Patent Publication Number: US-2023140772-A1

Title: Light-emitting device and projector

Description:
The present application is based on, and claims priority from JP Application Serial Number 2021-176377, filed Oct. 28, 2021, 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. 
     2. Related Art 
     Semiconductor lasers are promising next-generation light sources having high luminance. In particular, semiconductor lasers to which nano-columns are applied are expected to be able to realize high-power light emission at a narrow radiation angle due to an effect of a photonic crystal derived from the nano-columns. 
     For example, JP-A-2021-7136 describes a light-emitting device including a plurality of column portions having a light-emitting layer and an electrode provided on the plurality of column portions. According to the description, by providing a plurality of holes in the electrode, light absorption can be reduced in proportion to the holes. 
     As an example of a method of further reducing light absorption in the electrode, it is conceivable to increase the diameter of holes provided in the electrode. However, when the diameter of holes is greater than the wavelength of light generated by the light-emitting layer, scattering of the light generated by the light-emitting layer in the holes may increase. 
     SUMMARY 
     One aspect of the light-emitting device according to the present disclosure includes 
     a substrate, 
     a laminated structure having a plurality of column portions, and 
     an electrode provided on a side of the laminated structure opposite from the substrate, wherein 
     each of the plurality of column portions includes a light-emitting layer, 
     the electrode is provided with a plurality of first holes, 
     a diameter of each of the plurality of first holes is less than a wavelength of light generated by the light-emitting layer, and 
     a distance between adjacent first holes of the plurality of first holes is less than the wavelength of light generated by the light-emitting layer. 
     One aspect of the projector according to the present disclosure includes one aspect of the light-emitting device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a cross-sectional view schematically illustrating a light-emitting device according to the present embodiment. 
         FIG.  2    is a plan view schematically illustrating column portions and first holes of a light-emitting device according to the present embodiment. 
         FIG.  3    is a cross-sectional view schematically illustrating a step of producing a light-emitting device according to the present embodiment. 
         FIG.  4    is a cross-sectional view schematically illustrating a step of producing a light-emitting device according to the present embodiment. 
         FIG.  5    is a cross-sectional view schematically illustrating a step of producing a light-emitting device according to the present embodiment. 
         FIG.  6    is a cross-sectional view schematically illustrating a light-emitting device according to a first variation of the present embodiment. 
         FIG.  7    is a cross-sectional view schematically illustrating a light-emitting device according to a second variation of the present embodiment. 
         FIG.  8    is a cross-sectional view schematically illustrating a light-emitting device according to a third variation of the present embodiment. 
         FIG.  9    is a diagram schematically illustrating a projector according to the present embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the embodiments described hereinafter is not intended to unreasonably limit the content of the present disclosure as set forth in the claims. In addition, not all of the configurations described below are essential constituent requirements of the present disclosure. 
     1. Light-Emitting Device 
     1.1. Overall Configuration 
     First, a light-emitting device according to the present embodiment will be described with reference to the drawings.  FIG.  1    is a cross-sectional view schematically illustrating a light-emitting device  100  according to the present embodiment.  FIG.  2    is a plan view schematically illustrating the light-emitting device  100  according to the present embodiment. Note that  FIG.  1    is a cross-sectional view taken along a line I-I in  FIG.  2   . 
     As illustrated in  FIG.  1   , the light-emitting device  100  includes, for example, a substrate  10 , a laminated structure  20 , a first electrode  40 , and a second electrode  42 . The light-emitting device  100  is, for example, a semiconductor laser. 
     The substrate  10  is, for example, a Si substrate, a GaN substrate, a sapphire substrate, or a SiC substrate. 
     The laminated structure  20  is provided at the substrate  10 . In the illustrated example, the laminated structure  20  is provided on the substrate  10 . The laminated structure  20  includes, for example, a buffer layer  22  and a plurality of column portions  30 . Note that for convenience, members in addition to the column portions  30  are not illustrated in  FIG.  2   . 
