Enhancing Light Emission of Nanostructured Vertical Light-Emitting Diodes by Minimizing Total Internal Reflection

Abstract

Nanostructured vertical light-emitting diodes (V-LEDs) with a very dense forest of vertically aligned ZnO nanowires on the surface of N-face n-type GaN are reported with a dramatic improvement in light extraction efficiency (similar to 3.0x). The structural transformation (i.e., dissociation of the surface nitrogen atoms) at the nanolevel by the UV radiation and Ozone treatments contributes significantly to the initial nucleation for the nanowires growth due to the interdiffusion of Zn into GaN, evident by the scanning photoemission microscopy (SPEM), high-resolution transmission electron microscopy (HR-TEM), and ultraviolet photoelectron spectroscopy (UPS) measurements. This enables the growth of densely aligned ZnO nanowires on N-face n-type GaN. This approach shows an extreme enhancement in light extraction efficiency (>2.8x) compared to flat V-LEDs, in good agreement with the simulation expectations (similar to 3.01x) obtained from 3D finite-difference time-domain (FDTD) tools, explained by the wave-guiding effect. The further increase (similar to 30%) in light extraction efficiency is also observed by optimized design of nanogeometry (i.e., MgO layer on ZnO nanorods).