Comparative study between the photoelectrochemical behaviors of metal-loaded n- and p-GaAs

GaAs electrodes are coated electrochemically with thin films of Pt, Ni, Cu, Au, Cd and Pb. The thickness of metal film is estimated from the number of coulombs passes during its electrodeposition. The current-voltage curves of the metal/GaAs systems are registered under illumination in a three-electrode electrochemical cell. Metal additives to n-GaAs causes displacement in the direction of a negative potential in the order Pt, Ni, Cu and in the positive direction in the order Cd, Pb. Correspondingly, for metal/p-GaAs systems the onsetpotential of the photocurrent show behaviors opposite to those of the metal/n-GaAs systems, i.e. the onsetpotential of the photocurrent shifts towards the positive direction in the order Pt, Ni and Cu and in the negative direction in the order Cd and Pb. The results for the metal/n-GaAs systems are explained within view of the Schottky barrier model. According to this model, the extent of the negative shift in the onsetpotential of the photocurrent is proportional to the work function of the deposited metal. On the other hand, the photoelectrochemical behaviors of metal/p-GaAs systems are explained in accordance to the eletrocatalytic model. In this regard deposition of a metal of a high activity towards hydrogen evolution shifts the onsetpotential of p-GaAs towards more positive potential. (C) 1999 Elsevier Science S.A. All rights reserved.