     In the present specification, when a light-emitting layer  34  of the column portion  30  is used as a reference along a lamination direction of the laminated structure  20  (hereinafter, also simply referred to as “lamination direction”), the direction from the light-emitting layer  34  toward a second semiconductor layer  36  of the column portion  30  is referred to as “upward”, and the direction from the light-emitting layer  34  toward a first semiconductor layer  32  of the column portion  30  is referred to as “downward”. A direction orthogonal to the lamination direction is referred to as “in-plane direction”. Additionally, the phrase “lamination direction of laminated structure  20 ” refers to the lamination direction of the first semiconductor layer  32  and the light-emitting layer  34 , which is the direction of a line N perpendicular to the substrate  10 . Specifically, the phrase “line N perpendicular to substrate  10 ” refers to a line on the upper surface of the substrate  10 . 
     The buffer layer  22  is provided on the substrate  10 . The buffer layer  22  is, for example, an n-type GaN layer doped with Si. A mask layer  24  for growing the column portions  30  is provided on the buffer layer  22 . The mask layer  24  is, for example, a titanium layer, a silicon oxide layer, a titanium oxide layer, or an aluminum oxide layer. 
     The column portions  30  are provided on the buffer layer  22 . The column portions  30  have a columnar shape protruding upward from the buffer layer  22 . In other words, the column portions  30  protrude upward from the substrate  10  with the buffer layer  22  interposed therebetween. The column portions  30  are also referred to as, for example, nano-columns, nano-wires, nano-rods, or nano-pillars. A planar shape of the column portion  30  is, for example, a polygon such as a hexagon, or a circle. In the example illustrated in  FIG.  2   , the planar shape of the column portion  30  is a regular hexagon. 
     A diameter of the column portion  30  is, for example, from 50 nm to 500 nm. By setting the diameter of the column portion  30  to be 500 nm or less, a light-emitting layer  34  of high quality crystals can be obtained, and a distortion inherent in the light-emitting layer  34  can be reduced. This makes it possible to amplify light generated in the light-emitting layer  34  with high efficiency. 
     Note that, when the planar shape of the column portion  30  is a circle, the phrase “diameter of column portion  30 ” refers to the diameter of the circle, and when the planar shape of the column portion  30  is not a circle, the phrase “diameter of column portion  30 ” refers to the diameter of the smallest circle containing the planar shape of the column portion  30 . For example, when the planar shape of the column portion  30  is a polygon, the diameter of the column portion  30  is the diameter of the smallest circle containing the polygon, and when the plane shape of the column portion  30  is an ellipse, the diameter of the column portion  30  is the diameter of the smallest circle containing the ellipse. 
     The column portion  30  is provided in plurality. The spacing between adjacent column portions  30  is, for example, from 1 nm to 500 nm. The plurality of column portions  30  are arranged in a predetermined direction at a predetermined pitch when viewed from the lamination direction. The plurality of column portions  30  are arranged in, for example, a triangular lattice, or a square lattice. In the example illustrated in  FIG.  2   , the plurality of column portions  30  are arranged in a regular, triangular lattice. The plurality of column portions  30  can develop the effect of photonic crystal. 
     Note that the phrase “pitch of column portions  30 ” refers to a distance between centers of the column portions  30  adjacent to each other in a predetermined direction. When the planar shape of the column portion  30  is a circle, the phrase “center of column portion  30 ” refers to the center of the circle, and when the planar shape of the column portion  30  is not a circle, the phrase “center of column portion  30 ” refers to the center of the smallest circle containing the planar shape of the column portion  30 . For example, when the planar shape of the column portion  30  is a polygon, the center of the column portion  30  is the center of the smallest circle containing the polygon, and when the plane shape of the column portion  30  is an ellipse, the center of the column portion  30  is the center of the smallest circle containing the ellipse. 
     As illustrated in  FIG.  1   , the column portion  30  includes, for example, the first semiconductor layer  32 , the light-emitting layer  34 , and the second semiconductor layer  36 . 
     The first semiconductor layer  32  is provided on the buffer layer  22 . The first semiconductor layer  32  is provided between the substrate  10  and the light-emitting layer  34 . The first semiconductor layer  32  is a first conductive type semiconductor layer. The first semiconductor layer  32  is, for example, an n-type GaN layer doped with Si. 
     The light-emitting layer  34  is provided between the first semiconductor layer  32  and the second semiconductor layer  36 . The light-emitting layer  34  generates light when an electric current is injected. The light-emitting layer  34  includes, for example, a well layer and a barrier layer. The well layer and the barrier layer are i-type semiconductor layers that are not intentionally doped with impurities. The well layer is, for example, an InGaN layer. The barrier layer is, for example, a GaN layer. The light-emitting layer  34  has a Multiple Quantum Well (MQW) structure including the well layer and the barrier layer. 
