Patent Publication Number: US-8537872-B2

Title: Light emitting device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. application Ser. No. 12/722,792 filed Mar. 12, 2010 which claims priority to Japanese Patent Application No. 2009-062502 filed Mar. 16, 2009 both of which are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a light emitting device. 
     2. Related Art 
     In recent years, a high-intensity laser device superior in color reproducibility has become a promising light emitting device for a light source of a display device such as a projector or a monitor display. However, in some cases, there might arise a problem of a speckle noise caused by mutual interference of scattered light on a screen surface. To solve this problem, for example, there has been proposed a method of fluctuating the screen to vary the speckle pattern for reducing the speckle noise in JP-A-11-64789. 
     However, according to the method disclosed in the document mentioned above, there might arise another problem that the screen is limited, and that an additional member for moving the screen such as motor is required, and that a noisy sound is caused by the motor or the like. 
     Further, it is also possible to use a general light emitting diode (LED) for the light source in order to reduce the speckle noise. However, there might be the case in which the LED fails to provide a sufficient output power. 
     SUMMARY 
     An advantage of the invention is to provide a novel light emitting device capable of reducing the speckle noise and providing a high output power. 
     According to an aspect of the invention, there is provided a light emitting device including a first cladding layer, an active layer formed above the first cladding layer, and a second cladding layer formed above the active layer, wherein the active layer includes a first side surface and a second side surface parallel to the first side surface. At least a part of the active layer constitutes a first gain region and a second gain region, a reflectance of the second side surface is higher than that of the first side surface at a wavelength of light generated in the first gain region and the second gain region. A part of a first end surface of the first gain region located on a side of the second side surface and a part of a second end surface of the second gain region located on a side of the second side surface overlap with each other in an overlapping plane. The first gain region is disposed from the first end surface to a third end surface, which is located on the side of the first side surface, obliquely to a perpendicular line of the first side surface, and the second gain region is disposed from the second end surface to a fourth end surface, which is located on the side of the first side surface, obliquely to the perpendicular line of the first side surface. A first center line connecting a center of the first end surface and a center of the third end surface and a second center line connecting a center of the second end surface and a center of the fourth end surface have an intersection point, and the overlapping plane is shifted from the intersection point in a direction from the second side surface toward the first side surface. 
     In the light emitting device according to the aspect of the invention, the laser oscillation of the light generated in the gain regions can be suppressed or prevented as described later. Therefore, the mutual interference of the scattered light can be suppressed, and thus the speckle noise can be reduced. Further, in the light emitting device according to the invention, the light generated in the gain regions can proceed while receiving a gain in each gain regions, and then be emitted to outside. Therefore, it is possible to obtain a higher output power than that of the general LED of the related art. As described above, according to the aspect of the invention, a novel light emitting device capable of reducing the speckle noise with high output power can be provided. 
     It should be noted that in the descriptions related to the invention, the term “above” is used in such a phrase as “a specific object (hereinafter referred to as “B”) is formed “above” another specific object (hereinafter referred to as “A”).” In the descriptions related to the invention, in such a case as this example, the term “above” is used in order to include the case of forming B directly on A and the case of forming B on A via something else. 
     According to another aspect of the invention, in the light emitting device of the above invention, it is also possible that a width of the first gain region in the vicinity of the overlapping plane and a width of the second gain region in the vicinity of the overlapping plane are equal to each other in a plan view, and that the displacement L and the width W satisfy the following formula 1, assuming that a displacement between the intersection point and the overlapping plane is L, and the width of the first gain region in the vicinity of the overlapping region and the width of the second gain region in the vicinity of the overlapping region are W.
 
0 &lt;L&lt;W   (1)
 
     According to another aspect of the invention, in the light emitting device of the above invention, it is also possible that the displacement L and the width W satisfy the following formula 2.
 
( W/ 4)≦ L ≦(3 W/ 4)  (2)
 
     According to another aspect of the invention, in the light emitting device of the above invention, it is also possible that the displacement L and the width W satisfy the following formula 3.
 
 L =( W/ 2)  (3)
 
     According to another aspect of the invention, in the light emitting device of the above invention, it is also possible that the first gain region is disposed from the first end surface to the third end surface with a constant width, and the second gain region is disposed from the second end surface to the fourth end surface with a constant width, and that the width of the first and the second gain regions are equal to each other. 
     According to another aspect of the invention, in the light emitting device of the above invention, it is also possible that the second side surface is provided with a reflecting section. 
     According to another aspect of the invention, in the light emitting device of the above invention, it is also possible that a planar shape of the first gain region and a planar shape of the second gain region are axisymmetrical with each other about a perpendicular line of the overlapping plane. 
