SIMULTANEOUS OBSERVATION OF STRONG AND WEAK QUANTUM CONFINEMENT EFFECT IN CHEMICALLY DEPOSITED CDSE THIN-FILMS - A SPECTRO-STRUCTURAL STUDY

CdSe thin films deposited chemically on glass substrates for 4, 8, and 16 h, and subsequently annealed al 400 degrees C for 1 h, have been s tudied by a combination of spectroscopic (photoluminescence and Raman scattering) and structure-determining (x-ray diffraction and atomic fo rce microscopy) techniques. Due to a size distribution of constituent grains, photoluminescence spectra of the as-deposited films show weak but broad bands at similar to 2.2 eV (strongly confined band) and simi lar to 1.73 eV (weakly confined band). On annealing, intensity of the weakly confined band, at similar to 1.7 eV increases as a result of an improvement in the crystalline quality of CdSe nanoclusters. A surfac e-optic Raman mode at similar to 250 cm(-1) in as-deposited samples ha s been observed for the first time. The x-ray diffraction studies of a nnealed samples show II diffraction peak at 2 theta= 13 degrees from t he (001) plane. The improvement in crystallinity of the films as obser ved by atomic force microscopy and photoluminescence techniques, the a ppearance of (001) reflection in the x-ray diffraction pattern, the di sappearance of surface-optic Raman made, and the enhancement of weakly confined band-all as a consequence of annealing-have been discussed a nd correlated with 1 each. other. A film deposition mechanism has been described, which explains the origin of the simultaneous existence of strong and weak quantum confinement effects; the significance this ob servation in the development of high efficiency photovoltaic solar cel ls has been emphasized. (C) 1997 American Institute of Physics.