Comparison of structural and optical properties of polar and non-polar ZnO/Zn0.9Mg0.1O MQWs fabricated on sapphire substrates by pulsed laser deposition

Abstract

This work investigates the structural and optical properties of polar and non-polar ZnO/Zn0.9Mg0.1O multiple quantum wells (MQWs), which have been fabricated on c-plane and r-plane sapphire substrates by pulsed laser deposition (PLD). The orientations of the MQWs are identified by the X-ray diffraction (XRD) pattern. The MQWs grown on c-plane sapphire substrates have a typical high c-orientation. The MQWs grown on r-plane sapphire substrates have a pure a-axis non-polar orientation. The polar and non-polar MQWs show different surface morphologies with root mean square (rms) roughnesses of 1.15nm and 1.53nm, respectively. For the non-polar MQWs, stripes elongated along the c-axis are clearly observed. Low temperature photoluminescence (PL) is investigated to reveal that the non-polar MQWs exhibit confinement but no indication of the quantum confined Stark (QCS) effect when well width is larger than 5nm, contrary to what is observed in polar MQWs.