Resonant Cavity–Enhanced Photodiodes for Spectroscopy of C-H Bonds

Resonant cavity-enhanced photodiodes targeted within the spectral region of absorption by C-H bonds are demonstrated. The 3.0 – 3.3 μm 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 <40 nm . 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 ≈3.3 μm, closely tuned to an absorption peak of methane to allow precise sensing of this gas. At 300 K a quantum efficiency of 52% is achieved, with a specific detectivity of 2.5×1010 cm√Hz/푊. The InAsSb-based device is sensitive at ≈3.7 μm, 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.