Design and optimization of an Al doped ZnO in Si-slot for gas sensing

A Silicon waveguide incorporating a vertical slot filled with Al+3 doped 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-vectorial 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 anti-crossing modes appear which can significantly alter the device performances and thus should be avoided.