Emission enhancement from nonpolar a-plane III-nitride nanopillar

A nonpolar a -plane GaN-based light emitting structure was patterned by self-assembled SiO₂ nanosphere lithography and subsequent inductively coupled plasma (ICP) etch to define an array of nanopillar light emitters. The photoluminescence (PL) intensity was enhanced by ∼110% after the anisotropic ICP etch, compared with an unprocessed sample, which is attributed to a reduction in wave-guiding effects in the thin film. Additionally, the anisotropic ICP etch caused minimal wavelength shift in the dominant 3.34 eV near-bandedge radiative transition. A subsequent photoelectrochemical (PEC) etch process of the a -plane GaN nanopillars preferentially etched the underlying n -type layers, leaving a wider p -type cap. The n -type layers wet-etched by recession of the N-polar (000-1) plane (perpendicular to the a -plane growth axis) via formation of the distinctive pyramid-shaped facets. The PL intensity was enhanced by ∼168% after ICP and PEC etching although the peak emission occurred at a lower energy. The combination of nanosphere lithography and ICP was highly effective in improving the light extraction efficiency in a -plane nonpolar GaN-based light emitting diodes.