Selective heteroepitaxy of InGaP/GaAs/silicon devices as low-cost photovoltaic/photoelectrolysis cells for generating hydrogen from sunlight

InGaP/GaAs photovoltaic-photoelectrochemical (PV-PEC) cells made by MOCVD on GaAs substrates have demonstrated high conversion efficiencies for the direct generation of hydrogen from sunlight and water. The present work is an experimental effort to develop and assess potential low-cost alternative fabrication technologies for such PV-PEC cells. Our strategy is to utilize a cheap silicon substrate and simple epitaxial growth techniques. Since PV-PEC cells do not require a semiconductor p-n junction nor front metallization, a mesa-array device structure is proposed that can be made by selective epitaxy. Selective epitaxy of small-area (10 to 100 microns on a side) mesas should yield significant stress and defect reduction. We describe the fabrication of such cells with GaAs-on-silicon heteroepitaxy by a close-spaced vapor transport (CSVT) technique in combination with selective InGaP liquid-phase epitaxy (LPE).