Growth of non-polar ZnO/(Zn,Mg)O quantum well structures on R-sapphire by plasma-assisted molecular beam epitaxy

Zinc oxide (ZnO) has recently attracted considerable attention because of its unique physical properties and its potential applications in the blue and UV spectral range. Up to now, ZnO-based heterostructures have mostly been grown in a c-orientation. The growth of non-polar layers along the a  -direction [112¯0] was proposed to avoid any built-in electric fields in the c-direction. A series of A  -plane (112¯0) ZnO quantum wells (QWs) and multiple QWs embedded in (Zn,Mg)O barriers were grown on an optimized (Zn,Co)O buffer. After the structural and optical characterization of the buffers and the QWs, we have compared the PL emission of a-oriented and c-oriented QWs. From this comparison, we demonstrate that the QWs exhibit confinement but no indication of quantum-confined Stark effect, contrary to what is observed in c-oriented structures.