Zn1−x Mg x O (0≤x≤0.05) nanowalls grown on catalyst-free sapphire substrates by high-pressure PLD and their photoluminescence properties

We report the growth of Zn1−x Mg x O (x=0, 0.02, 0.05 at.%) nanowalls on sapphire substrates without any metal catalysts by a high-pressure pulsed laser deposition (PLD). The influences of the experimental parameters like growth pressure, temperature, and target-substrate distance on the growth of Zn1−x Mg x O nanowalls were systemically studied and the growth mechanism was discussed. It was found that large area and uniform Zn1−x Mg x O nanowalls with c-orientation can be grown on sapphire substrates when the growth temperature and pressure were 950 °C and 400 Torr at a target-substrate distance of 2 cm. A thin layer assisted vapor-solid (VS) process was proposed for Zn1−x Mg x O nanowalls growth. The photoluminescence spectrum shows the bandgap of Zn1−x Mg x O nanowall was effectively expanded together with defect-related levels formation in a forbidden gap, which also induced enhancement of visible emission.