Patent Publication Number: US-2021194209-A1

Title: Light Emitting Device And Projector

Description:
The present application is based on, and claims priority from JP Application Serial Number 2019-231182, filed Dec. 23, 2019, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a light emitting device and a projector including the light emitting device. 
     2. Related Art 
     A semiconductor laser is expected as a next-generation light source which has high luminance. In particular, a semiconductor laser which has a nanostructure called a nanocolumn, a nanowire, a nanorod, a nanopillar, or the like is expected to implement a light emitting device capable of emitting light with high output at a narrow emission angle due to an effect of a photonic crystal. 
     JP-A-2009-152474 discloses a semiconductor light emitting device having a plurality of nanocolumns. In JP-A-2009-152474 (FIG. 3), a transparent electrode is formed by using a vapor deposition method on the nanocolumns forested at a constant pitch. An insulating film is formed on a side surface of a columnar nanocolumn, and a p-type GaN layer is exposed on a planar top portion, and the transparent electrode is formed so as to cover the top portion. Since the transparent electrode is formed so as to cover the forested nanocolumns, the transparent electrode recesses at gap portions between adjacent nanocolumns, and a surface of the transparent electrode is wavy. 
     However, in the technique of JP-A-2009-152474, it is difficult to establish stable electrical connection between the transparent electrode and the plurality of nanocolumns. Since a top portion of an actual nanocolumn has a dome shape with a curved surface or a cone shape with a gentle taper, adhension of the transparent electrode formed of an oxide film is not good as compared with the case where the top portion is planar. In addition, when the transparent electrode is formed of indium tin oxide (ITO), it may be difficult for a current to flow between the transparent electrode and the p-type GaN layer. Specifically, since the p-type GaN layer with a work function of about 6.7 eV and the ITO with a work function of about 4.3 eV have large energy barrier at an interface therebetween, it is difficult for the current to flow due to hole transport. 
     SUMMARY 
     An object of the present disclosure is to provide a light emitting device that secures stable electrical connection and a highly reliable projector. 
     A light emitting device according to the present application includes: a substrate; a laminated structure that is provided on the substrate and that includes a plurality of columnar portions; and an electrode provided at an opposite side of the laminated structure from the substrate. The columnar portion includes a first semiconductor layer, a second semiconductor layer of a conductivity type different from that of the first semiconductor layer, and a light emitting layer located between the first semiconductor layer and the second semiconductor layer. The electrode is connected to the second semiconductor layers in the plurality of columnar portions, and includes a first electrode layer formed of a material that has a work function smaller than that of the second semiconductor layer, and a second electrode layer that is connected to the first electrode layer and that has a work function smaller than that of the first electrode layer. An interface between the first electrode layer and the second electrode layer has an uneven shape. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a light emitting device according to a first embodiment. 
         FIG. 2  is a cross-sectional view of the light emitting device. 
         FIG. 3  is an enlarged view of a g-portion in  FIG. 2 . 
         FIG. 4  is a band diagram before and after contact between a metal and a semiconductor. 
         FIG. 5  is a flowchart showing a manufacturing method of the light emitting device. 
         FIG. 6A  is a process diagram showing a product form in a manufacturing process. 
         FIG. 6B  is a process diagram showing a product form in the manufacturing process. 
         FIG. 6C  is a process diagram showing a product form in the manufacturing process. 
         FIG. 7  is a schematic configuration diagram of a projector according to a second embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     First Embodiment 
     Outline of Light Emitting Device 
       FIG. 1  is a plan view of a light emitting device according to the present embodiment.  FIG. 2  is a cross-sectional view of the light emitting device taken along a line f-f of  FIG. 1 . First, an outline of a light emitting device  100  according to the present embodiment will be described with reference to  FIGS. 1 and 2 . The light emitting device  100  is a semiconductor laser light source including a plurality of nanocolumns that are fine columnar crystal structures that combine electrons and holes in a semiconductor to emit light. When the light emitting device  100  is actually used as a light source, an assembly in which a plurality of light emitting devices  100  are regularly arranged is often used as a surface light source. 
