Light-emitting device of gallium nitride compound semiconductor

Abstract

A light-emitting diode of GaN compound semiconductor emits a blue light from a plane rather than dots for improved luminous intensity. This diode includes a first electrode associated with a high-carrier density n+ layer and a second electrode associated with a high-impurity density [iH-layer] H-layer. These electrodes are made up of a first Ni layer (110 ANGSTROM thick), a second Ni layer (1000 ANGSTROM thick), an Al layer (1500 ANGSTROM thick), a Ti layer (1000 ANGSTROM thick), and a third Ni layer (2500 ANGSTROM thick). The Ni layers of dual structure permit a buffer layer to be formed between them. This buffer layer prevents the Ni layer from peeling. The direct contact of the Ni layer with GaN lowers a drive voltage for light emission and increases luminous intensity.

What is claimed is: 
     
       1. A light-emitting device of gallium nitride compound semiconductor material comprising: an n-layer of n-type gallium nitride compound semiconductor material (Al x  Ga 1-x  N, x≧0); and   .[.an i-layer of i-type.]. .Iadd.a p-type impurity doped layer .Iaddend.gallium nitride compound semiconductor material (Al x  Ga 1-x  N, x≧0) .[.doped with a p-type impurity.].;   wherein a first electrode layer including Ni is formed in contact with said .[.i-layer.]. .Iadd.p-type impurity doped layer .Iaddend.and functions as an electrode .[.therefore.]. .Iadd.therefor.Iaddend.; and   wherein said first electrode layer is a multi-layer structure having a first Ni layer of predetermined thickness formed over said .[.i-layer.]. .Iadd.p-type impurity doped layer.Iaddend., a second Ni layer which is thicker than said first Ni layer and formed thereon, an Al layer formed over said second Ni layer, a Ti layer formed over said Al layer, and a third Ni layer which is thicker than said first Ni layer formed over said Ti layer.   
     
     
       2. A light-emitting device of gallium nitride compound semiconductor material comprising: an n-layer of n-type gallium nitride compound semiconductor .Iadd.material .Iaddend.(Al x  Ga 1-x  N, x≧0) .[.material.].; and   .[.an i-layer of i-type.]. .Iadd.a p-type impurity doped layer .Iaddend.gallium nitride compound semiconductor .Iadd.material .Iaddend.(Al x  Ga 1-x  N, x≧0) .[.material doped with a p-type impurity.].;   wherein each of said n-layer and said .[.i-layer.]. .Iadd.p-type impurity doped layer .Iaddend.include respective electrodes formed on a same relative surface, the electrode for said .[.i-layer.]. .Iadd.p-type impurity doped layer .Iaddend.being composed of at least one layer with each said at least one layer being made of one of Ni, Ag, Ti, an alloy including Ni, an alloy including Ag, and an alloy including Ti; and   wherein the electrode for said .[.i-layer.]. .Iadd.p-type impurity doped layer .Iaddend.has an over layer formed thereon which is made of one of Al and an alloy containing Al.   
     
     
       3. A light-emitting device of gallium nitride compound semiconductor, comprising: at least two layers of gallium nitride compound semiconductor material (Al x  Ga 1-x  N, x≧0);   a first electrode layer for one layer of said at least two layers; and   a second electrode layer for another of said at least two layers;   said first and second electrode layers provide an improved luminous intensity of said light-emitting device;   wherein at least one layer of said first and second electrode layers includes a contact layer made of one of Ni, Ag, an alloy including Ni, an alloy including Ag, and an alloy including Ti, said contact layer being directly contacted with any of said at least two layers of gallium nitride compound semiconductor material (Al x  Ga 1-x  N, x≧0).   
     
     
       4. A light-emitting device of gallium nitride compound semiconductor according to claim 3, wherein said contact layer of said first electrode layer is uniformly formed on a light emitting surface of said one layer, said one layer being .[.an i-layer of semi-insulation doped with a p-type impurity.]. .Iadd.p-type impurity doped layer .Iaddend.and said another layer being an n-layer with n-type conduction. 
     
     
       5. A light-emitting device of gallium nitride compound semiconductor according to claim 3, wherein said second electrode layer includes a contact layer made of one of Ni, Ag, an alloy including Ni, an alloy including Ag, and an alloy including Ti, said contact layer being directly contacted with said another layer and said another layer being an n-layer with n-type conduction. 
     
     
       6. A light-emitting device of gallium nitride compound semiconductor according to claim 3, wherein said first electrode layer is a multi-layer structure having a first Ni layer of predetermined thickness formed over said one layer, a second Ni layer which is thicker than said first Ni layer and formed thereon, an Al layer formed over said second Ni layer, a Ti layer formed over said Al layer, and a third Ni layer which is thicker than said first Ni layer formed over said Ti layer. 
     
     
       7. A light-emitting device of gallium nitride compound semiconductor according to claim 3, wherein at least one layer of said first and second electrode layers has an over layer which is made of one of Ni, Ag, Ti, an alloy including Ni, an alloy including Ag, and an alloy including Ti. 
     
     
       8. A light-emitting device of gallium nitride compound semiconductor material according to claim 4, wherein at least one layer of said first and second electrode layers has an over layer which is made of one of Ni, Ag, Ti, an alloy including Ni, an alloy including Ag, and an alloy including Ti. 
     
