24% Single‐Junction GaAs Solar Cell Grown Directly on Growth‐Planarized Facets Using Hydride Vapor Phase Epitaxy

A 24%‐efficient single‐junction GaAs solar cell grown directly on a faceted, spalled (100) GaAs substrate after in situ planarization growth by hydride vapor phase epitaxy (HVPE) is achieved. Controlled spalling, a promising low‐cost substrate reuse technique, produces large facets in (100)‐oriented GaAs substrates due to the orientation of the fracture planes used for lift‐off. Planarization by HVPE offers a path toward direct use of these spalled substrates without costly polishing steps. Here, the growth rate anisotropy enabling planarization arising from diffusion and differences in the adsorption of growth species on {n11}B‐type facets relative to (100) is determined. Consecutive planarization and device growth that results in a solar cell with a minimal performance difference relative to a control cell grown on an epitaxy‐ready substrate are demonstrated. These results show that controlled spalling coupled with HVPE planarization is a viable pathway for lowering the cost of III‐V photovoltaics. In this work, planarization growth by hydride vapor phase epitaxy (HVPE) is studied as a method of enabling the direct use of spalled substrates without polishing. A 24%‐efficient solar cell is achieved after in situ growth planarization of 3‐µm‐tall facets with equivalent open‐circuit voltage compared to a device grown on a traditional planar substrate.