"Defects in electron irradiated ZnO single crystals "

HERNÁNDEZ FENOLLOSA, MA. ANGELES; LAURA CRISTINA DAMONTE; MARI, B.

SUPERLATTICES AND MICROSTRUCTURES

Elsevier

Año: 2005 vol. 38 p. 336 - 343

0749-6036

Point defects were introduced in ZnO single crystals by means of irradiation with several fluences of 10 MeV electrons giving rise to irradiation doses between 60 and 240 Gy. Irradiation defects were subsequently studied by positron annihilation lifetime spectroscopy (PALS) a sensitive technique for open volume defects and photoluminescence (PL). After irradiation, samples were annealed in air atmosphere from 100 to 1000ºC in order to follow the evolution of irradiation defects and their effect on the emission properties. Positron lifetimes and intensities measured by PALS as a function of radiation doses show that the generated defects act as effective positron traps. The PL spectra for all the analyzed samples consist of a near-band-edge (NBE) emission centred at 369 nm and a broad deep-level (DL) emission around 550 nm. The main observation is that the most intense PL emission is found for the higher electron dose used, i.e. 240 Gy. This effect is similar to that observed after processes leading to an improvement of the crystal quality but it should be interpreted as the annihilation of the non radiative recombination centres which strongly enhances the radiative recombination mechanisms. The trends observed by both experimental techniques were discussed in terms of the possible origin, nature and state of charge of the radiation induced defects involved.