Growth of non-polar Zn_1−x Mg _x O thin films with different Mg contents on r-plane sapphire substrates by plasma-assisted molecular beam epitaxy

Abstract

We report the growth and characterization of a series of non-polar Zn_1−x Mg _x O thin films with different Mg contents, which have been prepared on r-plane sapphire substrates by plasma-assisted molecular beam epitaxy. Structural properties are anisotropic and surfaces of films show stripes running along the c-axis direction. The films exhibit atomically smooth surface with the minimal root mean square surface roughness of 0.36 nm. Non-polar Zn_1−x Mg _x O thin film is much easier to obtain pure a-plane single crystal orientation when Mg content is high. The quality of the non-polar Zn_1−x Mg _x O thin films is evidenced by X-ray diffraction (XRD) rocking curves full-width at half-maximum of 1,350 arcsec for the ($11\overline{2} 0$) reflection and 1,760 arcsec for the ($10\overline{1} 1$) reflection, respectively. Room temperature photoluminescence peak shifts monotonously from 3.29 to 3.56 eV as Mg content increases from 0 to 0.13. Alloying with Mg is found to widen the bandgap energy of the ZnO.