Resonant cavity infrared detectors for scalable gas sensing

For some applications, resonant cavity infrared detectors (RCIDs) offer advantages over traditional broadband photodetectors. The addition of a resonant cavity allows for higher external quantum efficiency (EQE), faster response time, and narrower spectral response for enhanced selectivity. Recently, the US Naval Research Laboratory demonstrated RCIDs with EQE of 34% and D^∗ of 7 × 10⁹ at room temperature, centered at 4.0 µm (46 nm FWHM). Princeton University has demonstrated that these RCIDs can detect gas-phase nitrous oxide (N₂O) at room temperature with only a broadband light source and no other optical components. The results imply that a simple RCID-LED pair manufactured on a semiconductor wafer would provide a viable gas sensor. The manufacturing process could be completely automated, resulting in mass-producible optical gas sensors. Progress has been made for developing RCIDs at other wavelengths. Based on the achieved detection limit of 4% N₂O at 4.0 µm, with 3 cm path length, leak detection of percentage-level concentrations of gases is definitely viable. The potential for operating at a more optimal wavelength to attain high-precision measurements at part-per-million (ppm) levels is still under investigation.