     According to another aspect of the invention, in the light emitting device of the above invention, it is also possible that the first gain region has a reflecting plane between the first end surface and the third end surface, and the reflecting plane is adapted to reflect light proceeding in the first gain region. The light emitted from the third end surface and the light emitted from the fourth end surface can proceed in the same direction by introducing the reflecting plane in the first gain region. 
     According to another aspect of the invention, in the light emitting device of the above invention, it is also possible in a plan view from the side of the first side surface of the active layer that there is no overlap between the first end surface and the third end surface of the first gain region, and that there is no overlap between the second end surface and the fourth end surface of the second gain region. 
     According to another aspect of the invention, in the light emitting device of the above invention, it is also possible that a part of the light generated from the first gain region is reflected by the overlapping plane and is emitted from the fourth end surface of the second gain region, and that a part of the light generated from the second gain region is reflected by the overlapping plane and is emitted from the third end surface of the first gain region. 
     According to another aspect of the invention, in the light emitting device of the above invention, it is also possible that a first electrode electrically connected to the first cladding layer and a second electrode electrically connected to the second cladding layer are further provided. 
     It should be noted that in the descriptions related to the invention, the term “electrically connected” is used in such a phrase as “a specific member (hereinafter referred to as a “member D”) “electrically connected” to another specific member (hereinafter referred to as a “member C”).” In the descriptions related to the invention, in such a case as this example, the term “electrically connected” is used in order to include the case in which the member C and the member D are electrically connected while having direct contact with each other and the case in which the member C and the member D are electrically connected via another member. 
     According to another aspect of the invention, in the light emitting device of the above invention, it is also possible that a contact layer is further provided above the second cladding layer, and is in ohmic contact with the second electrode. At least the contact layer and a part of the second cladding layer can constitute a columnar section, and a planar shape of the columnar section can be identical to that of the first gain region and the second gain region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with reference to the accompanying drawings, wherein numbers refer to the elements of the device of the invention. 
         FIG. 1  is a perspective view schematically showing a light emitting device according to the present embodiment. 
         FIG. 2  is a plan view schematically showing the light emitting device according to the present embodiment. 
         FIG. 3  is a cross-sectional view schematically showing the light emitting device according to the present embodiment. 
         FIG. 4  is a diagram of an active layer according to the present embodiment viewed from a first side surface side in a planar manner. 
         FIG. 5  is a cross-sectional view schematically showing a manufacturing process of the light emitting device according to the present embodiment. 
         FIG. 6  is a cross-sectional view schematically showing the manufacturing process of the light emitting device according to the present embodiment. 
         FIG. 7  is a cross-sectional view schematically showing the manufacturing process of the light emitting device according to the present embodiment. 
         FIG. 8  is a plan view schematically showing the manufacturing process of the light emitting device according to the present embodiment. 
         FIG. 9  is a plan view schematically showing a model used as an experimental example of the light emitting device according to the present embodiment. 
         FIG. 10  is a graph showing a result of the experimental example of the light emitting device according to the present embodiment. 
         FIG. 11  is a plan view schematically showing a light emitting device according to a modified example of the present embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     A preferred embodiment of the invention will be described hereinafter with reference to the accompanying drawings. 
     1. Light Emitting Device 
     Firstly, a light emitting device according to the present embodiment will be explained with reference to the accompanying drawings.  FIG. 1  is a perspective view schematically showing the light emitting device  100  according to the present embodiment.  FIG. 2  is a plan view schematically showing the light emitting device  100  according to the present embodiment.  FIG. 3  is a cross-sectional view along the III-III line shown in  FIG. 2 , and schematically shows the light emitting device  100  according to the present embodiment. In  FIGS. 1 and 2 , a second electrode  114  is omitted from illustration for the sake of convenience. Further, the case which the light emitting device  100  is an InGaAlP type (red) semiconductor light emitting device will be explained here. 
     As shown in  FIGS. 1 through 3 , the light emitting device  100  includes a first cladding layer  104 , an active layer  106 , and a second cladding layer  108 . The light emitting device  100  can further include a substrate  102 , a contact layer  110 , an insulating layer  116 , a first electrode  112 , and a second electrode  114 . 
     As the substrate  102 , a GaAs substrate with a first conductivity type (e.g., n-type), for example, can be used. 
     The first cladding layer  104  is formed on the substrate  102 . As the first cladding layer  104 , for example, an n-type InGaAlP layer can be used. Although not shown in the drawings, it is also possible to form a buffer layer between the first substrate  102  and the first cladding layer  104 . As the buffer layer, an n-type GaAs layer, an n-type InGaP layer, and so on can be used. 
     The active layer  106  is formed on the first cladding layer  104 . The active layer  106  has, for example, a multiple quantum well (MQW) structure obtained by stacking three quantum well structures each composed of an InGaP well layer and an InGaAlP barrier layer. 
