Date of Graduation

12-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Physics (PhD)

Degree Level

Graduate

Department

Physics

Advisor

Hugh O.H. Churchill

Committee Member

Jin Hu

Second Committee Member

Salvador Barraza-Lopez

Keywords

2D Semiconductors, Nanotechnology, Near-Field Radiative Heat Transfer, Optoelectronics, Photoconductive Antennas, Terahertz Emission

Abstract

The main focus of this work is to investigate two potential optical and optoelectronic applications of black phosphorus (BP): the near-field radiative heat transfer in plasmonic heterostructures with graphene and terahertz emission from multi-layer BP photoconductive antennas. When the separation distance between graphene-black phosphorene is much smaller than or comparable to the thermal wavelength at different temperatures, a near-field radiation heat transfer breaks the Planck blackbody limit. The magnitude of the near-field radiation enhancement acutely depends on the gate voltage, doping, and vacuum gap of the graphene and BP pair. The strong near-field radiation heat transfer enhancement of the specific optical properties of the heterogeneous 2D material is due to the strong coupling of propagating surface plasmon polaritons. The tunable anisotropic properties of BP provide another parameter to enable dynamic control of the total near-field radiative heat transfer regardless of the optical conductivity of graphene. For terahertz emission from multi-layer BP photoconductive antenna, this work mainly describes the fabrication and characterization of dipole photoconductive antennas where BP is used as the photoconductor. Because of the air sensitivity of BP, another two-dimensional material, hexagonal boron nitride (hBN), is used as a protective capping layer. The transfer matrix method is implemented to maximize the absorption within the BP layer and predict the thickness of BP and hBN. Since the in-plane armchair axis of BP has higher carrier mobility than the other in-plane axis (zigzag), the armchair axis is aligned with the anode-cathode gap of the antennas, and differential reflection anisotropy measurement is used to determine the crystal direction. Photoconductivity, photocurrent density, responsivity, and photocurrent imaging are performed under illumination with 100 fs pulses at 780 and 1560 nm. Terahertz time-domain spectroscopy is used to measure and characterize the generated terahertz signal. Polarization, bias voltage, and pump fluence dependence on the terahertz signal generation from BP photoconductive antennas are also investigated.

Available for download on Friday, February 17, 2023

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