Patent Publication Number: US-2010117109-A1

Title: Light emitting element

Description:
The present application is based on Japanese patent application No. 2008-287314 filed on Nov. 10, 2008, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a light emitting element. In particular, this invention relates to a light emitting element having a high brightness. 
     2. Description of the Related Art 
     Conventionally, a light emitting element is known that includes a light emitting layer, a light transmitting layer disposed on the light emitting layer so as to have a textured surface on a light extraction surface, and a smoothing layer made of silicon and disposed on the light transmitting layer so as to have no void between the light transmitting layer and the smoothing layer and to cover the textured surface, wherein the smoothing layer has a lower refractive index than that of the light transmitting layer and the exposed surface of smoothing layer is smoother than the textured surface (for example, refer to Patent Literature 1). 
     The light emitting element described in Patent Literature 1 includes the light transmitting layer which has the textured surface on the light extraction surface and the smoothing layer made of silicon which covers the textured surface, and then air bubbles are not easily to be trapped between the light emitting element and a sealing material for sealing the light emitting element, so that the element can prevent the air bubbles from forming voids in the sealing material. 
     Patent Literature 1: JP-A-2007-266571 
     However, in case of the light emitting element described in Patent Literature 1, if silicon is embedded in the textured surface for enhancing a light extraction efficiency, namely, a surface having concave and convex portions, a breaking may occur in the concave and convex portions due to a thermal shock applied to the light emitting element. If the concave and convex portions are broken, the light extraction efficiency of the light emitting element may be reduced. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the invention to solve the above-mentioned problem and provide a light emitting element that has a high brightness.
     (1) According to one embodiment of the invention, a light emitting element comprises:   

     a semiconductor stacked structure comprising a first semiconductor layer of first conductivity type, a second semiconductor layer of second conductivity type different from the first conductivity type and an active layer sandwiched between the first semiconductor layer and the second semiconductor layer; 
     a plurality of convex portions formed on one surface of the semiconductor stacked structure; and 
     an embedded part for transmitting a light emitted from the active layer and reducing stress generated in the plurality of convex portions, the embedded part being formed between two adjacent convex portions of the plurality of convex portions. 
     In the above embodiment (1), the following modifications and changes can be made. 
     (i) The plurality of convex portions comprise a cross sectional structure that gradually narrows in a direction from the active layer to the one surface of the semiconductor stacked structure. 
     (ii) The embedded part comprises a material with a refractive index between that of the plurality of convex portions and that of a resin for covering the light emitting element. 
     (iii) The embedded part comprises a material with a linear expansion coefficient of not more than 1×10 −5 /K. 
     (iv) The plurality of convex portions comprise, in a cross section, a length of a horizontal part thereof along a horizontal plane parallel to the active layer is not more than a length of a height part thereof in a direction perpendicular to the horizontal plane. 
     (v) The embedded part comprises a plurality of stacked materials with linear expansion coefficients different from each other. 
     (vi) The embedded part is formed to cover a tip portion of the plurality of convex portions. 
     (vii) The plurality of convex portions comprise a trapezoidal form in a cross section. 
     (viii) The semiconductor stacked structure further comprises a sidewall layer formed at least on a side face of the active layer. 
     Points of the Invention 
     According one embodiment of the invention, a light emitting element is constructed such that plural convex portions are formed on the light extraction surface, a concave portion formed between two adjacent ones is embedded with a material with a linear expansion coefficient close to that of a semiconductor material composing the convex portions. Thereby, even when thermal shock is applied to a light emitting device produced by sealing the light emitting element with a resin, stress occurred in the convex portions can be reduced. Thus, the convex portions are suppressed from being cracked or broken so as not to lower the light extraction efficiency of the light emitting device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The preferred embodiments according to the invention will be explained below referring to the drawings. 
         FIG. 1A  is a schematic cross-sectional view showing a light emitting element in a first preferred embodiment according to the invention; 
         FIGS. 1B and 1C  are each schematic perspective views showing a convex portion in the first embodiment according to the invention; 
         FIG. 1D  is a cross-sectional view cut along the line A-A in  FIGS. 1B and 1C ; 
         FIGS. 2A to 2Q  are each schematic cross-sectional views showing the flow of a production method of a light emitting element in the first embodiment according to the invention; 
         FIG. 3  is a schematic cross-sectional view showing a light emitting device mounting the light emitting element in the first embodiment according to the invention; 
         FIGS. 4A and 4B  are schematic perspective views showing convex portions in modification of the first embodiment according to the invention; 
         FIG. 4C  is a cross-sectional view cut along the line B-B in  FIGS. 4A and 4B ; 
         FIG. 5  is a schematic cross-sectional view showing a part of a light emitting element in a second preferred embodiment according to the invention; 
         FIG. 6  is a schematic cross-sectional view showing a part of a light emitting element in a third preferred embodiment according to the invention; 
         FIGS. 7A and 7B  are each schematic cross-sectional views showing a part of light emitting elements in modification of the third embodiment according to the invention; and 
         FIG. 8  is a schematic cross-sectional view showing a light emitting element in a fourth preferred embodiment according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       FIG. 1A  is a schematic cross-sectional view showing a light emitting element in a first embodiment according to the invention.  FIGS. 1B and 1C  are schematic perspective views showing convex portions in the first embodiment according to the invention, and  FIG. 1D  is a cross-sectional view cut along the line A-A in  FIGS. 1B and 1C . 
     Schematic Structure of Light Emitting Element  1   
     Referring to  FIG. 1A , the light emitting element  1  according to the first embodiment includes a semiconductor stacked structure  10  including an active layer  105  for emitting a light having a predetermined wavelength, a surface electrode  110  electrically connected to a partial region of one surface of the semiconductor stacked structure  10 , a contact part  120  brought into ohmic contact with a partial region of another surface of the semiconductor stacked structure  10 , a transparent layer  140  disposed so as to contact the another surface of the semiconductor stacked structure  10  excluding a region where the contact part  120  is disposed, and a reflecting part  130  disposed on a surface of the contact part  120  and the transparent layer  140 , the surface being located opposite to the surface of the contact part  120  and the transparent layer  140  which contacts the another surface of the semiconductor stacked structure  10 . 
     Further, the light emitting element  1  includes an adhesion layer  200  having an electrical conductivity and disposed on a surface of the reflecting part  130 , the surface being located opposite to the surface of the reflecting portion  130  which contacts the contact part  120  and the transparent layer  140 , and a supporting substrate  20  disposed on a surface of the adhesion layer  200 , the surface being located opposite to the surface of the adhesion layer  200  which contacts the reflecting part  130 . And, the supporting substrate  20  has a rear surface electrode  210  disposed on a surface of the supporting substrate  20 , the surface being located opposite to the surface of the supporting substrate  20  which contacts the adhesion layer  200 , namely, disposed on a rear surface of the supporting substrate  20 . 
