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Journal of the Electrochemical Society, Vol.157, No.2, G67-G70, 2010
Optical Spectra and Direct Optical Transitions in Amorphous and Crystalline ZnO Thin Films and Powders
Comparative studies of ZnO crystalline and amorphous thin films and nanocrystalline powders are reported. The UV-visible optical spectra were analyzed with special attention paid to the direct optical bandgap. Atmospheric radio-frequency barrier torch discharge and pulsed hollow cathode sputtering techniques for the film fabrication were used. For the crystalline films, similar values of the direct optical bandgap were found independent of the growth method used. The analysis of the amorphous films and powders revealed a pronounced Urbach-like exponential absorption tail approaching the bandedge. For the powders, the bandgap energies were larger than those for the crystalline and amorphous films. A decrease in the powder particle size in the powders leads to an increased direct optical bandgap.
Keywords:amorphous semiconductors;energy gap;II-VI semiconductors;nanofabrication;nanoparticles;optical constants;particle size;plasma deposition;semiconductor growth;semiconductor thin films;sputter deposition;ultraviolet spectra;visible spectra;wide band gap semiconductors;zinc compounds