Bruno Baert

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 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.

Electrical characterization of pGeSn/nGe diodes

I-V characteristics of pGeSn/nGe diodes have been measured and show very interesting properties. Simulations of the same structure are able to reproduce most of the observed behavior and point to the predominant influence of parameters such as the band gap energy of the GeSn layer. C-V characteristics showing little frequency dependence have also been measured, and their analysis for the determination of the carrier concentration is confirmed by simulations. More investigations of the effect of temperature, of other observed features in the C-V characteristics and of other defects at the interface or in the bulk of either layers, are still required in order to explain some of the observed behaviors, notably the reverse saturation current.

Electrical Characterization of P-Ge1-xSnx/P-Ge and P-Ge1-xSnx/n-Ge Heterostructures by Numerical Simulation of Admittance Spectroscopy

In this paper, a numerical simulation method was used, based on the solution of the basic semiconductor equations. This gives an access to microscopic and macroscopic properties of the structure, and thereon, to an understanding of the electrical properties of Ge1-xSnx/Ge by linking quantities such as admittance spectra to microscopic variations in the structure. A 200 nm thick p-doped Ge1-xSnx layer (x≈0.05) on top of a 100 μm por n-Ge substrate was modeled, including a Shockley Read Hall trap with energy near the valence band.