Electrochemical Passivation of Homoepitaxial InP (100) Thin Films for Light Induced Hydrogen Evolution: A Synchrotron Radiation Photoelectron Spectroscopy Study

Abstract

Recent synchrotron radiation photoelectron spectroscopy (SRPES) investigations on the surface chemistry of electrochemically conditioned surfaces of homo-epitaxial p-InP(100) layers deposited by MOVPE are described. The electrochemical conditioning, consisting in a voltammetric cycling in an HCl solution under illumination and a subsequent photo-electrochemical deposition of Rh, yields efficient photoelectrodes for light induced hydrogen evolution. The deconvolution of the In 3d5/2 and P 2p lines reveals that the oxide film consists of InPO3, In2(PO3)3 and In2O3. The presence of In2O3, with a band gap of 2.6 eV and an affinity of 4.3 eV can explain the conductivity of the oxide film, of about 7 nm thickness, by resonance tunneling. The detection of minute amounts of adsorbed Cl-atoms, presumably at the InP-oxide interface, is in agreement with the formation of interfacial dipoles responsible for the photoelectrochemical activation as confirmed by ultraviolet photoelectron spectroscopy (UPS)-measurements.