In optical transmission systems an operation at 1.3um and 1.55um wavelengths is preferred, due to the low attenuation in fiber-optic cables. Germanium is an attractive candidate for high-speed photodetector applications, due to its high electron mobility and high optical absorption coefficient in this wavelength range. Recently, a bandwidth of 10GHz has been demonstrated at a wavelength of 1.3um for a PIN-photodiode, fabricated in epitaxial Ge-on-Si technology. The use of Ge-on-Si technology allows the integration of germanium-based PIN-photodiodes with CMOS circuits on a silicon chip so that optical communication receivers can be built with low fabrication costs. However, the accurate simulation of ion implantation processes, particularly in germanium, is required for the optimization of doping profiles in optical applications. Boron and arsenic implantations have been studied in high germanium content SiGe alloys (Ge content >50%) and in pure germanium by using our Monte Carlo ion implantation simulator MCIMPL-II and SIMS measurements. We have shown that the calibrated ion implantation simulator can accurately predict the dopant profiles for different energies and doses. The simulator can estimate the vacancies and amorphized regions produced in the crystal, which are associated with a specific implantation profile. We found that the generated point defects in germanium are significantly reduced compared to silicon, which is consistent with former experimental observations indicating that boron-implanted germanium remains essentially crystalline. The simulated point responses revealed that the boron distribution is significantly reduced in germanium in the vertical direction, while the lateral profile is quite similar in silicon and germanium. The figure shows the schematic top and cross-sectional views of interdigitated germanium PIN-photodiodes as well as the simulated 15keV boron implantation step for the p+ finger formation in the germanium layer using a photoresist mask.