Systematic study of a tapered waveguide for Ge vertical PIN photodetector

Here, a systematic study of the tapered waveguide is considered for the Ge on Si waveguide-based vertical PIN photo detector, in order to achieve the highest possible power coupling efficiency. The effect of the length and width of the tapered waveguide and the number of modes on the power coupling efficiency is investigated. The taper optimization is carried out by the eigenmode expansion method and the finite difference time domain and drift-diffusion methods are implemented for the optical and electrical analysis. The dark current, photocurrent, and responsivity are extracted for different tapers which prove the optimum taper design.