PAC Studies of Defects in AgCI and II-VI Compounds

Abstract

ABSTRACTThe Perturbed Angular Correlation (PAC) method has been used to study In -vacancy complexes in AgCl and II - VI compounds. Although these materials are quite different in structure and properties, they are related by photoconductive properties which make them interesting intrinsically and for application to photography (silver halides) and to the design of photodetectors and photovoltaic cells (II - VI compounds). We have obtained the first PAC results for silver halides and ternary II-VI compounds.For AgCl, measurement at 77 K clearly reveals two different 111In - vacancy complexes characterized by quadrupole interaction frequencies Vq1 = 21.5 MHz and Vq2=43 MHz, both having axially symmetric electric field gradient (EFG) tensors with principle axes along <100> directions. Temperature dependence of the PAC signal allows a determination of the activation energy and attempt frequency for vacancy motion by measurement of the damping arising from dynamic effects.For 4% Zn - doped bulk CdTe samples, vacuum annealed in the range 400°C to 550°C, PAC shows that a large fraction of the 111 In probe atoms occupy non-cubic lattice sites having an EFG characterized by vQ = 60 MHz, η = 0.2. The concentration of this complex was decreased by annealing between 400°C and 600°C in a Cd overpressure, suggesting tha the observed EFG is caused by a 111In - cadmium vacancy complex. Similar measurements of Cd0.8Mn0.2Te showed an identical EFG which, however, appeared at a lower annealing temperature.