A Path to III-V Photovoltaic Cost Reduction Combining GaAs (211) Spalling with Halide Vapor Phase Epitaxy

The high costs of substrates and epitaxial growth present significant barriers to the scaling of III-V photovoltaics, despite their remarkable efficiencies. Combining methods for device exfoliation, substrate recovery and reuse, and a rapid epitaxial growth technique may significantly lower the manufacturing cost of III-V photovoltaics. In this work, we investigate controlled spalling of the (211)B gallium arsenide (GaAs) substrate orientation and epitaxial growth of GaAs devices on spalled (211)B wafers with high-growth-rate halide vapor phase epitaxy (HVPE). The selection of substrate orientation is crucial, as it must result in a flat surface after spalling, with minimal faceting, while also being suitable for high-performance epitaxial regrowth. The (211)B orientation demonstrates significant potential in meeting both requirements. Initial spalling results from 50 mm diameter (211)B substrates reveal large, specular, and facet-free areas with root mean square (RMS) roughness of 0.98 nm across a 75 ..mu..m x 75 ..mu..m atomic force microscopy (AFM) scan that are promising for device regrowth. We studied the effect of HVPE growth parameters, including GaCl partial pressure, AsH3 carrier flow and deposition temperature on roughness and growth rate of GaAs on (211)B-oriented substrates. Finally, we fabricated an upright GaAs photovoltaic device on a spalled (211)B wafer that showed performance equivalent to a reference device deposited on an unspalled, epi-ready (211)B wafer with an open-circuit voltage (VOC) of 1.01 V measured under the AM1.5G spectrum. These results suggest that (211)B-oriented GaAs is a promising platform for low-cost III-V photovoltaics manufacturing.