Abstract
Silicon-based optical phase modulators were studied. Two and three terminal devices integrated into rib waveguides were interrogated using device physics and optical modelling software packages. The device performance benchmarks are the drive current required to achieve a given phase shift and the device transient rise and fall times. The slower of the two provides the device operating bandwidth. Among the n-p-n devices with a silicon overlayer thickness of 0.98mum studied, the most efficient device is one with constant doping profiles at a concentration of 1020atoms/cm3 in each contact, the side dopant profiles extended right up to the buried oxide and are located close to the rib edge. This device was predicted to require a pi-phase shift current of 0.5mA with rise and fall times of 0.3ns and 0.12ns respectively, which gives an operating bandwidth of approximately 1.7GHz. Optimised side dopants for the n-p-n and p-n-p variants were developed. An alternative theoretical voltage waveform was developed which is predicted to increase nominal operating bandwidth tremendously. A n-p-p device excited by this waveform obtained operating bandwidth in excess of 40GHz. At the time this work was carried out, this was the fastest prediction for a silicon-based optical phase modulator. It is concluded that silicon-based modulators studied in this work is capable of achieving MHz and GHz modulation. Numerous variants of the two most promising device designs were fabricated. They are the n-p-n and p-n-p variants. Critical fabrication aspects such as rib spacer thickness, doping, and annealing temperatures were studied. Modelling and experimental results are in agreement. This suggests that the additional theoretical results for devices not fabricated are reliable. A large number of the devices failed optically and a methodological failure analysis method was established. Failure analysis observations were consistent with experimental results.