Gallium-containing light-emitting semiconductor device and method of fabrication

Abstract

An LED comprising a light-generating semiconductor region having an active layer sandwiched between two confining layers of opposite conductivity types. A cathode is arranged centrally on one of the opposite major surfaces of the semiconductor region from which is emitted the light. An array of discrete gold regions are formed via transition metal regions on the other major surface of the semiconductor region at which is exposed one of the confining layers which is of n-type AlGaInP semiconductor material. The gold is thermally diffused into the confining layer via the transition metal regions at a temperature less than the eutectic point of gold and gallium, thereby creating an array of ohmic contact regions of alloyed or intermingled gold and gallium, which are less absorptive of light than their conventional counterparts, to a thickness of 20 to 1000 angstroms. After removing the transition metal regions and gold regions from the surface of the light-generating semiconductor region, a reflective layer of aluminum is formed so as to cover both the ohmic contact regions and the exposed surface portions of the AlGaInP confining layer. An electroconductive base-plate of doped silicon is then bonded to the reflective layer.

1 . A light-emitting semiconductor device of improved efficiency, comprising: 
 (a) a light-generating semiconductor region having a first major surface from which light is emitted and a second major surface which is opposite to the first major surface, the light-generating semiconductor region comprising a plurality of compound semiconductor layers including a gallium-containing compound semiconductor layer which is exposed at the second major surface of the semiconductor region;    (b) an electrode on the first major surface of the semiconductor region;    (c) an ohmic contact region held in ohmic contact with at least part of the second major surface of the light-generating semiconductor region, the ohmic contact region being made from a mixture of at least two metals including gallium; and    (d) a reflective layer of electrically conducting material held against at least either of the ohmic contact region and that part, if any, of the gallium-containing compound semiconductor layer of the light-generating semiconductor region which is exposed at the second major surface of the semiconductor region through the ohmic contact region, for reflecting the light from the semiconductor region back toward the semiconductor region for emission from the first major surface thereof.    
   
   
       2 . A light-emitting semiconductor device as defined in  claim 1 , wherein the ohmic contact region is of a mixture of gallium and gold.  
   
   
       3 . A light-emitting semiconductor device as defined in  claim 1 , wherein the ohmic contact region is from abut 20 to about 1000 angstroms in thickness.  
   
   
       4 . A light-emitting semiconductor device as defined in  claim 1 , wherein the gallium-containing compound semiconductor layer of the light-generating semiconductor region is made from one of the following three compound semiconductors and a conductivity-type determinant: 
 (a) a first compound semiconductor that is generally expressed as Al x Ga y In 1-x-y P where the subscript x is a numeral that is equal to or greater than zero and less than one; the subscript y is a numeral that is greater than zero and equal to or less than one;    and the sum of x and y is greater than zero and equal to or less than one;    (b) a second compound semiconductor that is generally expressed as Al x Ga y In 1-x-y As where the subscript x is a numeral that is equal to or greater than zero and less than one; the subscript y is a numeral that is greater than zero and equal to or less than one; and the sum of x and y is greater than zero and equal to or less than one; and    (c) a third compound semiconductor that is generally expressed as Al x Ga y In 1-x-y N where the subscript x is a numeral that is equal to or greater than zero and less than one; the subscript y is a numeral that is greater than zero and equal to or less than one; and the sum of x and y is greater than zero and equal to or less than one.    
   
   
       5 . A light-emitting semiconductor device as defined in  claim 1 , wherein the reflective layer is made from a metal that is more reflective than the metals of the ohmic contact region.  
   
   
       6 . A light-emitting semiconductor device as defined in  claim 5 , wherein the reflective layer is of aluminum.  
   
   
       7 . A light-emitting semiconductor device as defined in  claim 1 , further comprising an electroconductive baseplate attached to the reflective layer.  
   
   
       8 . A light-emitting semiconductor device as defined in  claim 7 , wherein the baseplate is of doped silicon, and wherein a second electrode is formed on the baseplate.  
   
   
       9 . A light-emitting semiconductor device as defined in  claim 1 , wherein the ohmic contact region is open-worked to expose part of the second major surface of the light-generating semiconductor region, and wherein the reflective layer covers both the ohmic contact region and the exposed part of the second major surface of the semiconductor region.  
   
   
       10 . A light-emitting semiconductor device as defined in  claim 1 , wherein the gallium-containing compound semiconductor layer of the light-generating semiconductor region exposed at the second major surface thereof is a lower cladding, and wherein the semiconductor region further comprises: 
 (a) an active layer of gallium-containing compound semiconductor material on the lower cladding; and    (b) an upper cladding of gallium-containing compound semiconductor material on the active layer, the upper cladding being opposite in conductivity type to the lower cladding.    
   
