High-speed CMOS-compatible photodetectors for optical interconnects

Abstract

We have developed high-speed germanium (Ge) photodetectors using standard complementary metal-oxide-semiconductor (CMOS) process technology. We describe the design considerations that led to the devices reported on here. We have characterized these detectors in terms of the following detector metrics: speed, responsivity, dark current and capacitance. The photodetectors exhibit responsivities greater than 0.2 A/W at both 850 and 1550 nm, making them compatible with both long- and short-haul communication systems. Impulse response measurements at both of the above wavelengths indicate 3 dB cutoff frequencies greater than 10 GHz and open eye diagrams have been measured at 20 Gb/s. Dark currents are on the order of 10 to 1000 μA at a bias of 1 V depending on device size. Capacitances measured were on the order of 0.1-10 fF. The performance of the detectors indicates that they are suitable for high speed on-chip optical links. Device simulation models indicate that the fundamental upper limit on the speed of the devices, based on ideal material properties, is high enough to support a number of process generations. Calibration of the models to our experimental data is presented, and areas for improvement are defined.