     Note that the numbers of the well layers and the barrier layers constituting the light-emitting layer  34  are not limited. For example, only one layer of the well layer may be provided, in which case the light-emitting layer  34  has a Single Quantum Well (SQW) structure. 
     The second semiconductor layer  36  is provided on the light-emitting layer  34 . The second semiconductor layer  36  is provided between the light-emitting layer  34  and the second electrode  42 . The second semiconductor layer  36  is a second conductive type semiconductor layer different from the first conductive type. The second semiconductor layer  36  is, for example, a p-type GaN layer doped with Mg. The first semiconductor layer  32  and the second semiconductor layer  36  are cladding layers having a function of confining light to the light-emitting layer  34 . 
     Note that, although not illustrated, an Optical Confinement Layer (OCL) including an i-type InGaN layer and a GaN layer may be provided either between the first semiconductor layer  32  and the light-emitting layer  34  or between the light-emitting layer  34  and the second semiconductor layer  36 , or both between the first semiconductor layer  32  and the light-emitting layer  34  and between the light-emitting layer  34  and the second semiconductor layer  36 . Additionally, the second semiconductor layer  36  may have an Electron Blocking Layer (EBL) including a p-type AlGaN layer. 
     In the light-emitting device  100 , the p-type second semiconductor layer  36 , the i-type light-emitting layer  34  not intentionally doped with impurities, and the n-type first semiconductor layer  32  constitute a pin diode. In the light-emitting device  100 , when a forward bias voltage of a pin diode is applied between the first electrode  40  and the second electrode  42 , an electric current is injected into the light-emitting layer  34 , and recombination of electrons and holes occurs in the light-emitting layer  34 . This recombination causes light emission. The light generated in the light-emitting layer  34  propagates in an in-plane direction, forms a standing wave due to an effect of photonic crystal caused by the plurality of column portions  30 , and receives a gain in the light-emitting layer  34  to generate laser oscillation. Then, the light-emitting device  100  emits+first order diffracted light and -first order diffracted light as laser light in the lamination direction. 
     Note that, although not illustrated, a reflection layer may be provided between the substrate  10  and the buffer layer  22 , or below the substrate  10 . The reflective layer is, for example, a Distributed Bragg Reflector (DBR) layer. The reflective layer can reflect light generated at the light-emitting layer  34 , allowing the light-emitting device  100  to emit light only from the second electrode  42  side. 
     The first electrode  40  is provided on the buffer layer  22 . The buffer layer  22  may be in ohmic contact with the first electrode  40 . The first electrode  40  is electrically coupled to the first semiconductor layer  32 . In the illustrated example, the first electrode  40  is electrically coupled to the first semiconductor layer  32  via the buffer layer  22 . The first electrode  40  is one electrode for injecting an electric current into the light-emitting layer  34 . The first electrode  40  that may be used is, for example, one obtained by stacking a Cr layer, an Ni layer, and an Au layer in this order from the buffer layer  22  side. 
     The second electrode  42  is provided on a side opposite to the substrate  10  of the laminated structure  20 . The second electrode  42  is provided on the second semiconductor layer  36 . The second semiconductor layer  36  may be in ohmic contact with the second electrode  42 . The second electrode  42  is another electrode for injecting an electric current into the light-emitting layer  34 . The second electrode  42  that may be used is, for example, Indium Tin Oxide (ITO) or the like. 
     Note that, although the description above is about a InGaN-based light-emitting layer  34 , various types of material capable of emitting light when an electric current is injected can be used in the light-emitting layer  34  in accordance with the wavelength of light emitted. For example, AlGaN-based, AlGaAs-based, InGaAs-based, InGaAsP-based, InP-based, GaP-based, or AlGaP-based semiconductor materials can be used in the light-emitting layer  34 . 
     1.2. First Holes Provided in Second Electrode 
     A plurality of first holes  44  are provided in the second electrode  42 . The first holes  44  extend through the second electrode  42 , for example. In the illustrated example, the first holes  44  extend through the second electrode  42  in the lamination direction. The first holes  44  are through holes. In the illustrated example, the first holes  44  are gaps. Note that, although not illustrated, the first holes  44  may be filled with a member having a refractive index lower than that of the second electrode  42 . 
