| Over 100 papers have been published on resonant tunneling diodes (RTD's) and resonant tunneling transistors (RTT's). Because of the small device dimensions and short transit times it is hoped that these devices will operate at high speeds. However, only limited high speed performance has been obtained. By studying diode circuits, this thesis has attempted to determine the limits of device speed, appropriate figures of merit, and suitable circuit applications for all resonant tunneling devices.; An equivalent circuit was developed for high speed RTD's. In this circuit, it was found that the quantum mechanical time constants can be neglected relative to the much slower device RC time constants. Using this equivalent circuit, diode pulse forming circuits were studied so that the limits of device switching speed could be understood. The analysis showed the importance of maximizing the current density while minimizing the device capacitance, key figures of merit which had been overlooked by some researchers.; To achieve the best switching performance, the device design was examined and devices were grown with lower reflectivity barriers. This resulted in a lowering of Q for the electron cavity so that a greater fraction of the supply electrons could tunnel through the structure, with consequent higher current density. To ensure that high speed operation was not compromised, a microwave compatible fabrication process was developed. This process employed stripe geometry devices, to reduce the series resistance, and proton implantation for device isolation and reduction of parasitic capacitances. High speed 50 Ohm pulse forming structures were fabricated.; To test the equivalent circuit, device scattering parameters were measured at up to 26 GHz. Close agreement was found between the measured scattering parameters and the predicted scattering parameters, validating the proposed equivalent circuit. The device switching speed was measured be electo-optic sampling. A 2 GHz sine wave was applied to the input of the device and an output pulse with a 6 ps risetime was measured.; High speed performance was obtained with resonant tunneling diode pulse forming structures; however, the performance was dominated by classical effects and the hoped for benefit from the high speed of quantum mechanical processes was not observed. The implications of the diode measurements for three-terminal devices are discussed and it is concluded that in most applications resonant tunneling transistors will not be competitive with traditional devices. |
