Optimization of the Growth Conditions for Molecular Beam Epitaxy of MgxZn1-xO (0 <= x <= 0.12) Films on Zn-Polar ZnO Substrates

We report on optimization of the growth conditions for MgxZn1-xO (x = 0, 0.04, 0.05, 0.12) thin films grown on c-plane Zn-polar ZnO single crystal substrates by using plasma-assisted molecular beam epitaxy (PAMBE). A normal vector to the ZnO substrate surfaces was angled at 0.5 +/- 0.1 degrees off from the [0001] c-axis toward the [1 (1) over bar 00] direction, leading to a stable step-and-terrace structure. A growth temperature (T-g) higher than 800 degrees C led to the ZnO films presenting the first excited state luminescence of A-free excitons in photoluminescence (PL) spectra at 12 K. A T-g higher than 800 degrees C enhanced optical attributes of a MgxZn1-xO film. The longest PL lifetime of fast-decay components reached 3.5 ns in time-resolved PL measurement for an Mg0.12Zn0.88O film grown at 900 degrees C, indicating a concentration of nonradiative recombination centers is substantially eliminated compared to the previously reported PL lifetime of 60 ps for an Mg0.11Zn0.89O film grown by pulsed laser deposition. (C) 2010 The Japan Society of Applied Physics