Effects of gas-phase and wet-chemical surface treatments on substrates induced vertical, valley–hill & micro-granular growth morphologies of close space sublimated CdTe films

Abstract

We implemented gas-phase (argon plasma) and wet-chemical (HNO₃) surface treatments on close space sublimated (CSS) Cadmium Telluride (CdTe) thin films exhibiting morphologies of (i) vertically aligned walls on copper (Cu) and stainless steel (SS) substrates, (ii) valley–hills on aluminum (Al) substrates and (iii) micro-granules on nickel (Ni). As all the growth conditions (temperature, pressure, duration and source/substrate distance) were exactly the same in the CSS process to coat CdTe films, it is asserted that the various microstructures were raised only on Cu, Al, Ni and SS substrates. Plasma and HNO₃ surface treatments on metal substrates did not affect the CdTe morphologies in terms of specific structures but it was observed that structural, optical and electrical charge transport characteristics were highly tunable by the two surface treatments. Thus, substrate driven morphological evaluation followed by surface treatments was enabled. The present study demonstrated various microstructures of CdTe films on metallic thin foil substrates to attempt the establishment of flexible opto-electronics based on CdTe.