Post-annealing modification in structural properties of ZnO thin films on p-type Si substrate deposited by evaporation

Zinc oxide (ZnO) films of thickness ∼380 nm were deposited on p-type Si (1 1 1) substrate maintained at 300 °C under 3×10−6 Torr by a radio frequency (RF) heating source. Transmission Fourier transform infrared (FTIR) spectrum exhibited a clear Zn–O bond excitation frequency of ∼408 cm−1. X-ray diffraction spectrum demonstrated four peaks (P1–P4) at 2θ (deg) ∼36±0.06, 40±0.09, 82±0.17 and 86±0.2, which originated from (1 0 0), (0 0 2), (2 0 1) and (0 0 4) hexagonal planes, respectively. P2 being the highest intensity peak indicated that the growth of ZnO predominantly occurred along the c-axis i.e. (0 0 2) plane. Micrographs of the samples obtained from scanning electron microscopy (SEM) and atomic force microscopy (AFM) identically displayed scattered nanocrystallites, which grew bigger with the increase of sample annealing temperature (°C) in the range of 400–1000. AFM pictures, in particular, exposed the hexagonal structure of the deposited films along with voids. However, ZnO composition ∼6:1 (Zn:O) as calculated from the energy dispersive spectrum (EDS) revealed that the formation of ZnO was not stoichiometric, rather of Zincsuboxide structure ZnOx (x<1). Arrhenius plot of the resistivity data yielded a donor level (zinc interstitial and/or Zn–on–O site) with ionization energy Ec–1.26 eV, thereby it supports our measured results, in general.