Advanced DFT–NEGF Transport Techniques for Novel 2-D Material and Device Exploration Including HfS<sub>2</sub>/WSe<sub>2</sub> van der Waals Heterojunction TFET and WTe<sub>2</sub>/WS<sub>2</sub> Metal/Semiconductor Contact
Aryan Afzalian, Elaheh Akhoundi, Gautam Gaddemane, Rutger Duflou, Michel Houssa
Abstract
We present, here, advanced density functional theory and nonequilibrium Green’s function (DFT–NEGF) techniques that we have implemented in our ATOmistic MOdeling Solver (ATOMOS) to explore transport in novel materials and devices, particularly in van der Waals (vdW) heterojunction transistors. We describe our methodologies using plane-wave DFT, followed by a Wannierization step, and a linear combination of atomic orbital DFT that lead to orthogonal and nonorthogonal NEGF models, respectively. We then describe in detail our nonorthogonal NEGF implementation including the Sancho–Rubio method and electron–phonon (e–ph) scattering within a nonorthogonal framework. We also present our methodology to extract e–ph coupling from first principles and include them in our transport simulations. Finally, we apply our methods to the exploration of novel 2-D materials and devices. This includes 2-D material selection and the dynamically doped FET for ultimately scaled MOSFETS, the exploration of vdW tunneling field-effect transistors (TFETs), in particular the HfS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /WSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> TFET that could achieve high ON-current levels, and the study of Schottky barrier height and transport through a metal-semiconducting WTe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> vdW junction transistor.