Electronic and Optoelectronic Devices Based on Quasi-Metallic Carbon Nanotubes.

摘要

Electronic devices have become the backbone of our daily life usage. In recent years, new types of electronics have emerged such as wearable electronics, flexible electronics, and optoelectronics. In particular, the idea of converting light into electricity with high efficiency, by carefully engineering the device structure, has become an active area of research. In this thesis, carbon nanotube electronic and optoelectronic devices are investigated which are based on suspended quasi-metallic carbon nanotubes. These quasi-metallic nanotube electronics exhibit semi-ballistic electron transport at room temperature, which gives them high sensitivity to gaseous environment. Once the nanotube is in contact with a substrate, the mini-gap in their energy band structure diminishes due to fixed charges in the oxide. Moreover, quasi-metallic carbon nanotube tunnel field-effect-transistors (TFETs) using an electrostatically tunable pn junction are engineered and studied. Although these devices do not show any diode behavior at room temperature, they show a finite photocurrent due to the existence of a space charge region. At cryogenic temperatures, these transistors show a tunable band-to-band (zener) tunneling with sub-threshold swing ~1mV/decade. At room temperature, these devices can produce photocurrent upon light exposure. The mechanism underlying the generated photocurrent in these devices reveals two different mechanisms. Devices with small band gaps (Egap < 75meV) exhibit photothermoelectric effect, while devices with larger band gaps, photo-induced electron hole separation by a built-in electric field (photovoltaic effect) dominates the photocurrent transport. Upon photothermal heating of these devices at cryogenic temperatures, an oscillatory behavior occurs in the current-voltage characteristics with a very low frequency of oscillation. This oscillatory behavior is found to be caused by opto-mechanical action where the nanotube is thermally coupled to an optical cavity.