Structural reconstruction of hexagonal to cubic ZnO films on Pt/Ti/SiO2/Si substrate by annealing

Abstract

It is well known that ZnO generally has the wurtzite structure. We report the growth of both hexagonal and cubic ZnO on Pt(111)/Ti/SiO2/Si substrate by a solution deposition. The wurtzite structure of ZnO film is enhanced up to the annealing temperature of 600 °C, and disappeared for annealing temperatures above 700 °C. The Pt(111)/Ti/SiO2/Si substrate is reoriented to hexagonal-Pt3Ti(004)/Ti/SiO2/Si when annealed at 700 °C and above due to the Ti out-diffusion and the ZnO thin film grown on the substrate has a cubic structure. The diffusion of Ti was evidenced by Auger electron spectroscopy measurements. From the photoluminescence measurement, the band gap of the wurtzite structure of ZnO film grown by the annealing below 600 °C was 3.37 eV, as is already known, but the cubic ZnO had a band gap of 3.28 eV, which suggests a zinc blende structure. The stability of the zinc blende structure on Zn2TiO4 layer was checked by the calculation of the lattice mismatch using the extended atomic distance mismatch model. Additionally the formation of the zinc blende ZnO could be prevented by using the Pt(111)/TiO2/SiO2/Si substrate.