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Proceedings Paper

Nanofabrication of GaN surfaces by ultrashort laser pulses
Author(s): Seisuke Nakashima; Koji Sugioka; Takuma Ito; Hiroshi Takai; Katsumi Midorikawa
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Paper Abstract

Wet-chemical-assisted femtosecond (fs) laser ablation has been developed for high-efficiency, high-quality nanofabrication of gallium nitride (GaN) surface. In this technique, an fs laser beam is focused on the surface of a single-crystal GaN substrate immersed in 35% hydrochloric (HCl) acid by a high-numerical-aperture objective lens. This method produced higher quality ablation craters with sharper edges, smoother surfaces, and less residual debris than conventional fs-laser ablation in air followed by etching in HCl (two-step processing method). This is presumably due to a photochemically or photothermally assisted chemical reaction associated with the HCl acid solution. Using the second harmonic of an fs laser (λ = 387 nm), nanocraters with diameters as small as 320 nm (full width at half maximum) were formed at a GaN substrate surface. Assuming that this process is based on two-photon absorption, we theoretically calculated the diameters of ablation craters. The calculation results agree well with the experimental results, particularly in the low-energy region. Multiscan irradiation was performed to fabricate a two-dimensional (2D) array of nanoholes with a high aspect ratio of ~1.6, which is much higher than that obtained using single-pulse irradiation. The aspect ratio was found to depend on the refractive index of the medium above the GaN substrate. The fabricated 2D array of nanoholes on a GaN surface could be used as a 2D photonic crystal for enhancing the light extraction efficiency of GaN-based blue LEDs.

Paper Details

Date Published: 28 February 2011
PDF: 12 pages
Proc. SPIE 7996, Fundamentals of Laser-Assisted Micro- and Nanotechnologies 2010, 79960G (28 February 2011); doi: 10.1117/12.887323
Show Author Affiliations
Seisuke Nakashima, RIKEN (Japan)
Koji Sugioka, RIKEN (Japan)
Takuma Ito, RIKEN (Japan)
Tokyo Denki Univ. (Japan)
Hiroshi Takai, Tokyo Denki Univ. (Japan)
Katsumi Midorikawa, RIKEN (Japan)

Published in SPIE Proceedings Vol. 7996:
Fundamentals of Laser-Assisted Micro- and Nanotechnologies 2010
Vadim P. Veiko; Tigran A. Vartanyan, Editor(s)

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