Effect of surface morphology on GaAs solar cells grown on planarized spalled (100) GaAs substrates

We analyze the effect of surface morphology created by planarizing spalled GaAs wafers on GaAs solar cells grown by HVPE. Controlled spalling of (100)-oriented GaAs has potential to reduce substrate costs for III-V photovoltaics (PV); however, it creates regularly faceted surfaces that complicate the growth of high quality III-V PV devices. We leverage the crystallographic-direction-dependent growth capability of hydride vapor phase epitaxy (HVPE) to planarize these faceted GaAs substrates, reducing the surface roughness and degree of faceting. We then demonstrate that GaAs solar cells grown on planarized surfaces are nominally identical to those grown on a planar, epi-ready GaAs surface. We observe slightly degraded device performance in cases where facets are not completely removed. We use device-scale imaging techniques combined with characterization of device cross sections to analyze this performance degradation. Lastly, we discuss the growth mechanisms that contribute to the planarization of faceted surfaces. These investigations into the mechanisms of both device degradation and planarizing growth will ultimately enable high-performing III-V PV with the cost reduction potential of controlled spalling. This advancement, when combined with low-cost epitaxy by HVPE, provides one of the most promising routes to low-cost III-V PV to date.