Properties of ZnO thin films prepared by reactive evaporation

This work describes a novel system implemented to grow in situ highly transparent n⁺-ZnO and i-ZnO thin films by plasma assisted reactive evaporation process. A virtual instrument (VI) was developed to control the process using PID (proportional integral differential) and PWM (pulse width modulation) as control algorithms. The optimization of the preparation parameters was achieved through a figure of merit defined in terms of transmittance and the resistivity. n⁺-ZnO and i-ZnO films with resistivities around 8×10^-4 Ωcm and 5×10³ Ωcm respectively and transmittances greater than 85% (in the visible region) were obtained with this method. Grain size and lattice tension due to dislocations of the material were determined through XRD measurements using Scherrer equation; grain size values determined from XRD measurements agree with those obtained from AFM measurements. The influence of the Zn⁺/O₂^- ratio on the Urbach energy and dislocation density was evaluated to get information regarding presence of structural defects.