Quantum simulations on the physics of quasi-two-dimensional electronics systems for device applications




Wu, Xian (Ph. D. in electrical and computer engineering)

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The underlying physics of various quasi-two-dimensional (quasi-2D) electronics systems and associated quantum effects is studied using numerical simulations based on quantum mechanical theories. These systems and effects are the foundation for novel devices that potentially could outperform the CMOS devices for particular or general applications in the long term. The single-electron resonant tunneling in the double-monolayer transition metal dichalcogenide (TMD) system is the basis of the proposed interlayer tunnel field-effect transistor (ITFET). I simulate this system using a quantum transport method with a multiband model for the TMD material. Gate-controllable interlayer tunneling peaks are presented suggesting the theoretical feasibility of realizing TMD-based ITFETs. The spatially-indirect exciton condensation in a bulk double-monolayer TMD system is then studied under equilibrium condition. The operation of the proposed bilayer pseudospin field-effect transistor (BiSFET) and the bilayer pseudospin junction transistor (BiSJT) relies on the existence of this many-body quantum effect. Using the self-consistent Hartree-Fock approximation, I simulate the formation of the exciton condensates and study the dependence of the condensation strength on various parameters. Based on the equilibrium exciton condensate properties, I subsequently study the current-voltage characteristics of a voltage-biased four-terminal double-monolayer TMD system with the presence of the exciton condensates in this energy gapped (in contrast to previously considered graphene) system using quantum transport simulations. The potential of and possible issues with pseudospin devices based on this system are addressed. Approaches to experimentally verify the formation of the exciton condensates are also suggested. Finally, I study the current-phase relation (CPR) in a multiterminal Josephson junction (MT-JJ) system with 2D semiconductor layer as the weak link. Quantum simulations based on the BCS mean-field theory are conducted. The simulation results suggest a simplified macroscopic model to describe the CPR. Using this simplified model, I study a current-biased MT-JJ system, and illustrate the possibility for, e.g., gain/fan-out in appropriately designed MT-JJs. Such MT-JJs potentially could be adapted to design ultra-low-power current-controlled transistors in cryogenic computing with circuits operating at voltages on the scale of superconducting energy gap divided by the electron charge e


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