     In  FIG. 1 , description is made with a light emitting region  5  as a center, a direction of an n-electrode terminal  24  as a +X direction and a direction of a p-electrode terminal  39  as a +Y direction. The +X direction is also referred to as a right direction and a −X direction is also referred to as a left direction. In  FIG. 2 , a stacking direction on a substrate  10  is defined as a +Z direction. The +Z direction is also referred to as an upper direction. 
     As shown in  FIG. 2 , the light emitting device  100  includes a laminated structure  30  including a plurality of columnar portions  20  on the substrate  10 . 
     The substrate  10  is a substrate, and a Si substrate is used as a preferred example. The substrate is not limited to the Si substrate, and a GaN substrate, a sapphire substrate, a glass substrate, or the like may be used. 
     A buffer layer  11  is formed at a surface of the substrate  10 . The buffer layer  11  is an n-type GaN layer doped with Si as a preferred example. Since the buffer layer  11  is a part of the substrate  10 , the substrate  10  may be regarded as including the buffer layer  11 . 
     A reflective layer may be provided between the substrate  10  and the buffer layer  11  or on a bottom surface of the substrate  10 . The reflective layer is a distributed bragg reflector (DBR) layer. Since light toward the substrate  10  among light emitted from a light emitting layer  16  can be reflected by the reflective layer, light utilization efficiency can be improved. 
     The columnar portion  20  is a nanocolumn formed on the buffer layer  11 , and includes a first semiconductor layer  15 , the light emitting layer  16 , and a second semiconductor layer  17 . Specifically, the columnar portion  20  is a columnar structure in which the first semiconductor layer  15 , the light emitting layer  16 , and the second semiconductor layer  17  are stacked in this order on the buffer layer  11 . In a preferred example, a height of the columnar portion  20  is about 1000 nm. The columnar portion  20  is also referred to as a nanowire, a nanorod, or a nanopillar. 
     The first semiconductor layer  15  is an n-type semiconductor layer. In a preferred example, the first semiconductor layer  15  is an n-type GaN layer which is doped with Si. 
     In a preferred example, the light emitting layer  16  has a multiple quantum well structure in which quantum well structures including an i-type GaN layer which is not doped with impurities and an i-type InGaN layer are stacked. The light emitting layer  16  emits light when a current is injected from a p-side electrode  8  to be described later. 
     The second semiconductor layer  17  is a p-type semiconductor layer of a different conductivity type from the first semiconductor layer  15 . In a preferred example, the second semiconductor layer  17  is a p-type GaN layer which is doped with Mg. The first semiconductor layer  15  and the second semiconductor layer  17  also function as a cladding layer that confines light to the light emitting layer  16 . An upper portion (end surface) of the columnar portion  20  formed of the second semiconductor layer  17  has a dome shape with a rounded top portion. The shape of the top portion may be an obtuse cone shape depending on a growth condition. 
     The columnar portion  20  is not limited to a configuration in which the first semiconductor layer  15 , the light emitting layer  16 , and the second semiconductor layer  17  are stacked in this order from the substrate  10  side, and a stacking order thereof may be reversed. For example, the columnar portion  20  may have a configuration in which the second semiconductor layer  17 , the light emitting layer  16 , and the first semiconductor layer  15  are stacked in this order on the substrate  10 . In this case, the current is injected from the substrate  10  side. 
     As shown in  FIG. 1 , the light emitting device  100  includes the light emitting region  5  in which light from the plurality of columnar portions  20  is emitted. The light emitting region  5  has a substantially circular shape in a plan view, and the plurality of columnar portions  20  are regularly arranged in the circular shape. 
