Physica B 340–342 (2003) 221–224 Infrared spectroscopy of hydrogen in annealed zinc oxide S.J. Jokela, M.D. McCluskey*, K.G. Lynn Department of Physics, Washington State University, Pullman, WA 99164, USA Abstract Zinc oxide (ZnO) has shown great promise as a wide band gap semiconductor with optical, electronic, and mechanical applications. First-principles investigations by C. G. Van de Walle (Phys. Rev. Lett. 85 (2000) 1012) suggest that hydrogen may act as a shallow donor in ZnO. These same predictions also apply to deuterium (D). Using IR spectroscopy we have observed O–H and O–D stretch modes at 3326.3 and 2470:3 cm 1 ; respectively, in the same sample at a temperature of 14 K: These frequencies are in good agreement with the theoretical predictions for hydrogen and deuterium in an antibonding configuration. We have also performed preliminary polarization measurements at room temperature showing that the dipole of the O–H complex does not lie parallel to the c-axis of wurtzite ZnO. r 2003 Elsevier B.V. All rights reserved. Keywords: Zinc oxide; Hydrogen; FTIR; Polarization In previous studies, it has been shown that hydrogen diffusion [1,2] into zinc oxide (ZnO) will form an O–H complex that is observable via a local vibrational mode (LVM) at 3336:8 cm 1 at room temperature and 3326:2 cm 1 at liquid- helium temperatures [3]. It was also shown that deuterium (D) diffusion into ZnO produces an LVM at 2470 cm 1 at liquid-helium temperatures. These frequencies are both in good agreement with the theoretical prediction for an antibonding configuration [4]. Previous studies have also shown that hydrogen acts as a shallow donor [4–6] and may be an important element in the growth and processing of n-type ZnO. In addition to hydrogen donors, hydrogen-vacancy complexes have been observed with LVM spectroscopy [7]. Mid-infrared (IR) absorption spectra were obtained with a Bomem DA8 vacuum Fourier transform spectrometer (FTIR) with a KBr beamsplitter. The measurements in this study were performed at room temperature ð300 KÞ and near liquid-helium temperatures (14–18 K). For both room temperature and near liquid-helium tem- perature measurements, an InSb detector was used. Liquid-helium measurements were per- formed with a Janis STVP continuous flow liquid-helium cryostat with wedged ZnSe win- dows. The spectral range was 1800–7000 cm 1 and the instrumental resolution was between 0.5 and 2 cm 1 : Single-crystal ZnO samples were obtained from EaglePicher [8] and Cermet [9]. The average thicknesses for each sample were 0.5 and 1:3 mm; respectively. IR absorption spectra were obtained for as-received ZnO samples prior to our anneal- ing treatments. Unpolarized and polarized IR light traveled along various physical axes of the crystal to search for different dipole orientations of defects and dopants. No evidence of O–H or O–D dipoles was found. The samples were then sealed into individual ampoules with 1 3 atm H 2 and ARTICLE IN PRESS *Corresponding author. Fax: +1-509-335-7816. E-mail address: mattmcc@wsu.edu (M.D. McCluskey). 0921-4526/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2003.09.023