Size Quantization in Electrodeposited CdTe Nanocrystalline Films

Abstract

We describe the deposition and characterization of nanocrystalline CdTe films which exhibit size quantization. The CdTe films were electrodeposited from a dimethylsulfoxide solution of tri-(n-butyl)phosphine telluride and cadmium perchlorate at 100 °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 indicated a typical crystal size of ca. 8 nm. Pulse reverse plating was used to improve the film stoichiometry. The nanocrystal size could be controlled by the pulse parameters, and almost stoichiometric films with average crystal sizes from 4 to 7 nm were obtained, showing increases in bandgap up to 0.8 eV. Annealing the films resulted in gradual crystal growth and corresponding spectral red shifts until the bulk bandgap was reached. X-ray photoelectron spectroscopy (XPS) showed phosphorous incorporation in the films. The small cryst...