EE PhD Oral Examination - Yiwen Rong, Friday, June 11, 2010; 2:00 p.m.

Yiwen Rong ryw at
Mon Jun 7 16:20:24 PDT 2010

Stanford University PhD Oral Defense - Department of Electrical Engineering

Speaker: Yiwen Rong

Advisor: James S. Harris

Date: Friday, June 11, 2010

Time: 2:00 p.m.

Location: CIS-X 101

Title: Sillicon-Gemanium Electroabsorption Modulator

Optical interconnections between electronics systems have attracted significant attention and development for a number of years because optical links have potential advantages for higher speed, lower power, and interference-immunity. With increasing system speed and greater bandwidth requirements, the distance over which optical communication is useful has continually decreased to where the frontier is now at the chip-to-chip and on-chip levels. Successful, monolithic integration of photonics and electronics will significantly reduce the cost of optical components and further combine the functionalities of chips on the same or different boards or systems.

The quantum-confined Stark effect (QCSE)  is a strong, electric field dependent change in optical absorption that has been observed in several groups of quantum well materials. The QCSE is used extensively for high-speed, low power dissipation optical modulators, for example, in telecommunications, and has also been used in large arrays of low power devices. To this point, most examples of the QCSE have been in III-V semiconductor quantum wells, such as GaAs with AlGaAs barriers , or InGaAs with InP barriers.  While these modulators are all based upon direct bandgap semiconductors, QCSE has been demonstrated in indirect bandgap AlGaAs/AlAs quantum wells and we previously demonstrated the QCSE in Ge quantum wells with SiGe barriers. The group IV quantum well structures are especially interesting as they would enable fully integrated modulators and driver circuits in silicon ICs for telecommunications applications and potentially on-chip communications. With reasonably low-power modulators, 

In this talk, We present observations of quantum confinement and quantum-confined Stark effect (QCSE) electroabsorption in Ge quantum wells with SiGe barriers grown on Si substrates. Though Ge is an indirect gap semiconductor, the resulting effects are at least as clear and strong as seen in typical III-V quantum well structures at similar wavelengths. We also designed and fabricated a coplanar high-speed modulator and demonstrated small signal modulation at 35GHz and a 3.125GHz eye diagram. That shows group IV quantum well structure has the potential to build high-speed optical communication components.
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