Use of light for the electrochemical deposition of Bi on n-GaAs substrates

Abstract

In this work, we have explored the possibility of using light to remove the adsorbed hydrogen layer that blocks the GaAs surface when electrodepositing Bi thin films on lower-doped n-GaAs(111)B substrates. A light pulse of a few seconds applied under open-circuit (zero-current) conditions before starting the electrodepositionof Bi in darkness has a small effect on the structural, morphological and interfacial electrical properties of the Bi film in comparison to layers deposited without the use of light. The potentiostatic curves recorded during the Bi nucleation show that the light pulse does not remove the adsorbed hydrogen layer but modifies the n-GaAs surface, inhibiting the reduction of Bi(III) ions. The atomic force microscopy analysis of the n-GaAs surface corroborates that the light degrades the surface by inducing photo-oxidation reactions, phenomenon that is correlated to the photocorrosion of the substrate. To maintain the electrical neutrality during photocorrosion, proton reduction and electroless deposition of Bi occur in parallel to the photo-oxidations. The simultaneity of these processes and the inhibition of Bi(III) ions to get reduced on those areas of the n-GaAs surface chemically altered enables the electroless deposition of unconnected Bi flakes with morphological, structural and interfacial electrical properties close to the state of the art of Bi thin films. Only the out of plane crystal quality of the Bi flakes show a small detriment whereas the Schottky barrier height slightly increases.