Picosecond Photoconductivity in Polycrystalline CdTe Films Prepared by UV-Enhanced OMCVD

Abstract

Ultrafast photoconductive detectors are often built from semiconductors possessing a large density of structural defects, which function as effective trapping and recombination centers. One of the earliest demonstrations of this approach was made with high defect density, low mobility amorphous silicon [1,2]. The low carrier mobilities severly limit the sensitivity of amorphous semiconductor devices in most applications. Improvements in the sensitivity over the early devices have been made by using Schottky barriers and novel transmission line configurations in amorphous silicon [3] and by the radiation damage of crystalline semiconductors [4]. Another approach which has not been fully exploited is the use of polycrystalline semiconductors [5,6], which have a large defect density at the grain boundary and a high mobility within the grain. In this work, we have made the first measurements of picosecond photoconductivity in thin films of polycrystalline CdTe grown by photon-assisted Organometallic Chemical Vapor Deposition (OMCVD). Photoconductivity measurements were made on three samples of CdTe, intentionally prepared under different deposition conditions to controllably alter the electronic transport. The fastest of these photodetectors had a carrier relaxation time of 3.7 psec and an average drift mobility of 59 cm²/Vsec.