Effects of reactive versus unreactive metals on the surface recombination velocity at CdS and CdSe(112̄0) interfaces

Direct measurements of the surface recombination velocity (SRV) on etched CdS(112̄0), CdSe(112̄0) and at their interfaces with various metal ions and metals (deposited by electrolyte aqueous solutions and in situ thermal evaporation, respectively) have been performed using ultrafast time-resolved photoluminescence (PL). Correlations with interface states types and energy positions have been found based on surface photovoltage spectroscopy (SPS). The results show that the original semiconductor SRV is retained, and in some cases even decreases, when these surfaces are covered with metals, which tend to react with the semiconductor's anion, such as Al, Ti, and Zn. On the other hand, the SRV increases sharply as a function of unreactive metals coverage, such as Cu, Au, etc. The PL results are explained in terms of metal-induced recombination centers at the semiconductor interface, which are introduced or eliminated as observed by SPS.