A self-biased optoelectronic methane sensor based on Fano resonance in a cryptophane-A-infiltrated GaAs photonic crystal integrated with an InGaAs/InP photodiode

We report the design and multiphysics simulation of a monolithically integrated optoelectronic methane (CH[Formula: see text]) sensor that operates without external electrical bias or spectroscopic instrumentation. The device comprises a methane-selective cryptophane-A-infiltrated GaAs photonic crystal slab, engineered to support a sharp Fano resonance at [Formula: see text] nm, monolithically integrated with an InP/In[Formula: see text]Ga[Formula: see text]As/InP p-i-n photodiode. Methane adsorption reduces the refractive index of the cryptophane-A layer, inducing a blueshift of the Fano resonance that is directly transduced into a photocurrent change in the underlying detector. Simulations predict a sensitivity of [Formula: see text] (A/cm[Formula: see text])/%CH[Formula: see text] with excellent linearity ([Formula: see text]) in self-powered mode, and an ultrafast photoresponse with [Formula: see text] GHz bandwidth-orders of magnitude faster than the methane adsorption kinetics. The InP/InGaAs heterojunction design, employing a wide-bandgap p-InP anode rather than conventional p-InGaAs, suppresses dark current to [Formula: see text] A/cm[Formula: see text] at zero bias while maintaining [Formula: see text] absorption efficiency in the 3 μm intrinsic layer. Fabrication tolerance analysis demonstrates robust performance against [Formula: see text] nm variations in hole radius and [Formula: see text] nm variations in analyte thickness, with sensitivity degradation below [Formula: see text]. Unlike passive ultrahigh-Q resonators that require external spectroscopy, this fully integrated platform combines high optical sensitivity, efficient photocarrier generation, and zero static power consumption in a compact, scalable architecture suitable for distributed environmental monitoring, industrial safety, and IoT applications.