     Each of the columnar portions  20  has a substantially regular hexagonal shape in a plan view. A diameter of a circle circumscribed to the hexagonal shape is about 280 nm in the preferred example. The diameter is not limited to thereto, and may be 10 nm or more and 500 nm or less. In the present embodiment, the diameter of the circumscribed circle is regarded as a diameter of the columnar portions  20 . A planar shape of the columnar portions  20  is not limited to the hexagonal shape, and may be another polygonal shape or a circle. 
     The plurality of columnar portions  20  are arranged in a hexagonal pattern at a constant pitch. An arrangement pitch of the adjacent columnar portions  20  is about 300 nm in the preferred example. The arrangement pitch is not limited to thereto, and may be 1 nm or more and 500 nm or less. A gap between the adjacent columnar portions  20  is from about 10 to 20 nm. The gap serves as an air layer. 
     In addition, an arrangement form is not limited to the hexagonal pattern, and may be regular. For example, a lattice shape, a triangular lattice shape, a square lattice shape may be used. 
       FIG. 2  will be described again. 
     A sidewall  21  is provided around a columnar portion group formed by the forested columnar portions  20 . The sidewall  21  is a silicon oxide layer in a preferred example. A material of the sidewall  21  is not limited thereto, and is preferably a material which has a refractive index lower than that of the light emitting layer  16 . For example, the sidewall  21  may be an aluminum oxide layer or a titanium oxide layer. In the present embodiment, a configuration portion including the plurality of columnar portions  20  and the sidewall  21  that covers the sidewall of the columnar portions  20  is used as the laminated structure  30 . 
     A first electrode layer  19  is provided to cover top portions of the plurality of columnar portions  20 . The first electrode layer  19  is a metal layer, and has a two-layer structure of a metal thin film. Details will be described later. 
     An insulating layer  22  is provided around the laminated structure  30 . The insulating layer  22  is an insulating protective layer that opens the light emitting region  5  at the top portion of the laminated structure  30  and covers the periphery of the laminated structure  30 . In the preferred example, the insulating layer  22  is formed of silicon oxide. Any material may be used as long as the material is an insulating material. For example, silicon nitride or polyimide may be used. 
     A second electrode layer  25  is provided to cover the first electrode layer  19  and a part of the insulating layer  22 . The second electrode layer  25  is a transparent electrode layer, and indium tin oxide (ITO) is used as the preferred example. The p-side electrode  8  as an electrode is formed of the first electrode layer  19  and the second electrode layer  25 . Details of the p-side electrode  8  will be described later. 
     The n-electrode terminal  24  is provided in the +X direction of the laminated structure  30 . The n-electrode terminal  24  is electrically connected to the first semiconductor layers  15  of the plurality of columnar portions  20  by a wiring (not shown). The n-electrode terminal  24  is formed of a metal wiring formed on the buffer layer  11 . 
       FIG. 1  will be described again. 
     The p-electrode terminal  39  is provided in the +Y direction of the laminated structure  30 . The p-electrode terminal  39  is electrically connected to the second electrode layer  25  of the p-side electrode  8 . In other words, the p-electrode terminal  39  is electrically connected to the second semiconductor layers  17  of the plurality of columnar portions  20 . 
     The n-electrode terminal  24  and the p-electrode terminal  39  are power input terminals. For example, a bonding wire is connected to the power input terminals and a drive signal for driving light emission is input. 
     Detailed Configuration of P-Side Electrode 
       FIG. 3  is an enlarged view of a g-portion in  FIG. 2 , and is an enlarged cross-sectional view around the p-side electrode  8 . 
     As described above, the top portion of the columnar portion  20  has a rounded dome shape. Further, since there is a gap between the adjacent columnar portions  20 , a surface (upper surface) connecting the top portions of the plurality of columnar portions  20  has a wavy shape as shown in  FIG. 3 . 
     Since the p-side electrode  8  is provided so as to cover the top portions of the plurality of columnar portions  20 , the p-side electrode  8  is formed following the wavy shape. 
