Growth control of nonpolar and polar ZnO/MgxZn1−xOZnO/MgxZn1−xO quantum wells by pulsed-laser deposition

Growth control of nonpolar and polar ZnO/MgxZn1−xOZnO/MgxZn1−xO quantum wells (QWs) is demonstrated by in situ RHEED during the pulsed laser deposition process. Nonpolar QWs were grown homoepitaxially on m-plane and on a-plane ZnO single crystals. For m  -plane (101¯0) ZnO QWs we report a change of growth mode from a two dimensional layer by layer growth evidenced by RHEED oscillations to the formation of surface nanostripes as observed by atomic force microscopy. The aspect ratio of the self organized nanostripes depends on the oxygen partial pressure. a  -lane (112¯0) ZnO QW-structures show a smooth surface with a rms-roughness of 0.3 nm. Homoepitaxial nonpolar QWs do not show the quantum-confined Stark effect while polar quantum wells on a-plane sapphire does with an internal electric field of approximately 0.53 MV/cm. Furthermore, by implementing a low temperature MgxZn1−xOMgxZn1−xO buffer layer, the interface quality of heteroepitaxially grown polar ZnO/MgxZn1−xOZnO/MgxZn1−xO QWs on a-plane sapphire substrates is considerably improved. RHEED oscillations were observed during the whole growth of such QWs.

► Nonpolar and polar ZnO/MgZnO quantum wells grown by PLD show a layer-by-layer growth.
► A low-temperature MgZnO buffer allows a full thickness control by counting RHEED-oscillations .
► Experimental QW transition energies compared with theory, reveal a QCSE for polar structures.
► Surface nanowires for m-ZnO and m-MgZnO thin films are strongly influenced by the Zn/O ratio.
► Quantum confinement is demonstrated for m- and a-plane grown ZnO/MgZnO quantum wells.