Optical and compositional properties of amorphous silicon-germanium films by plasma processing for integrated photonics

We report the study of hydrogenated amorphous silicon-germanium (a-Si1-XGeX:H) films prepared by low-frequency plasma-enhanced chemical vapor deposition (LF-PECVD) varying the composition (0 ≤ X ≤ 1). Silicon and germanium content is determined by energy dispersion spectroscopy (EDS). Refractive index, absorption coefficient and optical gap are estimated by transmittance measurements as well as by the use of PUMA software. Absorption coefficients obtained by using this software and by the Beer-Lambert law show good agreement according to absorption region. Results indicate that refractive index exhibits a linear behavior on germanium content for atomic percent (at.%). Employing these films and by the use of the finite-element software COMSOL, a single-mode low-contrast rib optical waveguide operating at the wavelength of 1550 nm is simulated, and later fabricated by using photolithography and plasma etching techniques. Measured optical losses are 7.6 dB/cm.