Hexagonal phase epitaxial cadmium sulfide on copper indium gallium selenide for a photovoltaic junction

Abstract

A method of manufacturing a photovoltaic structure includes forming a p-type semiconductor absorber layer containing a copper indium gallium selenide based material over a first electrode, forming a n-type cadmium sulfide layer over the p-type semiconductor absorber layer by sputtering in an ambient including hydrogen gas and oxygen gas, and forming a second electrode over the cadmium sulfide layer.

What is claimed is: 
     
         1 . A method of manufacturing a photovoltaic structure, comprising:
 forming a p-type semiconductor absorber layer comprising a copper indium gallium selenide based material over a first electrode;   forming a n-type cadmium sulfide layer over the p-type semiconductor absorber layer by sputtering in an ambient including hydrogen gas and oxygen gas; and   forming a second electrode over the cadmium sulfide layer.   
     
     
         2 . The method of  claim 1 , wherein:
 the ambient includes an inert sputtering gas; and   a total pressure of the ambient is in a range from 5 mTorr to 10 mTorr.   
     
     
         3 . The method of  claim 1 , wherein:
 hydrogen gas is flowed into a sputtering chamber at a first flow rate;   oxygen gas is flowed into the sputtering chamber at a second flow rate; and   a difference between the first flow rate and the second flow rate is in a range from 30 sccm to 80 sccm.   
     
     
         4 . The method of  claim 1 , wherein forming the n-type cadmium sulfide layer comprises forming a single crystal intrinsically doped or zinc doped cadmium sulfide layer having a predominant hexagonal crystal structure by sputtering in the ambient. 
     
     
         5 . The method of  claim 1 , wherein forming the n-type cadmium sulfide layer comprises forming a single crystal copper cadmium sulfide layer having a predominant hexagonal crystal structure by sputtering in the ambient. 
     
     
         6 . The method of  claim 5 , wherein the single crystal copper cadmium sulfide layer is composed predominantly of one or more hexagonal phase cadmium sulfide grains. 
     
     
         7 . The method of  claim 1 , wherein forming the n-type cadmium sulfide layer comprises forming a first single crystal copper cadmium sulfide layer having a predominant hexagonal crystal structure by sputtering in the ambient and forming a second single crystal cadmium sulfide layer having a predominant hexagonal crystal structure over the first single crystal copper cadmium sulfide layer by sputtering in the ambient. 
     
     
         8 . The method of  claim 1 , wherein forming the second electrode comprises forming a zinc containing oxide layer such that zinc diffuses into the n-type cadmium sulfide layer to form a zinc doped cadmium sulfide layer. 
     
     
         9 . The method of  claim 8 , wherein oxygen and the zinc diffuse into the n-type cadmium sulfide layer to form a zinc and oxygen doped cadmium sulfide layer. 
     
     
         10 . The method of  claim 1 , wherein the n-type cadmium sulfide layer is doped with one or more of copper, zinc, oxygen or hydrogen. 
     
     
         11 . The method of  claim 1 , wherein the step of forming the n-type cadmium sulfide layer by sputtering comprises sputtering the n-type cadmium sulfide layer from a CdS target in the ambient.