Positron traps in electron irradiated ZnO semiconductor

L.C.DAMONTE; M.HERNÁNDEZ FENOLLOSA; B.MARÍ; F.J.NAVARRO

La Plata, Argentina

Workshop; 35th Anniversary Hyperfine Interactions at La Plata; 2005

            Due to its attractive optical and electrical properties, ZnO is becoming the usual alternative to GaN in applications on UV optoelectronic. Intrinsic and induced point defects in ZnO lead to the generation of bounded states with important effects on the material properties. A complete knowledge of point defect structure is needed to understand its optical behaviour.             We have applied positron annihilation lifetime spectroscopy (PALS), a highly sensitive technique to probe point defects, on electron irradiated ZnO single crystals. The samples, commercially provided, were exposed to different 10 MeV electrons fluences giving rise to irradiation doses between 60 and 240 Gy. After irradiation, samples were annealed in air atmosphere from 100 to 1000ºC in order to follow the evolution of radiation defects and their effect on the positron parameters.             The average positron lifetime shows a non-monotonically behaviour with increases radiation dose, although its variation indicates that the generated defects act as effective positron traps. First steps of annealing seem to have no effect on positron characteristic, although further annealing induced new attractive centres for positrons.             The above features are compared with photoluminescence (PL) results which also indicate changes in the PL spectra with electron irradiation and heat treatments.             The possible origin, nature and state of charge of the radiation induced defects and their thermal evolution are tentative explain based on the recombination of electron induced with native defects. Keywords: Positron annihilation, ZnO, defects, semiconductors Email: damonte@fisica.unlp.edu.ar, ldamont@upvnet.upv.es