Synchrotron Photoemission Spectroscopy Study of p‑GaInP2(100) Electrodes Emersed from Aqueous HCl Solution under Cathodic Conditions

(Photo)­electrochemical processes occurring under cathodic polarization at the p-GaInP2(100)/1 M HClaq solution interface were investigated in detail by high-resolution surface sensitive synchrotron-radiation photo­emission spectroscopy. It was found that on application of the cathodic bias in the dark to the p-GaInP2(100)/1 M HClaq solution interface the electrochemical processes are started at a bias of about −1.0 V vs reversible hydrogen electrode (RHE), where cathodic current passing through the semiconductor/electrolyte interface starts to rise. Under higher cathodic bias applied in the dark, hydroxyl groups and metallic gallium are accumulated at the surface, which is accompanied by a decrease in work function of the semiconductor. Accumulation of hydroxyl groups can be related only to splitting of water molecules at the semiconductor/electrolyte interface, since the aqueous HCl solution contains no hydroxyl groups intrinsically. Accumulation of hydroxyl groups and metallic gallium is accelerated under visible light illumination, which indicates participation of photogenerated electrons in the surface electrochemical reactions. The formation of the metallic gallium without simultaneous metallic indium formation testifies that the In–P bonds of the GaInP2 compound are more stable against cathodic corrosion than the Ga–P bonds.