Improving HDVIP Performance Using Photonic Crystal Resonances.

This work reports on the prospect of using photonic crystal resonances to improve the performance of Leonardo DRS's Hg_1−xCd_xTe 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 Hg_1−xCd_xTe, even in the absence of an anti-reflective coating. Additionally, this same structure absorbs nearly 88% of the incident light even though the Hg_1−xCd_xTe 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]