Preparation and optical properties of ZnO/Zn0.9Mg0.1O multiple quantum well structures with various well widths grown on c-plane sapphire

A series of 5-period ZnO/Zn0.9Mg0.1O multiple quantum wells (MQWs) with different well layer thicknesses in the range of 3–10 nm have been fabricated on (0001) sapphire substrates by plasma-assisted molecular beam epitaxy (MBE) with combined MgO and low-temperature ZnO thin film as buffer layers. The good quality of ZnO/Zn0.9Mg0.1O MQWs is evidenced by the observation of readily resolved Pendellösung fringes and the small full-width at half-maximum (FWHM) value of exciton emission as low as 8.3 meV, as well as the observation of high order phonon replicas. The dominated photoluminescence (PL) peak in the MQWs shows a systematic blueshift with decreasing well width, which is consistent with a quantum confinement effect. In order to clarify the thermal quenching behavior of exciton emission in the MQWs, temperature-dependent PL is investigated and the relevant activation energies are calculated.