Gunn Effect in Heterostructure-Based Semiconductor Nanoconstrictions and its Application to THz Sensing
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The subject of this thesis is the exploration of the Gunn effect in novel semiconductor nanoconstrictions (NCs). While the Gunn effect has long been exploited as a means to realize versatile solid-state microwave sources, recent interest in this phenomenon has focused on its potential use in terahertz (THz) sources and detectors. In this thesis, we present experimental evidence for the Gunn effect in GaAs-based NCs, fabricated utilizing advanced nanofabrication techniques. Our studies reveal that the nonequilibrium current-voltage characteristics of these devices exhibit several distinct features that are collectively consistent with this phenomenon. These include current saturation arising from velocity overshoot, strongly-enhanced current instabilities due to impact ionization within high-field domains, and pronounced hysteresis accompanied by electroluminescence. Theoretical modeling indicates that the onset of the Gunn behavior is triggered by the full development of drain-induced barrier lowering (DIBL), which allows for the injection of high-energy carriers into the initially-depleted channels. We furthermore demonstrate the use of these NCs as room-temperature sensors, capable of demonstrating a clear photo-response at frequencies well beyond 1 THz. By taking advantage of signal rectification associated with the Gunn effect, we achieve competitive values for the sensor responsivity and noise equivalent power, in spite of the fact that our devices do not make use of any antenna structure to efficiently couple the radiation. Such observations suggest that our work may represent a useful step towards the realization of new classes of solid-state THz sources and detectors.