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High‑k Gate Stacks on Low Bandgap Tensile Strained Ge and GeSn Alloys for Field-Effect Transistors

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journal contribution
posted on 2015-01-14, 00:00 authored by Stephan Wirths, Daniela Stange, Maria-Angela Pampillón, Andreas T. Tiedemann, Gregor Mussler, Alfred Fox, Uwe Breuer, Bruno Baert, Enrique San Andrés, Ngoc D. Nguyen, Jean-Michel Hartmann, Zoran Ikonic, Siegfried Mantl, Dan Buca
We present the epitaxial growth of Ge and Ge0.94Sn0.06 layers with 1.4% and 0.4% tensile strain, respectively, by reduced pressure chemical vapor deposition on relaxed GeSn buffers and the formation of high-k/metal gate stacks thereon. Annealing experiments reveal that process temperatures are limited to 350 °C to avoid Sn diffusion. Particular emphasis is placed on the electrical characterization of various high-k dielectrics, as 5 nm Al2O3, 5 nm HfO2, or 1 nmAl2O3/4 nm HfO2, on strained Ge and strained Ge0.94Sn0.06. Experimental capacitance–voltage characteristics are presented and the effect of the small bandgap, like strong response of minority carriers at applied field, are discussed via simulations.