Effect of Porosity on the Impedance Response of Porous GaAs-Based NO2 Gas Sensors

Nitrogen dioxide (NO2) is a hazardous atmospheric pollutant that requires reliable detection technologies with high sensitivity and clear physical interpretability. In this study, the influence of porosity on the impedance response of porous gallium arsenide (GaAs)-based gas sensors was systematically investigated under NO2 exposure. A series of samples with controlled porosity in the range of 10–70% was fabricated by electrochemical etching and analyzed using impedance spectroscopy in the frequency range of 1–100 kHz. The results show that increasing porosity enhances impedance dispersion and gas sensitivity, particularly in the low-frequency region of 5–10 kHz, where the response to NO2 is most pronounced. The concentration dependence of the impedance magnitude exhibits nonlinear sigmoidal behavior, while the maximum relative sensitivity is observed at an intermediate porosity of approximately 52–53%. This indicates a balance between adsorption capacity and electrical conductivity. These findings show that porosity is a key parameter governing the impedance-based sensing behavior of the porous GaAs and support the use of frequency-domain analysis for studying morphology–response relationships in semiconductor gas sensors.