Patent Publication Number: US-7907651-B2

Title: Laser diode

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This present application is a Continuation Application of the patent application Ser. No. 11/123,168, filed May 6, 2005, which claims priority from Japanese Patent Applications JP 2004-142187 filed in the Japanese Patent Office on May 12, 2004, the entire contents of which being incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a laser diode such as a broad area type laser diode. 
     2. Description of the Related Art 
     An LD (laser diode) is not only used as a light source in an optical disk device such as a CD (Compact Disk) and a DVD (Digital Versatile Disk), but also applied to various fields such as a display, a printing product, fabricating materials, and medical care. In these application fields, high output is often desirable, and therefore, a high power laser diode is increasingly aspired. 
     As one method to improve output, in the case of a laser diode having a stripe-shape light emitting region, it is effective to widen a width of the light emitting region, that is, a stripe width. For example, in a laser diode for an optical disk, a typical value of the stripe width is about 2 μm to 3 μm. Meanwhile, of the laser diodes developed for high output use, a laser diode whose stripe width is widened to 50 μm to 100 μm has been introduced. The laser diode whose stripe width is widened as above is referred to as a broad area type laser diode. A specific numerical value of the stripe width, being a standard for the “broad area type” laser diode herein described has not been determined. However, in this specification, for example, the stripe width thereof shall be about 10 μm or more. 
     SUMMARY OF THE INVENTION 
     In general, a laser diode is susceptible to light returned to the laser itself reflected by an optical system or an illumination target after emission, that is, feedback light. When being affected by the feedback light, laser oscillation becomes unstable, which is undesirable in practice. In addition, in some cases, the laser may become deteriorated or get out of order. 
     Such effects of the feedback light have similarly become disadvantages in the case of the foregoing broad area type laser diode. Since the broad area type laser diode further includes characteristics of high power, it is difficult to inhibit effects of feedback light by utilizing an external device such as an isolator and a wavelength plate, and therefore, such disadvantages are more serious in the broad area type laser diode. 
     For example, Japanese Unexamined Patent Application Publication No. 2000-252583, as a laser diode used as a harmonic light source and the like, a laser diode, in which effects of feedback light from an exterior resonator are eliminated by narrowing a stripe width on the opposite side of a laser beam emitting side in the shape of a taper has been suggested. 
     In view of the foregoing, it is desirable to provide a laser diode capable of effectively inhibiting effects of feedback light. 
     According to an embodiment of the invention, there is provided a laser diode including a substrate and a laminated structure including a first conductive semiconductor layer, an active layer having a light emitting region, and a second conductive semiconductor layer having a projecting part on the surface thereof on the substrate, wherein a feedback light inhibition part is provided on a main-emitting-side end face, and effects of feedback light in the vicinity of lateral boundaries of the light emitting region are inhibited by the feedback light inhibition part. Here, “lateral boundary of the light emitting region” means a boundary between the light emitting region and a non light emitting region other than the light emitting region in the active layer. The laser diode is applicable to the following embodiments in particular. 
     As a first embodiment, a notch part can be provided at least in one corner of a projecting part in a main-emitting-side end face as the feedback light inhibition part. 
     As a second embodiment, a reflector film is included in a main-emitting-side end face as the feedback light inhibition part, and in the reflector film, laser light reflectance to the vicinity of a lateral center of a light emitting region is higher than laser light reflectance to the vicinity of lateral boundaries of the light emitting region. 
     As a third embodiment, two groove-like concave parts extending in the same direction are provided on the surface of a second conductive semiconductor layer as the feedback light inhibition part, and a width of the two groove-like concave parts in the vicinity of a main-emitting-side end face is larger than a width thereof in the vicinity of the center between the main-emitting-side end face and an opposite-side end face. 
     As a fourth embodiment, in a main-emitting-side end face, a normal end face, which includes vicinity of a lateral center of a light emitting region and is parallel to an opposite-side end face, and an inclined plane, which includes vicinity of a lateral boundary of the light emitting region and is inclined to the normal end face are provided as the feedback light inhibition part. 
     As a fifth embodiment, an impurity-doped region is provided at least in one corner of a main-emitting-side end face as the feedback light inhibition part, and the impurity-doped region includes a corner of a projecting part in the main-emitting-side end face. 
     In this specification, “lateral” means the direction perpendicular to both the extension direction (resonator direction) of the projecting part and the direction, in which the semiconductor layers including the active layer are laminated on the substrate (lamination direction). “Width” means a dimension in the lateral direction. “Length” means a dimension in the resonator direction. “Thickness” or “depth” means a dimension in the lamination direction. The lamination direction and the resonator direction are perpendicular to each other. 
     According to an embodiment of the invention, the feedback light inhibition part is provided in the main-emitting-side end face, and effects of feedback light in the vicinity of the lateral boundaries of the light emitting region are inhibited by the feedback light inhibition part. Therefore, even if the feedback light approaches or enters in the vicinity of the lateral boundaries of the light emitting region, the effects thereof can be inhibited. Consequently, the effects of feedback light can be effectively inhibited, and reliability can be improved. 
     In the first embodiment, the notch part is provided in the main-emitting-side end face as the feedback light inhibition part. Therefore, light emitting is not generated in the vicinity of the lateral boundary of the light emitting region. Consequently, even if feedback light approaches or enters, the effects thereof can be inhibited. 
     In the second embodiment, the reflector film is provided in the main-emitting-side end face as the feedback light inhibition part, and in the reflector film, the laser light reflectance to the vicinity of the lateral center of the light emitting region is set higher than the laser light reflectance to the vicinity of the lateral boundaries. Therefore, a light intensity distribution in the light emitting region is not uniform over the whole lateral region, but can be larger in the vicinity of the center and smaller in the vicinity of the boundaries. Consequently, even if feedback light approaches or enters in the vicinity of the lateral boundaries of the light emitting region, an optical absolute amount coupling (interacting) with the feedback light becomes small, and effects of the feedback light can be effectively inhibited. 
     In the third embodiment, as the feedback light inhibition part, the width of the two groove-like concave parts in the vicinity of the main-emitting-side end face is larger than the width thereof in the vicinity of the center between the main-emitting-side end face and the opposite-side end face. Therefore, even if the width of a structural light emitting region defined by the two groove-like concave parts is uniform, the width of an effective light emitting region in the vicinity of the main-emitting-side end face can be narrowed. Consequently, even if feedback light approaches in the vicinity of the lateral boundaries of the structural light emitting region, the feedback light is hard to enter in the effective light emitting region, and the effects of feedback light can be effectively inhibited. 
