Microcavities in Semiconductor Materials

Positron beam and helium desorption techniques have been applied to different materials, in particular semiconductor materials, to determine the presence of defects. The positron technique yields values of the positron diffusion length and values of the Doppler broadening parameters. In principle, defect concentrations can be derived and an indication can be obtained about the nature of the defect. Results are presented which show that cavities can be easily detected. It is also demonstrated that gas accumulated in the cavities reduces the observed differences between the defected and the defect-free material. Large cavities were detected in solar cell hydrogenated amorphous silicon and low temperature deposited amorphous silicon. It was found that layers deposited under irradiation with low energy ions (ion assisted deposition) did not show evidence of microcavities. Desorption techniques were successfully employed to detect cavities in silicon.