Temperature dependence of current decay and trap evaluation in thin films of CDS

Abstract

The current decay process for the determination of trapping time, trap depth and the capture cross section for electrons in a semiconductor has been discussed. Because of the large number of unoccupied traps in the specimen of thin films the decoy of current is mainly due to the capture of majority carriers by the trapping centres.The method uses a specimen of vapour-deposited thin film which is subjected to an elevated temperature and a step voltage is applied across the specimen. The density of majority carriers in the conduction band is thus increased by the injection process and the equilibrium is disturbed. Due to the large numbers of shallow traps available in such films, capture of these excess carriers starts taking place and the current decays with time. This decay is found to be double exponential in nature. The total decay is thus due to the trapping at at least two discrete levels.From the study of this decay, evaluation of trap depths and capture cross sections has been made. The trap depths are found to be 006 ev and 0.08 ev and their corresponding capture cross sections are 0.4×10-24 cm2 and 0.04×10-24 cm2respectively, which are in fair agreement with the results reported earlier. © 1970, Taylor & Fancis Group, LLC.