The positron as a probe for studying bulk and defect properties in semiconductors

Positron lifetime measurements are used to study various doped and undoped III-V compound semiconductors like GaAs, GaP, InAs and InP. In some as-grown crystals native vacancies (V/sub As//sup 0/, V/sub P//sup O/) or their complexes with dopants (Te/sub As/V/sub Ga//sup -/, V/sup P/Zn/sub In/V/sub P//sup 0/) are detected with maximum concentrations of a few 1018 cm-3. In undoped GaAs neutral As vacancies V/sub As//sup 0/ are identified, the concentration of which varies locally. The vacancies have their origin in deviations from the stoichiometric composition of the compound. They disappear at 500 0C. At this temperature defects created by irradiation with fast neutrons anneal also out. The relation between the bulk positron lifetime and the density and polarization of valence electrons is analyzed. Further, the potential of the positron annihilation method in identifying and characterizing vacancy-type defects in semiconductors is discussed. (author)