Spalling methods to form multi-junction photovoltaic structure

Abstract

A method cleaving a semiconductor material that includes providing a germanium substrate having a germanium and tin alloy layer is present therein. A stressor layer is deposited on a surface of the germanium substrate. A stress from the stressor layer is applied to the germanium substrate, in which the stress cleaves the germanium substrate to provide a cleaved surface. The cleaved surface of the germanium substrate is then selective to the germanium and tin alloy layer of the germanium substrate. In another embodiment, the germanium and tin alloy layer may function as a fracture plane during a spalling method.

What is claimed is: 
     
         1 . A photovoltaic device comprising:
 a layer of germanium having a first conductivity and a thickness ranging from 1 micron to 10 microns, wherein the first layer of germanium has a variation of thickness across the entire width of the layer of germanium that is less than 1000 Å; and   a semiconductor layer present on the layer of the germanium, wherein the semiconductor layer has a second conductivity, wherein the second conductivity is opposite the first conductivity.   
     
     
         2 . The photovoltaic device of  claim 1 , wherein the semiconductor layer is a silicon-containing material, a germanium-containing material or the semiconductor layer is a compound semiconductor. 
     
     
         3 . The photovoltaic device of  claim 1 , wherein an intrinsic semiconductor layer is present between the layer of germanium and the semiconductor layer, and the photovoltaic device is a p-i-n solar cell. 
     
     
         4 . The photovoltaic device of  claim 1 , further comprising a metal or polymeric substrate, wherein the photovoltaic device is flexible. 
     
     
         5 . The photovoltaic device of  claim 1 , further comprising a front contact and a back contact.