Si/SiGe Terahertz Waveguides

A low loss waveguide is essential for producing a laser. For terahertz lasers this is a significant issue as the optical mode is tens of µm in diameter but the active region might only be 10 µm. In GaAs heavily doped layers form plasmon reflectors but in SiGe, the conductivity is too low to allow the imaginary dielectric constant become larger than the real part as in GaAs. Therefore another solution must be found to confine the mode and increase the modal overlap.

Our collaborators at the Queens University Belfast have used bond and etch back techniques to form a buried silicide layer which acts as a buried reflector. The modal overlap in this wafer with a virtual substrate and active region is 48% compared to 12% without the silicide reflector for waveguide losses of ~25 cm-1.