Thin film epitaxy and structure property correlations for non-polar ZnO films

Abstract

Heteroepitaxial growth and strain relaxation were investigated in non-polar a-plane (1 1 −2 0)ZnO films grown on r-plane (1 0 −1 2)sapphire substrates in the temperature range 200–700 °C by pulsed laser deposition. The lattice misfit in the plane of the film for this orientation varied from −1.26% in [0 0 0 1] to −18.52% in the [−1 1 0 0] direction. The alignment of (1 1 −2 0)ZnO planes parallel to (1 0 −1 2)sapphire planes was confirmed by X-ray diffraction θ−2 θ scans over the entire temperature range. X-ray ϕ-scans revealed the epitaxial relationship:[0 0 0 1]ZnO‖[−1 1 0 1]sap; [–1 1 0 0]ZnO‖[−1 −1 2 0]sap. Depending on the growth temperature, variations in the structural, optical and electrical properties were observed in the grown films. Room temperature photoluminescence for films grown at 700 °C shows a strong band-edge emission. The ratio of the band-edge emission to green band emission is 135:1, indicating reduced defects and excellent optical quality of the films. The resistivity data for the films grown at 700 °C shows semiconducting behavior with room temperature resistivity of 2.2 × 10 −3 Ω-cm.