Surface and Interface Properties of Metal-Organic Chemical Vapor Deposition Grown a-Plane MgxZn1–xO (0 ≤ x ≤ 0.3) Films

The a-plane MgxZn1−xO (0 ≤ x ≤ 0.3) films were grown on r-plane (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ 01\bar 12 $$\end{document}) sapphire substrates using metal-organic chemical vapor deposition (MOCVD). Growth was done at temperatures from 450°C to 500°C, with a typical growth rate of ∼500 nm/h. Field emission scanning electron microscopy (FESEM) images show that the films are smooth and dense. X-ray diffraction (XRD) scans confirm good crystallinity of the films. The interface of MgxZn1−xO films with r-sapphire was found to be semicoherent as characterized by high-resolution transmission electron microscopy (HRTEM). The MgxZn1−xO surfaces were characterized using scanning tunneling microscopy (STM) in ultrahigh vacuum (UHV). Low-energy electron diffraction (LEED) shows well-ordered and single-crystalline surfaces. The films have a characteristic wavelike surface morphology with needle-shaped domains running predominantly along the crystallographic c-direction. Photoluminescence (PL) measurements show a strong near-band-edge emission without observable deep level emission, indicating a low defect concentration. In-plane optical anisotropic transmission was observed by polarized transmission measurements.