Surface Disordering and Nitrogen Loss in GaN under Ion Bombardment
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Surface Disordering and Nitrogen Loss in GaN under Ion Bombardment S.O. Kucheyev,1 J.S. Williams,1 C. Jagadish,1 J. Zou,2 M. Toth,3 M.R. Phillips,3 H.H. Tan,1 G. Li,4 and S.J. Pearton5 1
Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, ACT 0200, Australia ( E-mail: [email protected] ) 2 Electron Microscope Unit and Australian Key Center for Microscopy and Microanalysis, The University of Sydney, Sydney, NSW 2006, Australia 3 Microstructural Analysis Unit, University of Technology, Sydney, Broadway, NSW 2007, Australia 4 Ledex Corporation, 23F, No 91 Chung-sun 2nd Rd, Kaohsiung, Taiwan 5 Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611
ABSTRACT The damage build-up and amorphization behavior in wurtzite GaN films under a wide range of implant conditions are studied by Rutherford backscattering / channeling spectrometry, transmission electron microscopy, and cathodoluminescence spectroscopy. A strong surface peak of lattice disorder, in addition to the expected damage peak in the region of the maximum of nuclear energy loss, has been observed for all implant conditions of this study. Capping of GaN with SiOx and SixNy layers prior to implantation does not eliminate surface disordering. This may suggest that nitrogen loss is not the main reason for the observed enhanced surface disorder, but, rather, the GaN surface acts as a strong sink for migrating point defects. However, pronounced loss of N during ion bombardment is observed for high dose implantation when the near-surface region is amorphized. Moreover, after amorphization, annealing at temperatures above about 400 oC leads to complete decomposition of the near-surface layer. INTRODUCTION For much of the past decade, extensive studies of GaN have demonstrated amazing success leading to the fabrication of a range of both electronic and photonic devices.1 However, the data reported in the literature on damage processes in GaN under ion bombardment is still rather limited and far from being understood (see, e.g., Refs. [2-8]). This is surprising since a successful application of ion implantation depends on understanding the production and annealing of radiation damage in GaN. We report here on the main features of disorder build-up in GaN for a wide range of implant conditions, as given in Table I. Our systematic study of the influence of ion irradiation parameters (ion species and energy, substrate temperature, and beam flux) on ion beam damage will be published elsewhere.9,10 Here we focus only on the enhanced surface disordering during ion bombardment observed for all implant conditions of this study (see Table I), even when samples are capped. Results suggest that the surface acts as a strong sink for accumulation of migrating point defects even at liquid nitrogen (LN2) temperature. However, the data also suggests that surface decomposition of GaN takes place for high dose implantation. EXPERIMENTAL The wu
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