Electron spin resonance of ultrahigh vacuum evaporated amorphous silicon: In situ and ex situ studies

Abstract

An in situ study of the electron spin resonance (ESR) of ultrahigh vacuum evaporated amorphous silicon is performed to define the characteristics of the signal as a function of preparation conditions. The influence of deposition rate, temperature of substrates, temperature of annealing, angle of incidence of the vapor beam, contamination by air exposure, and the presence of hydrogen during growth have been investigated. Porosity effects depending on thermal history and angle of incidence, which allow contamination, are observed by ESR. It is found that the spin density is mainly determined by the thermal history and varies only within a factor of about 3 when contamination effects are not involved. This is contrary to other results which we believe were obtained from contaminated specimens. Related variations of linewidth and saturation behavior are observed. Ex situ measurements of linewidth, saturation behavior, and ESR susceptibility are done as a function of temperature. The results of these measurements are discussed in terms of two extreme possibilities for spins: individual spins randomly distributed and clusters of spins. The question of a possible association of spins with voids is also discussed. The results are compatible with a model of individual spins randomly distributed. An approach to the relation between spins and conductivity is presented. © 1978 The American Physical Society.