     In the fourth embodiment, the inclined plane is provided in the main-emitting-side end face as the feedback light inhibition part. Therefore, even if feedback light approaches in the vicinity of the lateral boundaries of the light emitting region, the feedback light is diagonally reflected by the inclined plane and is hard to enter, and effects of the feedback light can be effectively inhibited. 
     In the fifth embodiment, the impurity-doped region is provided in the main-emitting-side end face as the feedback light inhibition part, and the impurity-doped region includes the corner of the projecting part in the main-emitting-side end face. Therefore, in the impurity-doped region, optical loss can be intentionally generated. Consequently, even if feedback light approaches or enters in the vicinity of the lateral boundaries of the light emitting region, the effects thereof can be inhibited. 
     Other and further objects, features and advantages of the invention will appear more fully from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a construction of a laser diode used in an experiment for examining effects of feedback light on the laser diode; 
         FIG. 2  is a plan view showing a pattern diagram of a shape of a light emitting region of the laser diode shown in  FIG. 1 ; 
         FIG. 3  is a view showing differences of L-I characteristics depending on presence of feedback light and entering positions in the laser diode shown in  FIG. 1 ; 
         FIGS. 4A ,  4 B and  4 C are views showing differences of profiles depending on presence of feedback light and entering positions in the laser diode shown in  FIG. 1 ; 
         FIG. 5  is a perspective view showing a construction of a laser diode according to a first embodiment of the invention; 
         FIG. 6  is a plan view showing a pattern diagram of a shape of a light emitting region of the laser diode shown in  FIG. 5 ; 
         FIGS. 7A and 7B  are perspective views showing the steps of manufacturing the laser diode shown in  FIG. 5 ; 
         FIG. 8  is a perspective view showing a construction of a laser diode according to a second embodiment of the invention; 
         FIG. 9A  is a plan view showing a pattern diagram of a shape of a light emitting region of the laser diode shown in  FIG. 8 ,  FIG. 9B  is a view showing a reflectance distribution in the lateral direction of a main-emitting-side end face, and  FIG. 9C  is a view showing a light power distribution in the lateral direction of the main-emitting-side end face; 
         FIG. 10  is a perspective view showing a construction of a laser diode according to a third embodiment of the invention; 
         FIG. 11A  is a cross section showing a cross section structure taken along line XIA-XIA of  FIG. 10 , and  FIG. 11B  is a cross section showing a cross section structure taken along line XIB-XIB of  FIG. 10 ; 
         FIG. 12A  is a plan view showing a pattern diagram of a position relation between a projecting part and a structural light emitting region of the laser diode shown in  FIG. 10 , and  FIG. 12B  is a plan view showing an effective light emitting region additionally to  FIG. 12A ; 
         FIG. 13  is a perspective view showing a modification of the laser diode shown in  FIG. 10 ; 
         FIG. 14  is a perspective view showing a construction of a laser diode according to a fourth embodiment of the invention; 
         FIG. 15  is a plan view showing a pattern diagram of a shape of a light emitting region of the laser diode shown in  FIG. 14 ; 
         FIG. 16  is a perspective view showing a construction of a laser diode according to a fifth embodiment of the invention and; 
         FIG. 17  is a plan view showing a pattern diagram of a shape of a light emitting region of the laser diode shown in  FIG. 16 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the invention will be hereinafter described in detail with reference to the drawings. 
     Though the following respective embodiments differ from each other in the embodied aspects of each feedback light inhibition part, these embodiments have in common the fact that effects of feedback light approaching or entering particularly in the vicinity of lateral boundaries of a light emitting region is focused attention on and is to be inhibited. Therefore, before descriptions of individual specific embodiments, descriptions will be given of differences of effects depending on entering positions of feedback light as a common assumption forming a basis of the invention based on experimental results. 
     (Experiment) 
     A GaAs broad area type laser diode as shown in  FIG. 1  was fabricated. The broad area type laser diode had a general structure as follows. On a substrate  110 , a laminated structure including an n-type semiconductor layer  120 , an active layer  130  having a light emitting region  131  having a width of 10 μm or more, and a p-type semiconductor layer  140  was provided. On the surface of the p-type semiconductor layer  140 , a projecting part (ridge)  150 , which is extended in the resonator direction A and a buried layer  160  on the both sides thereof were provided. Thicknesses and component materials of the respective layers were commonly used thicknesses and component materials. A planar shape of the light emitting region  131  was a rectangle as a shaded portion shown in  FIG. 2 . A width Wef in a main-emitting-side end face  111  was equal to a width Wer in an opposite-side end face  112  (Wef=Wer). 
     Regarding the obtained broad area laser diode, the case without feedback light (reference example 1), the case, in which feedback light entered in the vicinity of a lateral center  131 A of the light emitting region  131  (reference example 2), and the case, in which feedback light entered in the vicinity of lateral boundaries  131 B and  131 C of the light emitting region  131  (reference example 3) were examined in terms of L-I (light output-current) characteristics and profiles (spatial distributions of light intensity), respectively. The results thereof are shown in  FIGS. 3 ,  4 A,  4 B, and  4 C. 
     (Results) 
     As evidenced by  FIGS. 3 ,  4 A,  4 B, and  4 C, in the case, in which feedback light entered in the vicinity of the lateral center  131 A of the light emitting region  131  (reference example 2), results almost equal to the case without feedback light (reference example 1) were obtained both for the L-I characteristics and the profile. Meanwhile, in the case, in which feedback light entered in the vicinity of the lateral boundaries  131 B and  131 C of the light emitting region  131  (reference example 3), the optical output was lowered down to about half of the optical output of the case without feedback light (reference example 1), and the profile was significantly jumbled and became in the shape of twin peaks. 
     (Analysis of Results) 
     As above, it was found that effects of feedback light on laser oscillation varied according to entering positions of feedback light in the light emitting region  131 , and more major effects were given in the case that feedback light entered in the vicinity of the lateral boundaries  131 B and  131 C, rather than the case that feedback light entered in the vicinity of the lateral center  131 A of the light emitting region  131 . It is thinkable that one of the reasons thereof is as follows. In the vicinity of the lateral boundaries  131 B and  131 C of the light emitting region  131 , in addition to light containment by a laminated structure in the vertical direction (direction perpendicular to the PN junction), light containment by the lateral boundaries  131 B and  131 C in the horizontal direction (direction parallel to the PN junction) also exists. Therefore, the state of a light waveguide differs from in other regions, such as, in the vicinity of the lateral center  131 A. It is thinkable that such difference in structure is related to the fact that disturbance of resonance by feedback light in the vicinity of the lateral boundaries  131 B and  131 C became significant compared to in the vicinity of the lateral center  131 A. 
