Terahertz transmission line design for high resolution responses of GaAs/AlGaAs core/shell nanowires

Kevin Anthony Distelhurst

doi:10.17918/etd-3881

Faster circuits require not only research in next generation devices but careful consideration of signal interconnects. As the frequency component of a signal increases, the wavelength decreases allowing subtle interconnect discontinuities to begin attributing to degradation through reflection, attenuation and dispersion. Furthermore, certain interconnect structures are inherently poor at handling signals at higher frequencies. Many charge carrier dynamics within devices can occur on less than picosecond time scales. Observing signals from test setups that measure these dynamics require bandwidths reaching the terahertz frequency domain. Interconnects can alter the observed characteristics of these devices, characterization of the device and interconnect is vital in understanding their use in integrated circuits. GaAs/AlGaAs core/shell nanowire based devices are one type of next generation electronics that show promise for use in a high frequency regime. To observe and understand this behavior, THz interconnects are necessary. These nanowires have potential as high-speed optical devices in applications such as optical interconnects and photonic detectors. A deeper understanding of the nanowire device physics is needed for further study of high-speed optical applications. To achieve this, the majority of the work in this thesis deals with designing and fabricating transmission lines that support signals from tens to hundreds of gigahertz. The transmission lines can therefore support signals related to the carrier dynamics of the nanowires. Several different techniques exist for measuring the carrier dynamics that occur in the picosecond time-frame. Electro-optic sampling and THz spectroscopy are discussed and existing work is used as a foundation for the design of the required transmission line/nanowire system needed for high-speed interrogation. The creation of this system faces many obstacles in the fabrication process some of which have been overcome in this thesis and others which require further study devoted solely to fabrication techniques. In general, the difficulties are in fabricating interconnects that interface a nanoscale device such as nanowires to the macroscopic world while maintaining minimal degradation of the propagating characterizing signal. As a preliminary study for future high-speed work, a network analyzer is used to characterize the transmission line and nanowire. The hope is to design a transmission line that has little negative effect on the signals it propagates and to witness nanowire dependencies in the network analyzer data. The design of this system is verified using calculation, simulation and measurements. Results from measuring these test structures show promise for further study using higher speed and finer resolution techniques. A better understanding of the carrier dynamics of these devices and potentially others will aid in the attempt to uncover the physics behind recently discovered behaviors.

Terahertz transmission line design for high resolution responses of GaAs/AlGaAs core/shell nanowires

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Terahertz transmission line design for high resolution responses of GaAs/AlGaAs core/shell nanowires

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