Ge/Si Heterojunction Photodiodes Fabricated by Wafer Bonding

Ge/Si heterojunction photodiodes with a mesa structure were fabricated by wet wafer bonding. Photocurrents were observed for lights of 1.31 and 1.55 µm wavelengths with above 40% quantum efficiencies. The measured capacitance–voltage ( C – V ) characteristic indicated that photoelectrons were injected into the p-Si layer through the hetero-interface when the depletion layer reached the interface. The photodiode structure having a Ge/Si heterojunction can be applied to an avalanche photodiode (APD) having a multiplication noise lower than those of conventional InGaAs/InP APDs.