GaAs Solar Cells Grown on Unpolished, Spalled Ge Substrates

We spalled 2-inch Ge wafers using a Ni stressor layer and grew GaAs solar cells by hydride vapor phase epitaxy on the spalled Ge surface without other surface treatments. The controlled spalling procedure leaves behind arrest lines, which are parallel surface striations, perpendicular to the crack front, caused by the crack propagation repeatedly halting and restarting during the fracture. We show that small arrest lines do not significantly affect device performance, but larger lines act as regions for carrier recombination. We demonstrate a 12.8% efficient single-junction device, without anti-reflection coating, grown on a spalled surface containing arrest lines. The quantum efficiency of this device is similar to devices grown on non-spalled GaAs and Ge substrates.