Metalorganic chemical vapor deposition and characterizations of epitaxial Mg xZn 1− xO (0⩽ x⩽0.33) films on r-sapphire substrates

Abstract

High quality epitaxial Mg x Zn 1− x O films are essential for the fabrication of ZnO/Mg x Zn 1− x O heterostructures. In this work, Mg x Zn 1− x O (0⩽ x⩽0.33) thin films are epitaxially grown on ( 0 1 1 ̄ 2 ) r-sapphire substrates by metalorganic chemical vapor deposition. A thin ZnO buffer layer in the order of 50 Å is found to be critical for the growth of single crystal Mg x Zn 1− x O (0⩽ x⩽0.33) films with a wurtzite-type structure. The energy bandgap of Mg x Zn 1− x O films as a function of Mg composition was deduced using a UV-Visible spectrophotometer at room temperature in conjunction with Rutherford backscattering spectroscopy measurements. The epitaxial relationship between the wurtzite-type Mg x Zn 1− x O films and r-sapphire substrates is determined to be ( 1 1 2 ̄ 0 ) Mg x Zn 1− x O∥( 0 1 1 ̄ 2 ) Al 2O 3, and [ 0 0 0 1 ] Mg x Zn 1− x O∥[ 0 1 ̄ 1 1 ] Al 2O 3. In-plane X-ray diffraction reflections show the lower lattice mismatch along the c-axis of the Mg x Zn 1− x O films on r-sapphire substrates. High resolution transmission electron microscopy analysis of the film/substrate interface indicates the region in the film near the interface is crystalline though strained.