     That is, it can be expected that, if feedback light is inhibited from approaching or entering in the vicinity of the lateral boundaries  131 B and  131 C of the light emitting region  131  by providing a feedback light inhibition part in the main-emitting-side end face  111 , a laser diode less subject to effects of feedback light is to be realized (first and third to fifth embodiments). Otherwise, it is thinkable that, if an light intensity distribution in the light emitting region  131  in the vicinity of the lateral boundaries  131 B and  131 C is set smaller than in the vicinity of the lateral center  131 A by providing a feedback light inhibition part in the main-emitting-side end face  11 , a probability of coupling (interaction) between feedback light and light inside the light emitting region  131  can be decreased, and a laser diode less subject to effects of feedback light can be obtained (second embodiment). 
     Specific embodiments (first to fifth embodiments) will be hereinafter described based on these experiment results and the analysis thereof. 
     First Embodiment 
       FIG. 5  shows a construction of a laser diode according to the first embodiment of the invention.  FIG. 6  shows a planar shape of a light emitting region (shaded portion) of the laser diode shown in  FIG. 5 . The laser diode has a laminated structure including, for example, an n-type semiconductor layer  20 , an active layer  30 , and a p-type semiconductor layer  40  on a substrate  10 . On the surface of the p-type semiconductor layer  40 , a projecting part  50  for current confinement, which is extended in the resonator direction A is provided and a buried layer  60  is formed on the both sides thereof. 
     Further, in the laser diode, a main-emitting-side end face  11  and an opposite-side end face  12 , which are opposed in the resonator direction A are a pair of resonator end faces. On the main-emitting-side end face  11  and the opposite-side end face  12 , a reflector film (not shown) is formed. The reflector film on the main-emitting-side end face  11  is adjusted to have low reflectance, and the reflector film on the opposite-side end face  12  is adjusted to have high reflectance. Thereby, light generated in the active layer  30  travels between the pair of reflector films to be amplified, and is emitted as laser beams from the reflector film on the main-emitting-side end face  11 . 
     The substrate  10  is, for example, a thin film having a thickness of about 100 μm and made of n-type GaAs, to which an n-type impurity such as silicon (Si) is doped. The n-type semiconductor layer  20  has, for example, a thickness of 3 μm, and has an n-type cladding layer (not shown) made of an n-type AlGaAs mixed crystal, to which an n-type impurity such as silicon is doped. 
     The active layer  30  has, for example, a thickness of 30 nm, and is made of an AlGaAs mixed crystal, to which no impurity is doped. A central part of the active layer  30  is a light emitting region  31 , in which light emitting is generated by current injection through the projecting part  50 . A width Wem of the light emitting region  31  in the vicinity of the center between the main-emitting-side end face  11  and the opposite-side end face  12  (hereinafter referred to as “width Wem”) is, for example, 10 μm or more. That is, this laser diode is a broad area type laser diode. 
     The p-type semiconductor layer  40  has a construction, in which, for example, a p-type cladding layer and a p-side contact layer (not shown either) are sequentially laminated from the substrate  10  side. The p-type cladding layer has, for example, a thickness of 2 μm, and is made of a p AlGaAs mixed crystal, to which a p-type impurity such as zinc (Zn) is doped. The p-side contact layer has, for example, a thickness of 1 μm, and is made of p GaAs, to which a p-type impurity such as zinc (Zn) is doped. 
     In a pair of corners of the projecting part  50  in the main-emitting-side end face  11 , notch parts  51  are provided. Thereby, in the laser diode, a width Wef of the light emitting region  31  in the vicinity of the main-emitting-side end face  11  and the width Wem of the light emitting region  31  in the vicinity of the center between the main-emitting-side end face  11  and the opposite-side end face  12  satisfy a relation of Wef&lt;Wem. Therefore, in the vicinity of lateral boundaries  31 B and  31 C of the light emitting region  31 , light emitting is not generated, and even if feedback light approaches or enters, the effects thereof can be inhibited. The notch  51  corresponds to one specific example of the feedback light inhibition parts in the invention. 
     A width Waf of the notch part  51  is preferably, for example, 1% to 20% of a width Wrm of the projecting part  50  in the vicinity of the center between the main-emitting-side end face  11  and the opposite-side end face  12 . When this value is too large, an effective width of the resonator becomes small (narrow), and therefore, sufficient output may not be obtained. A length Laf of the notch part  51  is preferably, for example, 0.1% to 20% of a length L of the projecting part  50  in the resonator direction A. 
     A shape of the notch part  51  is not limited to the step-like shape as shown in  FIG. 5 , but may be a tapered shape or a curved shape. 
     The buried layer  60  is made of, for example, n-type GaAs. 
     On the p-type semiconductor layer  40  and the buried layer  60 , a p-side electrode (not shown) is provided. The p-side electrode has a structure, in which, for example, a titanium (Ti) layer, a platinum (Pt) layer, and a gold (Au) layer are sequentially laminated from the p-type semiconductor layer  40  side, and the lamination is alloyed by heat treatment. The p-side electrode is electrically connected to the p-type semiconductor layer  40 . Meanwhile, on the rear face side of the substrate  10 , an n-side electrode (not shown) is formed. The n-side electrode has a structure, in which, for example, an alloy layer of gold and germanium (Ga), a nickel (Ni) layer, and a gold (Au) layer are sequentially laminated from the substrate  10  side, and the lamination is alloyed by heat treatment. The n-side electrode is electrically connected to the n-type semiconductor layer  20  with the substrate  10  inbetween. 
     This laser diode can be manufactured, for example, as follows. 
       FIGS. 7A and 7B  show a method of manufacturing the laser diode in the order of steps. First, as shown in  FIG. 7A , for example, over the substrate  10  made of the foregoing material, the n-type semiconductor layer  20 , the active layer  30 , and the p-type semiconductor layer  40  having the foregoing thicknesses and materials are sequentially laminated by MOCVD (Metal Organic Chemical Vapor Deposition) method. 
