Electroabsorption Mechanisms in Germanium Quantum Well Material
Description:... One possible solution to make viable optoelectronic modulators that meet strict targets down to the scale of on-chip communication is to use germanium-rich materials. Ge/SiGe quantum wells grown on silicon substrates provide the strongest mechanism, the quantum-confined Stark effect (QCSE), and thereby can meet the strictest requirements for optical interconnects, including CMOS-compatibility. Using such a strong effect, Ge-based modulators can be ultra-compact, ultralow-power, large bandwidth and high-speed, making them a strong contender for the future of optoelectronic device integration to solve the bottleneck problem. In this thesis, we will discuss the physical properties of the Ge and SiGe material system then present designs of optoelectronic modulators at the important 1310 nm and 1550 nm communication wavelengths using a program we developed called the Simple Quantum Well Electroabsorption Calculator (SQWEAC). SQWEAC takes the important physical mechanisms present, such as QCSE and indirect absorption, to predict the electroabsorption profile of Ge-based quantum wells. QCSE was experimentally determined on a wide range of samples to show the predictive powers of SQWEAC. Additionally, indirect absorption was also experimentally determined to optimize the physical model for these Ge quantum well devices. In being able to design both 1310 nm and 1550 nm devices using this Ge material system, we provide a platform for designing optoelectronic devices that are Si CMOS compatible and operate over a wide range of wavelengths. These modulators have the capability of providing the large density of information at very low energies per bit required for future interconnect technologies.
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