Effect of N 2 Plasma Treatments on Dry Etch Damage in n- and p-type GaN
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Effect of N2 Plasma Treatments on Dry Etch Damage in n- and p-type GaN D.G. Kent(1), K.P. Lee(1), A.P. Zhang(2), B. Luo(2), M.E. Overberg(1), C.R. Abernathy(1), F. Ren(2), K.D. Mackenzie(3), S.J. Pearton(1), and Y. Nakagawa(4) (1) Department of Materials Science and Engineering, University of Florida, Gainesville, FL, 32611, U.S.A. (2) Department of Chemical Engineering, University of Florida, Gainesville, FL, 32611, U.S.A. (3) Unaxis U.S.A., Inc., St. Petersburg, FL, 33703. (4) Nichia Chemical Industries, Tokushima-Ken, Japan. ABSTRACT The extent of damage recovery by N2 plasma treatment of previously damaged nand p-GaN has been examined using current-voltage (I-V) characteristics from Schottky diodes. There are two contributions to the observed improvement in the I-V characteristics, namely a simple annealing effect and also a chemical effect from reactive nitrogen. However the N2 plasma treatment does not fully restore the initial electrical properties of the near-surface region.
INTRODUCTION The chemical resistance of GaN to wet acid solutions has placed the emphasis on plasma etching methods for pattern transfer.(1-5) Initial research on dry etching of GaN focused on achievement of high etch rates and smooth surface morphologies.(1-5) For conventional light-emitting or laser diode structures, the electrical effects of plasmainduced damage are actually beneficial because etching terminates in an n+ contact layer. The general effect of plasma damage in GaN is to create a degenerately-doped n+ surface region, which leaves n-ohmic contact resistance.(3-13) However this effect is not desirable in situations in which a gate recess is formed by selectively removing GaN from AlGaN in heterostructure field effect transistors or when the p-base region is exposed in npn heterojunction bipolar transistors.(1,4) Previous attempts at removing dry etch damage in GaN have focussed on annealing or wet etch clean-up steps.(3,6,9,11,14) The damaged region appears to be rapidly removed in hot KOH or acid solutions, but the underlying undamaged GaN does not etch at a measurable rate.(6,9) This process is attractive in situations allowed by the presence of existing contacts or by the mask material employed. While the wet etch clean-up of the damage restores the initial electrical properties of the surface, annealing does not appear to fully remove the damage.(6,9) Recently there have been reports of using elevated temperature N2 plasma exposures to reduce the effects of plasma damage in n-GaN.(15,16) In this process the expected mechanism is a reduction in the nitrogen vacancy concentration in the nearsurface region. In this paper we describe a study of the effects of N2 plasma exposure on both n- and p-GaN that had been previously damaged in an Inductively Coupled Plasma (ICP) of Ar to produce a significant change in the current-voltage (I-V) characteristics of Schottky diodes. We find there are two contributions to the improved I-V curves upon G3.16.1
N2 plasma exposure, namely a thermal annealing effect and an additional effec
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