THE MICROWAVE MEASUREMENT OF THE CONDUCTIVITY OF A SEMICONDUCTING FILM

Abstract

A sensitive microwave bridge has been assembled for the measurement of the complex propagation coefficient of a section of waveguide containing a semiconducting film. The bridge operating at a frequency of 9.25 Gc/s, can be balanced to one degree phase shift and 0.05 db attenuation. Films of indium antimonide have been prepared by vacuum deposition onto mica substrates. A multilayer construction with subsequent annealing was used in an attempt to obtain high mobilities. Four n-type InSb films with thicknesses 2160 Å, 2180 Å, 4700 Å and 4800 Å were produced. The Hall Mobilities were found in the range between 500 to 2 , 1000 cm /V-soc. Theoretical and numerical solutions of the complex propagation constant of a rectangular waveguide section containing a semiconducting film have been made. The analysis is based on the assumptions that the film thickness was negligible, the film surface was parallel to the narrow walls of the guide and that perfect electrical contact existed between the film and the broad walls of the guide. Measurements of complex propagation coefficients have been carried out with the film mounted between mica sheets in a slotted waveguide in preparation for experiments involving the application of high electric d.c. fields to the sample. The measured complex propagation agreed closely with the computed values confirming the validity of the theoretical model for this particular case. The design of a new type of a pulse generator for these high electric field experiments is described. The pulse generator features a continuously variable pulse width from 0.2 μ sec, to 5 μ sec. with a low output impedance of approximately 13 ohms and a repetition rate adjustable to 1, 2, 5 and 10 pulses per second.