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E3.5.1

Fabrication and characterization of GaN nanopillar arrays Y.D. Wang 1 S. Tripathy 2, S.J. Chua, 1, 2 and C.G. Fonstad 1,

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Singapore-MIT Alliance, E4-04-10, 4 Engineering Drive 3, Singapore 117576 Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602 3) Department of Electrical and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA 02139 2)

ABSTRACT Various nanofabrication technologies are currently under investigation to realize fine patterning of III-Nitrides. Dry and wet etching techniques have been explored in the past for the fabrication of GaN-based devices. However, due to etch-induced damage, it is still a major challenge to achieve high-quality GaN-based nanostructures with high aspect ratio. In this study, GaN nanopillars were fabricated by inductively coupled plasma etching (ICP) using anodic aluminium oxide (AAO) as a mask. High-spatial resolution optical techniques were employed to characterize these pillar arrays. The average diameter and length of these pillars are about 60-70 nm and 350-400 nm, respectively. Low temperature micro-photoluminescence spectra show a red shift compared with the spectrum recorded from the as-grown GaN, indicating stress relaxation in these nanopillars. The evidence of good crystalline quality is also confirmed by micro-Raman measurement where red shift of the E2(TO) mode from GaN nanopillars suggest partial relaxation of the compressive strain. INTRODUCTION III-nitride semiconductors have been investigated extensively in the last decade, and GaNbased light emitting diodes (LEDs) and laser diodes (LDs) with green, blue, and violet emission have already been demonstrated [1-3]. On the other hand, semiconductor materials with ordered nanostructures have generated considerable interest in both basic research field and commercial applications because of their new electronic, optical, magnetic properties. One-dimensional GaN nanostructures have previous been synthesized by laser ablation, carbon nanotube confined growth, photon-assisted anodic etching.[4-6] One simple way to make nanostructures is by etching epitaxial GaN films. For example, Demangeot et al. reported optical properties of microand nanoscale GaN pillars (100 nm to 5 µm) fabricated by reactive ion etching (RIE) through a mask produced by E-beam lithography.[7] However, conventional lithography is limited by the high cost and low throughout. In contrast, nanoporous anodic aluminium oxide (AAO), which is based on a self-organization process, provides a low-cost, efficient, and fundamentally simple means for fabricating nanostructures with critical dimensions below photolithographic resolution limits [8, 9]. The nanopores in AAO self-organized into highly ordered arrays with uniform diameter and pore spacing with pore orientation normal to the plane. Here we reported the

E3.5.2

fabrications of the ordered GaN nanopillars by inductively coupled plasma etching of a GaN film through an AAO film employed as an etch mask. EXPERIMENTAL DETAI