Formation of vacancy-interstitial Frenkel pairs, together with the properties of interstitials and vacancies in CdTe, ZnTe and their alloys were investigated using first-principles calculations. Generation of Frenkel pairs on the cation sub-lattice depended strongly upon the Fermi energy: the presence of excess free electrons reduced the energy barrier for pair generation from 2.5eV, in intrinsic samples, to 1.2eV. Moreover, EF determined both the stability of Frenkel pairs with respect to recombination and their binding energy, which varied from ~0.2 to ~1eV. A strong dependence on the Fermi energy, i.e., upon the charge state, was also found for stable sites and barriers for the diffusion of isolated interstitials. In particular, neutral interstitials had two (meta)stable sites, corresponding to 2 local minima in energy, and diffused by jumps between them. Positively charged interstitials had only one stable site, and diffused by double-length and curvilinear jumps. For the relevant charge states, the barriers for diffusion ranged from 0.5 to 1eV, which implied a high mobility of interstitials. Most of these properties were traced back to the defect-induced deep gap levels, their occupation and their dependence upon the defect's site. An important influence of the ionicity of the host was pointed out. On the other hand, the generation of Frenkel pairs on the anion sub-lattice required an energy of about 5eV, and was thus inefficient. The results obtained suggested that the formation of Frenkel pairs was the microscopic origin of 2 effects observed in Schottky junctions based upon CdZnTe and other II–VI alloys: the reversible changes in conductivity by a few orders of magnitude, and the ferroelectric-like behavior of polarization.

Generation of Vacancy-Interstitial Pairs as a Possible Origin of Resistivity Switching and Ferroelectric Properties in Cd1-xZnxTe. P.Jakubas, P.Bogusławski: Physical Review B, 2008, 77[21], 214104 (17pp)