Strain Engineering of Plasma Dispersion Effect for SiGe Optical Modulators

The plasma dispersion effect and free-carrier absorption in strained SiGe are analyzed using the six-band k·
p
method and the Drude model. Since the hole conductivity mass of SiGe is decreased by applying compressive strain, enhancement of the plasma dispersion effect, and free-carrier absorption in strained SiGe is expected. We predict that Si
_0.5
Ge
_0.5
coherently grown on Si will exhibit three times higher plasma dispersion and four times higher free-carrier absorption than Si. The modulation characteristics of SiGe quantum well metal-oxide-semiconductor (MOS) optical modulators are also analyzed by technology computer-aided design simulation and finite-difference optical mode analysis. An extremely small V
_π
L of 0.033 V-cm is predicted in the case of a compressively strained Si
_0.5
Ge
_0.5
quantum well in conjunction with a high-k gate dielectric MOS structure. The enhancement of free-carrier absorption in the SiGe high-k MOS modulator also makes in-line intensity modulation feasible and an intensity modulation efficiency of 9 dB/mm/V is predicted.