Algainp light emitting devices with thin active layers

Abstract

The extraction efficiency of a light emitting device can be improved by making the absorbing device layers as thin as possible. The internal quantum efficiency decreases as the device layers become thinner. An optimal active layer thickness balances both effects. An AlGaInP LED includes a substrate and device layers including an AlGaInP lower confining layer of a first conductivity type, an AlGaInP active region of a second conductivity type, and an AlGaInP upper confining layer of a second conductivity type. The absorbance of the active region is at least one fifth of the total absorbance in the light-emitting device. The device optionally includes at least one set-back layers of AlGaInP interposing one of confining layer and active region. The p-type upper confining layer may be doped with oxygen improve the reliability.

We claim:  
     
         1 . A light-emitting device comprising: 
 a semiconductor substrate having a first conductivity type;    device layers, formed on the semiconductor substrate, having a total absorbance, that include, 
 a lower confining layer, formed on the substrate, of an AlGaInP alloy of the first conductivity type;  
 an active region of AlGaInP, having an absorbance less than 0.2, formed on the lower confining layer, and  
 an upper confining layer, formed on the active region, of an AlGaInP alloy of a second conductivity type; and  
 wherein the absorbance of the active region is at least one fifth of the total absorbance.  
   
     
     
         2 . A light-emitting device, as defined in    claim 1   , further comprising a semiconductor window layer, formed on the upper confining layer, of the second conductivity type; and wherein the window layer is transparent to the light emitted by the active layer.  
     
     
         3 . A light-emitting device, as defined in    claim 1   , further comprising: 
 a set-back layer of an alloy of AlGaInP interposing the active region and one of the lower and upper confining layers; and    wherein the alloy composition of the set-back layer is (Al x GA 1−x ) y In 1−y P, where x>0.55 and 0<y<1.    
     
     
         4 . The light-emitting device, as defined in    claim 3   , wherein the upper confining layer is doped with oxygen and the concentration of the oxygen is greater than 10 17  cm −3  and less than 5×10 18  cm −3 .  
     
     
         5 . The light-emitting device, as defined in    claim 4   , wherein the set-back layer is positioned between the active region and the upper confining layer, the set-back layer is doped with oxygen and has an oxygen concentration greater than 10 15  cm −3  and less than 5×10 16  cm −3 .  
     
     
         6 . A light-emitting device, as defined in    claim 3   , the active region further comprising: 
 j active layers of an alloy of AlGaInP that emits light; and    j-1 barrier layers that are transparent to the light emitted by the active layers, each barrier layer interposing two active layers.    
     
     
         7 . A light-emitting device, as defined in    claim 1   , the active region further comprising 
 j active layers of an alloy of AlGaInP that emits light; and    j-1 barrier layers that are transparent to the light emitted by the active layers, each barrier layer interposing two active layers.    
     
     
         8 . A light-emitting device, as defined in    claim 1   , wherein the semiconductor substrate is transparent.  
     
     
         9 . A light-emitting device, as defined in    claim 8   , wherein: 
 the second conductivity type is p-type; and    the active region contains a p-type dopant concentration in excess of 10 17  cm −3  and less than 10 19  cm −3 .    
     
     
         10 . A light-emitting device, as defined in    claim 8   , further comprising: 
 a set-back layer of an alloy of AlGaInP interposing the active region and one of the lower and upper confining layers; and    wherein the alloy composition of the set-back layer is (Al x Ga 1−x ) y In 1−y P, where x>0.55 and 0<y<1.    
     
     
         11 . A light-emitting device, as defined in    claim 10   , the active region further comprising: 
 j active layers of an alloy of AlGaInP that emits light; and    j-1 barrier layers that are transparent to light emitted by the active layers, each barrier layer interposing two adjacent active layers.    
     
     
         12 . The light-emitting device, as defined in    claim 11   , wherein the active region is operative to emit a wavelength less than 600 nm and the total thickness of the active layers is between 1000 and 2500 Å.  
     
     
         13 . The light-emitting device, as defined in    claim 1     1 , wherein the active region is operative to emit a wavelength between 600 and 620 nm and the total thickness of the active layers is between 500 to 2500 Å.  
     
     
         14 . The light-emitting device, as defined in    claim 11   , wherein the active region is operative to emit a wavelength greater than 620 nm and the total thickness of the active layers is between 200 Å and 1500 Å.  
     
     
         15 . The light-emitting device, as defined in    claim 10   , wherein the upper confining layer is doped with oxygen and the concentration of the oxygen is greater than 10 17  cm −3  and less than 5× 10 18  cm −3 .  
     
     
         16 . The light-emitting device, as defined in    claim 15   , wherein the set-back layer is positioned between the active region and the upper confining layer, the set-back layer is doped with oxygen and the concentration of oxygen exceeds 10 15  cm −3  and less than 5×10 16  cm −3 .  
     
     
         17 . A light-emitting device, as defined in    claim 8   , the active region further including 
 j active layers of an alloy of AlGaInP that emits light; and    j-1 barrier layers that are transparent to the light emitted by the active layers, each barrier layer interposing two active layers.    
     
     
         18 . The light-emitting device, as defined in    claim 8   , wherein the active region is operative to emit a wavelength less than 600 nm and the total thickness of the active layers is between 1000 Å and 2500 Å.  
     
     
         19 . The light-emitting device, as defined in    claim 8   , wherein the active region is operative to emit a wavelength between 600 and 620 nm and the total thickness of the active layers is between 500 Å and 2500 Å.  
     
     
         20 . The light-emitting device, as defined in    claim 8   , wherein the active region is operative to emit a wavelength greater than 620 nm and the total thickness of the active layers is between 200 Å and 1500 Å.