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In the last years Ge/SiGe multiple quantum wells (MQW) have received a great attention in the context of silicon photonics for the realization of efficient electro-absorption modulators based on the quantum confined stark effect. At present day, one of the main problems to be addressed toward the integration of Ge/SiGe MQW modulators is their coupling with passive optical components such as waveguides. In particular, the integration with silicon waveguides is very difficult due to the presence of a thick SiGe layer which act as a virtual substrate (VS) for the MQW stack. In this work we demonstrate that the VS can be used as a low loss optical waveguide by choosing a suitable compositional mismatch with respect to the MQW stack. A photonic interconnection made by a Ge/SiGe MQW modulator connected to a Ge/SiGe MQW photodetector through a SiGe waveguide has been fabricated and tested in order to demonstrate the great potential of this approach. The whole structure has been deposited on a silicon substrate in a single epitaxial step by low energy plasma enhanced chemical vapor deposition. The optical insertion loss of the device is less than 5 dB/cm. 5 and 10 µA are obtained in the photodetector with 1V and 3V voltage swing at the modulator. The photodetector bias is -1V and the dark current is 10 nA. Similar performance can be obtained in a wide spectral range from 1430 nm to 1450 nm. This demonstration confirms that Ge quantum well interconnects are feasible for low-voltage broadband optical links integrated on silicon chips. Our approach can be extended to any kind of Ge-based optoelectronic devices working within telecommunication wavelengths as long as a suitable Ge concentration is selected for the Ge-rich virtual substrate.

Thermoelectric materials have great potential for a range of energy harvesting applications. The thermoelectric performance of Ge/SiGe heterostructures is presented with the aim of developing materials to be used as power sources for autonomous sensing applications. Seebeck coefficients up to 279.5 {plus minus} 1.2 µV/K with electrical conductivities of 77,200 S/m are demonstrated at room temperature with power factors of 6.02 {plus minus} 0.05 mW m-1K-2.

Si/SiGe bound-to-continuum quantum cascade emitters designed\ud by self-consistent 6-band k.p modeling and grown by low energy\ud plasma enhanced chemical vapour deposition are presented\ud demonstrating electroluminescence between 1.5 and 3 THz. The\ud electroluminescence is Stark shifted by an electric field and\ud demonstrates polarized emission consistent with the design.\ud Transmission electron microscopy and x-ray diffraction are also\ud presented to characterize the thick heterolayer structure.