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

We investigate the (211) GaAs substrate orientation as a pathway to enable lower cost III-V photovoltaics. Substrates and epitaxial growth are two major costs that limit the market for III-V photovoltaics despite their high efficiencies. The combination of a rapid epitaxial growth technique along with a method like controlled spalling for substrate recovery and reuse would enable dramatic reduction in the production cost of III V photovoltaics. The choice of substrate orientation must consider both aspects of the process flow, because a substrate orientation amenable to the spalling process may not enable high performance device epitaxy, and vice versa. Here, we present initial spalling results from a 50 mm diameter (211)B substrate, revealing a large, specular, and facet-free area that is promising for device regrowth. We measure a 0.98 nm root mean square surface roughness from 75 µm x 75 µm atomic force microscopy scan. We also use halide vapor phase epitaxy to grow a GaAs device on a polished, epitaxy-ready (211)B GaAs substrate and measure an open-circuit voltage of 1.020 V under the AM1.5G spectrum. Taken together, the spalling and device results demonstrate that (211) is a promising substrate orientation for low-cost manufacturing of III-V photovoltaics.