     Further, the semiconductor stacked structure  10  of the light emitting element  1  according to the embodiment includes a p-type contact layer  109  disposed so as to contact the contact part  120  and the transparent layer  140 , a p-type cladding layer  107  as a second semiconductor layer of second conductivity type disposed on a surface of the p-type contact layer  109 , the surface being located opposite to the surface thereof which contacts the transparent layer  140 , an active layer  105  disposed on a surface of the p-type cladding layer  107 , the surface being located opposite to the surface thereof which contacts the p-type contact layer  109 , a n-type cladding layer  103  as a first semiconductor layer of first conductivity type disposed on a surface of the active layer  105 , the surface being located opposite to the surface thereof which contacts the p-type cladding layer  107 , and a n-type contact layer  101  disposed on a partial region of the n-type cladding layer  103 , the partial region being located opposite to the surface thereof which contacts the active layer  105 . 
     The surface of the semiconductor stacked structure  10  being located opposite to the surface thereof which contacts the transparent layer  140  functions as a light extraction surface of the light emitting element  1  according to the embodiment. In particular, a partial surface of the n-type cladding layer  103 , the partial surface being located opposite to the surface thereof which contacts the active layer  105 , namely, a part excluding a region just under a surface electrode  110  functions as the light extraction surface. And, in the light extraction surface of the n-type cladding layer  103 , plural convex portions  103   a  are formed as a plurality of convexities. A concave portion  103   b  is formed between one convex portion  103   a  and the other convex portion  103   a  adjacent to the one convex portion  103   a.  And, in each of the plural concave portions  103   b,  an embedded part  150  is formed, the embedded part  150  being made of a material capable of transmitting a light emitted from the active layer  105 . The embedded part  150  can reduce stress which occurs in the convex portions  103   a  in comparison with a case that the embedded part  150  is not formed in the concave portion  103   b.    
     Further, the reflecting part  130  includes a reflecting layer  132  disposed so as to contact the contact part  120  and the transparent layer  140 , an alloying suppression layer  134  disposed so as to contact a surface of the reflecting layer  132 , the surface being located opposite to the surface thereof which contacts the portion  120  and the transparent layer  140  and a joining layer  136  disposed so as to contact a surface of the alloying suppression layer  134 , the surface being located opposite to the surface thereof which contacts the reflecting layer  132 . And, the adhesion layer  200  includes a joining layer  202  electrically and mechanically connected to the joining layer  136  of the reflecting part  130 , and a contact electrode  204  disposed on a surface of the joining layer  202 , the surface being located opposite to the surface thereof which contacts the reflecting part  130 . And, the rear surface electrode  210  is formed so as to include a rear surface contact electrode  212  brought into ohmic contact with the rear surface of the supporting substrate  20 , and a die bonding electrode  214  disposed on a surface of the rear surface contact electrode  212 , the surface being located opposite to the surface thereof which contacts the supporting substrate  20 . 
     The light emitting element  1  according to the embodiment is formed almost in a square shape on the plan view. As an example, the light emitting element  1  has dimensions in a plan view that a longitudinal dimension is 250 μm and a lateral dimension is 250 μm. Further, the light emitting element  1  is formed so as to have a thickness of almost 200 μm. Furthermore, the light emitting element  1  according to the embodiment can be also formed, for example, so as to have a dimension in a plan view of not less than 500 μm, and as an example, so as to have a large-scaled chip size of 1 mm square. 
     Convex Portion  103   a,  Concave Portion  103   b,  and Embedded Part  150   
     The convex portion  103   a  according to the embodiment is formed so as to have a cross section structure that becomes gradually narrow in the direction directed from the active layer  105  to the surface electrode  110  (or the light extraction surface). In this case, if the plural convex portions  103   a  are formed, simultaneously, concave portions  103   b  are relatively formed. Also, if the plural concave portions  103   b  are formed so as to have a cross section structure that becomes gradually narrow in the direction directed from the light extraction surface to the active layer  105 , simultaneously, the plural convex portions  103   a  are relatively formed. 
     In particular, each of the plural convex portions  103   a  having a cone shape shown in  FIG. 1B , or a pyramid shape shown in  FIG. 1C  on a perspective view is formed on the surface the n-type cladding layer  103 . In case that the convex portion  103   a  has a cone shape or a pyramid shape, a direction to which a vertex of the cone shape or a pyramid shape is directed becomes a direction to which a light finally outputted from the light emitting element  1  is directed, the light being originally emitted from the active layer  105 . 
     Further,  FIG. 1D  is a transverse cross-sectional view of the convex portions  103   a,  particularly, is a transverse cross-sectional view taken along the line A-A in  FIGS. 1B and 1C . The convex portion  103   a  according to the embodiment is formed so as to have a shape that a length W 1  of “horizontal portion” along a surface parallel to the active layer  105  is not more than a length H 1  of “height portion” in a direction perpendicular to the horizontal surface on a cross sectional view. Further, in case that the convex portion  103   a  has a three-sided pyramid shape, the cross section is defined as a surface that passes through a vertex of the three-sided pyramid shape, a vertex of triangular shape on the bottom face of the three-sided pyramid shape, and a midpoint of the bottom facing to the vertex of triangular shape. Namely, the convex portion  103   a  becomes to have a cross sectional shape of almost a triangular shape, and the convex portion  103   a  is formed to have a shape that a ratio of a height of the triangular shape to a base thereof becomes not less than 1. Therefore, the convex portion  103   a  according to the embodiment is formed in an acute-angled triangular shape. As an example, the convex portion  103   a  is formed so as to have an angle at the end of the cone shape or the pyramid shape of not more than 40 degrees. 
     The concave portions  103   b  are formed in regions surrounded by the plural convex portions  103   a.  And, an embedded part  150  is disposed in each of the concave portions  103   b,  the embedded part  150  being formed by embedding a material which transmits a light emitted from the active layer  105  in each of the concave portions  103   b.  The embedded part  150  is formed by embedding a material which can reduce stress occurring in the plural convex portions  103   a  in each of the concave portions  103   b.  Namely, the stress is reduced due to the fact that a difference between a linear expansion coefficient of a semiconductor material constituting the convex portion  103   a  and that of a material constituting the embedded part  150  is small. 
