Effect of deposition pressure on the microstructure and thermoelectric properties of epitaxial ScN(001) thin films sputt
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Dmitri N. Zakharov Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA; and Brookhaven National Laboratory, Upton, New York 11974, USA
Tela Favaloro School of Engineering, University of California Santa Cruz, Santa Cruz, California 95064, USA
Amr Mohammed School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA; and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
Eric A. Stachb) Brookhaven National Laboratory, Upton, New York 11974, USA
Ali Shakouri School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA; Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA; and School of Engineering, University of California Santa Cruz, Santa Cruz, California 95064, USA
Timothy D. Sands School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA; School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, USA; and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA (Received 4 September 2014; accepted 16 January 2015)
Four epitaxial ScN(001) thin films were successfully deposited on MgO(001) substrates by dc reactive magnetron sputtering at 2, 5, 10, and 20 mTorr in an Ar/N2 ambient atmosphere at 650 °C. The microstructure of the resultant films was analyzed by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Electrical resistivity, electron mobility and concentration were measured using the room temperature Hall technique, and temperature dependent in-plain measurements of the thermoelectric properties of the ScN thin films were performed. The surface morphology and film crystallinity significantly degrade with increasing deposition pressure. The ScN thin film deposited at 20 mTorr exhibits the presence of ,221. oriented secondary grains resulting in decreased electric properties and a low thermoelectric power factor of 0.5 W/mK2 at 800 K. The ScN thin films grown at 5 and 10 mTorr are single crystalline, yielding the power factor of approximately 2.5 W/mK2 at 800 K. The deposition performed at 2 mTorr produces the highest quality ScN thin film with the electron mobility of 98 cm2 V1 s1 and the power factor of 3.3 W/mK2 at 800 K. I. INTRODUCTION
Contributing Editor: Sam Zhang a) Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr-editor-manuscripts/ DOI: 10.1557/jmr.2015.30
physical properties, including high mechanical hardness, thermal, and chemical stability.1–4 ScN—an indirect n-type semiconductor—has a band gap of 0.9 eV.5 The values of the direct band gap lie in the range of 2.1–2.6 eV.6,7 An average electron mobility of about 100 cm2 V1 s1 has been reported for high quality sp
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