     Next, as shown in  FIG. 7A  similarly, for example, on the p-type semiconductor layer  40 , a resist film (not shown) is formed, and a mask layer  71  to form the projecting part  51  is formed by, for example, lithography technique. 
     Subsequently, as shown in  FIG. 7B , part of the p-type semiconductor layer  40  in the thickness direction is selectively removed by, for example, dry etching by using the mask layer  71  to form the projecting part  50  having the notch part  51 . After that, the mask layer  71  is removed. 
     After the projecting part  50  is formed, for example, as shown in  FIG. 5 , the buried layer  60  made of the foregoing material is formed on the both sides of the projecting part  50 . After the buried layer  60  is formed, the rear face side of the substrate  10  is lapped to obtain a thin film having the foregoing thickness, on which an alloy layer of gold and germanium, a nickel layer, and a gold layer are sequentially vapor-deposited. After that, heat treatment is provided to form the n-side electrode. Further, on the projecting part  50  of the p-type semiconductor layer  40  and the buried layer  60 , for example, a titanium layer, a platinum layer, and a gold layer are sequentially vapor-deposited. Further, heat treatment is provided to form the p-side electrode. 
     After the n-side electrode and the p-side electrode are formed, the substrate  10  is adjusted to a given size, and the reflector films (not shown) are formed on the main-emitting-side end face  11  and the opposite-side end face  12 . Thereby, the laser diode shown in  FIG. 5  is formed. 
     In the laser diode, when a given voltage is applied between the n-side electrode and the p-side electrode, a driving current supplied from the p-side electrode is current-confined by the projecting part  50 , and then injected into the light emitting region  31  of the active layer  30 . Then, light emitting is generated by electron-hole recombination. The light is reflected by the pair of reflector films (not shown), travels between them, generates laser oscillation, and is emitted outside as laser beams. Since the notch parts  51  are provided in the pair of corners of the projecting part  50  in the main-emitting-side end face  11 , light emitting is not generated in the vicinity of the lateral boundaries  31 B and  31 C of the light emitting region  31 . Therefore, even if feedback light approaches or enters, the effects thereof can be inhibited. 
     As above, in this embodiment, since the notch parts  51  are provided in the pair of corners of the projecting part  50  in the main-emitting-side end face  11 , light emitting is not generated in the vicinity of the lateral boundaries  31 B and  31 C of the light emitting region  31 . Therefore, even if feedback light approaches or enters, the effects thereof can be inhibited. 
     In this embodiment, the case that the notch parts  51  are provided in the both corners of the projecting part  50  in the main-emitting-side end face  11  has been described. However, the notch part  51  can be provided in only one corner. Further, the notch part  51  can be provided not only in the main-emitting-side end face  11 , but also in the opposite-side end face  12 . 
     Second Embodiment 
       FIG. 8  shows a construction of a laser diode according to the second embodiment of the invention.  FIGS. 9A ,  9 B, and  9 C show a planar shape of a light emitting region (shaded portion) of the laser diode shown in  FIG. 8 , a reflectance distribution in the main-emitting-side end face, and a light power distribution inside the light emitting region. The laser diode has the same construction as of the laser diode of the first embodiment, except that a first reflector film  211  is included in the main-emitting-side end face  11 , and in the first reflector film  211 , laser light reflectance to the vicinity of the lateral center  31 A of the light emitting region  31  is set higher than laser light reflectance to the vicinity of the lateral boundaries  31 B and  31 C. Therefore, descriptions will be given by giving the same reference symbols to the corresponding components. 
     The first reflector film  211  has a construction, in which, for example, a second coating layer  211 B covering the vicinity of a lateral center  31 A of the light emitting region  31  is provided on a first coating layer  211 A covering the whole area of the main-emitting-side end face  11 . The first coating layer  211 A and the second coating layer  211 B are made of, for example, aluminum oxide. The thicknesses thereof are desirably adjusted according to target reflectance or oscillation wavelengths. For example, the reflectance of the first coating layer  211 A is 10%, and reflectance of the second coating layer  211 B is 10%. In this case, reflectance to the vicinity of the lateral center  31 A of the light emitting region  31  where the first coating layer  211 A and the second coating layer  211 B are overlapped is, for example, 19%, and reflectance in other region where only the first coating layer  211 A is formed is 10%. The first reflector film  211  corresponds to one specific example of the feedback light inhibition parts in the invention. 
     As above, in this laser diode, in the main-emitting-side end face  11 , the first reflector film  211  is provided and in the first reflector film  211 , the laser light reflectance (19%) to the vicinity of the lateral center  31 A of the light emitting region  31  is set higher than the laser light reflectance (10%) to the vicinity of the lateral boundaries  31 B and  31 C. Thereby, in this laser diode, it is possible to adjust the light power distribution in the light emitting region  31  larger in the vicinity of the lateral center  31 A, and smaller in the vicinity of the lateral boundaries  31 B and  31 C. Therefore, even if feedback light approaches or enters in the vicinity of the lateral boundaries  31 B and  31 C of the light emitting region  31 , an absolute amount of light coupling with (interacting with) feedback light is decreased, and effects of feedback light can be effectively inhibited. 
     The laser light reflectance to the vicinity of the lateral center  31 A of the light emitting region  31  is preferably, for example, 15% to 40%, and the laser light reflectance to the vicinity of the lateral boundaries  31 B and  31 C is preferably, for example, 5% to 20%. When such reflectance is too large, a rate of light confined inside the light emitting region  31  becomes high, light becomes hard to be emitted from the main-emitting-side end face  11 , and therefore, sufficient output may not be obtained. 
     Further, a difference between the laser light reflectance to the vicinity of the lateral center  31 A and the laser light reflectance to the vicinity of the lateral boundaries  31 B and  31 C of the light emitting region  31  is preferably, for example, 5% to 30%. When this difference is too large, the light power distribution in the vicinity of the lateral center  31 A of the light emitting region  31  becomes too large, and therefore, end face deterioration may occur in the vicinity of the lateral center  31 A. 
     A width Wcf of the second coating layer  211 B, that is, a width of the region, in which the laser light reflectance to the vicinity of the lateral center  31 A of the light emitting region  31  is set relatively high is preferably 20% to 80% of the width Wem of the light emitting region  31  in the vicinity of the center between the main-emitting-side end face  11  and the opposite-side end face  12 . 
