Polarity control and enhanced luminescence characteristics of semi-polar ZnO nanostructures grown on non-polar MgO(100) substrates

Enhancing luminescence characteristics is one of the key challenges in ZnO nanostructures for highly efficient UV-blue LEDs and laser diodes. Non-conventional PLD growth parameters have been used to tailor the polar and semi-polar surfaces of ZnO nanostructures on MgO substrates. Despite the similar growth temperature, use of N2 ambient gas allowed the fabrication of well-aligned polar nanostructures; whereas, nanostructures grown with Ar ambient are semi-polar in nature. By means of cathodoluminescence spectroscopy, we demonstrate that the UV emission can be significantly enhanced by 11 times for semi-polar nanostructures. The enhanced luminescence is attributed to reduced polarization electric fields along the c-axis.