Selective heteroepitaxy of InGaP/GaAs/silicon devices as low-costphotovoltaic/photoelectrolysis cells for generating hydrogen fromsunlight

摘要

InGaP/GaAs photovoltaic-photoelectrochemical (PV-PEC) cells madeby MOCVD on GaAs substrates have demonstrated high conversionefficiencies for the direct generation of hydrogen from sunlight andwater. The present work is an experimental effort to develop and assesspotential low-cost alternative fabrication technologies for such PV-PECcells. Our strategy is to utilize a cheap silicon substrate and simpleepitaxial growth techniques. Since PV-PEC cells do not require asemiconductor p-n junction nor front metallization, a mesa-array devicestructure is proposed that can be made by selective epitaxy. Selectiveepitaxy of small-area (10 to 100 microns on a side) mesas should yieldsignificant stress and defect reduction. We describe the fabrication ofsuch cells with GaAs-on-silicon heteroepitaxy by a close-spaced vaportransport (CSVT) technique in combination with selective InGaPliquid-phase epitaxy (LPE)