     The second reflector film  212  is formed on the opposite-side end face  12 . The second reflector film  212  is constructed by, for example, alternately laminating an aluminum oxide layer and an amorphous silicon layer, and is adjusted to have high reflectance. Thereby, light generated in the active layer  30  travels between the first reflector film  211  and the second reflector film  212 , is amplified, and is emitted as laser beams from the first reflector film  211 . 
     This laser diode can be manufactured, for example, as follows. 
     First, as in the first embodiment, over the substrate  10 , the n-type semiconductor layer  20 , the active layer  30 , and the p-type semiconductor layer  40  are sequentially laminated by, for example, MOCVD method. 
     Next, on the p-type semiconductor layer  40 , a resist film (not shown) is formed, and a mask layer (not shown) to form the projecting part  50  is formed by, for example, lithography technique. Subsequently, part of the p-type semiconductor layer  40  in the thickness direction is selectively removed by, for example, dry etching by using the mask layer to form the projecting part  50 . After that, the mask layer is removed, and the buried layer  60  made of the foregoing material is formed on the both sides of the projecting part  50  by, for example, MOCVD method. 
     After the buried layer  60  is formed, the rear face side of the substrate  10  is lapped to obtain a thin film having the foregoing thickness. The n-side electrode and the p-side electrode are formed as in the first embodiment. 
     After the n-side electrode and the p-side electrode are formed, the substrate  10  is adjusted to a given size. On the main-emitting-side end face  11 , the first coating layer  211 A and the second coating layer  211 B made of the foregoing materials and having the foregoing reflectance are laminated to form the first reflector film  211 . Then, the second coating layer  211 B is formed only in the vicinity of the lateral center  31 A of the light emitting region  31 . Further, the second reflector film  212  is formed on the opposite-side end face  12 . Thereby, the laser diode shown in  FIG. 8  is formed. 
     In this laser diode, when a given voltage is applied between the n-side electrode and the p-side electrode, a driving current supplied from the p-side electrode is current-confined by the projecting part  50 , and then injected into the light emitting region  31  of the active layer  30 . Then, light emitting is generated by electron-hole recombination. The light is reflected by the first reflector film  211  and the second reflector film  212 , travels between them, generates laser oscillation, and is emitted outside as laser beams. Then, in the first reflector film  211  provided on the main-emitting-side end face  11 , the laser light reflectance to the vicinity of the lateral center  31 A of the light emitting region  31  is set higher than the laser light reflectance to the vicinity of the lateral boundaries  31 B and  31 C. Therefore, the light power distribution inside the light emitting region  31  is larger in the vicinity of the lateral center  31 A, and smaller in the vicinity of the lateral boundaries  31 B and  31 C. Consequently, even if feedback light approaches or enters in the vicinity of the lateral boundaries  31 B and  31 C of the light emitting region  31 , the absolute amount of light coupling with (interacting with) feedback light is decreased, and the effects of feedback light can be effectively inhibited. 
     As above, in this embodiment, the first reflector film  211  is provided in the main-emitting-side end face  11 , and in the first reflector film  211 , the laser light reflectance to the vicinity of the lateral center  31 A of the light emitting region  31  is set higher than the laser light reflectance to the vicinity of the lateral boundaries  31 B and  31 C. Therefore, the light power in the lateral boundaries  31 B and  31 C of the light emitting region  31  is decreased. Then, even if feedback light approaches or enters, the absolute amount of light coupling with (interacting with) the feedback light can be decreased. Consequently, the effects of feedback light can be effectively inhibited. 
     Third Embodiment 
       FIG. 10  shows a construction of a laser diode according to the third embodiment of the invention.  FIG. 11A  shows a cross section structure taken along line XIA-XIA of  FIG. 10 , and  FIG. 11B  shows a cross section structure taken along line XIB-XIB of  FIG. 10 . The laser diode has the same construction as of the laser diode of the first embodiment, except that, for example, two groove-like concave parts  351  and  352 , which are extended in the resonator direction A are provided on the surface of the p-type semiconductor layer  40 , and a part surrounded by the groove-like concave parts  351  and  352  of the p-type semiconductor layer  40  is the projecting part  50 . Therefore, descriptions will be given by giving the same reference symbols to the corresponding components. 
     The n-type semiconductor layer  20  has, for example, an n-type cladding layer  21 . The central part of the active layer  30  is a structural light emitting region  331  defined by the projecting part  50 . The p-type semiconductor layer  40  has, for example, a p-type cladding layer  41  and a p-side contact layer  42 . The n-type cladding layer  21 , the p-type cladding layer  41 , and the p-side contact layer  42  are constructed as in the first embodiment. 
     In the groove-like concave parts  351  and  352 , and on the surface of the p-type semiconductor layer  40  except for the projecting part  50 , an insulating layer  360  is formed. The insulating layer  360  has, for example, a thickness of 3 μm, and is made of silicon dioxide (SiO 2 ). 
     On the p-type semiconductor layer  40  in the projecting part  50  and on the insulating layer  360 , a p-side electrode  381  is provided. Meanwhile, an n-side electrode  382  is formed on the rear face side of the substrate  10 . The p-side electrode  381  and the n-side electrode  382  are constructed as in the first embodiment. 
       FIG. 12A  schematically shows a planar position relation between the projecting part  50  surrounded by the groove-like concave parts  351  and  352  and the structural light emitting region  331  (shaded portion) shown in  FIG. 10 . The width of the projecting part  50  shall be uniform, and the width Wem of the structural light emitting region  331  shall be uniform. 
       FIG. 12B  is a view, in which an effective light emitting region (half-tone dot meshed portion) is further added to  FIG. 12A . A width Wgf of the groove-like concave parts  351  and  352  in the vicinity of the main-emitting-side end face  11  is larger than a width Wgm in the vicinity of the center between the main-emitting-side end face  11  and the opposite-side end face  12 . Thereby, in the laser diode, index guide characteristics in the vicinity of the main-emitting-side end face  11  are enhanced to narrow the width of the effective light emitting region  332 . Therefore, even if feedback light approaches in the vicinity of lateral boundaries  331 B and  331 C of the structural light emitting region  331 , it is difficult to enter the light in the effective light emitting region  332 . 