     Some part of the active layer  106  constitutes a plurality of gain regions. In the example shown in the drawing, part of the active layer  106  constitutes a first gain region  160  and a second gain region  162 . Although not shown in the drawing, it is also possible that the active layer  106  has another gain region in addition to the first and the second gain regions  160 ,  162 , and that the plurality of gain regions including the gain regions  160 ,  162  is arranged to form an array. 
     The gain regions  160 ,  162  can generate light, and the light can receive gains in the gain regions  160 ,  162 . The shape of the active layer  106  is, for example, a rectangular solid (including a cube). As shown in  FIG. 2 , the active layer  106  has a first side surface  105  and a second side surface  107 . The first side surface  105  and the second side surface  107  is parallel to each other. At the wavelength of the light generated in the gain regions  160 ,  162 , the reflectance of the second side surface  107  is higher than that of the first side surface  105 . For example, as shown in  FIGS. 1 and 2 , the high reflectance can be obtained by covering the second side surface  107  with a reflective section  130 . The reflective section  130  has a high reflective structure such as a dielectric mirror or a metallic mirror. More specifically, as the reflective section  130 , it is possible to use, for example, a mirror having 10 pairs of layers of SiO 2  and Ta 2 O 5  stacked in this order from the side of the second side surface  107 . It is preferable that the reflectance of the second side surface  107  is 100% or almost 100%. In contrast, it is preferable that the reflectance of the first side surface  105  is 0% or almost 0%. For example, by covering the first side surface  105  with an antireflection coating (not shown), it is possible to obtain low reflectance. It should be noted that the reflective section  130  is not limited to the example described above. An Al 2 O 3  layer, a TiO 2  layer, a TiN layer, an SiN layer, and a multilayer film thereof, for example, can be used instead. 
     Each of the gain regions  160 ,  162  is disposed from the second side surface  107  to the first side surface  105  in a direction tilted with respect to the perpendicular line P of the first side surface  105  in a plan view shown in  FIG. 2 . Thus, the laser oscillation of the light generated in the gain regions  160 ,  162  can be suppressed or prevented. The first gain region  160  and the second gain region  162  are disposed in the directions different from each other. In the example shown in the drawing, the first gain region  160  is tilted toward one side at an angle θ with respect to the perpendicular line P. The second gain region  162  is tilted toward the other side (the side opposite to the one side) at an angle θ with respect to the perpendicular line P. 
     As shown in  FIG. 2 , the first gain region  160  has a first end surface  170  provided to the second side surface  107  and a third end surface  174  provided to the first side surface  105 . The second gain region  162  has a second end surface  172  provided to the second side surface  107  and a fourth end surface  176  provided to the first side surface  105 . The width of the first gain region  160  in the first end surface  170  and the width of the second gain region  162  in the second end surface  172  are equal to each other. In the example shown in the drawing, the first gain region  160  has a constant width W from the first end surface  170  to the third end surface  174 , and the second gain region  162  has a constant width W from the second end surface  172  to the fourth end surface  176 . In other words, the planar shape of the first gain region  160  and the second gain region  162  are parallelogram. In the example shown in the drawing, the width W of the first gain region  160  and the width W of the second gain region  162  are also equal to each other. 
     A part of the first end surface  170  and a part of the second end surface  172  overlap each other in an overlapping plane  178 . In other words, it can be said that the first end surface  170  and the second end surface  172  form a single continuous plane. The first end surface  170  can reflect the light generated in the first gain region  160 . The second end surface  172  can reflect the light generated in the second gain region  162 . The planar shape of the first gain region  160  and the planar shape of the second gain region  162  can be axisymmetrical with each other with respect to the perpendicular line P of the first side surface  105 . The planar shape of the first and the second gain regions  160 ,  162  can also be axisymmetrical with respect to a perpendicular line of the overlapping plane  178 . 
     Although not shown in the drawings, the first end surface  170  and the second end surface  172  can be provided to an opening section formed in the active layer  106  instead of the side surface of the active layer  106 . 
     As shown in  FIG. 2 , a first center line  160   a  connecting the center of the first end surface  170  and the center of the third end surface  174  of the first gain region  160  and a second center line  162   a  connecting the center of the second end surface  172  and the center of the fourth end surface  176  of the second gain region  162  have an intersection point A. The overlapping plane  178  (the second side surface  107 ) is shifted toward the side of the first side surface  105  (+X direction) away from the intersection point A. When denoting the displacement between the intersection point A and the overlapping plane  178  (i.e., the displacement between the intersection point A and the second side surface  107 ) as L, and the width of the gain regions  160 ,  162  as W, the displacement L and the width W satisfy the formula 1 described below.
 
0 &lt;L&lt;W   (1)
 
     Further, the displacement L and the width W preferably satisfy the formula 2 described below.
 
( W/ 4)≦ L ≦(3 W/ 4)  (2)
 
     Further, the displacement L and the width W preferably satisfy the formula 3 described below.
