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Calculating the Bandstructure of eSoM2-BN-Gr_h Heterostructure and Its Hopping Parameters for Tight Binding

Karimizadeh, Mohammad Ali | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55268 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Rahim, Faez
  7. Abstract:
  8. The purpose of this research is to introduce a heterostructure for Vertical Tunneling Field-Effect Transitors, calculating its band structure and finding the tight binding hopping parameters of its structure. To do this, we must first study different kinds of heterostructures and choose the most suitable one among them. In this research, we selected the three-layer graphene eSoM2-BN-Gr_h for its high on/off current ratio (〖10〗^6). To find the band structure, first we should construct unit cell and then find its crystal structure after relaxation. The lattice constant for graphene and is the same, but the lattice constant of graphene andeSoM2-BN-Gr_h is different . The number of atoms in the unit cell should be choosen such a way that the unit cell to be repeatable. In this unit cell, there are 32 C atoms, 16 B atoms, 16 N atoms, 9 Mo atoms, 18 Se atoms and a total of 91 atoms. The energy bands are then calculated using the density-functional theory. By analyzing them, the superior orbitals were identified. The impotant orbitals for different atoms are: P_z for C, B, and N, d for Mo, P_x, P_y and P_z for Se. Therfore we should consider 163 orbital for all atoms in the unit cell. Then, we should find the neighbors that have overlap to find hopping parameters for them. Then, the Hamiltion matrices with 163×163 dimension is written to calculate the energy bands using the tight binding method.Finally, the hopping parameters are found such a way that the energy bands computed by these two methods become close to each other. Using these parameters, one can find the transistor's properties. In this research, Quantum ESPRESSO & MATLAB were used for simulation and computations
  9. Keywords:
  10. Density Functional Theory (DFT) ; Tunneling Field Effect Transistor (TFET) ; Bandstructure Calculating ; Hopping Parameters ; Hetero Structure

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