Homoepitaxial growth of high-quality Zn-polar ZnO films by plasma-assisted molecular beam epitaxy

High-quality ZnO films have been grown on Zn-polar ZnO substrates by plasma-assisted molecular beam epitaxy. With increasing O/Zn ratio from the stoichiometric to the O-rich flux condition, the growth mode and the surface morphology changed from three-dimensional growth with a rough surface to two-dimensional growth with a smooth surface. The minimum linewidth from the (10 (1) over bar0) omega-rocking curve was 100 arcsec, and the n = 2 state of A-exciton was clearly observed in the photoluminescence at 4.2 K. Due to the reduction in the edge-type threading dislocation density, the residual carrier concentration in these homoepitaxial ZnO films was as low as 2.2 x 10(16) cm(-3), which is one order of magnitude lower than that previously reported for heteroepitaxial ZnO films.