   
       11 . A method of making a light-emitting semiconductor device of improved efficiency, which comprises: 
 (a) providing a light-generating semiconductor region having a first major surface from which light is emitted and a second major surface which is opposite to the first major surface, the light-generating semiconductor region comprising a plurality of compound semiconductor layers including a gallium-containing compound semiconductor layer which is exposed at the second major surface of the semiconductor region;    (b) creating a transition metal layer containing a transition metal on at least part of the second major surface of the light-generating semiconductor region;    (c) creating a diffusible metal layer on the first metal layer, the diffusible metal layer containing a metal that can be thermally diffused into the gallium-containing compound semiconductor layer of the light-generating semiconductor region through the transition meal layer;    (d) creating an ohmic contact region in the gallium-containing compound semiconductor layer of the light-generating semiconductor region by causing thermal diffusion of the diffusible metal from the diffusible metal layer into the gallium-containing compound semiconductor layer through the transition metal layer at a temperature less than the eutectic point of elements constituting the gallium-containing compound semiconductor layer and the diffusible metal;    (e) removing the transition metal layer and the diffusible metal layer from the light-generating semiconductor region; and    (f) creating a reflective layer of electrically conducting material on at least either of the ohmic contact region and that part, if any, of the gallium-containing compound semiconductor layer of the light-generating semiconductor region which is exposed at the second major surface of the semiconductor region through the ohmic contact region.    
   
   
       12 . A method of making a light-emitting semiconductor device as defined in  claim 11 , wherein the transition metal layer together with the diffusible metal layer thereon is formed in discrete regions on the second major surface of the light-generating semiconductor region, covering parts, and uncoverig the rest, of the second major surface, so that ohmic contact regions are created only in those parts of the gallium-containing compound semiconductor layer of the light-generating semiconductor region which have been covered by the discrete regions of the transition metal layer and the diffusible metal layer.  
   
   
       13 . A method of making a light-emitting semiconductor device as defined in  claim 12 , wherein the reflective layer is created on the complete second major surface of the light-generating semiconductor region.  
   
   
       14 . A method of making a light-emitting semiconductor device as defined in  claim 11 , wherein the gallium-containing compound semiconductor layer of the light-generating semiconductor region is made from one of the following three compound semiconductors and a conductivity-type determinant: 
 (a) a first compound semiconductor that is generally expressed as Al x Ga y In 1-x-y P where the subscript x is a numeral that is equal to or greater than zero and less than one; the subscript y is a numeral that is greater than zero and equal to or less than one; and the sum of x and y is greater than zero and equal to or less than one;    (b) a second compound semiconductor that is generally expressed as Al x Ga y In 1-x-y As where the subscript x is a numeral that is equal to or greater than zero and less than one; the subscript y is a numeral that is greater than zero and equal to or less than one; and the sum of x and y is greater than zero and equal to or less than one; and    (c) a third compound semiconductor that is generally expressed as Al x Ga y In 1-x-y N where the subscript x is a numeral that is equal to or greater than zero and less than one; the subscript y is a numeral that is greater than zero and equal to or less than one; and the sum of x and y is greater than zero and equal to or less than one.    
   
   
       15 . A method of making a light-emitting semiconductor device as defined in  claim 11 , wherein the gallium-containing compound semiconductor layer of the light-generating semiconductor region is made from a conductivity-type determinant and a compound semiconductor that is generally expressed as Al x Ga y In 1-x-y P where the subscript x is a numeral that is equal to or greater than 0.4 and less than 1.0; the subscript y is a numeral that is greater than zero and equal to or less than one; and the sum of x and y is greater than zero and equal to or less than one.  
   
   
       16 . A method of making a light-emitting semiconductor device as defined in  claim 15 , wherein the gallium-containing compound semiconductor layer of the light-generating semiconductor region contains the conductivity-type determinant with a concentration of not less than 10 18  cm −3 .  
   
   
       17 . A method of making a light-emitting semiconductor device as defined in  claim 11 , wherein the transition metal layer is selected from among: 
 (a) a layer of at least either of Cr, Ti, Ni, Sc, V, Mn, Fe, Co, Cu, Zn, and Be;    (b) a lamination of an Au sublayer, Cr sublayer, and another Au sublayer;    (c) a lamination of a Cr sublayer, Ni sublayer, and Au sublayer; and    (d) a lamination of a Cr sublayer, AuSi sublayer, and Au sublayer.    
   
   
       18 . A method of making a light-emitting semiconductor device as defined in  claim 11 , wherein the diffusible metal layer is selected from among: 
 (a) a gold layer:    (b) a lamination of an Au sublayer, Cr sublayer, and another Au sublayer;    (c) a lamination of a Cr sublayer, Ni sublayer, and Au sublayer; and    (d) a lamination of a Cr sublayer, AuSi sublayer, and Au sublayer.    
   
   
       19 . A method of making a light-emitting semiconductor device as defined in  claim 11 , wherein the diffusible metal is gold, which is so diffused into the gallium-containing compound semiconductor layer of the light-generating semiconductor region that the ohmic contact region created is of an alloy of gallium and gold.  
   
   
       20 . A method of making a light-emitting semiconductor device as defined in  claim 11 , wherein the ohmic contact region is from about 20 to about 1000 angstroms thick.  
   
   
       21 . A method of making a light-emitting semiconductor device as defined in  claim 11 , wherein the reflective layer is made from a metal selected to possess a higher reflectivity than does the ohmic contact region.  
   
   
       22 . A method of making a light-emitting semiconductor device as defined in  claim 21 , wherein the reflective layer is made from aluminum.  
   
   
       23 . A method of making a light-emitting semiconductor device as defined in  claim 11 , which further comprises joining an electroconductive baseplate to the reflective layer.  
   
   
       24 . A method of making a light-emitting semiconductor device as defined in  claim 23 , wherein the electroconductive baseplate is of doped silicon, and wherein the method further comprises joining an electrode to the baseplate.