Post-Annealing effects on the structural and the optical properties of ZnO thin films grown by using the hydrothermal method

ZnO thin films were grown on Si (111) substrates by using the hydrothermal method. Before the ZnO thin films growth, ZnO seed-layers were grown on the Si substrates by using plasma-assisted molecular beam epitaxy (PA-MBE). Three ZnO diffraction peaks were observed and indicated a c-axis preferred orientation. With increasing annealing temperature up to 700 °C, the texture coefficient (TC) ratio of the c-axis to the a-axis and the residual stress increased. The near-band-edge emission (NBE) peak intensity gradually increased as the annealing temperature was increased up to 700°C. At annealing temperatures above 800°C, however, the deep-level emission (DLE) peak's position was red-shifted and its intensity was increased. Among the ZnO thin films, the ZnO thin films annealed at a temperature of 700°C exhibited the largest improvement in the luminescent efficiency.