Side emitting illumination systems incorporating light emitting diodes

Abstract

The invention is a reflective light emitting diode. The light emitting diode reflects the externally incident light, thereby increasing the effective brightness of the light emitting diode. The light emitting diode reflects externally incident light with a reflectivity greater than 40 percent.

1 - 23 . (canceled) 
   
   
       24 . A reflective light emitting diode comprising
 a first doped semiconductor layer having an output surface;   a second doped semiconductor layer, said second doped semiconductor layer and said first doped semiconductor layer having opposite n and p conductivity types;   an active region interposed between said first doped semiconductor layer and said second doped semiconductor layer, said active region in electrical contact with said first doped semiconductor layer and said second doped semiconductor layer;   a first reflecting electrode in electrical contact with said first doped semiconductor layer;   a second reflecting electrode in electrical contact with said second doped semiconductor layer;   wherein said active region of said light emitting diode emits internally generated light through said output surface of said first doped semiconductor layer when a voltage is applied between said first reflecting electrode and said second reflecting electrode; and   wherein a portion of externally incident light incident on said light emitting diode is reflected by said first reflecting electrode and a portion of externally incident light incident on said light emitting diode is transmitted through said light emitting diode and reflected by said second reflecting electrode of said light emitting diode through said output surface, thereby increasing the effective brightness of said light emitting diode.   
   
   
       25 . The reflective light emitting diode of  claim 24  wherein said active region is a p-n homojunction, a p-n heterojunction, a double heterojunction, a single quantum well or a multiple quantum well. 
   
   
       26 . The reflective light emitting diode of  claim 24  wherein said first reflecting electrode and said second reflecting electrode are a reflecting metal or a partially transparent conducting oxide. 
   
   
       27 . The reflective light emitting diode of  claim 26  wherein said first reflecting electrode is a partially transparent conducting oxide and is partially reflective. 
   
   
       28 . The reflective light emitting diode of  claim 24  wherein the inner surface of said second reflecting electrode is adjacent to said second doped semiconductor layer; said inner surface of said second reflecting electrode is reflective to said internally generated light emitted by said active region and to said externally incident light. 
   
   
       29 . The reflective light emitting diode of  claim 24  wherein the inner surface of said first reflecting electrode is adjacent to said first doped semiconductor layer; said inner surface of said first reflecting electrode is reflective to said internally generated light emitted by said active region and to said externally incident light, wherein the outer surface of said first reflecting electrode is opposite said inner surface of said first reflecting electrode and said outer surface of said first reflecting electrode is reflective to said externally incident light. 
   
   
       30 . The reflective light emitting diode of  claim 24  wherein the inner surface of said second reflecting electrode is adjacent to said second doped semiconductor layer; said inner surface of said second reflecting electrode is reflective to said internally generated light emitted by said active region and to said externally incident light; and
 wherein the inner surface of said first reflecting electrode is adjacent to said first doped semiconductor layer; said inner surface of said first reflecting electrode is reflective to said internally generated light emitted by said active region and to said externally incident light, wherein the outer surface of said first reflecting electrode is opposite said inner surface of said first reflecting electrode and said outer surface of said first reflecting electrode is reflective to said externally incident light.   
   
   
       31 . The reflective light emitting diode of  claim 24  wherein said first reflecting electrode only partially covers said first doped semiconductor layer, said output surface of said first doped semiconductor layer being formed from the portions of said first doped semiconductor layer not covered by said first reflecting electrode. 
   
   
       32 . The reflective light emitting diode of  claim 24  wherein said first reflecting electrode and said second reflecting electrode are formed from one or more metals or metal alloys of silver, aluminum, nickel, titanium, chromium, platinum, palladium, rhodium, rhenium, ruthenium and tungsten. 
   
   
       33 . The reflective light emitting diode of  claim 24  wherein said first reflecting electrode has a reflectivity greater than 80 percent in the emitting wavelength range of said internally generated light. 
   
   
       34 . The reflective light emitting diode of  claim 33  wherein said first reflecting electrode is aluminum or silver. 
   