     In particular, the embedded part  150  is formed of a material having the linear expansion coefficient close to that of the semiconductor material constituting the convex portion  103   a  and the embedded part  150  is formed of a material which has a linear expansion coefficient of not more than 1×10 −5 /K. Further, the embedded part  150  can be also formed of a material having a refractive index less than that of the semiconductor material constituting the convex portion  103   a.    
     For example, the embedded part  150  can be formed of an insulating transparent material such as silicon oxide (SiO 2 ), silicon nitride (Si 3 N 4 ), magnesium fluoride (MgF 2 ), a transparent conductive material such as indium tin oxide (ITO), tin oxide (SnO 2 ), zinc oxide (ZnO), or a wide bandgap compound semiconductor material such as zinc sulfide (ZnS), zinc selenide (ZnSe). Further, in case that the embedded part  150  is formed of ITO, it is preferable to use an insulating ITO with high transparency obtained by being formed under a predetermined oxygen atmosphere so as to prevent an oxygen defection from ITO and control a dopant concentration. Further, in case that the embedded part  150  is formed of the wide bandgap compound semiconductor material, the semiconductor material can be formed of any one of single crystal and polycrystal, if it can transmit a light emitted from the active layer  105 . Furthermore, in case that the embedded part  150  is formed of a conductive material such as ITO, an effect is provided that electrical current supplied to the light emitting element  1  is dispersed in the embedded part  150 . 
     Semiconductor Stacked Structure  10   
     The semiconductor stacked structure  10  according to the embodiment is formed so as to have a AlGaInP-based compound semiconductor which is a III-V group compound semiconductor. For example, the semiconductor stacked structure  10  has a structure that the active layer  105  formed so as to have a quantum well structure of the AlGaInP-based compound semiconductor is sandwiched between the n-type cladding layer  103  formed so as to have a n-type AlGaInP and the p-type cladding layer  107  formed so as to have a p-type AlGaInP. 
     The active layer  105  emits a light having a predetermined wavelength, if electric current is externally supplied. For example, the active layer  105  is formed so as to have a quantum well structure emitting a red light having a wavelength of almost 630 nm. Further, as the quantum well structure, any of a single quantum well structure, a multiple quantum well structure and a strained quantum well structure can be adopted. Further, the n-type cladding layer  103  contains an n-type dopant such as Si, Se at a predetermined concentration. As an example, the n-type cladding layer  103  is formed of an n-type AlGaInP layer doped with Si. Further, the p-type cladding layer  107  contains a p-type dopant such as Zn, Mg at a predetermined concentration. As an example, the p-type cladding layer  107  is formed of a p-type AlGaInP layer doped with Mg. 
     Further, the p-type contact layer  109  constituting the semiconductor stacked structure  10  is formed of, as an example, a p-type GaP layer doped with high concentration of Mg. And, the n-type contact layer  101  is formed of, as an example, a n-type GaAs layer doped with high concentration of Si. Here, the n-type contact layer  101  is formed on a part of top surface of the n-type cladding layer  103  corresponding to a region where the surface electrode  110  is formed. 
     Contact Part  120   
     The contact part  120  is formed on a part of the surface of p-type contact layer  109 . The contact part  120  is formed of a material brought into ohmic contact with the p-type contact layer  109 , and as an example, is formed of a metal alloy material including Au and Be, or Au and Zn. The contact part  120  is formed so as to have a shape that on a plan view, electric current supplied from the surface electrode  110  can be supplied to almost the whole surface of the active layer  105 , for example, a comb shape. Further, the contact part  120  according to the embodiment is formed also on a part just under the surface electrode  110 , but in a modification example of the embodiment, the contact part  120  can be also formed on a region excluding the part just under the surface electrode  110 . 
     Transparent Layer  140   
     The transparent layer  140  is formed on a part of surface of the reflecting part  130  (or the surface of the p-type contact layer  109 ) corresponding to a region where the contact part  120  is not formed. The transparent layer  140  is formed of a material which transmits a light emitted from the active layer  105 , and as an example, is formed of a transparent dielectric layer such as SnO 2 , TiO 2 , SiNx. The transparent layer  140  has a function as an electric current inhibition layer that electric current is not transmitted in a part where the transparent layer  140  is disposed. The electric current supplied to the light emitting element  1  is not transmitted through the transparent layer  140  as the electric current inhibition layer, but is transmitted through the semiconductor stacked structure  10  and the supporting substrate  20  via the contact part  120 . 
     Reflecting Part  130   
     The reflecting layer  132  of the reflecting part  130  is formed of a conductive material having a high reflectivity to a light emitted from the active layer  105 . As an example, the reflecting layer  132  is formed of a conductive material having a reflectivity of not less than 80% to the light. The reflecting layer  132  reflects a light reached the reflecting layer  132  of the light emitted from the active layer  105  so as to be directed for the side of active layer  105 . The reflecting layer  132  is formed of, for example, a metal material such as Al, Au, Ag or an alloy containing at least one selected from the metal material. As an example, the reflecting layer  132  is formed of a Au film having a predetermined thickness. Further, the reflecting layer  132  is electrically connected to the contact part  120 . 
     The alloying suppression layer  134  of the reflective part  130  is formed of a metal material such as Ti, Pt, and as an example, is formed of a Ti film having a predetermined thickness. The alloying suppression layer  134  prevents a material constituting the joining layer  136  from diffusing to the reflecting layer  132 . Further, the joining layer  136  is formed of a material electrically and mechanically joined to the joining layer  202  of the adhesion layer  200 , as an example, is formed of a Au film having a predetermined thickness. 
     Supporting Substrate  20   
     The supporting substrate  20  is formed of a conductive material. For example, the supporting substrate  20  can be formed of a semiconductor substrate such as a p-type or n-type conductive Si substrate, Ge substrate, GaAs substrate, GaP substrate or a metal substrate formed of a metal material such as Cu. As an example, in the embodiment, as the supporting substrate  20 , a conductive Si substrate having a low resistance can be used. 
     And, the joining layer  202  of the adhesion layer  200 , as well as the joining layer  136  of the reflective part  130 , can be formed of a Au film having a predetermined thickness. Further, the contact electrode  204  is formed of a metal material such as Ti brought into ohmic contact with the supporting substrate  20 . And, the rear surface electrode  210  disposed on a rear surface of the supporting substrate  20  includes the rear surface contact electrode  212  formed of a metal material such as Al, Ti brought into ohmic contact with the supporting substrate  20  and the die bonding electrode  214  disposed on a surface of the rear surface contact electrode  212  opposite to the supporting substrate  20  and formed of a metal material such as Au. 
