High-quality ZnO epilayers grown on Zn-face ZnO substrates by plasma-assisted molecular beam epitaxy

Abstract

High-quality ZnO epilayers have been grown on Zn-face ZnO substrates by plasma-assisted molecular beam epitaxy. With increasing O/Zn flux ratio from the stoichiometric to the O-rich, the growth mode changed from three- to two-dimensional growth and the line widths of (0 0 0 2) and (1 0 1 ̄ 0) ω-rocking curves showed dramatic narrowing from 471 to 42 arcsec and from 1635 to 46 arcsec, respectively. These values are narrower compared to those of ZnO on sapphire and also those of device-grade MOCVD-grown GaN. Moreover, A-, B-excitons (FE A, FE B), and the n=2 state of FE A at 3.378, 3.393, and 3.424 eV, respectively, were clearly observed in the low-temperature (4.2 K) photoluminescence spectrum of ZnO grown under O-rich flux conditions. Our results show that growth under high O-rich flux conditions is required to produce high-quality Zn-polar ZnO films.