MICROCAVITIES IN SEMICONDUCTOR-MATERIALS

Positron beam and helium desorption techniques have been applied to di fferent 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 paramet ers. In principle, defect concentrations can be derived and an indicat ion can be obtained about the nature of the defect. Results are presen ted which show that cavities can be easily detected. It is also demons trated that gas accumulated in the cavities reduces the observed diffe rences between the defected and the defect-free material. Large caviti es were detected in solar cell hydrogenated amorphous silicon and low temperature deposited amorphous silicon. It was found that layers depo sited under irradiation with low energy ions (ion assisted deposition) did not show evidence of microcavities. Desorption techniques were su ccessfully employed to detect cavities in silicon.