This is an abstract from the article to be published in Progress in Surface Science, v.50, 1995
SERGUEI GRABTCHAK, MICHAEL COCIVERA
Guelph-Waterloo Centre for Graduate Work in Chemistry (GWC)2
University of Guelph
Guelph, Ontario, Canada N1G 2W1
Abstract
The Advanced Method of Transient Microwave Photoconductivity has been developed to simultaneously measure the kinetics of both the free and trapped electrons in single crystals of silicon and gallium arsenide, and polycrystalline CdSe. For Si wafers, hydrogen fluoride treatment removed the native oxide layer, and the change in surface state densities affected the transient decay rate of the photogenerated carriers. For Si having intermediate conductivity, the analysis was not straightforward because of the complicated relation between the measured parameters and the real and imaginary parts of the dielectric constant. For highly conductive Si, the so called "cross-talk" condition occurred, and the change of the cavity quality factor was proportional to the change of the real part instead of the imaginary part of the dielectric constant. This result differs from the simpler dependence developed by us for very resistive materials like CdSe. For a resistive material with a low concentration of shallow traps like intrinsic GaAs monocrystal, excess electrons remained in the conduction band for a relatively long time before trapping or recombination occurred. As a result, the sign of the frequency shift was positive instead of negative and was due the free electrons.