Emission enhancement from nonpolar a-plane III-nitride nanopillar

Abstract

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 similar to 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 similar to 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. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3545696]