The cause of carrier reduction in annealed n-type material was investigated by using positron annihilation methods. By isothermal annealing at 450C, the electron concentration in a Ga-doped film was reduced to 6.3 x 1013 from 7.9 x 1016/cm3. The intensity of the radiative recombination of neutral donor bound excitons was also decreased, and the intensity of deep emission at an energy of about 2.0eV increased in low-temperature (4.2K) photoluminescence spectra. The results which were obtained by using the positron annihilation method showed that the concentration of negatively charged vacancy-type defects in annealed films did not increase and was comparable to that in as-grown film. Therefore, isothermal annealing did not lead to the formation of negatively charged vacancy-type defects, such as Zn vacancies, in Ga-doped ZnSe. It was concluded that the carrier reduction which occurred upon annealing Ga-doped ZnSe was not related to negatively charged vacancy-type defects.

T.Miyajima, H.Okuyama, K.Akimoto, L.Wei, S.Tanigawa: Materials Science Forum, 1993, 117-118, 483-8