Asymmetric effect of (000 $\bar{1}$ ) and (0001) facets on surface and interface properties of CdS single crystal

Abstract

A different effect of (0001) and (000\(\bar{1}\)) crystal facets of the cadmium sulfide (CdS) wurtzite structure terminated with Cd and S atoms, respectively, was observed in respect to the properties of the crystal surface and interface with metal or organic semiconductor contacts. In addition to the different surface morphology, a bare CdS single crystal showed different features in photoluminescence from the Cd- and S-terminated surfaces. Different adhesive behavior of poly(3,4-ethylenedioxythiophene): poly(styrene sulfonic acid) (PEDOT:PSS) films in respect to the Cd- and S-terminated facets of the crystal has also been found. Photovoltaic properties of hybrid CdS/PEDOT:PSS heterojunctions have been shown to be sensitive in respect to the crystal facet used. Thin films of aluminum (Al) equally deposited onto the opposite crystal facets revealed much smaller sheet resistance on the sulfur facet than on the cadmium one, which has been assigned to the difference in both chemical interaction with the surface atoms and surface morphology. Current–voltage characteristics of an apparently symmetric Al/CdS/Al structure with Al electrodes deposited onto the opposite crystal facets showed asymmetric behavior depending on the bias direction applied to the Cd or S-terminated facet, with the barrier for electrons at the Al/S-terminated interface, respectively.