   
       35 . The reflective light emitting diode of  claim 24  wherein said second reflecting electrode has a reflectivity greater than 98 percent in the emitting wavelength range of said internally generated light. 
   
   
       36 . The reflective light emitting diode of  claim 35  wherein said second reflecting electrode is silver. 
   
   
       37 . The reflective light emitting diode of  claim 24  wherein the absorption coefficient of said first doped semiconductor layer, said active region and said second doped semiconductor layer in the emitting wavelength range of said internally generated light is less than 50 cm −1 . 
   
   
       38 . The reflective light emitting diode of  claim 24  wherein a current spreading layer is positioned between said first reflecting electrode and said first doped semiconductor layer, said current spreading layer having the same conductivity type as said first doped semiconductor layer or wherein a current spreading layer is positioned between said second reflecting electrode and said second doped semiconductor layer, said current spreading layer having the same conductivity type as said second doped semiconductor layer; and
 wherein said current spreading layer will improve the uniformity of current injection across said active region when a voltage is applied between said first reflecting electrode and said second reflecting electrode.   
   
   
       39 . The reflective light emitting diode of  claim 24  wherein an electron blocking layer is positioned between said first doped semiconductor layer and said active region or wherein an electron blocking layer is positioned between said second doped semiconductor layer and said active region; and
 wherein said electron blocking layer will reduce the escape of electrons from said active region.   
   
   
       40 . The reflective light emitting diode of  claim 24  wherein said light emitting diode is a plurality of said light emitting diodes. 
   
   
       41 . The reflective light emitting diode of  claim 40  wherein said plurality of said light emitting diodes emit more than one color of light. 
   
   
       42 . The reflective light emitting diode of  claim 24  wherein said light emitting diode reflects said externally incident light with a reflectivity greater than 40 percent. 
   
   
       43 . The reflective light emitting diode of  claim 24  wherein said light emitting diode reflects said externally incident light with a reflectivity greater than 60 percent. 
   
   
       44 . The reflective light emitting diode of  claim 24  further comprising a wavelength conversion layer that converts a portion of said internally generated light of a first color into light of a second color, different than said first color. 
   
   
       45 . The reflective light emitting diode of  claim 44  wherein said wavelength conversion layer is disposed on said output surface of said light emitting diode. 
   
   
       46 . A reflective light emitting diode comprising
 a first doped semiconductor layer having an output surface;   a second doped semiconductor layer, said second doped semiconductor layer and said first doped semiconductor layer having opposite n and p conductivity types;   an active region interposed between said first doped semiconductor layer and said second doped semiconductor layer, said active region in electrical contact with said first doped semiconductor layer and said second doped semiconductor layer;   a first reflecting electrode in electrical contact with said first doped semiconductor layer; wherein said first reflecting electrode only partially covers said first doped semiconductor layer, said output surface of said first doped semiconductor layer being formed from the portions of said first doped semiconductor layer not covered by said first reflecting electrode;   a second reflecting electrode in electrical contact with said second doped semiconductor layer;   wherein said active region of said light emitting diode emits internally generated light through said output surface of said first doped semiconductor layer when a voltage is applied between said first reflecting electrode and said second reflecting electrode;   wherein the inner surface of said first reflecting electrode is adjacent to said first doped semiconductor layer; said inner surface of said first reflecting electrode is reflective to said internally generated light emitted by said active region and to said externally incident light, wherein the outer surface of said first reflecting electrode is opposite said inner surface of said first reflecting electrode and said outer surface of said first reflecting electrode is reflective to said externally incident light.   wherein the inner surface of said second reflecting electrode is adjacent to said second doped semiconductor layer; said inner surface of said second reflecting electrode is reflective to said internally generated light emitted by said active region and to said externally incident light; and   wherein a portion of externally incident light incident on said light emitting diode is reflected by said first reflecting electrode and a portion of externally incident light incident on said light emitting diode is transmitted through said light emitting diode and reflected by said second reflecting electrode of said light emitting diode through said output surface, thereby increasing the effective brightness of said light emitting diode.