Photodetectors for 1.3 μm and 1.55 μm wavelengths using SiGe undulating MQW's on SOI substrates

For Si-based photonic integrated circuits (PICs), photodiodes with good responsivity at 1.3 mu m and 1.55 mu m wavelengths made of Si-based materials are highly desirable. Previously, work has been reported using epitaxial SiGe planar multiple quantum wells (MQWs) on Si substrates. Since the high lattice mismatch limits the maximum Ge concentration and SiGe layer thickness, responsivity at 1.55 mu m was limited. Under appropriate growth conditions, strained SiGe QW's grow with periodic thickness variations along the surface plane. Ge tends to migrate towards the thickness maxima. This increase in local Ge concentration and the reduced quantum confinement at the coherent wave crest produces strained QW's with significantly lower band-gaps compared to planar QW's with the same nominal composition. In this paper, we report the first MSM SiGe waveguide photodetectors fabricated using coherent wave growth mode with a band gap below 800 meV. The heterostructures were grown on a SOI substrate by an ultra-high vacuum chemical vapor deposition (UHVCVD) system. The 2 mu m thick Si/SiGe/Si on oxide structure provides waveguiding for the detector structures and permits effective fiber coupling. Preliminary measurements have demonstrated internal responsivities of approximately 1 A/W at 1.3 mu m wavelength and 0.1 A/W at 1.55 mu m wavelength for a 240 mu m long device.