     The p-side electrode  8  has a two-layer structure including the first electrode layer  19  and the second electrode layer  25 . 
     The first electrode layer  19  has a two-layer structure including a first metal layer  19   a  and a second metal layer  19   b . In a preferred example, Ni is used for the first metal layer  19   a  and Au is used for the second metal layer  19   b . A thickness of the first metal layer  19   a  formed of the Ni layer is about 10 nm, and a thickness of the second metal layer  19   b  formed of the Au layer is about 10 nm, which form a thin film which has a total thickness of about 20 nm. Translucency is secured by making the film thin as described above. The thickness is not limited thereto, and any thickness can be used as long as the required translucency can be secured. 
     Further, since the metal thin film is flexible, the metal thin film also fits the shape of the wavy upper surface formed by the plurality of columnar portions  20 . Since the columnar portion  20  is a crystal, the surface thereof is smooth, but the metal thin film can be formed on the surface with good adhesion. 
     The second electrode layer  25  formed of a transparent electrode layer is provided on the second metal layer  19   b  in the first electrode layer  19 . In the preferred example, ITO is used as the second electrode layer  25 , and a film thickness is increased to about 200 nm in order to reduce electric resistance. 
     Here, an uneven shape  23  is provided at an interface between the second metal layer  19   b  of the first electrode layer  19  and the second electrode layer  25 . Specifically, the uneven shape  23  is formed on a surface of the second metal layer  19   b  formed of the Au layer, and the second electrode layer  25  provided on the second metal layer  19   b  also has a shape following the uneven shape  23 . The uneven shape  23  has a fine uneven shape of 10 nm or less, and is formed on the entire surface of the second metal layer  19   b . A method of forming the uneven shape  23  will be described later. 
       FIG. 4  is a band diagram before and after contact between a metal and a semiconductor. 
     A left side of  FIG. 4  is a band diagram of a metal  34  and a semiconductor  33  before contact, and a right side is a band diagram after contact. In  FIG. 4 , a Fermi level of the metal  34  is E fm , a Fermi level of the semiconductor  33  is E fs , and an electron affinity of the semiconductor is X s . 
     When a metal electrode is connected to the semiconductor, an ohmic contact is ideally formed if a work function Φ m  of the metal  34 &gt;the work function Φ s  of the semiconductor  33 . However, it is difficult to satisfy such a relationship in the configuration of the present embodiment. Specifically, a relationship in which the work function Φ s  of the second semiconductor layer  17  formed of the p-type GaN layer of the columnar portion  20  is as large as about 6.7 ev, while the work function Φ s  of the second electrode layer  25  formed of ITO is as small as about 4.3 ev is obtained. Therefore, as shown in the right side diagram of  FIG. 4 , after the contact between the metal and the semiconductor, an energy barrier ΦB is generated, and it is difficult for the current to flow due to the contact resistance. 
     In view of this point, a configuration in which the energy barrier is gradually relaxed is adopted. Specifically, in order to gradually reduce the energy barrier ΦB, the first electrode layer  19  which has the two-layer structure is interposed between the second semiconductor layer  17  and the second electrode layer  25 . 
     First, the second semiconductor layer  17  which has the work function Φ s  of about 6.7 ev is brought into contact with the first metal layer  19   a  formed of the Ni layer which has the work function Φm of about 5.2 ev. Then, the second metal layer  19   b  formed of the Au layer which has the work function Φm of about 4.7 eV is provided on the first metal layer  19   a . Then, the second electrode layer  25  formed of ITO which has the work function Φm of about 4.3 eV is provided on the second metal layer  19   b . That is, by adopting a configuration in which the work function has a relationship that a work function of the second semiconductor layer  17 &gt;a work function of the first metal layer  19   a &gt;a work function of the second metal layer  19   b &gt;a work function of the second electrode layer  25 , the energy barrier ΦB is gradually reduced to facilitate flowing of the current. 
