Effect of Material Choice on Spalling Fracture Parameters to Exfoliate Thin PV Devices

The use of fracture to exfoliate thin layers of semiconductor single crystals and single crystal-based devices has recently gained attention as an opportunity to create high-quality photovoltaic devices with reduced material consumption. A planar fracture that runs parallel to the material surface can be initiated by a sufficiently high tensile stress in an applied surface film in a process called spalling. In order to realize optimization of spall fracture depth accuracy and minimize material waste, the experimental parameters that affect fracture depth during the spalling of semiconductors must be better understood and tabulated. This work examines the application of spalling to common single-crystal photovoltaic materials including Ge, Si, and GaAs, to identify how the mechanical properties of the substrate and stressor layer, as well as the substrate thickness, impact the spalling depth. Experimental data for thin films spalled from (100) GaAs using a nickel stressor film are shown to be on trend with theoretical predictions, thus illustrating the utility of these calculations to better predict spall depth within the semiconductor.