Performance enhancement of waveguide-coupled Ge-on-Si photodetector with additional p-i-n junction

Waveguide-coupled germanium (Ge) p-i-n photodetectors (PDs) have attracted much attention and have been investigated widely due to their high performance and enable on-chip integration. In this paper, we report on the fabrication and experimental demonstration of an integrated lateral waveguide p-i-n PD with additional Si doping. In order to achieve a high performance detector, we used a novel silicon substrate doping to improve the electric field intensity in the active region. It is demonstrated by experiment that the strategy using additional Si doping to decrease dark current and to increase the bandwidth is more favorable. Using the additional Si doped p-i-n junction, the waveguide coupled Ge-on-Si p-i-n PD shows a comprehensive performance improvement. With comparison to the conventional waveguide coupled Ge-on-Si p-i-n PD, such a PD, owns an about 60% improvement on the tested -3 dB opto-electrical cut-off frequency and shows the smaller dark current at voltage of -1 V. We obtained at a reverse voltage of 1V a dark current lower than 30 nA, a responsivity higher than 1.1 A/W at 1550 nm wavelength, and a -3 dB optoelectrical cut-off frequency over 25 GHz. Evidently, the waveguide coupled Ge-on-Si p-i-n PD with additional p-i-n junction is very effective to promote the performance of device, which is very promising to be applied in the further high power Ge-on-Si PD fabrication.