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Materials 2015, 8(12), 8169-8182;

Electrical Properties and Interfacial Studies of HfxTi1–xO2 High Permittivity Gate Insulators Deposited on Germanium Substrates

Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3GJ, UK
Center for Materials and Structures, School of Engineering, University of Liverpool, Liverpool L69 3GH, UK
Department of Physics, University of Liverpool, Liverpool L69 7ZE, UK
Nano and Advanced Materials Institute, Hong Kong University of Science and Technology, Kowloon 999077, Hong Kong, China
Department of Electrical and Electronic Engineering, Xi’an Jiaotong-Liverpool University, Suzhou 215123, China
Department of Chemistry, Xi’an Jiaotong-Liverpool University, Suzhou 215123, China
Author to whom correspondence should be addressed.
Academic Editor: Peter J. King
Received: 24 September 2015 / Revised: 17 November 2015 / Accepted: 24 November 2015 / Published: 2 December 2015
(This article belongs to the Special Issue Atomic Layer Deposition of Functional Materials)
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In this research, the hafnium titanate oxide thin films, TixHf1–xO2, with titanium contents of x = 0, 0.25, 0.9, and 1 were deposited on germanium substrates by atomic layer deposition (ALD) at 300 °C. The approximate deposition rates of 0.2 Å and 0.17 Å per cycle were obtained for titanium oxide and hafnium oxide, respectively. X-ray Photoelectron Spectroscopy (XPS) indicates the formation of GeOx and germanate at the interface. X-ray diffraction (XRD) indicates that all the thin films remain amorphous for this deposition condition. The surface roughness was analyzed using an atomic force microscope (AFM) for each sample. The electrical characterization shows very low hysteresis between ramp up and ramp down of the Capacitance-Voltage (CV) and the curves are indicative of low trap densities. A relatively large leakage current is observed and the lowest leakage current among the four samples is about 1 mA/cm2 at a bias of 0.5 V for a Ti0.9Hf0.1O2 sample. The large leakage current is partially attributed to the deterioration of the interface between Ge and TixHf1–xO2 caused by the oxidation source from HfO2. Consideration of the energy band diagrams for the different materials systems also provides a possible explanation for the observed leakage current behavior. View Full-Text
Keywords: Ge substrate; titanium-doped hafnium oxide; XPS; XRD; AFM Ge substrate; titanium-doped hafnium oxide; XPS; XRD; AFM

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Lu, Q.; Mu, Y.; Roberts, J.W.; Althobaiti, M.; Dhanak, V.R.; Wu, J.; Zhao, C.; Zhao, C.Z.; Zhang, Q.; Yang, L.; Mitrovic, I.Z.; Taylor, S.; Chalker, P.R. Electrical Properties and Interfacial Studies of HfxTi1–xO2 High Permittivity Gate Insulators Deposited on Germanium Substrates. Materials 2015, 8, 8169-8182.

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