Photoelectrode/electrolyte interfacial band lineup engineering with alloyed III–V thin films grown on Si substrates

Abstract

In this work, we demonstrate how the classical concept of band gap engineering usually used in III–V semiconductor devices can be extended to the engineering of the band lineup between semiconducting photoelectrodes and electrolytes. The performances of photoelectrodes made of GaP_1−xAs_x epilayers in the full compositional range and grown on low-cost Si substrates were studied and compared with those of photoelectrodes grown on GaAs and GaP substrates. We first show that the changes of incident photon to current conversion efficiency (IPCE) with the As content in GaP_1−xAs_x alloys are related to the band gap nature (direct or indirect) and band gap energy variations. Then, from flat band potential measurements during Mott–Schottky experiments, valence and conduction band energies of GaP_1−xAs_x alloys are positioned versus the reversible hydrogen potential. A weak change of conduction band energies and a large evolution of valence band energies are obtained, in good agreement with expected theoretical trends. Such results show that both band gaps and semiconductor/electrolyte band lineups can be engineered through alloying of III–V semiconductors deposited on silicon substrates. This band lineup engineering strategy is expected to be of great interest to address specific redox reactions in the electrolyte, provided that suitable protecting or passivating layers can be used to limit surface/interface recombinations.