     A planar shape of the first hole  44  is, for example, a circle. Note that the shape of the first hole  44  may be an ellipse, or may be a polygon. In the example illustrated in  FIG.  2   , the plurality of first holes  44  have the same size as each other. The plurality of first holes  44  are separated from each other. 
     When viewed from the lamination direction, a diameter D of the first hole  44  is less than a wavelength of light generated by the light-emitting layer  34 . The diameter D of the first hole  44  is less than a wavelength of the standing wave formed by the photonic crystal effect caused by the plurality of column portions  30 . That is, the diameter D of the first hole  44  is less than the oscillation wavelength. The diameter D of the first hole  44  is less than the diameter of the column portion  30 . 
     Note that, when the planar shape of the first hole  44  is a circle, the phrase “diameter D of first hole  44 ” refers to the diameter of the circle, and when the planar shape of the first hole  44  is not a circle, the phrase “diameter D of first hole  44 ” refers to the diameter of the smallest circle containing the planar shape of the first hole  44 . For example, when the planar shape of the first hole  44  is a polygon, the diameter D of the first hole  44  is the diameter of the smallest circle containing the polygon, and when the plane shape of the first hole  44  is an ellipse, the diameter D of the first hole  44  is the diameter of the smallest circle containing the ellipse. 
     A distance between adjacent first holes  44  is less than the wavelength of light generated by the light-emitting layer  34 . The distance between adjacent first holes  44  is less than the wavelength of the standing wave formed by the photonic crystal effect caused by the plurality of column portions  30 . That is, the distance between adjacent first holes  44  is less than the oscillation wavelength. The distance between adjacent first holes  44  is less than a distance between adjacent column portions  30 . When viewed from the lamination direction, the number of first holes  44  present per unit region of a predetermined shape is greater than the number of column portions  30  present per unit region of the predetermined shape. 
     The phrase “distance between adjacent first holes  44 ” refers to the shortest distance in a plan view from the lamination direction between one first hole  44  and another first hole  44  of the plurality of first holes  44  that is the closest to the one first hole  44 . For example, a distance L, which is the distance between a first hole  44   a  of the plurality of first holes  44  and a first hole  44   b  of the plurality of first holes  44  that is the closest to the first hole  44   a , is less than the wavelength of light generated by the light-emitting layer  34 . In the illustrated example, in all the first holes  44 , the distance between adjacent first holes  44  is less than the wavelength of light generated by the light-emitting layer  34 . 
     The number of the first holes  44  is greater than the number of the column portions  30 . The plurality of first holes  44  are not arranged periodically when viewed from the lamination direction. The plurality of first holes  44  are arranged at random, for example. In the illustrated example, viewed from the lamination direction, while there is a first hole  44  of the plurality of first holes  44  provided at a position overlapping with the column portion  30 , there is also a first hole  44  of the plurality of first holes  44  provided at a position not overlapping with the column portion  30 . The second electrode  42  may have a porous structure because the second electrode  42  is provided with the plurality of first holes  44 . The plurality of column portions  30  are arranged periodically when viewed from the lamination direction. In the illustrated example, one column portion  30  overlaps with multiple first holes  44  when viewed from the lamination direction. The first hole  44  is provided between adjacent column portions  30 . 
     1.3. Functions and Advantages 
     In the light-emitting device  100 , each of the plurality of column portions  30  includes a light-emitting layer  34 ; a plurality of first holes  44  are provided in the second electrode  42 ; the diameter D of each of the plurality of first holes  44  is less than the wavelength of light generated by the light-emitting layer  34 ; and the distance between adjacent first holes  44  of the plurality of first holes  44  is less than the wavelength of light generated by the light-emitting layer  34 . As such, in the light-emitting device  100 , light generated by the light-emitting layer  34  is less likely to be affected by the first holes  44 , and scattering of light generated by the light-emitting layer  34  in the first holes  44  can be reduced, when compared to a case in which a diameter of a first hole is greater than a wavelength of light, or in a case in which a distance between adjacent first holes is greater than a wavelength of light. Furthermore, the number of the first holes  44  per predetermined region can be increased, and thus absorption of light in the second electrode  42  can be reduced when compared to a case in which a distance between adjacent first holes is greater than a wavelength of light. Also, the resonance mode generated by the photonic crystal effect caused by the plurality of column portions  30  can be restrained from being disturbed by the first holes  44 . 
