Bikowski, A.; Welzel, T.; Ellmer, K.: The impact of negative oxygen ion bombardment on electronic and structural properties of magnetron sputtered ZnO:Al films. Applied Physics Letters 102 (2013), p. 242106/1-4
10.1063/1.4811647

Abstract:
In order to study the impact of negative oxygen ion bombardment on the electronic transport properties of ZnO:Al films, a systematic magnetron sputtering study from ceramic targets with excitation frequencies from DC to 27 MHz, accompanied by strongly varying discharge voltages, has been performed. Higher plasma excitation frequencies significantly improve the transport properties of ZnO:Al films. The effect of the bombardment of the films by energetic particles (negative oxygen ions) can be explained by the dynamic equilibrium between the formation of acceptor-like oxygen interstitials compensating the extrinsic donors and the self-annealing of the interstitial defects at higher deposition temperatures.