     Allowing the width of the effective light emitting region  332  in the vicinity of the main-emitting-side end face  11  to be narrowed is enabled by utilizing the fact that effects on the effective refractive index difference between the projecting part  50  of the p-type semiconductor layer  40  and outside parts thereof becomes variable since the width Wgf of the groove-like concave parts  351  and  352  in the vicinity of the main-emitting-side end face  11  is widened. That is, in the vicinity of the center between the main-emitting-side end face  11  and the opposite-side end face  12 , since the width Wgm of the groove-like concave parts  351  and  352  is narrow, the refractive index difference between the projecting part  50  and the outside parts thereof is small. Therefore, the gain guide characteristics are enhanced, and the effective light emitting region  332  becomes in a slightly laterally widened state compared to the structural light emitting region  331 . Meanwhile, in the vicinity of the main-emitting-side end face  11 , the width Wgf of the groove-like concave parts  351  and  352  is wide, and therefore, the refractive index difference between the projecting part  50  and the outside parts thereof is large. Therefore, the index guide characteristics are enhanced, and the width of the effective light emitting region  332  becomes narrower than of the structural light emitting region  331 . Consequently, as described above, even if feedback light approaches the lateral boundaries  331 B and  331 C of the structural light emitting region  331 , the feedback light is hard to enter in the effective light emitting region  332 . 
     Changes of the width of the effective light emitting region  332  vary according to changes of the width of the groove-like concave parts  351  and  352 . For example, as shown in  FIGS. 12A and 12B , when the groove-like concave parts  351  and  352  are widened in the shape of a taper toward the main-emitting-side end face  11 , a transition region, in which light confinement is gradually intensified toward the main-emitting-side end face  11  is formed in the effective light emitting region  332 . Further, the shape of the groove-like concave parts  351  and  352  is not limited to the tapered shape as shown in  FIGS. 12A and 12B , but can be a step-like shape or a curved shape. 
     The width Wgf of the groove-like concave parts  351  and  352  in the vicinity of the main-emitting-side end face  11  is preferably 0.1% to 10% of the width Wem of the structural light emitting region  331 . When this value is too small, the index guide characteristics in the vicinity of the main-emitting-side end face  11  may not be sufficiently obtained, and therefore, effects become small. Meanwhile, when this value is too large, the refraction difference between the projecting part  50  and the outside parts thereof in the vicinity of the main-emitting-side end face  11  becomes too large, and therefore, effects such as disturbance of light emitting mode may occur. 
     A length Lgf in the part where the width Wgf is set larger than the width Wgm of the groove-like concave parts  351  and  352  is preferably 1% to 50% of the length L of the groove-like concave parts  351  and  352  in the resonator direction A. When the length Lgf is less than 1%, the part with the narrowed width of the effective light emitting region  332  is small, and therefore, effects are not sufficient. Meanwhile, when the length Lgf is more than 50%, changes in the width of the effective light emitting region  332  becomes too modest, and therefore, sufficient effects may not be obtained. 
     Further, when the groove-like concave parts  351  and  352  are in the shape of a taper as shown in  FIGS. 12A and 12B , an angle θg in the part where the width Wgf is set larger than the width Wgm is preferably, for example, 0.3° to 20°. When the angle θg is too small, changes in the width of the effective light emitting region  322  are too modest, and therefore, effects are not sufficient. Meanwhile, when the angle θg is too large, the refractive index difference between the projecting part  50  and the outside parts thereof in the vicinity of the main-emitting-side end face  11  becomes too large, and therefore, effects such as disturbance of the light emitting mode may be caused. 
     This laser diode can be manufactured, for example, as follows. 
     First, for example, as in the first embodiment, over the substrate  10 , the n-type semiconductor layer  20 , the active layer  30 , and the p-type semiconductor layer  40  are sequentially laminated by, MOCVD method. 
     Next, on the p-type semiconductor layer  40 , a resist film (not shown) is formed, and a mask layer (not shown) to form the groove-like concave parts  351  and  352  is formed by, for example, lithography technique. Subsequently, the p-type semiconductor layer  40  is selectively removed by, for example, dry etching by using the mask layer to form the groove-like concave parts  351  and  352 . Then, the mask layer is removed. 
     After that, for example, by vapor deposition method and lithography technique, the insulating layer  360  made of the foregoing material is formed in the groove-like concave parts  351  and  352  and on the surface of the p-type semiconductor layer  40  except for the projecting part  50 . 
     After the insulating layer  360  is formed, the rear face side of the substrate  10  is lapped to obtain a thin film having the foregoing thickness. The n-side electrode  382  and the p-side electrode  381  are formed as in the first embodiment. 
     After the n-side electrode  382  and the p-side electrode  381  are formed, the substrate  10  is adjusted to a given size. On the main-emitting-side end face  11  and the opposite-side end face  12 , reflector films (not shown) are formed. Thereby, the laser diode shown in  FIG. 10  is formed. 
     In this laser diode, when a given voltage is applied between the n-side electrode  382  and the p-side electrode  381 , a driving current supplied from the p-side electrode  381  is current-confined by the projecting part  50 , and then injected into the structural light emitting region  331  of the active layer  30 . Then, light emitting is generated by electron-hole recombination. The light is reflected by the pair of reflector films (not shown), travels between them, generates laser oscillation, and is emitted outside as laser beams. Then, the width Wgf of the groove-like concave parts  351  and  352  in the vicinity of the emitting side end face  11  is larger than the width Wgm in the vicinity of the center between the main-emitting-side end face  11  and the opposite-side end face  12 . Therefore, the index guide characteristics in the vicinity of the main-emitting-side end face  11  are enhanced, and the width of the effective light emitting region  332  is narrowed. Thereby, even if feedback light approaches in the vicinity of the lateral boundaries  331 B and  331 C of the structural light emitting region  331 , the feedback light is hard to enter in the effective light emitting region  332 . 
     As above, in this embodiment, since the width Wgf of the groove-like concave parts  351  and  352  in the vicinity of the main-emitting-side end face  11  is set larger than the width Wgm in the vicinity of the center between the main-emitting-side end face  11  and the opposite-side end face  12 . Therefore, the index guide characteristics in the vicinity of the main-emitting-side end face  11  can be enhanced, and the width of the effective light emitting region  332  can be narrowed. As a result, even if feedback light approaches in the vicinity of the lateral boundaries  331 B and  331 C of the structural light emitting region  331 , the feedback light is hard to enter in the effective light emitting region  332 , and the effects of feedback light can be effectively inhibited. 
     In this embodiment, the case, in which the width Wgf of both the groove-like concave parts  351  and  352  in the vicinity of the main-emitting-side end face  11  is widened has been described. However, it is possible to widen the width Wgf of only one groove-like concave part. Further, for example, as shown in  FIG. 13 , regarding the groove-like concave parts  351  and  352 , not only the width Wgf in the vicinity of the main-emitting-side end face  11 , but also a width Wgr in the vicinity of the opposite-side end face  12  can be widened. 
