SIZE QUANTIZATION IN ELECTRODEPOSITED CDTE NANOCRYSTALLINE FILMS

We describe the deposition and characterization of nanocrystalline CdT e films which exhibit size quantization. The CdTe films were electrode posited from a dimethylsulfoxide solution of tri-(n-butyl)phosphine te lluride and cadmium perchlorate at 100 degrees C. The stoichiometry of the films depends on applied potential and solution composition. The films contained about 5-10% Te excess and exhibited small blue shifts (0.1-0.2 eV) in their optical spectra. XRD and electron microscopy ind icated a typical crystal size of ca. 8 nm. Pulse reverse plating was u sed to improve the film stoichiometry. The nanocrystal size could be c ontrolled by the pulse parameters, and almost stoichiometric films wit h average crystal sizes from 4 to 7 nm were obtained, showing increase s in bandgap up to 0.8 eV. Annealing the films resulted in gradual cry stal growth and corresponding spectral red shifts until the bulk bandg ap was reached. X-ray photoelectron spectroscopy (XPS) showed phosphor ous incorporation in the films. The small crystal size was attributed to capping of the depositing CdTe by phosphine groups and could be con trolled by the duty cycle of the plating pulsed current, whereby a lon ger off-time allowed more efficient capping and therefore smaller nano crystal size.