     Further, the light emitting element  1  is mounted at a predetermined position of a stem formed of a metal such as Cu by using a conductive joining material such as a Ag paste or an eutectic material such as AuSn, in a state that the rear surface of the supporting substrate  20  (namely, the exposed surface of the rear surface electrode  210 ) is directed downward. The light emitting element  1  mounted on a predetermined region of the stem can be provided as a light emitting device by that the surface electrode  110  and the predetermined region of the stem are connected by a wire made of Au or the like and simultaneously, the whole of the light emitting element  1  and the wire are covered with a transparent resin such as epoxy resin, silicon resin. 
     Modification 
     The light emitting element  1  according to the embodiment emits a red light having a wavelength of almost 630 nm, the wavelength emitted from the light emitting element  1  is not limited to the above-mentioned wavelength. A structure of the active layer  105  of the semiconductor stacked structure  10  can be controlled so as to form the light emitting element  1  emitting a light having a predetermined wavelength range. The light emitted from the active layer  105  includes a light having a wavelength range of such as an orange light, a yellow light, a green light. Further, the semiconductor stacked structure  10  constituting the light emitting element  1  can be formed of a GaN compound semiconductor including the active layer  105  emitting a light of an ultraviolet region, a violet region or a blue region. 
     The convex portion  103   a  according to the embodiment is formed so as to have a cone shape or a pyramid shape, but in the modification of the embodiment, the convex portion  103   a  is not limited to being formed in the cone shape or the pyramid shape, if each surface constituting the convex portion  103   a  is formed of a surface that intersects at an acute angle to a horizontal surface parallel to the active layer  105 . Further, the convex portion  103   a  of the modification can be formed so as to have a convex shape that the end portion is sharpened and the cross section has an aspect ratio. As an example, the convex portion  103   a  according to the modification of the embodiment can be formed in a three-sided pyramid shape. Further, the end portion of the convex portion  103   a  is not needed to have a steeple shape, and can be formed so as to have a somewhat round part or a microscopic flat surface (a microscopic surface parallel to the active layer  105 ). 
     In the embodiment, the embedded part  150  is formed so as to have a flat surface, but can be also formed so as to have some concavities and convexities in the surface, if the stress occurring in the convex portion  103   a  can be reduced. Further, the embedded part  150  can be formed so as to have a flat surface and simultaneously, to have air bubbles formed in the bottom of the embedded part  150  (the bottom of the concave portions  103   b ), namely, in the side of the n-type cladding layer  103  of embedded part  150 . In this case, due to the existence of the air bubbles, the stress occurring in the convex portion  103   a  can be further reduced. 
     Further, in the embodiment, the end portion of the convex portion  103   a  and the surface of the embedded part  150  are formed so as to be almost in the same plane, but the surface of the embedded part  150  can be located lower than the end portion of the convex portion  103   a,  namely, closer to the side of the active layer  105 . In this case, although the end portion of the convex portion  103   a  does not contact the surface of the embedded part  150 , the vicinity of the end portion of the convex portion  103   a  is surrounded by the embedded part  150  so that the stress occurring in the convex portion  103   a  can be reduced. 
     Further, the embedded part  150  can include phosphor dispersed in a material transmitting the light emitted from the active layer  105 , the phosphor being capable of emitting a wavelength conversion light different from the wavelength of the light emitted from the active layer  105  if it is excited by the light emitted from the active layer  105 . For example, in case that the light emitted from the active layer  105  is a light of a blue region, a YAG phosphor can be dispersed in the embedded part  150 , the YAG phosphor emitting a yellow light if excited by the blue light. 
     Further, the semiconductor stacked structure  10  composing the light emitting element  1  can have compound semiconductor layers with an opposite conductivity type to those in the first embodiment. For example, the n-type contact layer  101  and the n-type cladding layer  103  may be changed into p-type conductivity, and the p-type cladding layer  107  and the p-type contact layer  109  may be changed into n-type conductivity. Further, a wire-bonding pad may be formed on the top surface of the surface electrode  110 . For example, when the surface electrode  110  is composed of a circular part and a thin wire electrode, the wire-bonding pad can be formed directly on the circular part. 
     The semiconductor stacked structure  10  may further have an n-side current spreading layer with a resistivity lower than the n-type cladding layer  103  between the n-type contact layer  101  and the n-type cladding layer  103 . Further, the semiconductor stacked structure  10  may further have a p-side current spreading layer with a resistivity lower than the p-type cladding layer  107  between the p-type contact layer  109  and the p-type cladding layer  107 . The semiconductor stacked structure  10  may have one or both of the n-side current spreading layer and the p-side current spreading layer. Due to the n-side current spreading layer and/or the p-side current spreading layer, current fed to the surface electrode  110  can spread in the surface direction of the light emitting element  1  to enhance the emission efficiency of the light emitting element  1 . Further, due to the n-side current spreading layer and/or the p-side current spreading layer, the drive voltage can be reduced. The active layer  105  may have a bulk structure. For example, the active layer  105  can be formed of an undoped AlGaInP based compound semiconductor. 
     Fabrication Method of the Light Emitting Element  1   
       FIG. 2A to 2Q  show a fabrication process flow for the light emitting element in the first embodiment of the invention. 
     First, as shown in  FIG. 2A , an AlGaInP based semiconductor stacked structure  11  including plural compound semiconductor layers is formed on an n-type GaAs substrate  100  by, e.g., MOCVD (metal organic chemical vapor deposition). In this embodiment, the semiconductor stacked structure  11  is composed, formed on the n-type GaAs substrate  100 , an etching stop layer  102 , the n-type cladding layer  103 , the active layer  105  and the p-type cladding layer  107 . 
     For example, on the n-type GaAs substrate  100 , the etching stop layer  102  of GaInP, the n-type contact layer  101  of n-type GaAs, the n-type cladding layer  103  of n-type AlGaInP, the quantum well type active layer  105  of AlGaInP, the p-type cladding layer  107  of p-type AlGaInP, and the p-type contact layer  109  of p-type GaP are formed in this order by MOCVD. Thereby, an epitaxial wafer is formed in which the semiconductor stacked structure  11  is formed on the n-type GaAs substrate  100 . As described later, by forming the n-type contact layer  101  and the p-type contact layer  109 , good electrical contact can be easy provided between the surface electrode  110  and the n-type contact layer  101  and between the p-type contact layer  109  and the contact part  120 , respectively. 
