A CMOS-compatible high-speed silicon lateral trench photodetector

Silicon-based photodetectors have difficulty in achieving both high bandwidth and high responsivity due to the long absorption depth of silicon (15 μm) at 850 nm. Metal-semiconductor-metal (MSM) detectors have been demonstrated on SOI with very high bandwidth gained at the expense of low responsivity. Using a trench MSM structure, higher responsivity has been reported. Lateral p-i-n photodiodes on SOI substrates have demonstrated 1-2 GHz bandwidths and 18-25% peak external quantum efficiencies at 3 V. In the present work, we have fabricated fully CMOS-compatible silicon lateral p-i-n photodiodes with deep trenches to enhance the collection of deep photocarriers. The devices exhibit a bandwidth of 2.5 GHz at 670 nm and a 3 V bias. Successful operation at 2.5 Gb/s and 845 nm has been achieved at 3.3 V. The responsivity is 0.45 A/W at 845 nm, corresponding to an external quantum efficiency of 66%. To the authors knowledge, these devices have the best overall function (highest speed-responsivity at low bias) among silicon-based photodetectors.