| As feature sizes of electronic devices are scaled for improved speed, device operating frequencies have surpassed the frequency limitations of conventional measurement instruments. For example, while field-effect transistors with current gain cut-off frequencies of over 300 GHz have been reported, traditional measurement tools such as sampling oscilloscopes and network analyzers are limited to 50 GHz resolution. Thus, although device simulations have predicted non-equilibrium carrier transport phenomena such as velocity overshoot in high-speed electronic devices on the picosecond time scale, previous to this work, there were no direct time-resolved measurements of these electron transport dynamics.;This thesis will present a system capable of measuring the step response of III-V electronic devices with sub-picosecond resolution, minimal parasitics, and no requirement in device design or epitaxy. In this system, the electronic device-under-test (DUT) is monolithically integrated with a specially designed photoconductive switch, which provides a voltage step to turn on the DUT. The DUT output response is measured by direct electro-optic sampling, a technique that uses the electro-optic effect inherent in the III-V substrate to measure voltages on circuits using a laser beam. The electro-optic sampling system described in this thesis has a sensitivity of better than 1 mV, and a calculated measurement bandwidth of over 750 GHz. With this system, we have observed 77 GHz current oscillations in photoconductors, the fastest time-resolved oscillations reported in GaAs to date. This measurement system has also been used in a carefully designed experiment to make time-resolved measurements of electron transport in short-channel electronic devices on the picosecond time scale, including the first measurements of electron transit time effects in short-channel electronic devices, as well as the fastest time-resolved FET responses measured to date. |
