Enhancing terahertz photoconductive switches using nanotechnology

Abstract

In this thesis we use three main approaches to enhance the performance of terahertz photoconductive switches (THz PC switches). We first propose two novel materials (GaBiAs and carbon nanotubes) for the substrate. The resulting enhancement in THz emission and reception are significant for GaBiAs. As thoroughly analyzed and addressed in Chapter 2, both the emission bandwidth and the emission amplitude of the device are improved by these materials. A systematic study of CNTs predicts 2 orders of magnitude enhancement in THz emission and one order of magnitude enhancement in THz reception. Experimental results for GaBiAs indicate 0.5 THz increase in bandwidth and 68% increase in the emitted THz wave amplitude. The bandwidth enhancement is in comparison to premium commercial devices. The optical excitation of the PC switch is studied and optimized next as the second enhancement approach (Chapter 3). The study presented in Chapter 3 provides an insight on the subwavelength dynamics of the optical excitation E-field at the edge of the electrodes. The study reveals that majority of the fast photocarriers are collected at the edge of the electrode in a subwavelength scale area. This insight leads to optimization of illumination profile and also the third enhancement approach, namely, the enhancement of electrode structure (Chapter 4). In Chapter 4 we have engineered the electrodes down to nanometer scale. This significantly enhances the optical excitation of the substrate and also overcomes the undesired properties of some substrate materials such as long carrier lifetime. Fabricated devices and fabrication processes are assessed in Chapter 5. Results (Chapter 6) highlight more than two orders of magnitude enhancement for nanostructures on GaAs.