     
       9. A light-emitting device of gallium nitride compound semiconductor according to claim 3, wherein at least one layer of said first and second electrode layers has over layer formed thereon which is made of one of Al and an alloy containing Al. 
     
     
       10. A light-emitting device of gallium nitride compound semiconductor according to claim 4, wherein at least one layer of said first and second electrode layers has over layer formed thereon which is made of one of Al and an alloy containing Al. 
     
     
       11. A light-emitting device of gallium nitride compound semiconductor according to claim 7, wherein at least one layer of said first and second electrode layers has over layer formed thereon which is made of one of Al and an alloy containing Al. 
     
     
       12. A light-emitting device of gallium nitride compound semiconductor according to claim 8, wherein at least one layer of said first and second electrode layers has over layer formed thereon which is made of one of Al and an alloy containing Al. 
     
     
       13. A light-emitting device of gallium nitride compound semiconductor according to claim 4, wherein said second electrode layer is made of one of Al and an alloy containing Al, and said first electrode has an over layer which is made of one of Ni, Ag, Ti, an alloy including Ni, an alloy including Ag, and an alloy including Ti. 
     
     
       14. A light-emitting device of gallium nitride compound semiconductor material according to claim 4, wherein said first electrode layer is a multi-layer structure having a first Ni layer of predetermined thickness formed over said i-layer, a second Ni layer which is thicker than said first Ni layer and formed thereon, an Al layer formed over said second Ni layer, a Ti layer formed over said Al layer, and a third Ni layer which is thicker than said first Ni layer formed over said Ti layer. .Iadd.15. A light-emitting device of gallium nitride compound semiconductor, comprising: a first layer of gallium nitride compound semiconductor material (Al x  Ga 1-x  N, x≧0) doped with p-type impurity;   a second layer of n-type gallium nitride compound semiconductor material (Al x  Ga 1-x  N, x≧0);   a first electrode layer for said first layer;   a second electrode layer for said second layer; and   wherein said first electrode layer is made of at least one of Ni, Ag, an alloy including Ni, an alloy including Ag, and an alloy including Ti and said second electrode layer is made of at least one of Al, Ti, an alloy   
     
     
        including Al, and an alloy including Ti. .Iaddend..Iadd.16.  A light-emitting device of gallium nitride compound semiconductor according to claim 15, wherein said first and second layers are formed on a buffer layer and said buffer layer is formed on a sapphire substrate. .Iaddend..Iadd.17. A light-emitting device of gallium nitride compound semiconductor according to claim 15, wherein said second layer is gallium nitride (GaN) of low resistivity doped with silicon (Si) for uniform flow 
     
     
        of current through said first layer. .Iaddend..Iadd.18.  A light-emitting device of gallium nitride compound semiconductor according to claim 17, wherein said first electrode layer is made of one of Ni and an alloy including Ni and second electrode layer is made of one of Al and an alloy including Al. .Iaddend..Iadd.19. A light-emitting device of gallium nitride compound semiconductor according to claim 15, wherein said first electrode layer further comprises a multi-layer structure having at least one over layer made of metal different from metal of a layer under said over layer. .Iaddend..Iadd.20. A light-emitting device of gallium nitride compound semiconductor according to claim 15, wherein said first electrode layer is uniformly formed on a light emitting surface of said first layer. 
     
     
        .Iaddend..Iadd.21.  A light-emitting device of gallium nitride compound semiconductor according to claim 15, wherein at least one layer of said first and second electrode layers further comprises at least one over layer made of one of Ni, Ti, an alloy including Ni, and an alloy including Ti. .Iaddend..Iadd.22. A light-emitting device of gallium nitride compound semiconductor according to claim 15, wherein said second electrode layer further comprises at least one over layer made of one of Al and an alloy containing Al. .Iaddend..Iadd.23. A light-emitting device of gallium nitride compound semiconductor according to claim 18, wherein said first electrode layer further comprises at least one over layer made of metal 
     
     
        excluding Ni. .Iaddend..Iadd.24.  A light-emitting device of gallium nitride compound semiconductor, comprising: a first layer of gallium nitride compound semiconductor material (Al x  Ga 1-x  N, x≧0) doped with p-type impurity;   a second layer of n-type gallium nitride compound semiconductor material (Al x  Ga 1-x  N, x≧0);   a first electrode layer for said first layer;   a second electrode layer for said second layer; and   wherein said first electrode layer is made of at least one of Ni and an alloy including Ni and said second electrode layer is made of Al, Ti, an   
     
     
        alloy including Al, and an alloy including Ti. .Iaddend..Iadd.25.  A light-emitting device of gallium nitride compound semiconductor according to claim 24, wherein said first electrode layer has a multi-layer structure comprising at least one over layer made of metal different from metal of a layer under said over layer. .Iaddend..Iadd.26. A light-emitting device of gallium nitride compound semiconductor according to claim 3, wherein said improved luminous intensity is achieved by reduction of driving voltage for supplying a predetermined current. .Iaddend..Iadd.27. A light-emitting device of gallium nitride compound semiconductor according to claim 3, wherein said at least one layer of said first and second electrode layers further comprises at least one over layer made of a metal excluding a metal of said contact layer. .Iaddend.