 
 L =( W/ 2)  (3)
 
     It should be noted that the first center line  160   a  can be the line intermediate of the two sides of the first gain region  160  that is not on the first end surface  170  or the third end surface  174  in the plan view as shown in  FIG. 2 . Similarly, the second center line  162   a  can be the line intermediate of the two sides of the second gain region  162  that is not on the second end surface  172  or the fourth end surface  176 . The width W of the first gain region  160  is the distance between the two sides of the first gain region  160  parallel to the first center line  160   a  in the plan view as shown in  FIG. 2 . Similarly, the width W of the second gain region  162  is the distance between the two sides of the second gain region  162  parallel to the second center line  162   a.    
     If the displacement L and the width W satisfy the relations described above, the light emitting device  100  can efficiently emit light. The details explanation of that will be described later. 
       FIG. 4  is a diagram of the active layer  106  viewed from the side of the first side surface  105  in a planar manner. As shown in  FIG. 4 , the first end surface  170  and the third end surface  174  of the first gain region  160  do not overlap with each other. Similarly, the second end surface  172  and the fourth end surface  176  of the second gain region  162  do not overlap with each other. Thus, it is possible to prevent the direct multiple reflection of the light generated in the first gain region  160  between the first end surface  170  and the third end surface  174 , and the direct multiple reflection of the light generated in the second gain region  162  between the second end surface  172  and the fourth end surface  176 . As a result, since it is possible to prevent constitution of the direct resonator, it becomes possible to more reliably suppress or prevent the laser oscillation of the light generated in the gain regions  160 ,  162 . Therefore, the light emitting device  100  can emit non-laser light. In the case shown in  FIG. 4 , for example, it is sufficient that the shift width x between the first end surface  170  and the third end surface  174  takes a positive value. 
     As shown in  FIGS. 1 and 3 , the second cladding layer  108  is formed on the active layer  106 . As the second cladding layer  108 , for example, an InGaAlP layer of a second conductivity type (e.g., p-type), can be used. 
     For example, a pin diode is formed by the p-type second cladding layer  108 , the active layer  106  with no impurity doped, and the n-type first cladding layer  104 . Each of the first cladding layer  104  and the second cladding layer  108  has a forbidden band gap larger than that of the active layer  106  and a refractive index smaller than that of the active layer  106 . The active layer  106  has a function of amplifying the light. The first cladding layer  104  and the second cladding layer  108  have a function of confining injection carriers (electrons and holes) and the light in the active layer  106 . 
     In the light emitting device  100 , when applying a forward bias voltage of the pin diode between a first electrode  112  and a second electrode  114 , there occurs recombination of the electron and the hole in the gain regions  160 ,  162  of the active layer  106 . The recombination causes the light emission. Originating from the generated light, stimulated emission occurs and the light intensity is amplified inside the gain regions  160 ,  162 . For example, as shown in  FIG. 1 , a part of the light generated in the first gain region  160  is amplified inside the first gain region  160 , and then reflected at the overlapping plane  178  and emitted from the fourth end surface  176  of the second gain region  162  as outgoing light  20 . In this case, the intensity of the part of the generated light  10  is also amplified inside the second gain region  162  after the reflection. Similarly, a part of the light generated in the second gain region  162  is also amplified inside the second gain region  162 , and then reflected at the overlapping plane  178  and emitted from the third end surface  174  of the first gain region  160  as outgoing light  22 . In this case, the intensity of part of the generated light is also amplified inside the first gain region  160  after the reflection. It should be noted that some of the light generated in the first gain region  160  is emitted directly from the third end surface  174  as the outgoing light  22 . Similarly, some of the light generated in the second gain region  162  is emitted directly from the fourth end surface  176  as the outgoing light  20 . Such light is also amplified inside the respective gain regions  160 ,  162  in the similar manner. 
     As shown in  FIGS. 1 and 3 , the contact layer  110  is formed on the second cladding layer  108 . As the contact layer  110 , the layer having an ohmic contact with the second electrode  114  can be used. As the contact layer  110 , a p-type GaAs layer, for example, can be used. 
     The contact layer  110  and part of the second cladding layer  108  can form a columnar section  111 . As shown in  FIG. 2 , the planar shape of the columnar section  111  is, for example, the same as that of the gain region  160 ,  162 . In other words, the current channel between the electrodes  112 ,  114  is determined by the planar shape of the columnar section  111 , for example, and as a result, the planar shapes of the gain regions  160 ,  162  are determined. Although not shown in the drawings, the columnar section  111  can also be constituted with, for example, the contact layer  110 , a part of the second cladding layer  108 , a part of the active layer  106 , and a part of the first cladding layer  104 . Although not shown in the drawings, the side surfaces of the columnar section  111  can be tilted. 
