Blue light-emitting diode with high external quantum efficiency
First Claim
1. A light emitting diode that emits light in the blue portion of the visible spectrum with high external quantum efficiency, said diode comprising:
- a single crystal silicon carbide substrate having a first conductivity type;
a first epitaxial layer of silicon carbide on said substrate and having the same conductivity type as said substrate;
a second epitaxial layer of silicon carbide on said first epitaxial layer and having the opposite conductivity type from said first layer,said first and second epitaxial layers forming a p-n junction; and
ohmic contacts for applying a potential difference across said p-n junction; and
whereinsaid second epitaxial layer has side walls and a top surface that define the top surface and top side walls of said diode, and said second epitaxial layer is sufficiently thick to increase the solid angle at which light emitted by the junction will radiate externally from said side walls, but less than the thickness at which internal absorption in said second layer would substantially reduce the light emitted from said top surface of the diode.
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Abstract
A light emitting diode is disclosed that emits light in the blue portion of the visible spectrum with high external quantum efficiency. The diode comprises a single crystal silicon carbide substrate having a first conductivity type, a first epitaxial layer of silicon carbide on the substrate and having the same conductivity type as the substrate, and a second epitaxial layer of silicon carbide on the first epitaxial layer and having the opposite conductivity type from the first layer. The first and second epitaxial layers forming a p-n junction, and the diode includes ohmic contacts for applying a potential difference across the p-n junction. The second epitaxial layer has side walls and a top surface that forms the top surface of the diode, and the second epitaxial layer has a thickness sufficient to increase the solid angle at which light emitted by the junction will radiate externally from the side walls, but less than the thickness at which internal absorption in said second layer would substantially reduce the light emitted from said top surface of the diode.
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Citations
53 Claims
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1. A light emitting diode that emits light in the blue portion of the visible spectrum with high external quantum efficiency, said diode comprising:
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a single crystal silicon carbide substrate having a first conductivity type; a first epitaxial layer of silicon carbide on said substrate and having the same conductivity type as said substrate; a second epitaxial layer of silicon carbide on said first epitaxial layer and having the opposite conductivity type from said first layer, said first and second epitaxial layers forming a p-n junction; and ohmic contacts for applying a potential difference across said p-n junction; and
whereinsaid second epitaxial layer has side walls and a top surface that define the top surface and top side walls of said diode, and said second epitaxial layer is sufficiently thick to increase the solid angle at which light emitted by the junction will radiate externally from said side walls, but less than the thickness at which internal absorption in said second layer would substantially reduce the light emitted from said top surface of the diode. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A light emitting diode that emits light in the blue portion of the visible spectrum with high external quantum efficiency, said diode comprising:
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a single crystal silicon carbide substrate having a first conductivity type; a first epitaxial layer of silicon carbide on said substrate and having the same conductivity type as said substrate; a second epitaxial layer of silicon carbide on said first epitaxial layer and having a compensated conductivity type opposite from the conductivity type of said first layer, said first and second epitaxial layers forming a p-n junction; ohmic contacts for applying a potential difference across said p-n junction; and a third epitaxial layer upon said second epitaxial layer and having the same conductivity type as said second epitaxial layer, said third layer having side walls and a top surface that forms the top surface of said diode, and said third epitaxial layer having a thickness sufficient to increase the solid angle at which light emitted by the junction will radiate externally from said side walls, but less than the thickness at which internal absorption in said third layer would substantially reduce the light emitted from said top surface of the diode. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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27. A light emitting diode that emits light in the blue portion of the visible spectrum with high external quantum efficiency, said diode comprising:
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a single crystal silicon carbide substrate having a first conductivity type; a first epitaxial layer of silicon carbide on said substrate and having the same conductivity type as said substrate; a second epitaxial layer of silicon carbide on said first epitaxial layer and having the opposite conductivity type from said first layer, said first and second epitaxial layers forming a p-n junction; and ohmic contacts for applying a potential difference across said p-n junction; and
whereinsaid second layer has side walls and a top surface that forms the top surface of said diode, and said second epitaxial layer has a thickness of about 25 microns and said top surface has an area of about 200 by 200 square microns. - View Dependent Claims (28, 29, 30, 31, 32, 33, 34)
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35. A light emitting diode that emits light in the blue portion of the visible spectrum with high external quantum efficiency, said diode comprising:
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a single crystal silicon carbide substrate having a first conductivity type; a first epitaxial layer of silicon carbide on said substrate and having the same conductivity type as said substrate; a second epitaxial layer of silicon carbide on said first epitaxial layer and having the opposite conductivity type from said first layer, said first and second epitaxial layers forming a p-n junction; and a highly reflective metal ohmic contact adjacent said second layer, said metal contact forming a highly reflective surface from which light generated by said diode will reflect rather than be absorbed. - View Dependent Claims (36, 37, 38, 39, 40, 41, 42, 43)
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44. A light emitting diode that emits light in the blue portion of the visible spectrum with high external quantum efficiency, said diode comprising:
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a single crystal silicon carbide substrate having a first conductivity type; a first epitaxial layer of silicon carbide on said substrate and having the same conductivity type as said substrate; a second epitaxial layer of silicon carbide on said first epitaxial layer and having the opposite conductivity type from said first layer, said first and second epitaxial layers forming a p-n junction; and a transparent conductive contact on said second layer. - View Dependent Claims (45, 46, 47, 48, 49, 50, 51, 52)
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53. A light emitting diode that emits light in the blue portion of the visible spectrum with high external quantum efficiency, said diode comprising:
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a single crystal silicon carbide substrate having a first conductivity type; a first epitaxial layer of silicon carbide on said substrate and having the same conductivity type as said substrate; a second epitaxial layer of silicon carbide on said first epitaxial layer and having the opposite conductivity type from said first layer, said first and second epitaxial layers forming a p-n junction; an unannealed metal ohmic contact adjacent said second layer, said metal contact forming a reflective surface from which light generated by said diode will reflect rather than be absorbed; and a highly doped layer between said second layer and said unannealed metal contact, said highly doped layer having the same conductivity type as said second layer, and said highly doped layer having a dopant concentration sufficient to lower the barrier between said metal contact and said second epitaxial layer sufficiently to provide ohmic behavior between said unannealed metal and said second epitaxial layer, said highly doped layer being thin enough to prevent the dopant concentration from substantially reducing the light emitted from said top surface of said second epitaxial layer.
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Specification