     The raw material used for MOCVD can be organic metal compounds such as trimethylgallium (TMGa), trimethylgallium (TEGa), trimethylaluminum (TMAl), trimethylindium (TMIn) etc., and hydrides such as arsine (AsH 3 ), phosphine (PH 3 ) etc. The raw material for the n-type dopant can be disilane (Si 2 H 6 ). The raw material for the p-type dopant can be biscyclopentadienyl magnesium (Cp 2 Mg). 
     The raw material for the n-type dopant may be hydrogen selenide (H 2 Se), monosilane (SiH 4 ), diethyltellurium (DETe) or dimethyltellurium (DMTe). The raw material for the p-type dopant may be dimethylzinc (DMZn) or diethylzinc (DEZn). 
     The semiconductor stacked structure  11  on the n-type GaAs substrate  100  may be formed by MBE (molecular beam epitaxy), HVPE (halide vapor phase epitaxy) etc. 
     Then, as shown in  FIG. 2B , the epitaxial wafer in  FIG. 2A  is taken out of the MOCVD apparatus, and the transparent layer  140  is then formed on the p-type contact layer  109 . For example, SiO 2  film as the transparent layer  140  is formed on the p-type contact layer  109  by using a plasma CVD (chemical vapor deposition) apparatus. The transparent layer  140  may be formed by the vacuum deposition. 
     Then, as shown in  FIG. 2C , openings  140   a  are formed in the transparent layer  140  by using the photolithography and etching techniques. For example, a photoresist pattern with grooves at regions for forming the openings  140   a  is formed on the transparent layer  140 . The opening  140   a  is formed extending from the surface of the transparent layer  140  to the interface between the p-type contact layer  109  and the transparent layer  140 . For example, the opening  140   a  is formed in the transparent layer  140  by removing the transparent layer  140  at regions without the photoresist pattern by using a hydrofluoric etchant diluted with pure water. The opening  140   a  is formed at regions for forming the contact parts  120 . 
     Then, as shown in  FIG. 2D , AuBe alloy as a material for forming the contact part  120  is formed in the opening  140   a  by the vacuum deposition and liftoff techniques. For example, AuBe is vacuum deposited in the opening  140   a  by using as a mask the photoresist pattern used for forming the opening  140   a  so as to form the contact part  120 . 
     Then, as shown in  FIG. 2E , an Au layer as the reflecting layer  132 , a Ti layer as the alloying suppression layer  134 , and an Au layer as the joining layer  136  are formed on the transparent layer  140  and the contact part  120  by using the vacuum deposition and sputtering. Thereby, a semiconductor stacked structure  1   a  is formed. The alloying suppression layer  134  can be formed by stacking a high melting point material layer such as a Ti layer and a Pt layer insofar as it can suppress the material of the joining layer  136  from diffusing into the reflecting layer  132 . Between the transparent layer  140  and the reflecting layer  132 , an adhesion thin film may be further formed for enhancing the adhesion of the reflecting layer  132  to the transparent layer  140 . The adhesion thin film can have a thickness substantially not absorbing light emitted from the active layer  105 . The reflecting layer  132  can be formed of a high-reflectivity material selected according to the wavelength of light emitted from the active layer  105 . 
     Then, as shown in  FIG. 2F , Ti as the contact electrode  204  and Au as the joining layer  202  are in this order formed on the Si substrate as the supporting substrate  20  by vacuum deposition. Thereby, the supporting structure  20   a  is formed. Then, the joining surface  136   a  as the surface of the joining layer  136  of the semiconductor stacked structure  1   a  is stacked on the joining surface  202   a  of the joining layer  202  of the supporting structure  20   a,  and the stacking state is retained by using a fixture formed of a carbon etc. 
     Then, the fixture for retaining the stacking state of the semiconductor stacked structure  1   a  and the supporting structure  20   a  is carried into a wafer lamination apparatus (e.g., a wafer lamination apparatus for micromachines). The internal pressure of the wafer lamination apparatus is reduced to a predetermined pressure. Then, substantially uniform pressure is applied to the stacked semiconductor stacked structure  1   a  and the supporting structure  20   a  via the fixture. Then, the fixture is heated to a predetermined temperature at a temperature rise speed. 
     For example, the fixture is heated to 350° C. After the temperature of the fixture reaches about 350° C., the fixture is kept at the temperature for about one hour. Then, the fixture is cooled down. For example, the fixture is sufficiently cooled to a room temperature. After the temperature of the fixture lowers, pressure applied to the fixture is released. Then, the internal pressure of the wafer lamination apparatus is back to atmospheric pressure and the fixture is taken out of the apparatus. Thereby, as shown in  FIG. 2G , a joined structure  1   b  is formed in which the semiconductor stacked structure  1   a  and the supporting structure  20   a  are mechanically joined between the joining layer  136  and the joining layer  202 . 
     In this embodiment, the semiconductor stacked structure  1   a  has the alloying suppression layer  134 . Therefore, even when the semiconductor stacked structure  1   a  and the supporting structure  20   a  are joined via the joining surface  136   a  and the joining surface  202   a,  the material composing the joining layer  136  and the joining layer  202  can be suppressed from diffusing into the reflecting layer  132  to prevent the deterioration of the reflection performance of the reflecting layer  132 . 
     Then, the joined structure  1   b  is attached to a fixture of a polishing apparatus by using an attaching wax. For example, the supporting substrate  20  side is attached to the fixture. Then, the n-type GaAs substrate  100  of the joined structure  1   b  is polished to a predetermined thickness. For example, the n-type GaAs substrate  100  is polished until the remaining thickness of the n-type GaAs substrate  100  becomes about 30 μm. Then, the polished joined structure  1   b  is released from the fixture of the polishing apparatus and the wax on the surface of the supporting substrate  20  is removed by washing. Then, as shown in  FIG. 2H , the n-type GaAs substrate  100  is selectively and perfectly removed from the polished joined structure  1   b  by using the etchant for etching GaAs so as to form a joined structure  1   c  with the etching stop layer  102  exposed thereon. For example, the GaAs etching etchant can be a mixed solution of ammonia water and hydrogen peroxide water. Alternatively, the n-type GaAs substrate  100  may be all removed by etching without polishing. 
     Then, as shown in  FIG. 2I , the etching stop layer  102  is removed from the joined structure  1   c  by etching by using a predetermined etchant. Thereby, a joined structure  1   d  without the etching stop layer  102  can be formed. When the etching stop layer  102  is formed of GaInP, the etchant can be an etchant including hydrochloric acid. Thereby, the surface of the n-type contact layer  101  is exposed. 
