Sublimation crystal growth of yttrium nitride Li Du a , J.H. Edgar a,n , Roberta A. Peascoe-Meisner b , Yinyan Gong c , Silvia Bakalova c , Martin Kuball c a Kansas State University, Department of Chemical Engineering, Durland Hall, Manhattan, KS 66506-5102, USA b Department of Materials Science and Engineering, University of Tennessee/High Temperature Materials Laboratory, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA c H.H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, United Kingdom article info Article history: Received 4 March 2010 Received in revised form 2 June 2010 Accepted 7 June 2010 Communicated by Dr. M. Skowronski Available online 11 June 2010 Keywords: A1. Crystal morphology A1. Crystal structure A1. X-ray diffraction A2. Growth from vapor B1. Yttrium compounds B1. Nitrides abstract The sublimation–recombination crystal growth of bulk yttrium nitride crystals is reported. The YN source material was prepared by reacting yttrium metal with nitrogen at 1200 1C and 800 Torr total pressure. Crystals were produced by subliming this YN from the source zone, and recondensing it from the vapor as crystals at a lower temperature (by 50 1C). Crystals were grown from 2000 to 2100 1C and with a nitrogen pressure from 125 to 960 Torr. The highest rate was 9.64  10 5 mol/h (9.92 mg/h). The YN sublimation rate activation energy was 467.1 721.7 kJ/mol. Individual crystals up to 200 mm in dimension were prepared. X-ray diffraction confirmed that the crystals were rock salt YN, with a lattice constant of 4.88 ˚ A. The YN crystals were unstable in air; they spontaneously converted to yttria (Y 2 O 3 ) in 2–4 h. A small fraction of cubic yttria was detected in the XRD of a sample exposed to air for a limited time, while non-cubic yttria was detected in the Raman spectra for a sample exposed to air for more than 1 h. & 2010 Elsevier B.V. All rights reserved. 1. Introduction The transition metal nitrides exhibit a wide range of physical (electrical, magnetic, and optical) and chemical properties that are of technological interest and have commercial applications. Examples include TiN [1] and HfN [2] diffusion barriers for integrated circuits [3]; CrN for hard, wear resistant coatings; ScN for high temperature Ohmic contacts to IIIA nitride semiconduc- tors [4]; and VN which is being investigated as a catalyst [5]. The transition metal nitrides also form alloys, which can be exploited to control their lattice constants and electrical properties, as has been demonstrated with Ti 1 x Sc x N [6] and Y 1 x Sc x N [7]. Many researchers are investigating the possibility of combin- ing transition metal nitrides with the IIIA nitride semiconductors (aluminum nitride, gallium nitride, and indium nitride) either as layered structures or as alloys, to realize new functional proper- ties. The similar lattice constants and the shared common element (N) have inspired efforts to combine layers as epitaxial films. Scandium nitride [8] and zirconium nitride [9] have been employed as buffer layers between silicon substrates and GaN epitaxial films, to block the initiation and propagation of defects. Additions of chromium, magnesium, and iron to AlN and GaN have all been studied in attempts to create a ferromagnetic semiconductor [10,11]. Yttrium nitride is particularly intriguing because it is one of the few transition metal nitrides that is also a semiconductor (as is scandium nitride). Several groups reported the rocksalt crystal structure for YN with lattice constants between 4.8 and 4.9 ˚ A [12–15]. No other crystal structure has been experimentally reported for YN, but a recent first principle calculation compared the wurtzite and bcc structures to the rocksalt structure (the latter was the most stable) [16]. Although no measurement has been reported, studies predicted an indirect bandgap for YN of 0.8 eV [16], 0.85 eV [17], and 0.544 eV [18]. Yttrium nitride is also predicted to exhibit a high Mn solubility, which could impart it will good magnetic properties while retaining its semiconductor properties [19]. In the past, only a few studies have reported the synthesis of YN. In the 1950s, a group produced YN powder by first converting yttrium metal to YH 2 by reacting with hydrogen at 550 1C in a quartz tube, then heating this gas to 900 1C in the presence of nitrogen [12]. Later in the 1960s, YN powders were obtained by reacting yttrium metal with nitrogen at 1400 1C [13] and arc-melting under 0.3 MPa nitrogen [14]. Recently, YN thin films were grown on both silicon and sapphire substrates by laser ablation deposition [20] and reactive magnetron sputtering [21], respectively. Although the lattice constants reported from these different material preparation methods are very close, there are still variations. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2010.06.011 n Corresponding author. E-mail addresses: lidu@ksu.edu (L. Du), edgarjh@ksu.edu (J.H. Edgar). Journal of Crystal Growth 312 (2010) 2896–2903