     If the relationship is satisfied, the material of the metal layer or the transparent electrode may be changed. For example, indium zinc oxide (IZO) which has the work function Om of about 4.6 eV may be used instead of the ITO of the second electrode layer  25 . 
       FIG. 2  will be described again. 
     In the light emitting device  100  having such a configuration, the p-type second semiconductor layer  17 , the light emitting layer  16 , and the n-type first semiconductor layer  15  of the columnar portion  20  form a pin diode. When a forward bias voltage of the pin diode is applied between the p-electrode terminal  39  ( FIG. 1 ) and the n-electrode terminal  24 , a current is injected into the light emitting layer  16  to recombine electrons and holes in the light emitting layer  16 . The recombination causes light emission. 
     The light generated in the light emitting layer  16  propagates through the air layer of the gap in a direction orthogonal to the stacking direction of the first semiconductor layer  15  and the second semiconductor layer  17 , forms a standing wave by an effect of a photonic crystal based on the plurality of columnar portions  20 , and laser oscillates by receiving gain in the light emitting layer  16 . Then, the light emitting device  100  emits positive first-order diffracted light and negative first-order diffracted light as laser light from the light emitting region  5 . 
     Manufacturing Method of Light Emitting Device 
       FIG. 5  is a flowchart showing a manufacturing method of the light emitting device.  FIGS. 6A to 6C  are process diagrams showing a product form in the manufacturing process. Here, a manufacturing method of the light emitting device will be described mainly with reference to  FIG. 5  and with reference to  FIGS. 2 and 6A to 6C  as appropriate. 
     The light emitting device  100  can be basically manufactured by a method used in known semiconductor processes such as a chemical vapor deposition (CVD) method, a photolithography method (patterning), a sputtering method, a vapor deposition method (vacuum vapor deposition method), an etching method, a chemical mechanical planarization (CMP) method, or a combination thereof. Although a suitable manufacturing method will be mainly described, another manufacturing method may be used as long as an equivalent structure can be formed and the function and characteristics of the structure can be satisfied. 
     In step S 1 , the substrate  10  is prepared prior to formation of the nanocolumns. Specifically, as shown in  FIG. 6A , the buffer layer  11  is epitaxially grown on the substrate  10 . As a method of epitaxial growth, a metal organic chemical vapor deposition (MOCVD) method, a molecular beam epitaxy (MBE) method, or the like is used. Next, a selection mask  12 , which is a hard mask for partitioning a formation region of the columnar portions  20 , is formed on the buffer layer  11 . Ti is used as the selection mask  12  in a preferred example. In  FIG. 6A , the entire formation region of the plurality of columnar portions  20  is used as an opening of the selection mask  12 . However, in reality, an opening corresponding to each columnar portion  20  is formed. The selection mask  12  is formed by, for example, forming a film by the sputtering method and then performing patterning. 
     In step S 2 , the plurality of columnar portions  20  are formed. Specifically, the first semiconductor layer  15 , the light emitting layer  16 , and the second semiconductor layer  17  are epitaxially grown in this order on the buffer layer  11  in the opening of the selection mask  12 . As a method of the epitaxial growth, the MOCVD method, the MBE method, or the like is used. Accordingly, as shown in  FIG. 6B , the plurality of columnar portions  20  can be formed. The thickness of the columnar portion  20  and the shape of the top portion can be changed by adjusting growth conditions. 
     In step S 3 , the first electrode layer  19  is formed on the upper surfaces of the plurality of columnar portions  20 . First, a resist mask which has an opening in a region for the first electrode layer  19  is formed, and a Ni layer serving as the first metal layer  19   a  is film-formed on the entire surface by the vapor deposition method. Next, an Au layer serving as the second metal layer  19   b  is film-formed on the entire surface by the vapor deposition method, which overlaps the Ni layer. Next, the resist mask is removed. That is, as shown in  FIG. 6B , the first electrode layer  19  is formed on the upper surfaces of the plurality of columnar portions  20  by lift-off. 
