Towards high-efficiency GaAs thin-film solar cells grown via close space vapor transport from a solid source

GaAs is an attractive photovoltaic material, but its widespread implementation is limited in part by the high cost of metal-organic chemical vapor deposition, which employs toxic and pyrophoric gas-phase precursors. We study close-space vapor transport, which uses solid GaAs as a source and water vapor as a transport agent as an alternative technique for depositing GaAs films. Epitaxial n-GaAs thin films were grown on n⁺-GaAs substrates while varying the water vapor concentration and the source/substrate temperatures. The photovoltaic properties of the films were evaluated using a non-aqueous photoelectrochemical test cell containing the ferrocene/ferrocenium redox couple. We found that a wide range of growth conditions were suitable for growing GaAs films with diffusion lengths over 1 μm and open circuit voltages similar to what has been observed for GaAs grown using metal-organic chemical vapor deposition (~ 820 mV).