Ge-rich SiGe-on-insulator for waveguide optical modulator application fabricated by Ge condensation and SiGe regrowth

We have numerically analyzed plasma dispersion effect in a Ge-rich SiGe layer for optical modulator applications. Since strain induces reduction in effective masses of electron and hole, we expect enhanced plasma dispersion effect in a strained Ge-rich SiGe layer. The plasma dispersion effects of Si(0.15)Ge(0.85) on Si(0.2)Ge(0.8) for hole and electron are expected to be approximately 3.0 and 1.5 times larger than those of Si. To realize Ge-rich SiGe-based waveguide optical modulators, we have also investigated the fabrication procedure of SiGe-on-insulator (SGOI) wafers. We have successfully fabricated Ge-rich SGOI wafers without any thick SiGe buffer layers by using Ge condensation in conjunction with the SiGe regrowth technique. We have evaluated the SGOI by Raman spectroscopy, atomic force microscopy (AFM), reflected high energy electron diffraction (RHEED) and transmission electron microscopy (TEM). Ge-rich SiGe waveguides have been fabricated on the SGOI wafer. The propagation loss was found to be approximately 13 dB/mm, which can be reduced to be below 2 dB/mm by optimizing the Ge condensation process. We expect that strained SiGe grown on the fabricated SGOI exhibits more than 2.3 times higher plasma dispersion than Si in case of a carrier injection type, suitable for high-performance waveguide optical modulators.