Strain-induced enhancement of plasma dispersion effect and free-carrier absorption in SiGe optical modulators

摘要

The plasma dispersion effect and free-carrier absorption are widely used forchanging refractive index and absorption coefficient in Si-based opticalmodulators. However, these free-carrier effects in Si are not large enough formaking the footprint of the Si modulators small. Here, we have theoreticallyand experimentally investigated the enhancement of the plasma dispersion effectand free-carrier absorption by strain-induced mass modulation insilicon-germanium (SiGe). The application of compressive strain to SiGe reducesthe conductivity hole mass, resulting in the enhanced free-carrier effects.Thus, the strained SiGe-based optical modulator exhibits more than twicemodulation efficiency as large as that of the Si modulator. To the best of ourknowledge, it is the first demonstration of the enhanced free-carrier effectsin strained SiGe at the near-infrared telecommunication wavelength. Thestrain-induced enhancement technology for the free-carrier effects is expectedto boost the modulation efficiency of the most Si-based optical modulatorsthanks to high complementary metal-oxide-semiconductor (CMOS) compatibility.