Paper EM-ThM9
STM, LEED and ARXPS Study of MOCVD Grown a-plane ZnO and Mg_xZn_1-xO (0 <= x <= 0.3) Thin Films

Thursday, October 18, 2007, 10:40 am, Room 612

ZnO and Mg_xZn_1-xO (0 <= x <= 0.3) thin films with a-plane orientation were grown on r-plane (011bar2) sapphire substrates using metal-organic chemical vapor deposition (MOCVD). The surface morphology of ZnO films with various thickness (20 - 2000 nm) was characterized by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) in ultrahigh vacuum (UHV). LEED patterns show well-ordered (1x1) surfaces. STM images reveal uniform surfaces with small, rectangular terraces during the initial growth stage (20 nm-thick film). Films with thicknesses of 100 and 450 nm have a characteristic wave-like surface morphology with needle-shaped domains running along the crystallographic c-direction. Films with a thickness of 2000 nm exhibit more flat surfaces with 20-100 nm wide domains running perpendicular to the c-axis, indicating variation in the strain effect caused by mismatch between substrate and film. On these thickest films, areas with facets of a different surface termination were observed as well. Angle-resolved x-ray photoemission spectroscopy (ARXPS) analysis of Mg_xZn_1-xO films show that Mg atoms substitute for Zn atoms in the lattice. LEED shows that the incorporation of Mg atoms into the lattice reduces the surface roughness.