     In step S 4 , the sidewall  21  and the insulating layer  22  are formed. 
     First, the sidewall  21  is formed. The silicon oxide layer is film-formed on the entire surface including the plurality of columnar portions  20 . In the preferred example, an Atomic layer deposition (ALD) method is used for the film formation. Next, a resist mask which has an opening in the region of the first electrode layer  19  is formed, and patterning including dry etching is performed. Accordingly, as shown in  FIG. 6C , the sidewall  21  is formed on side surfaces of the plurality of columnar portions  20 . 
     Next, the insulating layer  22  is formed. Specifically, after the silicon oxide layer is film-formed on the entire surface, the patterning including the dry etching is performed to form the insulating layer  22  in a state in which the light emitting region  5  is opened, as shown in  FIG. 6C . 
     In step S 5 , the uneven shape  23  is formed on the surface of the second metal layer  19   b . Specifically, by performing plasma processing of a dry process using a mixed gas in which oxygen is mixed with argon gas, the uneven shape  23  is formed on the surface of the Au layer. Accordingly, the fine uneven shape  23  of 10 nm or less is formed on the surface of the Au layer. The uneven shape  23  is also formed in valleys of the wavy upper surface formed by the plurality of columnar portions  20  in the same manner as the top portions. The method is not limited thereto, and a method capable of forming a similar uneven shape may be used. 
     In step S 6 , the second electrode layer  25  is formed on the upper surface of the first electrode layer  19 . Specifically, after the ITO layer is film-formed on the entire surface by the sputtering method, the patterning including the dry etching is performed to form the second electrode layer  25  that covers the first electrode layer  19  and a part of and the insulating layer  22 , as shown in  FIG. 2 . Accordingly, the p-side electrode  8  is formed. The vapor deposition method may be used for the film formation. 
     In step S 7 , a lead wiring and the p-electrode terminal  39  are formed. The p-electrode terminal  39  and the lead wiring that couples the p-side electrode  8  and the p-electrode terminal  39  are formed by forming the metal layer film by the vapor deposition method and then performing the patterning including the dry etching. In the same step, the n-electrode terminal  24  is also formed. Accordingly, the light emitting device  100  shown in  FIGS. 1 and 2  is formed. 
     According to the present embodiment, the following effects can be obtained. 
     The p-side electrode  8  includes the first electrode layer  19  formed of a material which has the work function smaller than that of the second semiconductor layer  17  and connected to the second semiconductor layer  17  in the plurality of columnar portions  20 , and the second electrode layer  25  which has the work function smaller than that of the first electrode layer  19  and connected to the first electrode layer  19 . The interface between the first electrode layer  19  and the second electrode layer  25  has the uneven shape  23 . 
     According to the configuration, since the work function of the first electrode layer  19  is smaller than that of the second electrode layer  25 , the energy barrier between the first electrode layer  19  and the second semiconductor layer  17  formed of the p-type GaN layer is smaller than a case where the second semiconductor layer  17  and the second electrode layer  25  are indirect contact with each other. In other words, by interposing the first electrode layer  19 , the energy barrier between the second semiconductor layer  17  and the second electrode layer  25  is gradually reduced and relaxed, so that the current easily flows. 
     Furthermore, since a contact area between the first electrode layer  19  and the second electrode layer  25  is increased due to the uneven shape  23 , the contact resistance is reduced and, the adhesion between the first electrode layer  19  and the second electrode layer  25  is improved. 
     Therefore, it is possible to provide the light emitting device  100  that secures stable electrical connection 
     The first electrode layer  19  is a metal layer, and includes the first metal layer  19   a  and the second metal layer  19   b . The work function of the first metal layer  19   a  connected to the second semiconductor layer  17  is larger than the work function of the second metal layer  19   b.    
