Browsing by Author "Laturia, Akash A."
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Item Modeling of Electron Transport in Nanoribbon Devices Using Bloch Waves(Institute of Electrical and Electronics Engineers Inc.) Laturia, Akash A.; Van De Put, Maarten L.; Fischetti, Massimo V.; Vandenberghe, William G.; 0000-0001-5926-0200 (Fischetti, MV); 21146635654041982414 (Vandenberghe, WG); Laturia, Akash A.; Van De Put, Maarten L.; Fischetti, Massimo V.; Vandenberghe, William G.One-dimensional (1D) materials present the ultimate limit of extremely scaled devices by virtue of their spatial dimensions and the excellent electrostatic gate control in the transistors based on these materials. Among 1D materials, graphene nanoribbon (a-GNR) prove to be very promising due to high carrier mobility and the prospect of reproducible fabrication process [1]. Two popular approaches to study atomistically the electronic properties expand the wavefunction on either a plane-wave basis set, or through the linear combination of localized atomic orbitals. The use of localized orbitals, especially in the tight-binding (TB) approximation, enables highly scalable numerical implementations. Through continuous improvements in methods and computational capabilities, atomistically describing electronic transport in devices containing more than thousands of atoms has become feasible. Plane waves, while not as scalable, are very popular as the basis of accurate ab-initio software [2]. However, for modeling of transport through larger devices, the computational burden prohibits the direct use of a plane wave basis [3]. Here, we demonstrate a study of the transport characteristics of nanoribbon-based devices using a hybrid approach that combines the benefits of plane waves while retaining the efficiency provided by the TB approximation. © 2018 IEEE.Item Study of the Electrical Properties of Low-Dimensional Materials Using Plane-Wave Computational Methods(2020-11-11) Laturia, Akash A.; Vandenberghe, WilliamAs transistor channel dimensions have continuously reduced, research efforts have been directed at finding alternative channel materials to overcome the limitations of Si-based planar Complementary Metal Oxide Semiconductor(CMOS) technology. Low dimensional materials like two-dimensional Transition Metal Dichalcogenides (TMDs) and one-dimensional nanostructures have emerged as promising candidates for future technology nodes due to the excellent electrostatic gate control they offer. In view of the great interest in low-dimensional materials we focus on the computational study of the electronic properties of these materials using a recently developed Bloch-wave based quantum transport solver. We focus our attention on improving the knowledge surrounding two important inputs to the Bloch-wave based quantum transport solver namely the dielectric constant (needed for accurate electrostatic analysis) and the empirical pseudopotentials used to build the Bloch-wave basis set. At first we compute the macroscopic dielectric constant for monolayer, bilayer and bulk TMDs, and hexagonal boron nitride (h-BN). Our calculations show that the electronic contribution dominates the dielectric response of 2H-TMDs and h-BN in both in-plane and out-of-plane directions whereas ionic contribution dominates the in-plane response for 1T-TMDs. The very high in-plane dielectric response can lead to enhanced polar optical scattering thereby negatively impacting its mobility. Next, we developed a general method for calibrating empirical pseudopotentials (EP) using ab-initio data. These generated EPs with the help of Virtual Crystal Approximation (VCA) are then used to study the device performance of gateall-around Si1−xGex alloy (x is alloy composition) nanowire based Field-Effect-Transistors. Our calculations suggest that the ON current increases monotonically with the increasing value of x for the h100i crystallographic orientation whereas it shows negligible variation for the h110i orientated nanowires. For a given alloy composition, the h100i crystallographic orientation seems to have superior performance compared against its h110i counterpart. Also, the performance gap quantified by the difference in the device ON current increases for higher values of x. The use of a virtual crystal approximation technique to study the Si1−xGex alloy nanowire overestimates the drive current for nanowires with sub 1 nm body sizes. Therefore, one must be careful when deriving the quantitative estimates about the device performance using VCA, especially for smaller width Si1−xGex alloy nanowires. However, VCA can still be used for obtaining qualitative behaviour of alloy nanowire devices for various alloy compositions, even at smaller widths.