     As shown in  FIGS. 1 and 3 , the insulating sections (also referred to as the insulating layer)  116  can be disposed on the second cladding layer  108  and lateral to the columnar sections  111 . The insulating sections  116  have contact with the side surfaces of the columnar sections  111 . The upper surfaces of the insulating sections  116  can be contiguous to the upper surface of the contact layer  110 . As the insulating section  116 , for example, an SiN layer, an SiO 2  layer, and a polyimide layer can be used. If such materials are used as the insulating sections  116 , the current between the electrodes  112 ,  114  can flow through the columnar sections  111  while avoiding the insulating sections  116 . It is possible for the insulating sections  116  to have a refractive index smaller than the refractive index of the active layer  106 . In this case, the effective refractive index of the vertical section in which the insulating section  116  is provided becomes smaller than that of the vertical section in which the insulating section  116  is not provided, namely the section in which the columnar section  111  is provided. Thus, it becomes possible to efficiently confine the light inside the gain regions  160 ,  162  with respect to the planar direction. It is also possible to eliminate the insulating sections  116 . In other words, the insulating sections  116  can be an air. In this case, it is required to exclude the active layer  106  and the first cladding layer  104  from the columnar sections  111 , or to prevent the second electrode  114  from having direct contact with the active layer  106  and the first cladding layer  104 . 
     The first electrode  112  is formed on the entire bottom surface of the substrate  102 . The first electrode  112  can have contact with the layer (the substrate  102  in the example shown in the drawings) having an ohmic contact with the first electrode  112 . The first electrode  112  is electrically connected to the first cladding layer  104  via the substrate  102 . The first electrode  112  is one side of the electrodes for driving the light emitting device  100 . As the first electrode  112 , for example, a stacking layer obtained by forming a Cr layer, an AuGe layer, an Ni layer, and an Au layer in this order from the side of the substrate  102  can be used. It is also possible to form the electrode  112  by disposing a second contact layer (not shown) between the first cladding layer  104  and the substrate  102 , exposing the second contact layer using a dry etching process, and then disposing the first electrode  112  on the second contact layer. Thus, a single-sided electrode structure can be obtained. This form is particularly effective in the case that the substrate  102  is an insulating layer. 
     As shown in  FIG. 3 , the second electrode  114  is formed on the contact layer  110  (on the columnar sections  111 ). Although not shown in the drawings, the second electrode  114  can be formed on the entire upper surfaces of the contact layer  110  and the insulating sections  116 . The second electrode  114  is electrically connected to the second cladding layer  108  via the contact layer  110 . The second electrode  114  is the other side of the electrodes for driving the light emitting device  100 . As the second electrode  114 , for example, a stacking layer obtained by forming a Cr layer, an AuZn layer, and an Au layer in this order from the side of the contact layer  110  can be used. As shown in  FIG. 2 , the contact surface between the second electrode  114  and the contact layer  110  has substantially the same planar shape as those of the gain regions  160 ,  162 . 
     As an example of the light emitting device  100 , the case of InGaAlP type is explained above. However, according to the present embodiment, any material type capable of forming a light emitting gain region can be used in the light emitting device  100 . In the case of semiconductor materials, such as an AlGaN type, an InGaN type, a GaAs type, an InGaAs type, a GaInNAs type, a ZnCdSe type can be used. 
     The light emitting device  100  according to the present embodiment can be applied to the light source for a projector, a monitor display, an illumination device, and a measuring device, for example. 
     The light emitting device  100  according to the present embodiment has the following features, for example. 
     According to the light emitting device  100 , the laser oscillation of the light generated in the gain regions  160 ,  162  can be suppressed or prevented as described above. Therefore, the speckle noise can be reduced. Further, according to the light emitting device  100 , the light generated in the gain regions  160 ,  162  can proceed in the gain regions  160 ,  162  while receiving a gain to be emitted to outside. Therefore, it is possible to obtain a higher output power than that of the general light emitting diode (LED) of the related art. 
     According to the light emitting device  100 , the displacement L between the intersection point A and the overlapping plane  178  and the width W of the gain regions  160 ,  162  can satisfy the formula 1 described above, further the formula 2 described above, and still further the formula 3 described above. Therefore, the light emitting device  100  can emit the generated light efficiently. The details thereof will be described later. 
     According to the light emitting device  100 , the part of the light  10  generated in the first gain region  160  is reflected by the overlapping plane  178 , and can also proceed in the second gain region  162  while receiving a gain. Further, the same can be applied to part of the light generated in the second gain region  162 . Therefore, according to the light emitting device  100 , since the distance for amplifying the intensity of the light becomes longer compared to the case that the light is not reflected by the overlapping plane  178 , the higher output power can be obtained. 
