INSTITUTE OF PHYSICS PUBLISHING NANOTECHNOLOGY Nanotechnology 17 (2006) 3299–3303 doi:10.1088/0957-4484/17/13/036 Photo-assisted local oxidation of GaN using an atomic force microscope Jih Shang Hwang 1,4 , Zhan Shuo Hu 1 , Ton Yuan Lu 1 , Li Wei Chen 1 , Shi Wei Chen 1 , Tai Yuan Lin 1 , Ching-Lien Hsiao 2 , Kuei-Hsien Chen 3 and Li-Chyong Chen 2 1 Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung, Taiwan 2 Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan 3 Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan E-mail: hjsspin@mail.ntou.edu.tw Received 15 April 2006, in final form 15 May 2006 Published 12 June 2006 Online at stacks.iop.org/Nano/17/3299 Abstract This paper introduces a photo-assisted atomic force microscope (AFM) local oxidation technique which is capable of producing highly smooth oxide patterns with heights reaching several tens of nanometres on both n- and p-types of GaN (and in principle on most semiconductors) without the use of chemicals. The novel methodology relies on UV illumination of the surface of the substrate during conventional AFM local oxidation. A low 1.2 V threshold voltage for n-type GaN was obtained, which can be explained by UV photo-generation of excess electron–hole pairs in the substrate near the junction, thereby reducing the electric field required to drive carrier flow through the tip–sample Schottky barrier. It was demonstrated that the presence or absence of light alone was sufficient to switch the growth of the oxide on or off. The photo-assisted AFM oxidation technique is of immediate interest to the semiconductor industry for the fabrication of GaN-based complementary metal–oxide–semiconductor devices and nanodevices, improves chances for AFM-type data storage, and presents new degrees of freedom for process control technique. (Some figures in this article are in colour only in the electronic version) 1. Introduction Local oxidation using an atomic force microscope (AFM), sometimes called AFM oxidation, nanooxidation or local oxidation nanolithography (LON), is a promising scanning- probe-based lithographic technique suitable for the fabrication of nanoscale structures and devices [1–8]. The AFM nanooxidation technique uses the very strong electric field that can occur between the AFM conducting tip and the substrate. In normal air or other humid atmosphere, both the AFM tip and the surface of the substrate are covered by a thin film of absorbed water. When the tip approaches sufficiently close to the surface, the two absorbed water layers automatically join and form a ‘water bridge’ (water meniscus). The oxidant for the oxidation reaction is provided by oxyanions such as 4 Author to whom any correspondence should be addressed. OH − and O 2− ions in the water bridge [2, 9]. The combined effect is capable of inducing anodic oxidation on the substrate and forming nanoscale oxide patterns. This technique has been used for local oxidation of various substrates such as silicon, GaAs [10], InP [11], silicon nitride [5, 12], silicon carbide [13], metals [14–18], transition metal nitrides [18] and even oxides [7, 19–21]. Various devices such as field effect transistors (FETs) [1, 7, 22, 23], single electron memories [4], Josephson junctions and superconducting quantum interference devices (SQUIDs) [6, 21] have been demonstrated. Various improved LON techniques have shown enhanced growth rates and oxide heights, for example by employing an UV-induced ozone-rich meniscus [24], ethyl alcohol meniscus [25] or metal deposition [11], making LON techniques of particular interest to researchers interested in mass-produced nanoscale devices. 0957-4484/06/133299+05$30.00 © 2006 IOP Publishing Ltd Printed in the UK 3299