The effect of Zn-vapour annealing upon as-grown Zn1-xMgxSe crystals, with x-values ranging from 0 to 0.6, was studied by means of positron lifetime and photoluminescence measurements. Experimental and theoretical evidence showed that the bulk lifetime of free positrons increased linearly with the Mg content. The average positron lifetime increased with temperature; thus indicating that both vacancies and negative ions trapped positrons. Decomposition of the lifetime spectra showed that the vacancy had a characteristic positron lifetime of 325ps. A comparison with theoretical calculations indicated that the lifetime of 325ps corresponded either to divacancies which relaxed inwards or to monovacancies which strongly relaxed outwards. The latter possibility was thought to be the more likely, and the positron lifetime of 325ps was attributed to a Zn vacancy or to a complex which involved VZn. The vacancy concentration was almost independent of Mg contents above x = 0.2, but decreased markedly at x = 0.56. The use of Zn-vapour annealing decreased the concentration of Zn vacancies. The intensity of the green photoluminescence was related to the concentration of VZn. It was concluded that the electron levels of the Zn vacancy were involved in the optical transition which led to the green photoluminescence.

Characterization of Defects in (ZnMg)Se Compounds by Positron Annihilation and Photoluminescence. F.Plazaola, K.Saarinen, L.Dobrzynski, H.Reniewicz, F.Firszt, J.Szatkowski, H.Meczynska, S.Legowski, S.Chabik: Journal of Applied Physics, 2000, 88[3], 1325-32