     2. Method of Manufacturing Light Emitting Device 
     Then, a method of manufacturing the light emitting device according to the present embodiment will be explained with reference to the accompanying drawings.  FIGS. 5 through 7  are cross-sectional views schematically showing the manufacturing process of the light emitting device  100  according to the present embodiment corresponding to  FIG. 3 .  FIG. 8  is a plan view schematically showing the manufacturing process of the light emitting device  100  according to the present embodiment. In  FIG. 8 , a second electrode  114  is omitted from illustration for the sake of convenience. 
     As shown in  FIG. 5 , the first cladding layer  104 , the active layer  106 , the second cladding layer  108 , and the contact layer  110  are epitaxially grown on the substrate  102  in this order. As a method for growing the layers epitaxially, a metal organic chemical vapor deposition (MOCVD) method, a molecular beam epitaxy (MBE) method, and so on can be used. 
     As shown in  FIG. 6 , the contact layer  110  and the second cladding layer  108  are patterned. The patterning is performed by using, for example, a photolithography technique or an etching technique. According to the present process, the columnar sections  111  can be formed. 
     As shown in  FIG. 7 , the insulating sections  116  are formed so as to cover the side surfaces of the columnar sections  111 . Firstly, an insulating layer (not shown) is formed as a film above the second cladding layer  108  (including the surface of the contact layer  110 ) using, for example, a chemical vapor deposition (CVD) method or a coating method. Subsequently, the upper surface of the contact layer  110  is exposed using, for example, an etching technique. Accordingly, the insulating sections  116  can be formed. 
     Subsequently, the second electrode  114  is formed on the contact layer  110 . The second electrode  114  is formed using, for example, a vacuum deposition method. 
     Subsequently, the first electrode  112  is formed under the bottom surface of the substrate  102 . The manufacturing method of the first electrode  112  is, for example, the same as that of the second electrode  114  described above. The order of forming the first electrode  112  and the second electrode  114  is not particularly limited. According to the process described above, a plurality of light emitting patterns can be formed inside a wafer. 
     Subsequently, as shown in  FIG. 8 , scribing lines  3  ( 3   a ,  3   b ,  3   c ) for separating a plurality of light emitting patterns  101  ( 101   a ,  101   b ,  101   c ) are provided to a wafer  1  having the plurality of light emitting patterns  101 . Although the number of light emitting patterns  101  is three in the example shown in the drawing, the number is not particularly limited. The scribing lines  3  are formed using, for example, a diamond cutter or a laser. The light emitting device  100  can be obtained by cleaving the wafer  1  along the scribing lines  3  to separate the light emitting patterns  101 . The scribing lines  3  can be provided for forming a cleavage surface including the second side surface  107 . The scribing lines  3  are preferably formed at a position with a displacement L from the intersection point A of the first center line  160   a  and the second center line  162   a  toward the +X direction (toward the side of the first side surface  105 ). The displacement L preferably has a value that is half as large as the width W of the gain regions  160 ,  162 . In other words, the displacement L between the scribing lines and the intersection point A preferably satisfies the formula 3 described above. In this invention, in case of forming the scribing lines  3   a  on both sides of the light emitting pattern  101   a  as shown in the drawing, the displacement L between the intersection point A and the scribing line  3  denotes the displacement between the intersection point A and the straight line connecting both sides of the scribing lines  3   a.    
     More specifically, as shown in  FIG. 8 , the scribing lines  3   a  are provided to the light emitting pattern  101   a  so as to satisfy the formula 3 described above, the scribing lines  3   b  are provided to the light emitting pattern  101   b  so as to satisfy the formula 3 described above, and the scribing lines  3   c  are provided to the light emitting pattern  101   c  so as to satisfy the formula 3 described above. In other words, the scribing lines  3  can be formed so as to satisfy the formula 3 described above with respect to the respective light emitting patterns  101 . Therefore, it is possible that each of the scribing lines  3  is not continuous like a straight line, and is formed as a broken line as shown in  FIG. 8 , for example. Thus, it becomes possible to form the cleavage surfaces more accurately so as to satisfy the formula 3 with respect to the respective light emitting patterns  101 . In particular, it is effective when displacement occurs in the patterning process and each of the light emitting patterns  101  is not formed along with the crystal plane. 
     Further, misalignment in manufacturing process might occur in the scribing process (forming scribing lines  3 ) themselves. For example, even if the scribing lines are formed aiming at the intersection point A, the scribing lines might be shifted in the −X direction (the opposite side of the first side surface  105 ) from the intersection point A. In this case, as described later, the light emitting device fails to emit light efficiently. Therefore, it is preferable to manufacture the scribing lines  3  aiming at the position satisfying the formula 3 described above in order to enhance the tolerance for the misalignment in the manufacturing process, and to obtain in a good yield the light emitting device  100  capable of emitting light efficiently. 
     As shown in  FIGS. 1 and 2 , the reflective section  130  is formed on the entire surface of the side of the second side surface  107 . The reflective section  130  is formed using, for example, a CVD method, a sputtering method, or an ion assisted deposition method. 