     In the light-emitting device  100 , each of the plurality of first holes  44  extends through the second electrode  42 . As such, in the light-emitting device  100 , the portion of the light-emitting device  100  with the second electrode  42  provided can have a smaller average refractive index in an in-plane direction when compared to a case in which the first holes do not extend through the second electrode. This can increase the optical confinement factor. 
     2. Method of Producing Light-Emitting Device 
     Next, a method of producing the light-emitting device  100  according to the present embodiment will be described with reference to drawings.  FIG.  3    to  FIG.  5    are cross-sectional views schematically illustrating steps of producing the light-emitting device  100  according to the present embodiment. 
     As illustrated in  FIG.  3   , the buffer layer  22  is epitaxially grown on the substrate  10 . Examples of the method for epitaxial growth include Metal Organic Chemical Vapor Deposition (MOCVD) and Molecular Beam Epitaxy (MBE). 
     Next, the mask layer  24  is formed on the buffer layer  22 . The mask layer  24  is formed by, for example, film formation by electron-beam vapor deposition or sputtering, and patterning. Patterning is performed, for example, by electron-beam lithography and dry etching. 
     As shown in  FIG.  4   , the first semiconductor layer  32 , the light-emitting layer  34 , and the second semiconductor layer  36  are epitaxially grown in this order on the buffer layer  22  by using the mask layer  24  as a mask. Examples of the method for epitaxial growth include MOCVD and MBE. The present step can form a plurality of column portions  30 . 
     As illustrated in  FIG.  5   , the second electrode  42  is formed on the second semiconductor layer  36 . The second electrode  42  is formed, for example, by sputtering, or vacuum vapor deposition. In the step of forming the second electrode  42 , oblique vapor deposition may be performed so that a material of electrode does not adhere to a side surface of the column portions  30 . 
     As illustrated in  FIG.  1   , the second electrode  42  is patterned to form the plurality of first holes  44 . Patterning is performed, for example, by electron-beam lithography and etching. The etching may be dry etching or wet etching, but wet etching can reduce the damage to the column portions  30 . 
     Next, the first electrode  40  is formed on the buffer layer  22 . The first electrode  40  is formed, for example, by sputtering, or vacuum vapor deposition. Note that the order of the step of forming the first electrode  40  and the step of forming the second electrode  42  are not limited. 
     The light-emitting device  100  can be produced by the above steps. 
     3. Variations of Light-Emitting Device 
     3.1. First Modified Example 
     Next, a light-emitting device  200  according to a first variation of the present embodiment will be described with reference to drawings.  FIG.  6    is a cross-sectional view schematically illustrating the light-emitting device  200  according to the first variation of the present embodiment. 
     Hereinafter, members of the light-emitting device  200  according to the first variation of the present embodiment having the same functions as the components of the light-emitting device  100  according to the present embodiment described above will be denoted by the same reference numerals, and detailed description of such members will be omitted. The same applies to the light-emitting devices according to a second variation and a third variation of the present embodiment to be described below. 
     As illustrated in  FIG.  1   , in the light-emitting device  100  described above, a gap is provided between adjacent column portions  30 . 
     In contrast, as illustrated in  FIG.  6   , in the light-emitting device  200 , a laminated structure  20  includes a light propagation layer  26  provided between adjacent column portions. 
     The light propagation layer  26  is provided on a mask layer  24 . The light propagation layer  26  is made of, for example, a dielectric material. Specifically, the light propagation layer  26  is a silicon oxide layer. More specifically, the light propagation layer  26  is a SiO 2  layer. Light generated by a light-emitting layer  34  propagates in the light propagation layer  26  in an in-plane direction. 
     A second hole  28  is provided in the light propagation layer  26 . The second hole  28  is coupled with a first hole  44 . The second hole  28  is provided in plurality. A bottom surface  29  of the second hole  28  is provided between the second semiconductor layers  36  of adjacent column portions  30 . The second hole  28  is not provided between the light-emitting layers  34  of adjacent column portions  30 . The second holes  28  do not extend all the way to the light-emitting layer  34  in the lamination direction. The bottom surface  29  is defined by the second semiconductor layer  36 . In the illustrated example, the second holes  28  are gaps. Note that, although not illustrated, the second holes  28  may be filled with a member having a refractive index lower than that of the light propagation layer  26 . Further, the second holes  28  may not be provided. 
