Amorphous germanium waveguides for medical diagnostics using mid-infrared spectroscopy

Molecules have 'fingerprint' absorptions in the mid-infrared, enabling their identification via infrared spectroscopy. For applications beyond the lab, such as medical diagnosis, fully integrated mid-infrared spectroscopy on chip would be ideal. Germanium offers low absorption in the mid-IR, making it an ideal candidate for waveguides for mid-IR spectroscopy via the evanescent field. Amorphous germanium could offer a low-cost fabrication route; our work compares methods to deposit amorphous germanium films via RF sputtering, e-beam evaporation and plasma-enhanced chemical vapour deposition (PECVD). In addition to standard germanium waveguides produced by etching a germanium film, an alternative manufacturing method is proposed, where silicon is etched to form pedestals, followed by deposition of amorphous germanium to produce waveguides. Pedestal waveguides offer potential for single-mode operation across a broad wavelength range, making them a strong candidate for spectroscopy applications.