High-speed and high-sensitivity silicon-on-insulator metal-semiconductor-metal photodetector with trench structure

The frequency response and quantum efficiency (QE) of silicon-on-insulator (SOI) metal-semiconductor-metal photodetectors in the near-infrared (similar to 800 nm) are greatly enhanced with a simple reactive ion etching to form electrodes inside the interdigitated trenches. Detectors with 1.25 mu m trench spacing were fabricated on a SOI substrate with a 6-mu m-thick silicon top layer. The unique device structure isolates carriers generated deep inside the semiconductor substrate and at the same time provides a highly uniform electric field throughout the active region of the detector, resulting in an instrumentation limited response time of 23 ps at 5 V bias and a -3 dB bandwidth of 2.3 GHz as measured at 790 nm. The dc responsivity is 0.12 A/W, corresponding to an external QE of 18.7\% and an internal QE of 88.5\%. The large bandwidth and good responsivity at the wavelength of interest, combined with their low operating voltages, make these detectors attractive for use in short-distance optical communication systems. (C) 1996 American Institute of Physics