     According to the configuration, since the first electrode layer  19  formed of a metal layer which has excellent adhesion is provided between the second semiconductor layer  17  and the second electrode layer  25 , the adhesion to the second semiconductor layer  17  of the columnar portions  20  is improved. Further, since the configuration in which the work function has a relationship that the work function of the second semiconductor layer  17 &gt;the work function of the first metal layer  19   a &gt;the work function of the second metal layer  19   b &gt;the work function of the second electrode layer  25  is adopted, the energy barrier OB is gradually reduced and the current can easily flow. 
     The second electrode layer  25  is a transparent electrode layer. The uneven shape  23  is provided at the interface between the second metal layer  19   b  and the second electrode layer  25 . As described above, although the second electrode layer  25  formed of the ITO is formed thick in order to lower the resistance, the second electrode layer  25  is likely to be peeled off when the thickness of the ITO is set to be thick, which is significant particularly in the valleys of the wavy shape between the adjacent columnar portions  20 . It is considered that film stress (contraction) during the formation of the ITO is applied in the valleys of the wavy shape in a state where the inclination of waves of the columnar portions  20  is large. 
     According to the configuration, by providing the uneven shape  23  and connecting the second metal layer  19   b  and the second electrode layer  25 , connection resilience is improved since both the second metal layer  19   b  and the second electrode layer  25  at the interface are firmly bonded to each other due to unevenness, and the contact area is increased. Accordingly, the second electrode layer  25  is prevented from being peeled off. In particular, it is effective for a case where the uneven shape in the valleys of the wavy shape is large. As described above, since an uneven degree of the uneven shape  23  is formed to be larger in the valleys of the wavy shape than in the top portions, it is possible to withstand the increase in the film stress in the valleys, and the second metal layer  19   b  and the second electrode layer  25  are reliably joined. Further, as the contact area increases, the contact resistance decreases. Therefore, it is possible to reliably couple the thick second electrode layer  25  and the second metal layer  19   b.    
     In the p-side electrode  8 , the first metal layer  19   a  is a Ni layer, the second metal layer  19   b  is an Au layer, and the uneven shape  23  is formed on the surface of the Au layer by plasma processing. 
     Accordingly, the uneven shape  23  can be efficiently formed on the surface of the Au layer which is the interface between the first electrode layer  19  and the second electrode layer  25 . 
     In addition, the uneven shape  23  is larger in the gap portion between the adjacent columnar portions  20  than in a portion that overlaps the columnar portions  20 . 
     Accordingly, in the gap between the adjacent columnar portions  20 , the large uneven shape  23  makes it possible to more closely adhere to the valley portion that is desired to be firmly coupled. 
     Second Embodiment 
     Outline of Projector 
       FIG. 7  is a schematic configuration diagram of a projector according to a second embodiment. 
     Here, a projector  200  according to the present embodiment will be described with reference to  FIG. 7 . 
     The projector  200  includes a housing (not shown), a red light source  110 R, a green light source  110 G, and a blue light source  110 B, which are provided in the housing and emit red light, green light, and blue light, respectively. 
     Each of the red light source  110 R, the green light source  110 G, and the blue light source  110 B includes the light emitting device  100  according to the first embodiment as a light source thereof. 
     The projector  200  further includes a first optical element  50 R, a second optical element  50 G, a third optical element  50 B, a first light modulation device  55 R, a second light modulation device  55 G, a third light modulation device  55 B, and a projection device  70 , which are provided in the housing. 
     The first light modulation device  55 R, the second light modulation device  55 G, and the third light modulation device  55 B are, for example, transmissive liquid crystal light valves. The projection device  70  is, for example, a projection lens. 
     The light emitted from the red light source  110 R is incident on the first optical element  50 R. The light emitted from the red light source  110 R is focused by the first optical element  50 R. The first optical element  50 R may have a function other than light focusing. The same applies to the second optical element  50 G and the third optical element  50 B to be described below. 
