Formation of GaN Self-Organized Nanotips by Nanomasking Effect
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Formation of GaN Self-Organized Nanotips by Nanomasking Effect Harumasa Yoshida, Tatsuhiro Urushido, Hideto Miyake and Kazumasa Hiramtsu Department of Electrical and Electronic Engineering, Faculty of Engineering, Mie University, 1515 Kamihama, Tsu, Mie 514-8507, Japan ABSTRACT We have successfully fabricated self-organized GaN nanotips by reactive ion etching using chlorine plasma, and have revealed the formation mechanism. Nanotips with a high density and a high aspect ratio have been formed after the etching. We deduce from X-ray photoelectron spectroscopy (XPS) analysis that the nanotip formation is attributed to nanometer-scale masks of SiO2 on GaN. The structures calculated by Monte Carlo simulation of our formation mechanism are very similar to the experimental nanotip structures.
INTRODUCTION GaN based III-nitride semiconductors are attractive wide direct band gap semiconductors for applications in optoelectronic and electronic devices such as ultraviolet-blue-green lightemitting diodes, laser diodes, field-effect transistors and high-temperature transistors. To fabricate nanometer-scale fine structure of GaN is one of the key technologies for further development of group-III nitride semiconductor devices. The formation of the fine tip and pillar structure of GaN becomes important in the advanced applications of stress-free epitaxy, coldcathode field emitters and quantum dots. The stress-free epitaxy on GaN nanocolumn structure was carried out by molecular beam epitaxy (MBE) [1]. The GaN pyramid structure formed by selective area growth is expected to be the application of a cold-cathode field emitter [2]. Selfassembled GaN quantum dots grown by plasma-assisted MBE were demonstrated [3]. The GaN whiskers formed by photoelectrochemical (PEC) wet etching [4] and metalorganic vapor phase epitaxy (MOVPE) were reported [5]. It was reported that the former whiskers were related to threading dislocations in the GaN layer. However, there are no reports on the formation and the mechanism of GaN fine tips by the dry etching technique. It is difficult for conventional lithographic methods to meet this requirement due to the limitation of lithographic technique. In this paper, we demonstrate a novel method and the mechanism of forming the self-organized nanotips of GaN by reactive ion etching (RIE).
EXPERIMENTAL PROCEDURE RIE of GaN was carried out using chlorine plasma. A GaN layer was grown by MOVPE on buffer layer deposited at low temperature on (0001) sapphire substrate. The thickness of the GaN was ~2 µm. After the deposition of a SiO2 film (300 nm thickness) on the GaN by RF I3.52.1
sputtering, stripe windows of 5 µm width with a periodicity of 10 µm were developed by conventional photolithography technique in the directions of the GaN layer, in order to examine the etch rates and to form banks for the protection of fine tips. The dry etching apparatus used in this study was a RIE system with a 6 inch sample stage of the cathode electrode (Samco RIE-5). A quartz (SiO2) plate was put on the cathode electrode, t
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