     Then, the surface electrode  110  is formed at a predetermined position on the n-type contact layer  101  by using the photolithography and vacuum deposition techniques. For example, as shown in  FIG. 2J , the surface electrodes  110  are formed on the n-type contact layer  101 . The surface electrode  110  is composed of a circular part with a diameter of 100 μm, and plural thin wire electrodes extending from the circular part to the outside of the circular part. The surface electrode  110  is formed by depositing AuGe, Ni and Au in this order on the n-type contact layer  101 . Thereby, as shown in  FIG. 2J , a joined structure  1   e  with the surface electrodes  110  can be formed. 
     Then, as shown in  FIG. 2K , by using the surface electrode  110  in  FIG. 2J  as a mask, the n-type contact layer  101  except a part directly under the surface electrode  110  is removed by etching with a mixed solution of sulfuric acid, hydrogen peroxide water and water. Thereby, a joined structure  1   f  can be formed. By suing the mixed solution, the n-type contact layer  101  of GaAs can be etched selectively relative to the n-type cladding layer  103  of n-type AlGaInP. Thereby, in the joined structure  1   f,  the surface of the n-type cladding layer  103  is exposed. 
     Then, as shown in  FIG. 2L , plural convex portions  103   a  are formed at a part of the surface of the n-type cladding layer  103 . The plural convex portions  103   a  are formed conical or pyramidal as shown in  FIGS. 1B and 1C . For example, a mask pattern with patterns repeated at predetermined intervals for the convex portion  103   a  and the concave portion  103   b  is formed on the surface of the n-type cladding layer  103  by using the photolithography. The formed patterns are arranged in the form of a matrix, honeycomb etc. Using the mask pattern as a mask, the convex portions  103   a  and the concave portions  103   b  are formed on the surface of the n-type cladding layer  103  by dry etching. Then, the mask is removed to form a joined structure  1   g  with the convex portions  103   a  and the concave portions  103   b.    
     Then, an SiO 2  layer with the same height as the convex portion  103   a  is formed by CVD such that the concave portions  103   b  are filled with SiO 2 . Thereby, as shown in  FIG. 2M , a joined structure  1   h  is formed such that the concave portions  103   b  are each filled with SiO 2  and the SiO 2  layer is formed on the surface electrode  110 . The SiO 2  layer may be formed by the solution or coating technique. When the SiO 2  layer is formed by the solution or coating technique, the surface of the SiO 2  layer can be easy flattened and the uppermost surface of the embedded part  150  detailed later can be also easy flattened. When the concave portion  103   b  is embedded with a semiconductor material, the semiconductor layer may be epitaxially grown therein in place of the SiO 2  layer. The epitaxially grown semiconductor layer is excellent in crystalline quality so that transparency to light emitted from the active layer  105  can be enhanced. 
     Then, a mask is formed which has openings at regions corresponding to the surface electrode  110 . Then, the SiO 2  layer on the surface electrode  110  is removed which is exposed through the opening of the mask. Then, the mask is removed. Thereby, as shown in  FIG. 2N , a joined structure  1   h  is formed in which the plural concave portions  103   b  are embedded with SiO 2 . Then, on almost the entire back face of the supporting substrate  20 , the rear surface contact electrode  212  of Al and the die bonding electrode  214  of Au are formed by vacuum deposition. Thereby, as shown in  FIG. 2O , a joined structure  1   j  is formed which has the rear surface contact electrode  212  and the die bonding electrode  214 . Then, the joined structure  1   j  is subjected to an alloying process whereby electrical junctions are formed between the contact part  120  and the p-type contact layer  109  and between the surface electrode  110  and the n-type contact layer  101 , respectively. For example, the joined structure  1   j  is subjected to the alloying process at about 400° C. in a nitrogen inert atmosphere. 
     Then, a mask pattern for separation between light emitting elements is formed on the surface of the joined structure  1   j  by photolithography. For example, the mask pattern for light emitting element separation is formed on the surface of the n-type cladding layer  103  of the joined structure  1   j.  Then, by using the mask pattern as a mask, a section region from the surface side of the n-type cladding layer  103  to the p-type contact layer  109  is removed by wet etching such that the light emitting elements are separated each other. Thereby, as shown in  FIG. 2P , a joined structure  1   k  is formed which has plural separated light emitting elements. 
     Then, by using dicing equipment with a dicing blade, the joined structure  1   k  is diced into chips. Thereby, as shown in  FIG. 2Q , the plural light emitting elements  1  of this embodiment are obtained. As explained above, the semiconductor layers of the joined structure  1   k  including the active layer  105  are separated by wet etching, so that the semiconductor layers including the active layer  105  can be prevented from having mechanical defects that may be caused upon the element separation by using the dicing equipment. 
       FIG. 3  is a schematic cross-sectional view showing a light emitting device mounting a light emitting element in the first embodiment according to the invention. 
     The light emitting element  1  is mounted on a stem  7  formed of a metallic material such as Cu, Al etc. For example, the light emitting element  1  is mounted on an element mounting region  7   b  of the stem  7  via a conductive joining material  9  for joining mechanically the light emitting element  1  to the stem  7 . For example, the conductive joining material  9  can be a conductive adhesive such as Ag paste or an eutectic material such as AuSn. Then, the surface electrode  110  is bonded to a current feeding part  7   a  of the stem  7  by a wire  6  of Au etc. Then, the light emitting element  1  and the wire  6  are sealed with a transparent resin  8  such as epoxy resin, silicone etc. Thereby, a light emitting device  5  can be obtained. 
     In this embodiment, the embedded part  150  embedded in the concave portion  103   b  is formed of a material that has a linear expansion coefficient smaller than the resin  8  and close to that of the semiconductor material composing the convex portion  103   a.  In other words, the embedded part  150  is formed of such a material that the difference between the linear expansion coefficient of the semiconductor material composing the convex portion  103   a  and that of the material composing the embedded part  150  is smaller than the difference between the linear expansion coefficient of the material composing the embedded part  150  and that of the resin  8 . 
     For example, AlGaInP semiconductor composing the n-type cladding layer  103  has a linear expansion coefficient of about 4×10 −6  to 8×10 −6 /K. On the other hand, silicone used for the resin  8  has a linear expansion coefficient of about 100×10 −6  to 500×10 −6 /K. The embedded part  150  of the embodiment is formed of a material with a linear expansion coefficient of not more than 10×10 −6 /K. Thus, the convex portion  103   a  can be suppressed from being subjected to stress caused by temperature change. 
     The embedded part  150  may be composed of a material with a refractive index greater than the resin  8 . In this case, the refractive index lowers in the order of the semiconductor material composing the convex portion  103   a,  the material composing the embedded part  150 , and the material composing the resin  8 . Thus, the embedded part  150  is formed of the material with a refractive index between that of the material composing the convex portion  103   a  and that of the material composing the resin  8  for sealing the light emitting element  1 . 
