On-Chip $\mathbf{G}{{\mathbf{e}}_{1 - {\bm{x}}}}\mathbf{S}{{\mathbf{n}}_{\bm{x}}}$ Slot Optical Waveguides-Based Highly Sensitive Mid-Infrared Biochemical Sensors for Room Temperature Applications

In this work, we present the first proof of complementary metal-oxide-semiconductor-compatible GeSn slot optical waveguides (WGs)-based highly sensitive biochemical sensors for mid-infrared (MIR) applications. Moreover, proposed WGs are designed to achieve high sensitivity values in the MIR region, specifically at 3.67 μm for lipids detection. The simulation indicates that GeSn core height and width affect the confinement factor significantly in both the sensing and slot regions. In an optimized WG geometry (H = W = 300 nm), the proposed cross-slot waveguide (CS-WG) demonstrates the highest confinement factors of 43% and 50% in the slot and sensing regions, respectively, notably higher than the values obtained for the designed vertical-slot-WG and horizontal-slot-WG. Subsequently, the WG sensitivity is determined by taking into account the impact of changes in the thickness of the sensing layer. The results indicate that a biochemical sensor utilizing a cross-slot WG demonstrates the highest sensitivity compared to biochemical sensors based on either horizontal-slot or vertical-slot WGs. Furthermore, the CS-WG MIR sensor we propose demonstrates the sensitivity value of $2.8 \times {{10}^{ - 3}}\ \mathrm{n}{{\mathrm{m}}^{ - 1}}$, which is one order of magnitude higher than the sensitivity value of $4 \times {{10}^{ - 4}}\ \mathrm{n}{{\mathrm{m}}^{ - 1}}$ achieved by the earlier reported Si slot SWIR WG sensor. This comparison highlights the efficacy of our proposed biochemical sensors for MIR sensing applications.