     The light propagation layer  26  is formed by, for example, a CVD (Chemical Vapor Deposition) method, or a spin-coating method. The second holes  28  are formed by patterning the light propagation layer  26 . The second holes  28  are formed, for example, continued from the first holes  44 . 
     In the light-emitting device  200 , the laminated structure  20  includes the light propagation layer  26  provided between adjacent column portions  30  of the plurality of column portions  30 ; the light propagation layer  26  is provided with the second hole  28 ; the second hole  28  is coupled with one of the plurality of first holes  44 ; and the bottom surface  29  of the second hole  28  is positioned between the second semiconductor layers  36  of adjacent column portions  30  of the plurality of column portions  30 . As such, in the light-emitting device  200 , the portion of the light-emitting device  200  with the second hole  28  provided can have a smaller average refractive index in an in-plane direction when compared to a case in which the second hole is not provided. This can increase the optical confinement factor. Furthermore, since the light propagation layer  26  is provided between adjacent column portions  30 , adherence of a material of electrode to a side surface of the column portions  30  can be suppressed when the second electrode  42  is being formed. 
     3.2. Second Modified Example 
     Next, a light-emitting device  300  according to a second variation of the present embodiment will be described with reference to drawings.  FIG.  7    is a cross-sectional view schematically illustrating the light-emitting device  300  according to the second variation of the present embodiment. 
     As illustrated in  FIG.  1   , in the light-emitting device  100  described above, the first holes  44  extend through the second electrode  42 . 
     In contrast, as illustrated in  FIG.  7   , in the light-emitting device  300 , first holes  44  do not extend through a second electrode  42 . The first holes  44  are bottomed holes. 
     The second electrode  42  includes a first layer  42   a  not provided with the first holes  44  and a second layer  42   b  provided with the first holes  44 . The first layer  42   a  is provided on a plurality of column portions  30 . The first layer  42   a  defines bottom surfaces  45  of the first holes  44 . The first layer  42   a  is provided between the plurality of column portions  30  and the second layer  42   b . The second layer  42   b  is provided on the first layer  42   a . The first holes  44  may be formed by dry etching, or may be formed by wet etching. 
     In the light-emitting device  300 , each of the plurality of first holes  44  does not extend through the second electrode  42 . As such, in the light-emitting device  300 , damage to the column portions  30  caused by the etching for forming the first holes  44  can be suppressed. 
     3.3. Third Modified Example 
     Next, a light-emitting device  400  according to a third variation of the present embodiment will be described with reference to drawings.  FIG.  8    is a cross-sectional view schematically illustrating the light-emitting device  400  according to the third variation of the present embodiment. 
     As illustrated in  FIG.  1   , in the light-emitting device  100  described above, the diameter of the first semiconductor layer  32  of the column portion  30  is the same as the diameter of the light-emitting layer  34  of the column portion  30 . 
     In contrast, in the light-emitting device  400 , as illustrated in  FIG.  8   , a diameter of a first semiconductor layer  32  of a column portion  30  is smaller than a diameter of a light-emitting layer  34  of the column portion  30 . As a result, when compared to a case in which a diameter of the first semiconductor layer  32  of the column portion  30  is the same as a diameter of the light-emitting layer  34  of the column portion  30 , the difference between the average refractive index in an in-plane direction in the portion of the light-emitting device  400  with the first semiconductor layer  32  provided and the average refractive index in an in-plane direction in the portion of the light-emitting device  400  with the light-emitting layer  34  provided can be increased. This can increase the optical confinement factor. 
     In the light-emitting device  400 , the column portion  30  includes an optical confinement layer  38 . The optical confinement layer  38  is provided on the first semiconductor layer  32 . The optical confinement layer  38  is provided between the first semiconductor layer  32  and the light-emitting layer  34 . In the illustrated example, the optical confinement layer  38  has a portion in which the diameter of the column portion  30  gradually increases from the first semiconductor layer  32  toward the light-emitting layer  34 . The optical confinement layer  38  is composed of, for example, an i-type InGaN layer, or an i-type GaN layer. The In composition of the InGaN layer constituting the optical confinement layer  38  is smaller than the In composition of the InGaN layer constituting the light-emitting layer  34 . The optical confinement layer  38  is an OCL that confines light to the light-emitting layer  34 . 