     According to the process described above, the light emitting device  100  can be manufactured. 
     According to a method for manufacturing the light emitting device  100 , the light emitting device  100  capable of efficiently emitting the light can be obtained. The details thereof will be described later. 
     3. Experimental Example of Light Emitting Device 
     Then, an experimental example of the light emitting device according to the present embodiment will be explained with reference to the accompanying drawings. Specifically, a simulation in a model M obtained by modeling the first gain region  160 , the second gain region  162 , and the reflective section  130  of the light emitting device  100  according to the present embodiment will be explained.  FIG. 9  is a plan view schematically showing the model M of the light emitting device  100  according to the present embodiment.  FIG. 10  is a graph showing a result of the simulation in the model M of the light emitting device  100  according to the present embodiment. 
     Firstly, the configuration of the model M will be explained. 
     In the model M, the vicinity of the overlapping plane  178  of the light emitting device  100  according to the present embodiment is analyzed. More specifically, as shown in  FIG. 9 , an end of the calculation area on the side of the third end surface  174  and on the side of the fourth end surface  176  is defined as a calculation end section B-B line. The light  12  with the intensity I 12  proceeding from the vicinity of the calculation end section B-B line of the first gain region  160  toward the first end surface  170  are generated, and the light  13  with the intensity I 13  proceeding from the first end surface  170  toward the calculation end section B-B line and the light  14  with the intensity I 14  having reached the calculation end section B-B line of the second gain region  162  is monitored. It should be noted that in the model M, there used a absorbing boundary conditions that almost all light having reached the calculation end section B-B line is transmitted through the B-B line without reflected toward outside. In other words, all of the light  14  having reached the calculation end section B-B line is transmitted through the B-B line and then emitted to outside of the calculation area (to the +X direction side from the calculation end B-B line), and there is no light returning to inside the gain regions  160 ,  162 . Therefore, even if the end surface of the first gain region  160  in the calculation area overlaps when viewed from the side of the first side surface  105  in a planar manner by limiting the calculation area, the multiple reflection is never caused inside the first gain region  160 . Similarly, also in the second gain region  162 , the multiple reflection is never caused. As described above, since the multiple reflection is never caused in the model M, there is no chance to form a resonator. 
     In the model M, the intensity I 14  of the light  14  is monitored while fixing the position of the first side surface  105 , and varying the displacement L between the second side surface  107  (the overlapping plane  178 ) and the intersection point A of the first center line  160   a  and the second center line  162   a . In the model M, it is assumed that the light  12  proceeds inside the first gain region  160  from the vicinity of the calculation end section B-B line of the first gain region  160  toward the first end surface  170 , then proceeds inside the second gain region  162  via the overlapping plane  178 , then reaches the calculation end section B-B line of the second gain region  162  as the light  14 , and is then transmitted to outside the calculation area. In the model M, it is assumed that the light  12  does not receive a gain in the gain regions  160 ,  162  for the sake of calculation convenience. Therefore, in the model M, by monitoring the intensity I 14  of the light  14 , it becomes possible to calculate the loss with respect to the intensity I 12  of the light  12 . 
     In the model M, it is assumed that the effective refractive index of the gain regions  160 ,  162  (i.e., the effective refractive index of the columnar section) is 3.346, and that of the region without constituting the gain regions  160 ,  162  (i.e., the effective refractive index of the outside of the columnar section) is 3.344. In the model M, it is assumed that the angles θ of the gain regions  160 ,  162  with respect to the perpendicular line P of the first side surface  105  are both 10 degrees. In the model M, as the reflective section  130 , for example, a dielectric mirror having 10 pairs of layers of SiO 2  and Ta 2 O 5  stacked in this order from the side of the second side surface  107 . The SiO 2  layer is arranged to have a refractive index of 1.43, and the thickness of one layer of which is 113.61 nm. The Ta 2 O 2  layer is arranged to have a refractive index of 2.16, and the thickness of one layer of which is 75.22 nm. In the model M, the simulation is performed by setting the width W of the gain region  160 ,  162  to be 5 μm and 10 μm. 
     Then, the result of the simulation will be explained. 
     In the graph shown in  FIG. 10 , the horizontal axis represents the displacement L, and the vertical axis represents an intensity ratio R. In the displacement L on the horizontal axis, the point at which the intersection point A and the second side surface  107  overlap with each other corresponds to zero, the case in which the second side surface  107  is displaced to the side of the first side surface  105  (+X direction) corresponds to the positive value (i.e., the value of the displacement L is positive), and the case in which the second side surface  107  is displaced to opposite the side of the first side surface  105  (−X direction) corresponds to the negative value (i.e., the value of the displacement L is negative). The intensity ratio R on the vertical axis represents the ratio (I 14 /I 12 ×100(%)) of the intensity I 14  of the light  14  with respect to the intensity I 12  of the light  12 . In other words, it can be said that the higher the intensity ratio R is, the smaller the loss of the light is, and the more efficiently the light can be emitted. 
