| This thesis work studies the design, fabrication and characterization of nanoscale high-speed metal-semiconductor-metal (MSM) photodetectors. Smallest, fastest MSM photodetectors will be presented.;Important design issues such as carrier transit time, carrier recombination time, light penetration depth, and device parasitic elements are investigated. Carrier transport in nanoscale detectors is studied using a Monte Carlo method. Based on the theoretical and experimental data, scaling rules for high-speed operation of MSM photodetectors are proposed.;Nanoscale MSM photodetectors are fabricated using a custom-built ultra-high-resolution electron beam lithography system and a lift-off process. Different resist schemes and accurate dose control are essential to produce desired nanoscale structures. MSM photodetectors with finger spacing and width as small as 25 nm are fabricated on GaAs, Si and silicon-on-insulator (SOI) substrate. To our knowledge, they represent the smallest ever reported to date.;Sub-picosecond characterization of the detectors' impulse response is performed using an electro-optic system and a femtosecond laser. The fastest MSM photodetectors have a response time and a 3-dB bandwidth of, respectively, 0.87 ps and 510 GHz on low-temperature-grown GaAs, 1.5 ps and 300 GHz on bulk GaAs, 3.7 ps and 110 GHz on bulk Si, and 3.2 ps and 140 GHz on SOI. They are, to the best of our knowledge, the fastest photodetectors of their kind.;MSM photodetectors on GaAs and Si can also be used at 1.3 to 1.55 ;Finally, we will propose a new silicon Fabry-Perot planar waveguide modulator structure consisting of two Bragg mirrors, which are nanoscale trenches in the waveguide. Compared to conventional waveguide modulator designs, large modulation depth can be achieved with much smaller modulator length, leading to much less loss and higher speed. |
