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Monolithic integration of photodetector focal plane arrays with micropyramidal arrays in mid-wave infrared

One of the challenges of mid-wave infrared (MWIR) silicon (Si) photonics is related to the low absorption of Si-based photodetector focal plane arrays (FPAs), and therefore the reduced quantum yield. Another challenge is related to the significant thermal noise in uncooled FPAs which spoils the quality of imaging. It is proposed that the technology of Si anisotropic wet etching, capable of fabricating light concentrating arrays, can be used for solving these problems. The proposed designs are based on monolithic integration of Si micropyramids with metal/silicide Schottky barrier photodiodes (SBD). By using finite-difference time-domain (FDTD) modeling, it is shown that the photons can be spatially concentrated and resonantly trapped near the tips of the pyramids, allowing for multiple passes in the silicide layer and thus increasing the likeliness of photon absorption. This potentially leads to multispectral imaging functionality at the resonant frequencies. In addition, these resonances can be excited in a broad range of angles leading to MWIR FPAs with a wide angle-of-view. To demonstrate the proposed concept, micropyramidal arrays with three different geometrical parameters were fabricated and integrated with nickel/silicide (NiSi) SBDs. The choice of Ni was determined by the simplicity of short-wave IR (SWIR) testing at room temperature, but in the future, similar studies can be performed in the MWIR range by using Au or Pt. Preliminary testing results revealed a stronger photoresponse from micropyramids with smaller tops, but further studies are required to compare the performance of such novel photodetector arrays with an extensive range of geometrical parameters.