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-insul ator (SOI) metal-semiconductor-metal photodetectors in the near-infrar ed (similar to 800 nm) are greatly enhanced with a simple reactive ion etching to form electrodes inside the interdigitated trenches. Detect ors with 1.25 mu m trench spacing were fabricated on a SOI substrate w ith a 6-mu m-thick silicon top layer. The unique device structure isol ates 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 limite d 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 band width and good responsivity at the wavelength of interest, combined wi th their low operating voltages, make these detectors attractive for u se in short-distance optical communication systems. (C) 1996 American Institute of Physics.