     Further, in this embodiment, the case, in which the insulating layer  360  is buried in the groove-like concave parts  351  and  352  has been described. However, inside of the groove-like concave parts  351  and  352  can be air. 
     Fourth Embodiment 
       FIG. 14  shows a construction of a laser diode according to a fourth embodiment of the invention.  FIG. 15  shows a planar shape of a light emitting region (shaded portion) of the laser diode shown in  FIG. 14 . This laser diode has the same construction as of the laser diode of the first embodiment, except that a normal end face  411 A and inclined planes  411 B and  411 C are formed on the main-emitting-side end face  11 . Therefore, descriptions will be given by giving the same reference symbols to the corresponding components. 
     The normal end face  411 A includes the vicinity of the lateral center  31 A of the light emitting region  31 , and is parallel to the opposite-side end face  12 . Light generated in the light emitting region  31  is emitted in the direction perpendicular to the normal end face  411 A. 
     The inclined planes  411 B and  411 C include the vicinity of the lateral boundaries  31 B and  31 C of the light emitting region  31 , and each is inclined to the normal end face  411 A. Thereby, in the laser diode, even if feedback light approaches in the vicinity of the lateral boundaries  31 B and  31 C of the light emitting region  31 , the feedback light is diagonally reflected by the inclined planes  411 B and  411 C, and it is thus difficult to enter. An oblique angle θp made by the inclined planes  411 B,  411 C and the normal end face  411 A is preferably, for example, 0.1° or more. These inclined planes  411 B and  411 C correspond to one specific example of the feedback light inhibition parts in the invention. 
     This laser diode can be manufactured, for example, as follows. 
     First, for example, as in the first embodiment, over the substrate  10 , the n-type semiconductor layer  20 , the active layer  30 , and the p-type semiconductor layer  40  are sequentially laminated by, for example, MOCVD method. Then, the projecting part  50  and the buried layer  60  on the both sides thereof are formed. 
     After the buried layer  60  is formed, the rear face side of the substrate  10  is lapped to obtain a thin film having the foregoing thickness. The n-side electrode and the p-side electrode are formed respectively as in the first embodiment. 
     After the n-side electrode and the p-side electrode are formed, the substrate  10  is adjusted to a given size. On the main-emitting-side end face  11 , the inclined planes  411 B and  411 C are formed by, for example, etching. The etching method or the conditions can be similar to the etching method or the conditions used for forming the projecting part  50 . 
     After the inclined planes  411 B and  411 C are formed, reflector films (not shown) are formed on the main-emitting-side end face  11  and the opposite-side end face  12 . Thereby, the laser diode shown in  FIG. 14  is formed. 
     In this laser diode, when a given voltage is applied between the n-side electrode and the p-side electrode, a driving current supplied from the p-side electrode is current-confined by the projecting part  50 , and then injected into the light emitting region  31  of the active layer  30 . Then, light emitting is generated by electron-hole recombination. The light is reflected by the pair of reflector films (not shown), travels between them, generates laser oscillation, and is emitted outside as laser beams. Then, in the main-emitting-side end face  11 , the vicinity of the lateral boundaries  31 B and  31 C of the light emitting region  31  is included in the inclined planes  411 B and  411 C inclined to the normal end face  411 A. Therefore, even if feedback light approaches in the vicinity of the lateral boundaries  31 B and  31 C, the feedback light is reflected by the inclined planes  411 B and  411 C, and is difficult to enter. 
     As above, in this embodiment, the normal end face  411 A, which includes the vicinity of the lateral center  31 A of the light emitting region  31  and is parallel to the opposite-side end face  12 , and the inclined planes  411 B and  411 C, which include the vicinity of the lateral boundaries  31 B and  31 C of the light emitting region  31  and are inclined to the normal end face  411 A are formed in the main-emitting-side end face  11 . Therefore, even if feedback light approaches in the vicinity of the lateral boundaries  31 B and  31 C of the light emitting region  31 , the feedback light is diagonally reflected by the inclined planes  411 B and  411 C and is difficult to enter. As a result, effects of feedback light can be effectively inhibited. 
     In this embodiment, the case, in which the corresponding inclined planes  411 B and  411 C are formed for both the vicinity of the lateral boundaries  31 B and  31 C of the light emitting region  31  has been described. However, it is possible to form either of the inclined planes  411 B and  411 C correspondingly to one lateral boundary. Further, the inclined planes  411 B and  411 C can be formed not only in the main-emitting-side end face  11 , but also in the opposite-side end face  12 . 
     Fifth Embodiment 
       FIG. 16  shows a construction of a laser diode according to the fifth embodiment.  FIG. 17  shows a planar shape of a light emitting region (shaded portion) of the laser diode shown in  FIG. 16 . This laser diode has the same construction as of the laser diode of the first embodiment, except that the laser diode of this embodiment has an impurity-doped region  580  in a pair of corners of the main-emitting-side end face  11  side. Therefore, descriptions will be given by giving the same reference symbols to the corresponding components. In  FIGS. 16 and 17 , the impurity-doped region  580  is shown as a half-tone dot meshed portion. 
     The impurity-doped region  580  includes a corner of the projecting part  50  in the main-emitting-side end face  11 . Thereby, in this laser diode, optical loss is intentionally generated in the impurity-doped region  580 , so that even if feedback light approaches or enters in the vicinity of the lateral boundaries  31 B and  31 C of the light emitting region  31 , the effects thereof can be inhibited. A preferable impurity density of the impurity-doped region  580  is, for example, 1×10 16 /cm 3  to 1×10 20 /cm 3 . In this range, desirable and appropriate optical loss can be generated. The impurity-doped region  580  corresponds to one specific example of the feedback light inhibition parts in the invention. 
     An impurity included in the impurity-doped region  580  can be any typical impurity used for semiconductors regardless of materials of the laser diode. For example, silicon (Si), selenium (Se), tellurium (Te), magnesium (Mg), zinc (Zn), cadmium (Cd), or carbon (C) can be cited. 
     Further, when the active layer  30  is made of a group III-V compound semiconductor, the impurity included in the impurity-doped region  580  may be an element of group III or group V, which is not included in the active layer  30 . For example, when the active layer  30  is made of an AlGaAs mixed crystal in the GaAs laser diode as in this embodiment, boron (B), indium (In), nitrogen (N), phosphorous (P), or antimony (Sb) can be cited as an impurity. 
