UNCORRECTED PROOF The effect of rf power on the growth of InN films by modified activated reactive evaporation Kuyyadi P. Biju *, Mahaveer K. Jain Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India 1. Introduction Preparation and characterization of indium nitride thin films have been of great interest for their applications in optoelectronic devices, high efficiency solar cells, optical coatings, high speed and high power electronic devices, and various types of sensors [1,2]. Much of the research interests result from its unique set of properties such as high electron mobility, high saturation velocity, and high radiation resistance [3,4]. Growth of high-quality InN films is difficult due to higher vapor pressure of nitrogen over InN compared to AlN and GaN, and lack of proper substrates. It has been established for long time that the band gap of InN is around 1.9 eV for films grown by reactive sputtering [5–7]. Recent studies of infrared photoluminescence (PL) and optical absorption on InN grown by molecular beam epitaxy (MBE) [8–10] and metal organic vapor phase epitaxy (MOVPE) [11] has revealed that the band gap energy of InN is around 0.7 eV. The large variation in the band gap measurements has been attributed to the Moss–Burstein (MB) shift, the presence of oxide precipitates, the formation of Indium clusters, and other stoichiometry-related defects [10–15]. We demonstrate a commercially viable method called modified activated reactive evaporation (MARE), capable of growing high-quality InN thin films at room temperature. The MARE method is a combination of conventional activated reactive evaporation (ARE) [16,17] and biased sputtering. The ‘activation’ of the evaporated species as well as gaseous reactant by the plasma, helps to deposit high quality compound films at very low substrate temperature. In ARE, indium is thermally evaporated in the presence of rf plasma and the substrate is kept at ground or neutral electrode; whereas in the MARE, we place the substrate on the rf cathode itself. Hence, the substrate here is biased by the rf voltage of the cathode. The present method provides independent control of indium species by controlling the thermal evaporation rates, and nitrogen species by controlling the partial pressures and plasma power, as also in the case of ARE. But the key advantage of this method is that the energy of nitrogen species striking the substrate is much higher than the ARE, as they are accelerated by the cathode voltage. In MARE, plasma power levels are lower compared to sputtering. The higher energy of nitrogen ion enables the growth of InN thin films at room temperatures (no intentional substrate heating). The higher mobility of nitrogen ad-atoms (due to its high kinetic energy), and higher energy of deposited indium (as they are in excited states after passing though the plasma), ensures that nitrogen reaches to all deposited indium metal and gets reacted. As a result, no free metal clusters are left in contrast with conventional ARE [16] and reactive sputtering [18]. Muller et al. have reported the growth of GaN films by energetic neutral atomic beam lithography (ENABL) in which films were deposited Applied Surface Science xxx (2008) xxx–xxx 1 2 3 4 5 6 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 27 28 28 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 ARTICLE INFO Article history: Received 20 March 2008 Received in revised form 18 May 2008 Accepted 18 May 2008 Available online xxx Keywords: InN Modified activated reactive evaporation ABSTRACT We report the effect of rf power on the structural, optical and electrical properties of InN films grown by modified activated reactive evaporation. In this technique, the substrates were kept on the cathode instead of ground electrode. The films grown at higher rf power and show preferential c-axis orientations for both silicon and glass substrates. The films prepared at 100 W show best structural, electrical and optical properties. The c-axis lattice constant was found to decrease with increase in rf power which can be attributed to reduction in excess nitrogen in the films. The band gap decreases with increase in rf power due to Moss–Burstein shift. The decrease in carrier concentration and optical band gap with increase in rf power can also be related to excess nitrogen in the film. The Raman spectra shows a red shift in the A 1 (LO) and E 2 (high) mode from the reported value. The possible origin of the present large band gap is due to Moss–Burstein shift. The new film growth method opens opportunities for integrating novel substrate materials with group III nitride technologies. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +91 44 2257 4880; fax: +91 44 2257 4852. E-mail address: biju@physics.iitm.ac.in (K.P. Biju). G Model APSUSC 17214 1–7 Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc 0169-4332/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2008.05.297 Please cite this article in press as: K.P. Biju, M.K. Jain, The effect of rf power on the growth of InN films by modified activated reactive evaporation, Appl. Surf. Sci. (2008), doi:10.1016/j.apsusc.2008.05.297