Date of Graduation

12-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Physics (PhD)

Degree Level

Graduate

Department

Physics

Advisor/Mentor

Churchill, Hugh O.H.

Committee Member

Hu, Jin

Second Committee Member

Barraza-Lopez, Salvador

Keywords

Quantum dots; Nanostructures; Semiconductors

Abstract

This work focuses on the investigation of gate-defined quantum dots in two-dimensional transition metal dichalcogenide tungsten diselenide (WSe2) as a means to unravel mesoscopic physical phenomena such as valley-contrasting physics in WSe2 flakes and its potential application as qubit, as well as realizing gate-controlled quantum dots based on elementaltellurium nanostructures which may unlock the topological nature of the host material carriers such as Weyl states in tellurium nanowires.The fabrication and characterization of gate-defined hole quantum dots in monolayer and bilayer WSe2 are reported. The gate electrodes in the device design are located above and below the WSe2 nanoflakes to accumulate a hole gas. For some devices we additionally used gates to deplete the gas to define the dot. Temperature dependence of Coulomb-blockade peak height complies with single-level transport and the small size of the dot leads to observation of excited states in the Coulomb diamond measurements. Further, magnetic field dependence of the excited states in the bilayer devices provides a lower bound for g factors. For the chiral crystals of elemental Te, the intriguing property of combining Weyl physics with a small semiconducting bandgap enables the creation of gate-tunable devices to probe and utilize the topological properties of Te. The formation of gate-defined quantum dots in Te would allow Coulomb blockade spectroscopy to provide information about the strength of exchange interaction, spin-orbit coupling, and g-factors associated with discrete quantum states in Te nanostructures. Using low-pressure physical vapor deposition, Te nanowires are grown that permits local control of carrier density using electrostatic gates. While atomically flat hexagonal boron nitride (hBN) gate dielectrics haves been widely used for high quality layered material devices, the relatively weak adhesion to Te nanowires makes hBN-insulated Te device assembly challenging. Therefore, the configuration of the device underwent a few iterations. The gate electrodes design and insulating strategy compare different methods involving more traditional dielectrics, as well as a hybrid approach that uses a global Si backgate and hBN-insulated local top gates for these Weyl semiconductor devices. Early measurements of Te devices demonstrate density control in these devices. Future work must be aimed at quantum transport measurements in Te dots.

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