     Effects of the First Embodiment 
     The light emitting element  1  of the first embodiment is constructed such that the concave portion  103   b  formed on the light extraction side is embedded with the material with a linear expansion coefficient close to that of the semiconductor material composing the convex portion  103   a.  Therefore, even when thermal shock is applied to the light emitting device  5  produced by sealing the light emitting element  1  with the resin  8 , stress occurred in the convex portion  103   a  can be reduced. Thereby, the convex portion  103   a  is suppressed from being cracked or broken such that the light emitting element  1  and the light emitting device  5  can be enhanced in reliability. 
     The light emitting element  1  of the first embodiment is constructed such that the concave portion  103   b  is embedded with the material with a linear expansion coefficient close to that of the material composing the convex portion  103   a.  Therefore, even when thermal shock is applied to the light emitting device  5 , stress occurred in the convex portion  103   a  can be reduced. If the concave portion  103   b  is embedded with silicone, the convex portion  103   a  may be subjected to stress as large as 10 6  to 10 9  Pa so that the convex portion  103   a  with a sharp tip may be broken. In this embodiment, such a breakage can be significantly suppressed. 
     Further, the light emitting element  1  of the first embodiment is constructed such that the refractive-index difference between the embedded part  150  and the resin  8  is smaller than that between the n-type cladding layer  103  and the resin  8 . Therefore, the light extraction angle at the light extraction surface increases. Thereby, the light emitting device  5  using the light emitting element  1  in the embodiment can have significantly improved light extraction efficiency. 
     When the embedded part  150  is formed of an inorganic material such as SiO 2 , the surface of the n-type cladding layer  103  can be suppressed from deteriorating due to moisture or oxygen which may externally penetrate into the resin  8  composing the light emitting device  5 . Thus, the light emitting element  1  and the light emitting device  5  can be enhanced in moisture resistance and oxygen resistance. 
     Modification of the First Embodiment 
       FIGS. 4A to 4C  show convex portions in a modification of the first embodiment of the invention. 
     A light emitting element of the modification has the same composition as the light emitting element  1  of the first embodiment except that the shape of the convex portion is different. Thus, the detailed explanation of the components except the different components will be omitted below. 
     Referring to  FIG. 4A  (perspective view), a convex portion  103   c  may be shaped like a truncated cone. Referring to  FIG. 4B  (perspective view), a convex portion  103   c  may be shaped like a truncated pyramid.  FIG. 4C  is a cross sectional view of the convex portion  103   c,  i.e., a cross sectional view cut along the line B-B in  FIGS. 4A and 4B . 
     The convex portion  103   c  is formed such that, in the cross section, a width W 2  of a bottom portion thereof along a parallel plane to the active layer  105  is not more than a height H 2  thereof perpendicular to the parallel plane. In other words, the convex portion  103   c  is shaped like a trapezoid in the cross section, and the convex portion  103   c  is formed such that the ratio of the height to the base in the trapezoid is not less than 1. Thus, the cross section of the convex portion  103   c  is formed trapezoidal so that the breakage of the convex portion  103   c  can be significantly suppressed. 
     Second Embodiment 
       FIG. 5  is a schematic cross-sectional view showing a part of a light emitting element in a second preferred embodiment according to the invention. 
     The light emitting element  2  of the second embodiment has the same composition as the light emitting element  1  of the first embodiment except that the thickness of the embedded part  150  is different. Thus, the detailed explanation of the components except the different components will be omitted below. 
     The light emitting element  2  of the second embodiment is constructed such that the embedded part  150  is formed to cover the tip portion of the convex portion  103   a  as well as the inside of the concave portion  103   b.  Namely, the embedded part  150  of the second embodiment is formed to have a thickness greater than that of the first embodiment. The light emitting element  2  of the second embodiment can also reduce stress occurred in the convex portion  103   a  since the convex portion  103   a  is completely enclosed by the embedded part  150 . 
     Third Embodiment 
       FIG. 6  is a schematic cross-sectional view showing a part of a light emitting element in a third preferred embodiment according to the invention. 
     The light emitting element  3  of the third embodiment has the same composition as the light emitting element  1  of the first embodiment except that the structure of the embedded part  150  is different. Thus, the detailed explanation of the components except the different components will be omitted below. 
     The light emitting element  3  of the third embodiment is provided with the embedded part  150  composed of multiple embedded layers stacked. For example, a first embedded layer  150   a  is formed on the concave portion  103   b,  a second embedded layer  150   a  is formed on the first embedded layer  150   a,  and a third embedded layer  150   c  is formed on the first embedded layer  150   b.  Thus, the embedded part  150  of the third embodiment is composed of the first to third embedded layers  150   a  to  150   c.    
     The materials for forming the first to third embedded layers  150   a  to  150   c  composing the embedded part  150  may be different from each other. The material of the embedded part  150  can be a semiconductor material with a high refractive index (e.g., with a refractive index of about 2 to 3) or a semiconductor material with a low refractive index (e.g., with a refractive index of about 1.3 to 1.5). For example, it can be MgF 2  (1.38 in refractive index), SiO 2  (1.45 in refractive index), ZnS (2.37 in refractive index), Si 3 N 4  (2 in refractive index) etc. An example is made such that the refractive index lowers in the order of the first embedded layer  150   a,  the second embedded layer  150   b  and the third embedded layer  150   c.  Where the refractive index lowers gradually from the first embedded layer  150   a  to the third embedded layer  150   c,  the refractive index difference from that of the external air can be reduced gradually so that the reflectively (of light extracted through the embedded part  150 ) at the light extraction surface can be reduced. 
     According to the light emitting element  3  of the third embodiment, the embedded part  150  is in multilayer structure so that the light extraction efficiency and the reliability can be significantly enhanced. 
     Modification of the Third Embodiment 
       FIGS. 7A and 7B  are each schematic cross-sectional views showing a part of light emitting elements in modification of the third embodiment according to the invention. 
     The light emitting elements in modification of the third embodiment have the same composition as the light emitting element  1  of the first embodiment except that the structure of the embedded part  150  is different. Thus, the detailed explanation of the components except the different components will be omitted below. 
