Vertical stacks of two-dimensional (2D) materials, separated by the van der Waals gap and held together by the van der Waals forces, are immensely promising for a plethora of nanotechnological applications. Charge control in these stacks may be modeled using either a simple electrostatics approach or a detailed atomistic one. In this paper, we compare these approaches for a gated 2D transition metal dichalcogenide bilayer and show that recently reported electrostatics-based models of this system give large errors in band energy compared to atomistic (Density Functional Theory) simulations. These errors are due to the tails of the ionic potentials that reduce the electricalequivalent van der Waals gap between the 2D layers, and can be corrected by using the reduced gap in the electrostatic model. For a physical van der Waals gap (defined as the chalcogen to chalcogen distance) of 3Å in a 2D bilayer, the electrical-equivalent gap is less than 1Å. For the example of band-to-band tunneling based ultra low-power transistors, this is seen to lead to errors of several hundred millivolts and more in the threshold voltage estimated from electrostatics. arXiv:1803.10009v1 [cond-mat.mes-hall]

Memristor is a promising device as a fundamental building block for future unconventional system architectures such as neuromorphic computing, reconfigurable logic, and multibit memories. Therefore, to facilitate circuit design using memristors, accurate and efficient models spanning a wide range of programming voltages and temperatures are required. In the first part of this series, we propose a behavioral model for temperature dependence of nonvolatile switching dynamics of TiO x memristors. We begin by describing pulsed resistance transients (PRTs) of the memristors and then we use a multistage methodology to establish bias and temperature dependence of the model parameters. The proposed model is then shown to accurately describe the PRT characteristics of Pt/TiO x /Au and Pt/TiO x /Pt memristors.

The plasma assisted As doping (PLAD) technique is used to demonstrate multiple flatband voltages (multi-Vfb) on TiN/HfO2 Ge gate stacks for n-FinFET applications. Through detailed studies with varying doses, implant energies, and TiN cap thicknesses, we show that the PLAD As technique can be used to obtain effective work function (EWF) modulation from the near midgap to the conduction band edge (up to 280 meV) of Ge, a key technological requirement for multi-threshold voltage (VT) Ge n-FinFETs. Furthermore, there is no deterioration of key gate stack parameters such as gate leakage, effective oxide thickness, and gate/channel interface trap densities. From secondary ion mass spectroscopy data, we attribute the tuning of EWF to As accumulation and interfacial dipole formation at the TiN/HfO2 interface. The experimental observations are reinforced by ab initio simulations of near-interface As substitutions at the TiN/HfO2 interface. As substitution at N sites near the interface reduces the EWF, making it more suitable for n-MOS applications.

Germanium is a promising material for next-generation electronic and photonic devices, and engineering ohmic contacts to it can be expected to be a key challenge therein. The sensitivity of the Schottky barrier height of the NiGe/Ge contact to the detailed interfacial structure is revealed using the ab-initio study of pseudo-epitaxial NiGe(001)/Ge(100) contact using the computationally efficient meta-generalized-gradient-approximation, which can overcome the well-known bandgap underestimation problem. The p-type Schottky barrier height for an atomically flat pseudo-epitaxial NiGe(001)/Ge(100) contact is calculated to be 260 meV, an overestimate of about 160 meV compared to experiments. However, the estimated modulation of this barrier height, by about 270 meV, due to interface morphology points to a possible explanation for this discrepancy and suggests ways to engineer the contact for lesser resistivity.

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