Comparison of microstructures of CdTe layers electrodeposited from basic ammoniacal and acidic sulfate electrolytes

The microstructures of CdTe layers electrodeposited from basic ammoniacal electrolytes were investigated by transmission electron microscopy and compared with those from a conventional acidic sulfate electrolyte. As-deposited CdTe layers with a nearly stoichiometric composition from a basic electrolyte with a relatively high Cd(II)/Te(IV) concentration ratio were composed of randomly oriented crystallites with a grain size of ca. 10 nm, while those from an acidic electrolyte consisted of defective columnar grains with a (111) preferred growth orientation. Deposit containing around 65 atom % Te from a basic electrolyte with a relatively low Cd(II)/Te(IV) concentration ratio was found to be amorphous, which was easily crystallized into a mixture of CdTe, elemental Te, and a trace amount of Te2O5 by electron beam illumination. By annealing at 300degreesC for 1 h in an Ar atmosphere, CdTe grains from the basic electrolyte grew by about a factor of four, but at the same time, nano-voids were formed at the grain boundaries. In contrast, CdTe grains from the acidic electrolyte did not grow by annealing under the same conditions. (C) 2004 The Electrochemical Society.