Properties of Li-, P- and N-doped ZnO thin films prepared by pulsed laser deposition

We have studied the crystalline, optical and electrical properties of ZnO thin films prepared by pulsed laser deposition and doped with one of the acceptor elements Li, N or P, respectively. To fabricate ZnO:Li material, ZnO layers were epitaxially grown on c-LiNbO3 substrates, as Li diffusion is expected to occur at high temperatures. The corresponding thin film optical and electrical properties indicated n-type conduction, suggesting the formation of Li interstitial defects. ZnO/ZnO:P2O5 thin films with various amounts of P were fabricated using a ZnO:P2O5 doped target. The crystallinity and the luminescent properties of the ZnO material were strongly reduced upon incorporation Of P2O5. Both p- and n-conduction was observed in these samples, reflecting some electrical instability. An electron cyclotron resonance (ECR) plasma source, operated as an ion source, was mounted onto our deposition chamber for N incorporation in the samples. The nitrogen doping efficiency was studied as a function of the ion kinetic energy and the substrate temperature, respectively. The structural characteristics of the ZnO films grown by this plasma-assisted process were clearly affected. The sample grown at the temperature of 630 degrees C exhibited p-type conduction at room temperature. The corresponding low-temperature photoluminescence spectrum showed evidence of neutral-acceptor bound excitonic emission which further confirms the p-type nature of this material. (C) 2005 Elsevier Ltd. All rights reserved.