Compact and high-power Ge-on-Si photodetector based on butt-side-hybrid coupling

Germanium-on-silicon (Ge-on-Si) photodetectors (PDs) have been widely used in silicon photonics. However, their saturation power is often relatively low. Here, a compact and high-power lateral PIN Ge-on-Si PD featuring a novel, to the best of our knowledge, butt-side-hybrid coupling structure is proposed and demonstrated by simulation. The input light is split into 3 paths, where the center one is directly butt coupled to the Ge-on-Si waveguide and the other two facilitate the gradual side coupling through higher-order-mode excitation. By engineering the field distribution and mode conversion process, the optical power can be more uniformly distributed across the Ge region, to significantly mitigate the saturation effect. Simulation results show a saturation power of 23 mW under -3 V bias and a maximum current density of 5.60 mA/μm3. With a compact footprint of 7 μm × 30 μm, it is suitable for high-density silicon photonic integration.