     Referring to  FIG. 7A , a light emitting element in modification of the third embodiment is provided with the embedded part  150  composed of multiple embedded layers stacked. For example, a reflection preventing film  154  is formed on the concave portion  103   b,  and an embedded layer  156  is formed on the reflection preventing film  154 . The reflection preventing film  154  is formed of, e.g., Si 3 N 4 . The reflection preventing film  154  is formed to have a thickness of λ/4n, where λ is a wavelength of light emitted from the active layer  105  and n is a refractive index of the material thereof, e.g., Si 3 N 4 . Where the embedded layer  156  is formed on the reflection preventing film  154  and the surface of the embedded layer  156  is flattened, the light emitting element in modification of the third embodiment can have high output and high reliability. 
     Referring to  FIG. 7B , another light emitting element in modification of the third embodiment is provided with the embedded part  150  as composed below. First, a coated layer  158  is formed on the concave portion  103   b  by coating in such a thickness as to cover a part of the concave portion  103   b  or all of the concave portion  103   b  and the convex portion  103   a.  The coated layer  158  is formed of, e.g., SiO 2 . In general, since the coated layer  158  is formed along the shape of the convex portion  103   a  by coating, the surface of the coated layer  158  becomes waved. 
     By repeating the coating process, the concavo-convex form can be gradually flattened. For example, when the coating material composing the coated layer  158  is coated on the n-type cladding layer  103 , the coating material is embedded in the concave portions  103   b  and adhered to the tip portion of the convex portion  103   a  in a small thickness. Then, according as the coating process is repeated, the coating material is further embedded in the concave portion  103   b  so that the surface of the coated layer  158  can be gradually flattened by repeating the coating process. Thus, where a waved concavo-convex form is desired to be formed on the surface, the waved coated layer  158  can be formed by repeating multiple times the coating process. 
     Then, the embedded part  156  of SiO2 or Si3N4 excellent in crystalline quality is formed on the coated layer  158  by sputtering etc. Thereby, the embedded part  156  can prevent moisture etc. from externally penetrating into the n-type cladding layer  103  so that the light emitting elements in modification of the third embodiment can have high output and high reliability. According to the light emitting elements, the coated layer  158  has the waved surface or curved surface so that the light extraction efficiency can be enhanced by the lens effect. 
     Fourth Embodiment 
       FIG. 8  is a schematic cross-sectional view showing a light emitting element in a fourth preferred embodiment according to the invention. 
     The light emitting element of the fourth embodiment has the same composition as the light emitting element  1  of the first embodiment except that a sidewall layer  152  is formed at least on the side face of the active layer  105 . Thus, the detailed explanation of the components except the different components will be omitted below. 
     The light emitting element of the fourth embodiment is provided with the sidewall layer  152 , which is formed of the same material as the embedded part  150 , on the side face of the n-type cladding layer  103 , the active layer  105 , the p-type cladding layer  107  and the p-type contact layer  109 . The sidewall layer  152  is formed of an insulating material. 
     For [example, the sidewall layer  152  is formed as below. First, in the fabrication method of the light emitting element  1  in the first embodiment, after the joined structure  1   g  is formed as shown in  FIG. 2L , the element separation process as shown  FIG. 2P  is conducted by etching. Then, after the elements are separated from each other, the embedded part  150  is formed by conducting the same process as shown in  FIGS. 2M and 2N . Here, in the fourth embodiment, after the elements are separated from each other, the side face of the n-type cladding layer  103 , the active layer  105 , the p-type cladding layer  107  and the p-type contact layer  109  is exposed. Therefore, in forming the embedded part  150 , the sidewall layer  152  can be also formed on the side face of the n-type cladding layer  103 , the active layer  105 , the p-type cladding layer  107  and the p-type contact layer  109 . 
     The light emitting element  4  of the fourth embodiment is provided with the sidewall layer  152  that is formed contacting the side face of the n-type cladding layer  103 , the active layer  105 , the p-type cladding layer  107  and the p-type contact layer  109 . Thus, it can have an improved moisture resistance and a reduced leakage on the side face of the semiconductor stacked structure  10 . Further, after the sidewall layer  152  is formed, the element (wafer) is diced into chips by the dicing equipment. During the dicing process by the dicing equipment, the side face of the semiconductor stacked structure  10  can be prevented from damaging and scrapes occurred in operating the dicing equipment can be prevented from adhering to the side face of the semiconductor stacked structure  10  which may cause a malfunction in characteristics of the light emitting element  4 . 
     EXAMPLES 
     According to the structure of the light emitting element  1  in the first embodiment, a light emitting element in Example is produced as below. 
     The semiconductor stacked structure is composed of the n-type cladding layer  103  of n-type AlGaInP, the active layer  105  in quantum well structure, and the p-type cladding layer  107  of p-type AlGaInP. The transparent layer  140  is formed of SiO 2 . The contact part  120  is formed of AuBe. The reflecting layer  132  is formed of Au, the alloying suppression layer  134  is formed of Ti, and the joining layer  136  is formed of Au. Further, the joining layer  202  is formed of Au, and the contact electrode  204  is formed Al. 
     A conductive Si substrate with a thickness of 200 μm and low resistivity is used as the supporting substrate  20 . The rear surface contact electrode  212  is formed of Al. The surface electrode  110  is formed of AuGe/Ni/Au and shaped like a circle with a diameter of 100 μm. The light emitting element in Example thus composed has a rectangular shape (top view) of 250 μm square and a thickness of about 200 μm. 
     The light emitting element in Example is mounted on a stem, and the surface electrode  110  is wire bonded to the current feeding portion of the stem. Then, it is sealed with silicone resin. Thus, as shown in  FIG. 3 , a light emitting device is produced. The following results are obtained in the characteristics evaluation of the light emitting device. 
     When forward current of 20 mA is fed, it exhibits an emission wavelength of 630 nm and an optical output of 27 mW to 30 mW. It has a forward voltage as low as 1.95 V. 
     COMPARATIVE EXAMPLE 
     A light emitting element in Comparative Example is produced in which no embedded part  150  is formed in the concave portion  103   b.    
     The light emitting elements in Example and Comparative example are tested in a thermal shock test between −40° C. to 150° C. and at 3000 cycles. As a result, even after the thermal shock test, the light emitting element in Example exhibits stably the same characteristics as before the test. By contrast, after the thermal shock test, the light emitting element in Comparative Example exhibits a reduced optical output of 10 mW to 20 mW and dispersed between the samples. As in the light emitting element in Comparative Example, the reduced and dispersed optical output is presumed to be caused by a breakage occurred in the convex portions due to the thermal shock. 
     Although the invention has been described with respect to the specific embodiments and Examples for complete and clear disclosure, the appended claims are not to be thus limited. In particular, it should be noted that all of the combinations of features as described in the embodiment and Examples are not always needed to solve the problem of the invention.