Centroid shift of γ rays from positron annihilation in the depletion region of metal-oxide-semiconductor structures

Using metal-oxide-semiconductor (MOS) structures, the shift of centroid (peak) of γ-ray energy distributions emitted from positron annihilation has been measured as a function of incident positron energy. The Doppler centroid shift was found to be consistent with the positron motion in the MOS depletion region. The results are described by a one-dimensional positron diffusion model, and provide information on "effective" positron diffusion length under applied field.