A GeSi avalanche photodiode (APD includes an anti-reflection structure, a Ge absorption region, and a resonance cavity enhanced (RCE) reflector. The anti-reflection structure includes one or more dielectric layers and a top contact layer which is heavily doped with dopants of a first polarity. The RCE reflector includes: an intrinsic or lightly doped Si multiplication layer, a Si contact layer which is heavily doped with dopants of a second polarity opposite the first polarity, a Si cavity length compensation layer, a buried oxide (BOX) layer, and a Si substrate.