Design and implementation of high-speed planar Si photodiodes fabricated on SOI substrates

We report high-speed interdigitated (nonmetalized) p-i-n Si photodiodes fabricated on SOI substrates that operate at low bias voltages and that offer easy integration with transistor fabrication processes. Devices fabricated with a finger spacing of 2 μm and a 3.75-μm-thick active layer achieved a 1.1-GHz bandwidth at a bias of -3 V with a peak efficiency of 29% (0.2 A/W) at 850 nm. Photodiodes with the same geometry that were fabricated on a 2.71-μm-thick active layer exhibited a 3.4-GHz bandwidth and a quantum efficiency of 24% (0.16 A/W) at 840 nm when biased at -3 V. The dark current of the photodiodes was less than 25 pA at -3 V, and the capacitance of the photodiodes was less than 265 fF at an applied bias of -3 V