Investigation on non-polar m-plane ZnO and Na-doped p-type ZnO films grown by plasma-assisted molecular beam epitaxy

Abstract

Non-polar ZnO and Na-doped ZnO films were epitaxially grown on m-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The films exhibit dominant ( $$ 10\overline{1} 0 $$ ) (m-plane) orientation as identified by the X-ray diffraction pattern. The quality of the obtained m-plane ZnO film is evidenced by X-ray diffraction rocking curves full width at half maximum of 1125 arcsec for the ( $$ 10\overline{1} 0 $$ ) reflection and 1427 arcsec for the ( $$ 10\overline{1} 1 $$ ) reflection, respectively. Hall-effect measurements show that the m-plane Na-doped ZnO film exhibits p-type conductivity with a hole concentration of 2.50 × 1017 cm−3, while the m-plane ZnO film exhibits compensatory conductivity. Na atoms substituting for Zn atoms are believed to be the origin of p-type conductivity. The Na-related acceptor level is deduced to be ~120 meV by temperature-dependent photoluminescence, indicating the superiority of m-plane ZnO film in p-type doping compared with the polar ZnO film.