiconductor layer140in the region corresponding to the current injection region130A of the active layer130.

Subsequently, the p-side guide layer141, the active layer130, the n-side guide layer123, the aluminum arsenide layer122, and the n-side DBR layer121are selectively removed, for example, by etching, so that a mesa portion (not shown) is formed.

Subsequently, the aluminum arsenide layer122C exposed at side surfaces of the mesa portion (not shown) is oxidized, for example, by heating in a water vapor atmosphere. Since the oxidation annularly proceeds from the periphery to the center of the aluminum arsenide layer122C, when the oxidation is stopped at an appropriate timing, the annular high resistance region122B is formed, and the central portion which is not oxidized functions as the low resistance region122A. As a result, the current constriction layer122having the low resistance region122A and the high resistance region122B is formed.

After the current constriction layer122is formed, the p-side electrode161is formed on the upper surface of the second semiconductor layer140in the region other than that of the third semiconductor layer150, and the n-side electrode162is formed on the rear side of the substrate110. Accordingly, the semiconductor laser element1D shown inFIG. 12is obtained.

In this semiconductor laser element1D, when a predetermined voltage is applied between the n-side electrode162and the p-side electrode161, a drive current supplied from the n-side electrode162is constricted by the current constriction layer122and is then injected into the active layer130, and as a result, light emission occurs by electron-hole recombination. The light thus emitted reflects at the n-side DBR layer121and the third semiconductor layer150and reciprocates therebetween to generate laser oscillation, and as a result, laser beams are emitted outside from the upper surface of the third semiconductor layer150.

In a related surface emitting laser, since a p-type DBR layer is a high resistance region, there has been a serious problem in that a high speed device operation is difficult to perform. However, in this embodiment, since the third semiconductor layer150is formed on the upper surface of the second semiconductor layer140in the region corresponding to the current injection region130A of the active layer130, and the p-side electrode161is formed in the region other than that described above, no current flows through the third semiconductor layer150, but only reflection of light is performed thereby. Hence, the semiconductor laser element1D only has a significantly low series resistance component, and as a result, a high speed operation can be performed.

As described above, in this embodiment, since the third semiconductor layer150is formed on the upper surface of the second semiconductor layer140in the region corresponding to the current injection region130A of the active layer130, and the p-side electrode161is formed in the region other than that described above, no current flows through the third semiconductor layer150, the series resistance can be reduced, and a high speed operation can be performed.

The semiconductor laser array2and the semiconductor laser device3shown inFIGS. 2 and 4, respectively, are each mounted in a module (not shown) in a nitrogen atmosphere, whenever necessary, and are each used as a light source of a laser display or a laser irradiation apparatus. For example, in the laser display, laser light emitted from the module is collimated by a lens or the like, is spatially modulated by an optical element in accordance with two-dimensional image information, and is then radiated on a screen. As the optical element, for example, a liquid crystal or an optical micro electro mechanical system (MEMS), such as a digital light processing (DLP) system or grating light valve (GLV) system, may be used.

FIG. 13is a view showing an application example in which the broad-area semiconductor laser array2according to the embodiment of the present invention is applied to a laser display apparatus200. This laser display apparatus200includes light sources201a,201b, and201cemitting light beams, red (R), green (G), and blue (B), respectively, and as the light source201aemitting a red color, the semiconductor laser array2according to this embodiment is disposed. This laser display apparatus200further includes beam forming optical systems202a,202b, and202c, and liquid crystal panels203a,203b, and203c, which are provided to the light sources201a,201b, and201c, respectively; a cross prism204; a projection205; and a projection screen206.

In this laser display apparatus200, after light beams emitted from the light sources201a,201b, and201cof RGB colors pass through the beam forming optical systems202a,202b, and202c, respectively, the light beams are incident on the respective liquid crystal panels203a,203b, and203cand are spatially modulated to image information of RGB. Subsequently, the image information of RGB is synthesized by the cross prism204and is then projected on the projection screen206through the projection205.

FIG. 14is a schematic perspective view showing one application example in which the semiconductor laser device3according to the embodiment of the present invention is applied to a light source of a laser machining apparatus which is one example of the laser irradiation apparatus. In a laser irradiation apparatus300of this embodiment, laser light beams304emitted from a light source301are combined together at the surface of a workpiece303through an optical system302, so that machining is performed. Since the near field pattern (NFP) of a broad-area semiconductor laser having a large-width ridge is a rectangular shape, the beam pattern combined at the surface of the workpiece303also has a rectangular shape. Hence, in the case of machining of a rectangular and/or a line shape, the beam use efficiency is increased. In addition, this laser irradiation apparatus300may also applied to surface modification and inspection as well as to laser machining.

Heretofore, although the present invention has been described with reference to the embodiments, the present invention is not limited thereto and may be variously modified. For example, the materials and thicknesses of the individual layers described in the above embodiments, or the film forming methods and film forming conditions described above are not limited, and other materials and thicknesses, or other film forming methods and film forming conditions may also be used.

In addition, in the above embodiments, although the structures of the semiconductor laser element1, the semiconductor laser array2, and the semiconductor laser device3are particularly described, some of the layers described above may not be formed in some cases, and/or another layer may be further formed.

In addition, in the above embodiments, although the present invention has been described using an AlGaInP-based compound semiconductor laser by way of example, the present invention may also be applied to other compound semiconductor lasers, and as the other compound semiconductor lasers, for example, there may be mentioned an infrared semiconductor laser, such as a GaInAsP-based laser; a gallium nitride semiconductor laser, such as a GaInN-based or a AlGaInN-based laser; and a II-VI semiconductor laser including at least two of Be, Zn, Mg, Cd, S, Se, and Te in combination. In addition, the present invention may also be applied to a semiconductor laser, such as an AlGaAs-based, an InGaAs-based, an InP-based, and a GaInAsNP-based laser, in which the oscillation wavelength is not limited in a visible band. In particular, since the conduction type of the third semiconductor layer50can be made an n type or a non-doped type, when the present invention is applied to a material system in which a p type conduction is difficult to obtain (such as a II-VI compound semiconductor), the third semiconductor layer50may be used as an optical waveguide structure which is not relating to the current injection, and hence the present invention may be applied, for example, to a green laser technique.

In addition, in the embodiments and the like described above, the present invention has been described using a semiconductor laser having an index guide structure by way of example; however, the present invention is not limited thereto and may also be applied to a semiconductor laser having another structure, such as a gain guide structure.