High-speed resonant cavity enhanced Ge photodetectors on reflecting Si substrates for 1550-nm operation

We have designed and fabricated high-speed resonant cavity enhanced germanium (Ge) Schottky photodetectors on a silicon-on-insulator substrate. These back-illuminated detectors have demonstrated 3-dB bandwidths of more than 12 GHz at 3-V reverse bias and a peak quantum efficiency of 59% (R=0.73 A/W) at the resonant wavelength of /spl sim/1540 nm. Time domain measurements of our Ge photodetectors with diameters of up to 48 μm show transit-time limited impulse responses corresponding to bandwidths of at least 6.7 GHz, making these detectors compatible with 10-Gb/s data communication systems.

I. Introduction

The monolithic integration of photodetectors designed for operation around the long-haul communication wavelengths (1300, 1550 nm) with silicon-based technologies has been a long-standing goal within the optical communications industry. Although a number of methods exist for the integration of photodetectors with electronics, such as flip-chip bonding, a more attractive solution involves direct monolithic integration, given the relative ease of fabrication and potential cost advantage associated with this approach. Si-based photodetectors would be ideal for monolithic integration with Si-based electronics; however, such detectors would not be viable for operation around the long-haul communication wavelengths, given the Si energy bandgap cutoff wavelength of 1100 nm. The use of a semiconductor which is sensitive around the 1300–1550-nm wavelength range would be required in designing a photodetector for long-haul operation.