A Study on Optoelectronic Properties of Thermally Evaporated CdSe Thin Films.

摘要

In the present work, an experimental study on structural characterization and some optoelectronic properties of thermally evaporated polycrystalline CdSe thin films under different ambient conditions was carried out. The results incorporated in the thesis are presented in five chapters as detailed below.;Chapter-II : Equipments Used and Details of the Experimentals.;Chapter-III : Structural Characterization of CdSe Thin Films.;Chapter-IV : Optoelectronic Properties of CdSe Thin Films.;Chapter-I : General Introduction.;Chapter-V : Spectral Response, Rise and Decay of Photocurrents and Optical Properties.;A list of related references is included at the end of each chapter.;Chapter - I. General Introduction.;In this chapter a comprehensive discussion is made regarding importance of CdSe thin films for the fabrication of different optoelectronic devices. Along with CdSe, relevant properties of the other II-VI group of semiconductor compounds are also discussed. A solid thin film is a homogenous material which is formed by atom by atom or molecule by molecule condensation process, whose one dimension is reduced suitably to the order of a few mean free paths of the carriers under consideration. As such thin films cannot support themselves; the condensation of a thin film is made on a suitable solid surface called the substrate. The basic physical properties of a thin film depend upon several factors.;The thickness of the films has pronounced importance as far as various physical phenomenons of the films are concerned. If the thickness is comparable to or less than the mean free path of electrical conduction process, diffusion length, effective de-Broglie wavelength etc then thickness plays a key role on different electrical as well as optical processes like electrical conductivity, optical absorption etc. In such thin films the charge carriers invariable suffer surface collisions and thus the surface scattering process becomes a predominant factor.;All solid thin films irrespective of their deposition techniques are invariably associated with native defects like lattice disorder, stacking faults, twinning, dislocations, grain boundary defects etc which influence the electrical, optical as well as the mechanical properties of the films. Surface state of the films also has a dominating role in wide scale modification of the optoelectronic properties. The surface atoms are usually under the influence of imbalanced forces and remain in unsatisfied bond formation condition. So the absorption of gases on the thin film surface and solid state reactions are often observed in thin films rather than in bulk form. In the photoconductivity processes, the imperfections play a significant role. They either act as trapping or recombination centers of carriers.