PRIMARY REACTIONS IN THE PHOTOCORROSION OF CDSE THROUGH PHOTOCAPACITANCE MEASUREMENTS

CdSe/liquid junctions have been investigated through photocapacitance measurements in single and in double beam (i.e., with an auxiliary band-to-band laser light superimposed) conditions. Two surface states, E1 = E(c) - 0.7 eV and E2 = E(c) - 1.48 eV, two lattice defects, located at E(c) - 0.12 eV and E(c) - 1.15 eV, and a bulk state located at E(c) - 1.25 eV, have been resolved. The analysis of the results as a function of the solution composition shows that both surface states E1 and E2 are involved in the corrosion mechanism: the upper surface state (E(c) - 0.7 eV) corresponds to elemental selenium whereas the lower one (E(c) - 1.48 eV) corresponds to a Cd-related chemical intermediate. It is also shown that both lattice defects act as preferential surface sites where localized corrosion takes place.