High contrast GeTe4 waveguides for mid-infrared biomedical sensing applications

Realization of single-mode waveguides is essential for ultra-sensitive biosensing in the mid-infrared molecular "fingerprint" region for biomedical lab-on-chip applications. High contrast (Delta n approximate to 1) germanium telluride (GeTe4) single mode rib waveguides were fabricated on zinc selenide (ZnSe) substrates for evanescent field based sensing to detect analytes at low concentration. Amorphous GeTe4 thin films were deposited by RF-sputtering and were found to transmit over the spectral range from 2 mu m - 20 mu m. Photolithography followed by reactive ion etching was carried out to etch the film, forming rib waveguide structures with minimum surface roughness and vertical sidewalls. It was found that films deposited at room temperature have average roughness of about 5nm. Optical constants were determined by IR-VASE ellipsometry.