The design and characterization of mm-scale GaAs photovoltaic cells are presented and demonstrate highly efficient energy harvesting in the near infrared. Device performance is improved dramatically by optimization of the device structure for the near-infrared spectral region and improving surface and sidewall passivation with ammonium sulfide treatment and subsequent silicon nitride deposition. The power conversion efficiency of a 6.4 mm2 cell under 660 nW/mm2 NIR illumination at 850 nm is greater than 30 %, which is higher than commercial crystalline silicon solar cells under similar illumination conditions. Critical performance limiting factors of sub-mm scale GaAs photovoltaic cells are addressed and compared to theoretical calculations.
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