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 [Delta] alpha / alpha 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 >7dB by the measured parameter.