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

Abstract

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 Situ Smoothing of Facets on Spalled GaAs(100) Substrates during OMVPE Growth of III–V Epilayers, Solar Cells, and Other Devices: The Impact of Surface Impurities/Dopants

“…It should be mentioned that Zn:GaAs can be used effectively for substrate smoothing during hydride vapor-phase epitaxy (HVPE) growth . This difference is presumably linked to the differing growth environments for OMVPE and HVPE.…”

“…The reconstruction of Ga x In 1– x P­(100) is qualitatively different in OMVPE than in MBE, because OMVPE-prepared surfaces incorporate atomic hydrogen provided by precursors like PH 3 , and AsH 3 . For HVPE, the availability of Cl to the surface similarly creates possibilities not available to OMVPE or MBE . Etching pathways unique to OMVPE and HVPE are also enabled by reactive species like atomic H and Cl, which can react with surface atoms to form stable molecules that are then carried away from the surface in the vapor phase.…”

“…It should be mentioned that Zn:GaAs can be used effectively for substrate smoothing during hydride vapor-phase epitaxy (HVPE) growth. 17 This difference is presumably linked to the differing growth environments for OMVPE and HVPE. One obvious difference is the presence of Cl in an HVPE environment, which may enable some smoothing processes not accessible to OMVPE (except perhaps when supplied by a source like CCl 4 ).…”

“…One obvious difference is the presence of Cl in an HVPE environment, which may enable some smoothing processes not accessible to OMVPE (except perhaps when supplied by a source like CCl 4 ). A more detailed study of substrate smoothing for HVPE growth has been conducted in a related study by Braun et al 17 …”

“… 41 For HVPE, the availability of Cl to the surface similarly creates possibilities not available to OMVPE or MBE. 17 Etching pathways unique to OMVPE and HVPE are also enabled by reactive species like atomic H and Cl, which can react with surface atoms to form stable molecules that are then carried away from the surface in the vapor phase.…”