Integrated infrared sensor platform

Abstract

Infrared spectrum, especially mid-infrared range (2.512tm) covers the absorption peaks of many important chemicals including carbon monoxide, methane and water vapor. By analyzing the absorption spectrum of achemical, one can measure the concentration of the chemicals as well as distinguish the chemical species. The purpose of this work is to build a Si CMOS compatible integrated mid-infrared (MIR) platform for sensing. In this work, we evaluated the three major components (materials and devices) comprising an integrated mid-infrared (MIR) sensing platform: the light source, the waveguide sensor and the detector. To build an integrated MIR light source, we evaluated three approaches. 1) Germanium light source, which is the representative of the CMOS compatible semiconductor light source. By applying tensile strain as well as increasing doping and injection level, Ge is tuned to pseudo-direct or direct bandgap structure and the emission wavelength extends to MIR range. 2) Er-doped GaLaS (GLS) platform which is the representative of the rare earth doped material system. A new laser structure is designed for this system with a threshold power of 7.6 ptW and a slope efficiency of 10.26%. 3) Frequency comb generation which is a new area using nonlinearity to generate new frequencies. Thick Si3N4 material for comb structures are designed, fabricated and tested. In the waveguide sensor section, a waveguide structure based on chalcogenide glass (ChG) is built and tested. The sensing limit for methane reaches 2.5 vol. %. Besides, a ChG based small-footprint plasmonic optical switch is designed to work as an optical router for integrated spectrometer applications with a small (167 nm long) footprint. In the last part, a MIR PbTe based integrated detector has been successfully demonstrated for the first time. A further improvement in the material property and device structure yields a responsivity is about 1.4 A/W in the MIR regime.