Electrical Properties and Interfacial Studies of Hf x Ti1- xO₂ High Permittivity Gate Insulators Deposited on Germanium Substrates

Qifeng Lu; Yifei Mu; Joseph W Roberts; Mohammed Althobaiti; Vinod R Dhanak; Jingjin Wu; Chun Zhao; Ce Zhou Zhao; Qian Zhang; Li Yang; Ivona Z Mitrovic; Stephen Taylor; Paul R Chalker

doi:10.3390/ma8125454

Electrical Properties and Interfacial Studies of Hf _x Ti_{1- x}O₂ High Permittivity Gate Insulators Deposited on Germanium Substrates

Materials (Basel). 2015 Dec 2;8(12):8169-8182. doi: 10.3390/ma8125454.

Authors

Qifeng Lu¹, Yifei Mu², Joseph W Roberts³, Mohammed Althobaiti⁴, Vinod R Dhanak⁵, Jingjin Wu⁶, Chun Zhao⁷, Ce Zhou Zhao^{8

9}, Qian Zhang¹⁰, Li Yang¹¹, Ivona Z Mitrovic¹², Stephen Taylor¹³, Paul R Chalker¹⁴

Affiliations

¹ Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3GJ, UK. [email protected].
² Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3GJ, UK. [email protected].
³ Center for Materials and Structures, School of Engineering, University of Liverpool, Liverpool L69 3GH, UK. [email protected].
⁴ Department of Physics, University of Liverpool, Liverpool L69 7ZE, UK. [email protected].
⁵ Department of Physics, University of Liverpool, Liverpool L69 7ZE, UK. [email protected].
⁶ Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3GJ, UK. [email protected].
⁷ Nano and Advanced Materials Institute, Hong Kong University of Science and Technology, Kowloon 999077, Hong Kong, China. [email protected].
⁸ Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3GJ, UK. [email protected].
⁹ Department of Electrical and Electronic Engineering, Xi'an Jiaotong-Liverpool University, Suzhou 215123, China. [email protected].
¹⁰ Department of Chemistry, Xi'an Jiaotong-Liverpool University, Suzhou 215123, China. [email protected].
¹¹ Department of Chemistry, Xi'an Jiaotong-Liverpool University, Suzhou 215123, China. [email protected].
¹² Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3GJ, UK. [email protected].
¹³ Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3GJ, UK. [email protected].
¹⁴ Center for Materials and Structures, School of Engineering, University of Liverpool, Liverpool L69 3GH, UK. [email protected].

Abstract

In this research, the hafnium titanate oxide thin films, Ti_xHf_1-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 GeO_x 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 Ti_0.9Hf_0.1O₂ sample. The large leakage current is partially attributed to the deterioration of the interface between Ge and Ti_xHf_1-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.

Keywords: AFM; Ge substrate; XPS; XRD; titanium-doped hafnium oxide.