     The light-emitting device  400  includes a dummy column portion  430  spaced apart from the second electrode  42 . The dummy column portion  430  does not emit light. The configuration of the dummy column portion  430  is, for example, the same as the configuration of the column portion  30 . The dummy column portion  430  is provided in plurality, for example. The dummy column portions  430  are grown in the same steps as those for the column portions  30 , for example. 
     An insulating layer  440  is provided between the dummy column portions  430  and the second electrode  42 . The insulating layer  440  surrounds the dummy column portions  430  when viewed from the lamination direction. The insulating layer  440  covers the dummy column portions  430 . The insulating layer  440  is provided on a mask layer  24 . The insulating layer  440  is, for example, a silicon oxide layer. More specifically, the insulating layer  440  is a SiO 2  layer. The insulating layer  440  is formed by, for example, CVD, or spin-coating. 
     In the illustrated example, the first electrode  40  is provided in a portion where the buffer layer  22  is partially removed. For example, a portion of the buffer layer  22  is etched, and the first electrode  40  is formed at the etched portion of the buffer layer  22 . 
     An electrode pad  450  is provided on the second electrode  42 . The electrode pad  450  overlaps with the dummy column portions  430  when viewed from the lamination direction. The electrode pad  450  contains, for example, titanium, or gold. Wire bonding that is not illustrated, for example, is used for coupling of the electrode pad  450 . The electrode pad  450  is formed by, for example, CVD or sputtering. 
     4. Projector 
     Next, a projector according to the present embodiment will be described with reference to drawings.  FIG.  9    is a diagram schematically illustrating a projector  800  according to the present embodiment. 
     The projector  800  includes, for example, the light-emitting device  100  serving as a light source. 
     The projector  800  includes a housing that is not illustrated, a red light source  100 R that emits red light, a green light source  100 G that emits green light, and a blue light source  100 B that emits blue light. The red light source  100 R, the green light source  100 G, and the blue light source  100 B are provided in the housing. Note that, for convenience, the red light source  100 R, the green light source  100 G, and the blue light source  100 B illustrated in  FIG.  9    are simplified. 
     The projector  800  further includes, in the housing, a first optical element  802 R, a second optical element  802 G, a third optical element  802 B, a first optical modulation device  804 R, a second optical modulation device  804 G, a third optical modulation device  804 B, and a projection device  808 . The first optical modulation device  804 R, the second optical modulation device  804 G, and the third optical modulation device  804 B are, for example, a transmissive liquid crystal light valve. The projection device  808  is, for example, a projection lens. 
     Light emitted from the red light source  100 R is incident on the first optical element  802 R. The light emitted from the red light source  100 R is condensed by the first optical element  802 R. Note that the first optical element  802 R may have a function in addition to condensing. The same applies to the second optical element  802 G and the third optical element  802 B described below. 
     The light condensed by first optical element  802 R is incident on the first optical modulation device  804 R. The first optical modulation device  804 R modulates the incident light according to information of an image. The projection device  808  then expands an image formed by the first optical modulation device  804 R and projects the expanded image to a screen  810 . 
     Light emitted from the green light source  100 G is incident on the second optical element  802 G. The light emitted from the green light source  100 G is condensed by the second optical element  802 G. 
     The light condensed by the second optical element  802 G is incident on the second optical modulation device  804 G. The second optical modulation device  804 G modulates the incident light according to information of an image. The projection device  808  then expands an image formed by the second optical modulation device  804 G and projects the expanded image to the screen  810 . 
     Light emitted from the blue light source  100 B is incident on the third optical element  802 B. The light emitted from the blue light source  100 B is condensed by the third optical modulation device  802 B. 
     The light condensed by the third optical element  802 B is incident on the third optical modulation device  804 B. The third optical modulation device  804 B modulates the incident light according to information of an image. The projection device  808  then expands an image formed by the third optical modulation device  804 B and projects the expanded image to the screen  810 . 
     In addition, the projector  800  may include a cross dichroic prism  806  that synthesizes the light emitted from the first optical modulation device  804 R, the light emitted from the second optical modulation device  804 G, and the light emitted from the third optical modulation device  804 B and guides the synthesized light to the projection device  808 . 
