engleski

Structural properties and luminescence of nano- crystalline ZnO:Al thin films deposited by PLD in RF excited oxygen atmosphere

Nano-crystalline ZnO:Al thin films were deposited by pulsed laser deposition (PLD) in oxygen and in RF excited oxygen atmosphere at gas pressures between 10 and 70 Pa, and also in vacuum. Grazing incidence small angle x-ray scattering (GISAXS) and grazing incidence x-ray diffraction (GIXRD) showed that the roughness of film surfaces increases with increasing gas pressure, and the density decreases due to the formation of nano- voids. The nano-crystals sizes estimated from GIXRD were around 20 nm, while the sizes of the nano-voids increased from 1 to 2 nm with the oxygen pressure. The addition of excited oxygen particles from a RF plasma improves the structural ordering by lowering the defect level, which is evident from GISAXS and luminescence (PL) measurements. The PL consisted of 3 well defined peaks, UV emission that corresponds to a band-to- band transition, blue emission that appeared due to Zn vacancies, VZn, and red emission that is probably due to oxygen interstitials, Oi. For all pressures the RF excitation lowered the defect level related to blue emission and resulted in a narrower UV luminescence peak, indicating better structural ordering. The red emission peak is only seen using a RF excited oxygen atmosphere at 70Pa. The observed influence of the pressure and RF excitation on the films properties is a consequence of two main effects: the variation of the energy transfer from the laser plume to the growing film due to a different collision rate in the gaseous phase and changes of the growth chemistry due to various concentrations of active oxygen species.

ZnO:Al; PLD; GISAXS; GIXRD; photoluminescence

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