A Monolithically Integrated HgCdTe Short-Wavelength Infrared Photodetector and Micro-Electro-Mechanical Systems-Based Optical Filter

摘要

A monolithically integrated low-temperature micro-electro-mechanical systems (MEMS) and HgCdTe infrared (IR) detector technology is introduced,implemented,and characterized.The ultimate aim of this project is to develop a MEMS-based optical filter,integrated with an IR detector,that selects narrow wavelength bands within the short-wavelength IR (SWIR) region of the spectrum.The entire fabrication process is compatible with two-dimensional IR focal plane array technology,and needs to be compatible with a proposed electrically tunable MEMS filter based on a Fabry-Perot optical cavity.The fabricated device consists of an HgCdTe SWIR photoconductor,distributed Bragg mirrors formed of Ge-SiO-Ge,a sacrificial spacer layer within the cavity,and a silicon nitride membrane for structural support.Mirror stacks fabricated on silicon,identical to the structures that will form the optical cavity,have been characterized to determine the optimum filter characteristics.The measured full-width at half-maximum (FWHM) was 34 nm at the center wavelength of 1,780 nm with an extinction ratio of 36.6.Fully integrated filters on HgCdTe photoconductors with a center wavelength of approximately 1,950 nm give a FWHM of approximately 100 nm,and a peak responsivity of approximately 8 X 10~4 V/W.The experimental results are in good agreement with the optical model,which takes into account mirror reflectivity,absorption within the cavity by the spacer material,and absorption by the silicon nitride support structure.