Novel waveguide MSM photodetectors on SOI substrates using silicides

Novel Si waveguide MSM photodetector suitable for high speed/high quantum efficiency applications is proposed and demonstrated. Silicides are formed on a silicon-on-insulator (SOI) substrate through metal/Si reaction under heat treatment, in two areas separated by a narrow gap. The silicide sidewalls on the two sides of the narrow gap provide lateral waveguide confinement, and also serve as electrodes. The silicide/Si interface forms a Schottky junction, making the structure a MSM diode. The waveguide structure provides a long optical path length to increase the quantum efficiency at near infrared wavelengths. The distance between electrodes can be changed easily through photolithography, and can be made very small to reduce the transit time between electrodes for high-speed operation. Since the devices are made on SOI substrates, the drift component of the photocurrent can be eliminated, further facilitating high-speed operation. First set of photodetectors was made using PtSi on commercially available SOI substrates with 0.34micrometers Si layer. Initial experiments have demonstrated a responsivity of near 200mA/W at (lambda) equals980 nm for a detector with 486micrometers long electrodes and 2 micrometers gap size. The dark current was on the order of 0.1 nA/micrometers 2 at 5V bias.