     According to  FIG. 10 , it is understood that the intensity ratio R in the range (the range of the formula 1 described above) satisfying 0&lt;L&lt;W is substantially equivalent to or higher than the intensity ratio R at L=0. Further, it is understood that the intensity ratio R in the range satisfying (W/4)≦L≦(3W/4) (the range of the formula 2 described above) is surely higher than the intensity ratio R at L=0. Further, it is understood that in the case of L=(W/2) (the case of the formula 3) the intensity ratio R takes the maximum value, and the loss of light becomes minimum. 
     The reason that the loss of light becomes smaller due to the relationship between the displacement L and the width W described above can be inferred as follows. 
     The distance between the first gain region  160  and the second gain region  162  decreases as the first and second gain regions  160 ,  162  come closer to the second side surface  107 . Then, due to the evanescent coupling, some component of the light proceeding in the first gain region  160  toward the first end surface  170  begins to move to the second gain region  162  without going via the overlapping plane  178 . In other words, the light proceeding in the first gain region  160  toward the first end surface  170  senses the second gain region  162  as a highly refractive region, and some of the light begins to move toward the second gain region  162  and thereby be deflected. Assuming the case that the refractive index difference between the gain regions  160 ,  162  and the surrounding region is small, part of the light being deflected toward the second gain region  162  might pass through the second gain region  162  directly to cause the loss. In order to prevent such light from being loss and to input such light in the second gain region  162 , it is required to make the reflecting plane come closer in accordance with the path of the light thus deflected. Therefore, it can be inferred that the intensity ratio R can be raised because such light loss can be reduced by setting the L to be a positive value and the relationship between the displacement L and the width W to be the relationship expressed by the formula 1, preferably the formula 2, and further preferably the formula 3 described above. 
     As described above, in the light emitting device  100 , the displacement L and the width W can satisfy the formula 1, further the formula 2, and still further the formula 3 described above. Therefore, in the light emitting device  100 , the loss of light can be reduced, and the light can be emitted efficiently. Further, since the light emitting device  100  can emit light efficiently, miniaturization thereof can be achieved accordingly. 
     4. Modified Example 
     Then, a light emitting device  200  according to a modified example of the present embodiment will be explained with reference to the accompanying drawings.  FIG. 11  is a perspective view schematically showing the light emitting device  200 . Hereinafter, in the light emitting device  200  according to the modified example of the present embodiment, the constituents thereof having the same functions as those of the constituents of the light emitting device  100  according to the present embodiment will be denoted by the same reference symbols, and detailed explanations thereof will be omitted. In  FIG. 11 , the second electrode  114  is omitted from illustration for the sake of convenience. 
     As shown in  FIG. 11 , in the light emitting device  200 , the first gain region  160  is provided with a reflecting plane  261  between the first end surface  170  and the third end surface  174 . In the example shown in the drawing, the reflecting plane  261  is disposed on a third side surface  205  perpendicular to the first side surface  105  and the second side surface  107  of the active layer  106 . In the first gain region  160 , the light  210  proceeding from the first end surface  170  to the reflecting plane  261  can be reflected (e.g., totally reflected) by the reflecting plane  261  and thereby proceed from the reflecting plane  261  toward the third end surface  174 . Subsequently, the light  210  can be emitted from the third end surface  174  as the outgoing light  22 . In the example shown in the drawing, the light  22  emitted from the third end surface  174  and the light  20  emitted from the fourth end surface can proceed in the same direction. 
     Although not shown in the drawing, the reflecting plane  261  can be provided only to the second gain region  162  instead of the first gain region  160 , or can be provided to each of the gain regions  160 ,  162 . Further, the third end surface  205  provided with the reflecting plane  261  can also be provided with a reflecting section. The reflecting plane  261  can also be provided to an opening section formed in the active layer  106  by etching instead of the third end surface  205 . The light  22  emitted from the third end surface  174  and the light  20  emitted from the fourth end surface can also proceed in a converging direction. 
     According to the light emitting device  200 , the light  22  emitted from the third end surface  174  and the light  20  emitted from the fourth end surface  176  can proceed in the same direction or a converging direction. Thus, although not shown in the drawings, it becomes possible to miniaturize the optical system (the optical system to which the outgoing light  20 ,  22  incidents) compared to the case that the two outgoing light proceed in a diverging direction. 
     As described above, although the embodiment of the invention is explained in detail, it should be easily understood by those skilled in the art that various modifications not substantially departing from the novel matters and the effects of the invention are possible. Therefore, such modified examples should be included in the scope of the invention. 
     The entire disclosure of Japanese Patent Application No: 2009-062502, filed Mar. 16, 2009 is expressly incorporated by reference herein.