Defects in n-type bulk crystals were investigated by using positron annihilation. Positron lifetime spectroscopy revealed vacancies with a positron lifetime of 280 and 275ps in

ZnS:I and ZnSe:Al, respectively. The positron bulk lifetime was 241ps at 300K, determined in an undoped semi-insulating control sample. The vacancies were identified as being Zn-vacancy–donor complexes by combining the positron lifetime measurements with positron-electron annihilation momentum distributions. This was supported by previous electron paramagnetic resonance measurements. The samples exhibited differing degrees of electrical compensation; adjustable by heat treatment under suitable Zn vapor pressures. The vacancy concentration as measured by positron annihilation could quantitatively explain the de-activation of donors. Thus, the compensation of n-type conductivity in ZnSe was due to self-compensation by native Zn-vacancy–donor complexes.

Identification and Quantitative Evaluation of Compensating Zn-Vacancy–Donor Complexes in ZnSe by Positron Annihilation. J.Gebauer, R.Krause-Rehberg, M.Prokesch, K.Irmscher: Physical Review B, 2002, 66[11], 115206 (10pp)