Critical examination of growth rate for magnesium oxide (MgO) thin films deposited by molecular beam epitaxy with a molecular oxygen flux

The authors report a study of molecular beam deposition of MgO films on amorphous SiO(2) and (0001) GaN surfaces over a large range of temperatures (25-400 degrees C) and molecular oxygen growth pressures (10(-7)-10(-4) Torr). This study provides insight into the growth behavior of an oxide with volatile metal constituents. Unlike other materials containing volatile constituents (e.g., GaAs, PbTiO(3)), all components of MgO become volatile at normal epitaxial growth temperatures (>= 250 degrees C). Consequently, defining which species is the adsorption controller becomes ambiguous. Different growth regimes are delineated by the critical substrate temperature for Mg re-evaporation and the Mg:O flux ratio. These regimes have impact on phase purity, quartz crystal microbalance calibration, and film microstructure. The universal decay in deposition rate above growth 10(-5) Torr O(2) is also considered. By introducing a third flux of inert argon gas, rate reduction is attributed to increased molecular scattering and not oxidation of the metal source.