Growth and luminescence characteristics of zinc oxide thin films deposited by ALD technique

Abstract

A striking correlation is observed between the characteristic defect-mediated deep level luminescence and deposition temperature of the zinc oxide (ZnO) thin films made by atomic layer deposition (ALD) technique. Near-ideal and virtually defect-free zinc oxide films are deposited at a temperature of 150 °C. However, distinct long-wavelength broadband luminescence features are identified for yellow (maxima at 570 nm) and green (maxima at 500 nm) at lower and higher temperature regimes of 150 °C, respectively. The decay time for yellow and green luminescence is different, having slower decay components for the yellow luminescence. The multi-step relaxation process governing the luminescence is discussed under the theory of efficient trapping of a photo-generated hole at a surface species in the first step, and radiative recombination at a deep-level acceptor type defect in the final step. Excess non-radiative surface recombination at the surface species is responsible for the shortening of the decay time of green emission line.