     Otherwise, when the active layer  30  is made of GaInN in a nitride laser diode, aluminum (Al), boron (B), phosphorous (P), arsenic (As), or antimony (Sb) can be cited as an impurity. When the active layer  30  is made of GaInAsP in an InP laser diode, boron (B), aluminum (Al), nitrogen (N), or antimony (Sb) can be cited as an impurity. 
     Even if an impurity injection depth Di of the impurity-doped region  580  is shallow, effects can be obtained to some extent. However, Di preferably reaches the active layer  30 . Thereby, the width Wef of the light emitting region  31  in the vicinity of the main-emitting-side end face  11  can be surely narrower than the width Wem. Further, the impurity density of the impurity-doped region  580  is not such a value that changes the refractive index. Therefore, even if Di reaches the active layer  30 , troubles may be hardly caused. 
     A length Li of the impurity-doped region  580  is preferably 1% to 50% of the length L of the projecting part  50  in the resonator direction A. When the value is less than 1%, a narrow part of the width Wef of the light emitting region  31  in the vicinity of the main-emitting-side end face  11  becomes small, and therefore, its effects are not sufficient. Meanwhile, when the value is more than 50%, changes between the width Wem and the width Wef of the light emitting region  31  are too modest, and therefore, sufficient effects may not be obtained. 
     The width Waf and the length Laf, in the part the impurity-doped region  580  is overlapped with the corner of the projecting part  50  are similar to of the notch part  51  of the first embodiment. 
     This laser diode can be manufactured, for example, as follows. 
     First, for example, as in the first embodiment, over the substrate  10 , the n-type semiconductor layer  20 , the active layer  30 , and the p-type semiconductor layer  40  are sequentially laminated by MOCVD method. Then, the projecting part  50  and the buried layer  60  on the both sides thereof are formed. 
     After the buried layer  60  is formed, an unshown mask is formed on the p-type semiconductor layer  40  and the buried layer  60 . By using this mask, an impurity is doped to the pair of corners of the main-emitting-side end face  11  by, for example, ion implantation or diffusion to form the impurity-doped region  580 . Then, the impurity-doped region  580  shall fall on the corner of the projecting part  60  in the main-emitting-side end face  11 . 
     After the impurity-doped region  580  is formed, the rear face side of the substrate  10  is lapped to obtain a thin film having the foregoing thickness. The n-side electrode and the p-side electrode are formed respectively as in the first embodiment. After the n-side electrode and the p-side electrode are formed, the substrate  10  is adjusted to a given size. On the main-emitting-side end face  11  and the opposite-side end face  12 , reflector films (not shown) are formed. Thereby, the laser diode shown in  FIG. 16  is formed. 
     In this laser diode, when a given voltage is applied between the n-side electrode and the p-side electrode, a driving current supplied from the p-side electrode is current-confined by the projecting part  50 , and then injected into the light emitting region  31  of the active layer  30 . Then, light emitting is generated by electron-hole recombination. The light is reflected by the pair of reflector films (not shown), travels between them, generates laser oscillation, and is emitted outside as laser beams. Then, the impurity-doped region  580  provided in the pair of corners of the main-emitting-side end face  11  includes the corners of the projecting part  50  in the main-emitting-side end face  11 . Therefore, optical loss is generated in the impurity-doped region  580 . Consequently, even if feedback light approaches or enters in the vicinity of the lateral boundaries  31 B and  31 C of the light emitting region  31 , the effects thereof can be inhibited. 
     As above, in this embodiment, the impurity-doped region  580  is provided in the pair of corners of the main-emitting-side end face  11 , and this impurity-doped region  580  includes the corners of the projecting part  50  in the main-emitting-side end face  11 . Therefore, optical loss can be intentionally generated in the impurity-doped region  580 . Consequently, even if feedback light approaches or enters in the vicinity of the lateral boundaries  31 B and  31 C of the light emitting region  31 , the effects thereof can be inhibited. 
     In this embodiment, the case in which the impurity-doped region  580  is provided in both of the pair of corners of the main-emitting-side end face  11  has been described. However, it is possible to provide the impurity-doped region  580  only in one corner. Further, the impurity-doped region  580  can be provided not only in the main-emitting-side end face  11 , but also in the opposite-side end face  12 . 
     Though the invention has been described with reference to the embodiments, the invention is not limited to the foregoing embodiments, and various modifications may be made. For example, the materials, the thicknesses, the deposition methods, the deposition conditions and the like, which are described in the foregoing embodiments are not limited. Other material, other thickness, other deposition method, and other deposition conditions may be applied. For example, in the foregoing embodiments, silicon is used as an n-type impurity. However, other n-type impurity such as selenium (Se) may be used. 
     Further, in the foregoing embodiments, the case that the semiconductor layer is developed by MOCVD method has been described. However, the semiconductor layer may be developed by other method such as MBE (Molecular Beam Epitaxy) method. 
     Further, in the foregoing embodiments, constructions of the laser diode have been described with reference to the specific examples. However, the invention can be similarly applied to a laser diode having other structure. For example, an optical guide layer may be provided between the active layer and the n-type cladding layer or the p-type cladding layer. 
     In addition, in the foregoing embodiments, the broad area laser diode has been described. However, in the invention, the width of the light emitting region is not particularly limited. Therefore, the invention can be applied to a narrow stripe laser diode. 
     Further, in the foregoing embodiments, the materials for the laser diode have been described with reference to the specific examples. However, the invention can be widely applied not only to the GaAs device described in the foregoing embodiments, but also to the case using other semiconductor material such as a group III-V compound semiconductor such as AlGaInP and InP, a nitride group III-V compound semiconductor, and a group II-VI compound semiconductor. 
     Further, in the foregoing embodiments, the case that the physical or substantial shape of the projecting part  50  or the light emitting region  31  is changed, or the case that the light intensity distribution in the light emitting region  31  is adjusted have been described. However, it is possible to change the shape of the p-side electrode without changing the shape of the projecting part  50  or the light emitting region  31 . 
     This invention can be applied to a semiconductor light emitting device such as an LED (Light Emitting Diode) in addition to the laser diode. 
     The laser diode, particularly the broad area laser diode of the invention can be applied to various fields such as a light source for an optical disk device, a display, a printing product, fabricating materials, and medical care. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alternations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.