Remarkable Franz-Keldysh Effect in Ge-on-Si p-i-n Diodes

Ge-on-Si p-i-n diodes are fabricated by using two-step Ge film epitaxial technology on Si substrates. A remarkable Franz–Keldysh effect is observed in the wavelength range of 1620–1640 nm with a largest Δα/α of 2.8 at 1640 nm by optical responsivity measurement. The remarkable change of absorption coefficient in the considerable large wavelength range makes Ge−on-silicon a promising candidate for Si-based electro-absorption modulators. The initial design predicts a modulator of bandwidth ∼50 GHz, and the extinction ratio >7 dB by the measured parameter.