Resonant Cavity–Enhanced Photodiodes for Spectroscopy of CH Bonds

Resonant cavity‐enhanced photodiodes targeted within the spectral region of absorption by CH bonds are demonstrated. The – region of the infrared spectrum contains many substances that are useful to measure spectroscopically. However, the measurement of individual substances requires a high spectral specificity, that is achieved by the resonant cavity photodiodes with spectral response widths of . Two material systems are investigated for detection at this wavelength range—an InAs absorber on an InAs substrate and an InAsSb absorber lattice‐matched to a GaSb substrate. The resonance wavelength of the InAs‐based device responds at , closely tuned to an absorption peak of methane to allow precise sensing of this gas. At a quantum efficiency of is achieved, with a specific detectivity of . The InAsSb‐based device is sensitive at , but the structure could be tuned to the methane absorption peak. Devices could be simply created to target other substances in the C−H absorption region by altering the layer thicknesses in the structure. Both structures can be used for spectrally specific gas sensing in this region of the infrared.