Design and Optimization of an Al Doped ZnO in Si-Slot for Gas Sensing

A Silicon waveguide incorporating a vertical slot filled with Al+3doped ZnO is proposed for gas sensing. The effect of different device parameters, namely, slot-height, slot-width, and Si-width on two key optical features related to sensing, that is, difference in effective index and differential modal loss, before and after the exposure to gas are investigated using a fully-vectoral finite element method. The optimized sensor with a slot height of 400 nm, slot width of 100 nm and Si width of 65 nm yields the effective index difference of ~0.285 and differential loss ~4.35 dB/μm, indicating a viable device for gas sensing applications. Detailed numerical analyses also reveal that, at some structural parameters, two anticrossing modes appear which can significantly alter the device performances and, thus, should be avoided.