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

We present the epitaxial growth of Ge and Ge_0.94Sn_0.06 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 Ge_0.94Sn_0.06. 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.