Nitrogen doping of ZnO thin films grown by plasma-assisted pulsed-laser deposition

ZnO epitaxial thin films were grown on r-plane sapphire substrates, in a pulsed laser deposition apparatus assisted by an electron cyclotron resonance (ECR) N₂ plasma source. The resistivities and carrier concentrations (either n- or p-type) of the thin films were measured in a Hall effect apparatus as a function of the ECR source input microwave power and the substrate temperature, respectively. P-type conduction was observed in thin films grown in conditions of enhanced activation of the nitrogen ionic species. These experimental results are in qualitative agreement with recent theoretical calculations of the activation energies of the main donor defects compensating for N acceptors in ZnO.