     Lights of three colors modulated by the first optical modulation device  804 R, the second optical modulation device  804 G, and the third optical modulation device  804 B are incident on the cross dichroic prism  806 . The cross dichroic prism  806  is formed by bonding four right-angle prisms together; an inner surface of the cross dichroic prism  806  is provided with a dielectric multilayer film that reflects red light and a dielectric multilayer film that reflects blue light. These dielectric multilayer films synthesize the lights of the three colors to form light expressing a color image. The synthesized light is then projected onto the screen  810  by the projection device  808 , and an enlarged image is displayed. 
     Note that the red light source  100 R, the green light source  100 G, and the blue light source  100 B may directly form an image by controlling the light-emitting device  100  as a pixel of an image according to information of an image; in this scenario, the use of the first optical modulation device  804 R, the second optical modulation device  804 G, and the third optical modulation device  804 B becomes unnecessary. Also, the projection device  808  may enlarge the image formed by the red light source  100 R, the green light source  100 G, and the blue light source  100 B and project the enlarged image to the screen  810 . 
     In addition, in the example described above, a transmissive liquid crystal light valve is used as the optical modulation device, but a light valve other than 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 or a digital micro-mirror device. The configuration of the projection device is changed as appropriate depending on the type of the light valve used. 
     Further, the light source can be applied to a light source device of a scanning-type image display device having scanning means, the scanning means being an image formation device that displays an image of a desired size on a display surface by scanning light from the light source on a screen. 
     The light-emitting device according to the embodiment described above can also be used in applications in addition to projectors. Examples of applications in addition to projectors include indoor and outdoor lighting, displays, laser printers, scanners, automotive lights, sensing devices using light, light sources for communication devices, and display devices of head-mounted displays. Further, the light-emitting device according to the embodiment described above can also be applied to light emitting elements of Light Emitting Diode (LED) displays in which tiny light-emitting elements are arranged in an array to display an image. 
     The embodiment and variations described above are examples and are not serving as limitations. For example, the embodiment and variations can be combined as appropriate. 
     The present disclosure includes configurations that are substantially the same as a configuration described in an embodiment, such as configurations having the same function, method and result, or configurations having the same object and effect. Furthermore, the present disclosure includes configurations in which a non-essential part of a configuration described in an embodiment is replaced. The present disclosure also includes configurations having the same action and effect as a configuration described in an embodiment or configurations capable of achieving the same object. Further, the present disclosure includes configurations in which a known technology is added to a configuration described in an embodiment. 
     The following contents are derived from the above-described embodiment and variations. 
     One aspect of the light-emitting device includes: 
     a substrate, 
     a laminated structure having a plurality of column portions, and 
     an electrode provided on a side of the laminated structure opposite from the substrate, wherein 
     each of the plurality of column portions includes a light-emitting layer, 
     the electrode is provided with a plurality of first holes, 
     a diameter of each of the plurality of first holes is less than a wavelength of light generated by the light-emitting layer, and 
     a distance between adjacent first holes of the plurality of first holes is less than the wavelength of light generated by the light-emitting layer. 
     According to the light-emitting device, scattering of light generated by the light-emitting layer in the first holes can be reduced, and absorption of light in the electrode can be reduced. 
     In one aspect of the light-emitting device, 
     each of the plurality of first holes may extend through the electrode. 
     According to the light-emitting device, an optical confinement factor can be increased. 
     In one aspect of the light-emitting device, 
     each of the plurality of column portions may include: 
     a first semiconductor layer of a first conductive type, and 
     a second semiconductor layer of a second conductive type that is different from the first conductive type, wherein 
     the light-emitting layer may be provided between the first semiconductor layer and the second semiconductor layer, 
     the first semiconductor layer may be provided between the substrate and the light-emitting layer, 
     the laminated structure may include a light propagation layer provided between adjacent column portions among the plurality of column portions, 
     the light propagation layer may be provided with a second hole, 
     the second hole may be coupled with one of the plurality of first holes, and 
     a bottom surface of the second hole may be positioned between the second semiconductor layers of adjacent column portions of the plurality of column portions. 
     According to the light-emitting device, an optical confinement factor can be increased. 
     In one aspect of the light-emitting device, 
     each of the plurality of first holes may not extend through the electrode. 
     According to the light-emitting device, damage to the column portions  30  caused by the etching for forming the first holes can be suppressed. 
     One aspect of a projector includes 
     one aspect of the light-emitting device.