"Positron Trapping In ZnO-Based Nanocrystal Semiconductor Powders "

L.C.DAMONTE; M.HERNÁNDEZ FENOLLOSA; B.MARÍ

Coimbra, Portugal

Conferencia; 8th International Workshop on Positron and Positronium Chemistry (PPC8); 2005

With unique optical and electronic properties, the wide bandgap semiconductor ZnO is arising as a potential material for demanding technological applications, such as, blue and ultraviolet light emitters and detectors. However, its widespread utilisation is limited by the low density of carriers attained by doping, mainly due to the dopants association with compensating defects. Intrinsic and induced point defects in ZnO lead to the generation of bounded states with important effects on the material properties. Substitution on the cation site, for example, can change the direct bandgap of this semiconductor, decreasing (increasing) in the case of Cd (Mg). In consequence, a complete knowledge of point defect structure is needed to understand its optical behaviour. Mechanical milling is an effective, useful and simple processing technique to produce the synthesis of alloy phases including nanocrystalline materials. Under milling, the powders are subjected to severe plastic deformation giving rise to particle and grain refinement, creating, simultaneously, different kinds of defects. In this work we present a positron lifetime study (PALS) on M-doped ZnO (M: Cd, Mg) powders obtained by mechanical milling. The results indicate that positron and positronium trapping occur. The evolution of annihilation parameters with milling time were analyzed and related with the kind of mechanical induced defect involved. A comparation with PALS results in ZnO single crystals is also presented.