Boosting infrared absorption through surface plasmon resonance enhanced HgCdTe microcavity

As one of the most widely used infrared (IR) detectors, a mercury cadmium telluride (MCT) detector usually requires liquid nitrogen refrigeration to suppress thermally activated noise mechanisms that are inherent to its narrow bandgap, which limits its practical applications. Therefore, it is essential to develop strategies to suppress dark current with reduced cooling demand. In this work, a surface plasmon resonance (SPR) enhanced MCT microcavity was proposed to intensify optical absorption across a broadband while diminishing the thickness of the MCT layer to reduce intrinsic dark current proportional to the volume of the absorber. The microcavity is formed by sandwiching the MCT layer between a top well-designed hybrid golden-cross antenna array and a bottom golden reflector. The microcavity is employed to trap the incident light to amplify the absorption, and the golden-cross antenna array is introduced to not only significantly enhance the incident light field through the SPR effect but also to broaden the microcavity resonant mode. Numerical calculation indicated that an absorptance exceeding 95.3% can be attained at 3.4 mu m with the full width at half maxima (FWHM) extending beyond 1.38 mu m, which almost covers the absorption band of MCT in mid-wavelength IR (MWIR), all while the MCT layer is only 530 nm. Moreover, the prototype device unit was fabricated and tested. Measured peak absorption reached 98.7% @ 3.6 mu m and FWHM was as broad as 1.12 mu m. These results demonstrate that the high and wideband absorption in an ultrathin MCT layer is achieved based on the synergistic effects of SPR and microcavity resonance.