Modification of InN Properties by Interactions with Hydrogen and Nitrogen
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Modification of InN Properties by Interactions with Hydrogen and Nitrogen Maria Losurdo, Maria M. Giangregorio, Giovanni Bruno Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR, via Orabona, 4 – 70126 Bari, Italy Tong-Ho Kim, Pae Wu, Soojeong Choi, Mike Morse, April Brown Department of Electrical and Computer Engineering, Duke University, Durham, NC 27708, USA Francesco Masia, Antonio Polimeni, Mario Capizzi Dipartimento di Fisica, Università di Roma "La Sapienza", Piazzale A. Moro 2, 00185 Roma, Italy
ABSTRACT The interaction of InN epitaxial films grown by r.f. plasma assisted molecular beam epitaxy with atomic hydrogen and nitrogen, produced by remote r.f. H2 and N2 plasmas, is investigated. InN strongly reacts with both atomic hydrogen and nitrogen yielding depletion of nitrogen and concurrent formation of In droplets at the film surface. The impact of hydrogen treatments on the optical properties of InN is assessed using photoluminescence (PL). It is found that hydrogen suppresses the intense PL band peaked at approximately 0.7eV for the as-grown InN epitaxial layers, and yields a new PL band with a peak energy and intensity that increase with H-dose. The effect of exposure to atomic hydrogen and nitrogen on electrical properties of InN is investigated using Hall measurements. Atomic force microscopy is also used for studying the morphological changes of InN upon interaction with atomic hydrogen and nitrogen. INTRODUCTION The bandgap of InN has long been claimed to be approximately 1.9 eV. Recently, a much lower bandgap value (~0.7eV) has been reported, while values from 0.7 eV to 1.7 eV have been correlated with the measured free electron concentration [1,2]. However, the fundamental optical properties of InN and their dependence on defects are not fully understood and the impact of carrier concentration, doping, and defects on the bandgap and optical properties of InN is currently debated in the literature In this context, there is particular interest in investigating the effect of hydrogen [3] and nitrogen [4] on InN, since both hydrogen incorporation and nitrogen vacancies can contribute to the residual n-type carrier concentration of InN [5]. This work presents a study of the modification of InN structural, compositional (by X-ray photoelectron spectroscopy (XPS)), morphological (by atomic force microscopy (AFM)), optical (by photoluminescence and spectroscopic ellipsometry), and electronic properties (by Hall measurements) induced by interaction with hydrogen and nitrogen. InN epitaxial layers grown by r.f. plasma assisted MBE on 6H-SiC substrates have been used for the present investigation. Postgrowth exposure to atomic hydrogen and nitrogen in the downstream of hydrogen and nitrogen remote plasmas has been carried out at various temperatures in the range 25°-300°C. Few experiments of proton irradiation of InN have also been performed. All of the present data indicate that interaction of InN with both nitrogen and hydrogen leads to nitrogen depletion and indium surface enric
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