Silicon-germanium composition engineering for next generation multilayer devices and systems

We report a method of engineering constant composition, single crystal, defect free SiGe-on-insulator grown by a rapid melt growth technique using tailored tree-like structures. Branches emanating from the main SiGe strip act as Silicon “reservoirs” to prevent the usual gradation of the alloy composition. This technique enables multiple SiGe strips to be grown using the same single generic Ge deposition step, each with a different composition determined by the structural design. Using this technique, we envisage a silicon photonics platform for on-chip optical communications whereby both modulators and detectors can be fabricated with the same device design and therefore the same simple fabrication steps. This can be realised by exploiting the rapid melt growth SiGe composition engineering detailed in this paper to tune the bandgap of electro-absorption modulators for multi-channel links using wavelength division multiplexing, whilst simultaneously forming pure Ge photodetectors. This technology could open the way for a new multilayer photonic architecture or for extremely low power density, multi-channel on-chip optical communications by integrating the concept with the cascaded photonic crystal architecture demonstrated by Debnath et al. [1].