Electrical and optical characterization of monolayer WSe2 field effect transistor Open Access

Yao, Qiang (Summer 2018)

Permanent URL: https://etd.library.emory.edu/concern/etds/kh04dp73w?locale=en


Atomically thin transitional metal dichalcogenides (TMDs) encourage has attracted great attention due to its interesting optical and electrical properties. Similar to graphene, monolayer TMDs also have a honeycomb lattice structure with a two-atom basis. The band gap experiences a crossover from indirect to direct by reducing the thickness of the bulk TMDs to monolayers, which is promising for modern optoelectrical applications.

Excitons are electron-hole pairs bounded by Coulomb force with large a binding energy. When the excitons are trapped in the defects, localized quantum emitters [4] are formed, called quantum dots (QDs). To study the optical property of the QDs in monolayer TMDs, the photoluminescence spectra is utilized to observe the emission peaks and its gate voltage dependence. QDs in two dimensional TMDs have the potential to become highly efficient single photon emitters for future optoelectronics. In this thesis, I will show the electrical and optical measurement for the monolayer WSe2, especially the emission property of several QDs.

The inversion symmetry breaking generates a valley contrasting Berry curvature in K and –K valleys. Berry curvature is the effective magnetic field in momentum space and generates the valley Hall effect. The subtraction of the magnetization current from the total current in the transport system gives rise to the thermal Hall effect. The thermal Hall effect causes a valley imbalance effect which breaks the time reversal symmetry. Magneto-optic Kerr effect (MOKE) is employed to detect this time reversal symmetry and a low temperature MOKE setup is proposed for the detection.

Table of Contents


Introduction 1

   Transitional metal dichalcogenides (TMDs)                            1

   Excitons and quantum dots                                            4

   Berry phase effect and Valley Hall effect                            6

   Orbital magnetic moment and Thermal Hall effect            7

   Magneto-Optic Kerr Effect (MOKE)                                    11

Experiments and results                                                    12

   Monolayer WSe2 field effect transistor                            12

   Transport characterization                                            14

   Optical characterization                                                    15

   Power dependent PL spectra                                            16

   Backgate voltage (Vbg) dependent PL spectra                    17

   Photoluminescence excitation (PLE) spectroscopy            18

   Low temperature Kerr rotation setup                                    19

Conclusions                                                                    21

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