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This work reports on the prospect of using photonic crystal resonances to improve the performance of Leonardo DRS's Hg1−xCdxTe high-density vertically integrated photodiodes. Close examination of Leonardo DRS's unique photodiode architecture reveals that it is a photonic crystal by its very construction. As a result, by carefully tailoring the lattice parameters, it is possible to take advantage of guided-mode resonances to improve the performance in very thin film arrays. Of particular emphasis in this work is using such resonances to bolster the performance in thin-film arrays with a material cutoff in the longwave infrared. We begin the paper by describing guided-mode resonances and the benefits they afford. We continue by modeling both simplified and realistic high-density vertically integrated photodiodes using the finite-difference time-domain method. We present one structure with a longwave infrared material cutoff that, due to the presence of a guided-mode resonance, leads to near-perfect transmission into the Hg1−xCdxTe, even in the absence of an anti-reflective coating. Additionally, this same structure absorbs nearly 88% of the incident light even though the Hg1−xCdxTe material is only 1.0 µm thick. Following this theoretical study, we fabricated test structures and performed Fourier-transform infrared spectroscopy measurements. The measurements clearly revealed the presence of guided-mode resonances. Moreover, the measurements agree well with our modeling. Further modeling of the same structures suggests nearly 89% of the incident longwave infrared light can theoretically be absorbed near the presence of the guided-mode resonance. Being able to achieve similar quantum efficiencies in thinner longwave infrared materials would be a significant achievement, as the dark current should roughly decrease proportional to the volume of the absorber. Moreover, reducing our longwave infrared material thickness from nearly 6.0 µm to 1.0 µm has the added benefits of increasing material throughput and decreasing chamber downtime for material grown using molecular beam epitaxy. [ABSTRACT FROM AUTHOR]

The dependence of quantum efficiency (QE) on fill factor and pixel pitch is studied theoretically and experimentally in fully delineated type-II superlattice (T2SL) detectors. Theoretically, a 2-dimensional simulation model is used to compute the absorption in the array geometry, which shows an insensitivity of the optical response to the fill factor. This is a result of the photodiode array (PDA) geometry concentrating the light in the pixel area. QE measurements on PDAs with varying pixel pitch (from 225 to 10 μm) and fill factors (from 98% to 64%) confirm this independence of the QE on the fill factor and results in a 50% increase in the photocurrent density in 10 μm pitch PDAs compared to 225 μm pitch PDAs. Furthermore, measurements of the dark current density vs pixel size revealed an absence of surface leakage in these PDAs, which, combined with the increased photocurrent density results in an improved signal-to-noise ratio when reducing the pitch in these T2SL detectors. Finally, this result resolves the QE-modulation transfer function trade-off, as the electrical isolation of the pixel is carried out without impacting the QE of the array. [ABSTRACT FROM AUTHOR]