     The light focused by the first optical element  50 R is incident on the first light modulation device  55 R. The first light modulation device  55 R modulates the incident light in accordance with image information. Then, the projection device  70  enlarges an image formed by the first light modulation device  55 R and projects the image onto a screen  3 . 
     The light emitted from the green light source  110 G is incident on the second optical element  50 G. The light emitted from the green light source  110 G is focused by the second optical element  50 G. 
     The light focused by the second optical element  50 G is incident on the second light modulation device  55 G. The second light modulation device  55 G modulates the incident light in accordance with the image information. Then, the projection device  70  enlarges an image formed by the second light modulation device  55 G and projects the image onto the screen  3 . 
     The light emitted from the blue light source  110 B is incident on the third optical element  50 B. The light emitted from the blue light source  110 B is focused by the third optical element  50 B. The light focused by the third optical element  50 B is incident on the third light modulation device  55 B. The third light modulation device  55 B modulates the incident light in accordance with the image information. Then, the projection device  70  enlarges an image formed by the third light modulation device  55 B and projects the enlarged image onto the screen  3 . 
     The projector  200  includes a cross dichroic prism that combines the light emitted from the first light modulation device  55 R, the second light modulation device  55 G, and the third light modulation device  55 B and guides the combined light to the projection device  70 . 
     The light of three colors modulated by the first light modulation device  55 R, the second light modulation device  55 G, and the third light modulation device  55 B are incident on the cross dichroic prism  60 . The cross dichroic prism  60  is formed by bonding four right-angle prisms, and a dielectric multilayer film that reflects red light and a dielectric multilayer film that reflects blue light are arranged on an inner surface thereof. The light of three colors is combined by the dielectric multilayer films, and light representing a color image is formed. Then, the combined light is projected onto the screen  3  by the projection device  70 , and the enlarged image is displayed. 
     The red light source  110 R, the green light source  110 G, and the blue light source  110 B may directly form an image without using the first light modulation device  55 R, the second light modulation device  55 G, and the third light modulation device  55 B by controlling the light emitting device  100  as a pixel of the image according to the image information. Further, the projection device  70  may enlarge the image formed by the red light source  110 R, the green light source  110 G, and the blue light source  110 B and project the image onto the screen  3 . 
     As described above, the projector  200  includes the light emitting device  100  that secures stable electrical connection. Therefore, it is possible to provide the projector  200  with high reliability. 
     Although a transmissive liquid crystal light valve is used as a light modulation device in the above example, a light valve other than the liquid crystal light valve may be used, or a reflective light valve may be used. Examples of such a light valve include a reflective liquid crystal light valve and a digital micro mirror device. A configuration of the projection device is appropriately changed depending on a type of the light valve to be used. 
     The light source can also be applied to a light source device of a scanning type image display device which includes a scanning unit which is an image forming device that displays an image of a desired size on a display surface by scanning a screen with light from the light source. 
     The light emitting device  100  according to the embodiment described above can be used in addition to the projector. Applications other than the projector include, for example, indoor lighting, a backlight of a display, a laser printer, a scanner, in-vehicle light, a sensing machine using light, and a light source of such as a communication device. 
     First Modification 
     In the first embodiment described above, the case where the light emitting device  100  is a semiconductor laser using the columnar portions  20  is described, and the light emitting device  100  may be a super luminescent diode using the columnar portions  20  or a light emitting diode using the columnar portions  20 . 
     Second Modification 
     In the light emitting device  100  according to the first embodiment described above, the InGaN-based light emitting layer  16  is described, and various materials capable of emitting light by injecting a current can be used as the light emitting layer  16  in accordance with a wavelength of light to be emitted. For example, an AlGaN-based, AlGaAs-based, InGaAs-based, InGaAsP-based, InP-based, GaP-based, or AlGaP-based semiconductor materials can be used.