Surface and interface properties of metal-organic chemical vapor deposition grown a-plane MgxZn1-xO (0 <= x <= 0.3) films

The alpha-plane Mg(x)Zn(1-x)0 (0 = x = 0.3) films were grown on r-plane (0112) sapphire substrates using metal-organic chemical vapor deposition (MOCVD). Growth was done at temperatures from 450 degrees C to 500 degrees C, with a typical growth rate of similar to 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 MgZn1-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.