Tight binding parameterization from ab-initio calculations and its applications

Yaohua Tan, Purdue University

Abstract

Modern semiconductor nanodevices have reached critical device dimensions in the range of several nanometers. Innovative nano-electronic devices make use strain techniques and low dimensional geometries such as nanowire and superlattices to strengthen device performances. Except for typical semiconductors, esoteric materials such as transition metal dichalcogenide and black Phosphorus enter close device considerations. To predict device performances, it is critical to have a model that is capable to handle strains, interfaces and new materials. ab-initio methods are computationally too expensive for device level simulations; instead, the empirical tight binding(ETB) method is computationally much cheaper and thus is preferred in device level simulations. The reliability of ETB simulations depends strongly on the choice of basis sets and the transferability of ETB parameters. The traditional way of ETB parameterization is by fitting to experimental data rather than a foundational mapping. The parameters parameterized by traditional ways have potential transferability issues when applied to nano-structures such as ultrathin bodies and heterostructures. A further shortcoming of traditional ETB is the lack of explicit basis functions. In the present work, an algorithm that constructs ETB parameters and explicit basis functions from ab-initio calculations is developed. This method takes account of wave functions and band structures in the parameterization process. Parameters obtained by this process are more transferable than those obtained by traditional tting. The algorithm is applied to group IV and III-V semiconductors. Unstained materials and corresponding ultra-thin bodies are studied by ETB and ab-initio calculations. The ab-initio band structures of bulk materials matches the experimental results under room temperature. Tight binding band structures and wave functions agree well with ab-initio calculations in both bulk and ultra-thin bodies cases, while unphysical states are observed tight binding analysis of ultra-thin bodies using existing parameters and passivation models. For strained materials, a tight binding model that models the effect of arbitrary strain is developed. The tight binding parameters are obtained by considering ab-initio results of multiple strained systems in the presented parameterization algorithm. The tight binding parameters show good transferability, as the tight binding calculations of strained superlattices show agreement with corresponding ab-initio calculations well. Further more, the parameterization algorithm is applied to newly appeared 2D materials transition metal dichalcogenides and black phosphorus. Tight binding model and parameters that are generic for multilayer 2D materials are obtained.

Degree

Ph.D.

Advisors

Klimeck, Purdue University.

Subject Area

Physical chemistry|Electrical engineering

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