The mid-infrared wavelength range (3 -30 um, mid-IR) is a spectral range of significant importance. The mid-wave infrared (MWIR, 3 -5 um) transmission window, specifically, is vital for applications such as gas sensing and free-space communication, as well as thermal imaging of mechanical objects (engines, turbines, etc) that have temperatures ~580-970 K. For an infrared detector, efficient operation at high temperatures is typically the primary goal. While Mercury-Cadmium-Telluride (HgCdTe) detectors are the current state-of-art infrared detectors, the type-II superlattices (T2SLs) have shown to be a promising alternative material system. However, the comparatively lower absorption coefficient of the T2SL detectors presents a challenge, due to the trade-off (as a function of the absorber thickness) between large external quantum efficiency and higher collection efficiency/reduced dark current. This limitation can be addressed by incorporating thin detector absorber regions in resonant photonic architectures. One such architecture is the guided-mode resonance structure, comprising a high-refractive index grating layer sandwiched between two low-index layers[1]. Incident light diffracts into guided modes in the grating layer, which can then couple out to free space. When the outcoupled light interferes constructively/destructively with reflected/transmitted light, strong and narrow resonant peaks/dips can occur in the reflection/transmission spectra. We design a GMR structure where index-contrast required is achieved with highly doped (n**) which can be modeled with the Drude formalism, allowing for a lattice matched material system with extremely low semiconductor layers, refractive index in the MWIR, which can serve as a waveguide cladding layer. In this work, we build on our previous efforts[2], to demonstrate GMR-enhanced all-epitaxial uncooled (roomtemperature) MWIR nBn InAs/InAsSb T2SL detectors. We have designed, grown, fabricated and characterized GMR detectors showing such enhancement in a T2SL absorber only 250 nm thick. GaSb serves as a high-index grating layer which, together with the nBn detector (serving as a waveguide core), is sandwiched between a low-index n* virtual substrate and air. For grating periods A= 1.6 um and 1.8 um, resonances with enhancement of = 8x & 14 are shown at wavelengths, A= 4.4 um & 4.7 um respectively which is very close to the band-edge of the absorber (=5 um). Typically, due to the steep drop in absorption coefficient close to the band-edge, it is extremely difficult to obtain sufficient external quantum efficiency near the absorber band edge. Thus, detectors must be grown with lower energy cut-off, which will significantly increase dark current and degrade device detectivity. The ability to enhance EQE at the band edge of the absorber T2SL, allows us to use higher energy cut-off absorbers without degrading absorption efficiency. Moreover, the ultra-thin absorber, when compared to a typical MWIR detector, offers a significant reduction in dark current, when compared to traditional MWIR III-V detectors operating in same wavelength range, at similar temperatures. Significant improvement in both the optical and electrical performance of the GMR detectors results in superior specific detectivities. TE-polarized estimated specific detectivity D* = 1.2 x10 0 & 1 x19'0 cmvVHz/W are reported for the A= 1.6 um and 1.8 um devices, respectively. Future work will investigate polarization-independent detectors with substrate-side illumination for potential incorporation into focal-plane array architectures. The authors gratefully acknowledge United States Army under Prime Contract W9O09MY-20-P-0010 and National Science Foundation (ECCS-1926187 and ECCS-2025227). References: 1. S. S. Wang and R. Magnusson, Appl. Opt., vol. 32, no. 14, pp. 2606-2613, May 1993. 2. A. Kamboj, L. Nordin, P. Petluru, A. J. Muhowski, D. N. Woolf, and D. Wasserman, Appl. Phys. Lett., vol. 118, no. 20, p. 201102, 2021.

Guided-Mode Resonance Enhanced Room-Temperature Infrared Detectors

Abstract Body: Topological photonic or plasmonic systems have recently gained significant interest for their unique optical properties and potential applications in unidirectional waveguides, field enhancement, and lasing from topologically protected states. One of the simpler models available to investigate topological systems is a 1-D diatomic staggered chain of period Δ, the Su-Schrieffer-Heeger (SSH) model where adjacent resonant particles are spaced by βΔ/2 & (2-β)Δ/2, (β/2 ∈ (0,1)). In the commonly studied quasi-static (QS) limit, radiative damping is typically neglected and only the nearest neighbor effects are considered. Such an approach is reasonably accurate when the size of an individual particle is much smaller than either of the inter-particle spacings. However, as we approach experimental sizes, where the particle radii are on the order of the interparticle gap, radiative damping and long-range effects can become too significant to neglect[1]. In this work we investigate sub-wavelength resonators leveraging localized surface phonon resonances (LSPhR), taking into account radiative damping and long-range effects. We design, fabricate and characterize topological phononic chains consisting of aluminum nitride (AlN) pillars on a molybdenum (Mo) ground plane which support edge modes in the long-wave infrared regime. AlN has a negative permittivity in the spectral range bridging AlN longitudinal optical (LO) and transverse optical (TO) phonon energies (AlN Reststrahlen band). In this spectral range, AlN can support propagating and/or localized surface phonon modes at the interface between AlN and a dielectric medium. In the QS approach, an infinite staggered chain of particles is assumed, with periodic boundary conditions. Using the nearest neighbor model, one solves the 2×2 Bloch Hamiltonian matrix to obtain the dispersion relation for the chain. The edge mode, however, cannot be observed for such a case (infinite chain assumption). In order to do so, we must apply an open boundary condition, where each particle has a unique polarization due to its interaction with all the other particles in the chain, including those at the end of the chain. Therefore, for an N-particles chain, we obtain an N×N matrix. The solution for this system gives the dispersion relation, or the allowed frequencies of the finite chain for a given Δ, r & β. One observes that set of allowed frequencies, and the phononic band gap, are the same for β & (2 – β), however, presence of the edge modes is only observed (in the band gap) for β >1. The fabricated sample consists of 1.2μm thick AlN over 200nm of Mo on a silicon substrate. The topological chain of AlN pillars of radius, r = 1.5μm, Δ = 20μm is etched using a standard photo-lithography & ICP RIE process. Similarly, an isolated 3μm wide strip of Mo is etched under the AlN pillars on the edge of the sample, to be used for thermal excitation of the topological chain. The reflectance spectrum of the pillars is measured using a Bruker V80v Fourier transform infrared (FTIR) spectrometer. The collected spectra are compared to RCWA-simulated reflection spectra, as well as reflection from a bulk AlN sample. While the bulk sample shows the absorption feature at λ ≈ 11.2μm corresponding to the AlN Berreman mode[2], the pillar spectra show coupling to LSPhR modes at λ ≈ 12.1μm, in excellent agreement with the plasma frequency calculated for the pillars and our numerical simulations. Future work will look to collect the edge mode emission from one end of chain by thermal excitation of the chain's opposite end. Authors AK and DW gratefully acknowledge Air Force award #FA8075-18-D-0002 via Macauley-Brown Inc subcontract. Authors MSA and JWA are thankful for the funding support through AFOSR Lab Task 20RWCOR090 and the AFRL Munition Directorate’s Chief Scientist Office. 1. S. R. Pocock et al. ...V. Giannini, ACS Photonics, 5(6):2271–2279, 2018. 2. L. Nordin et al. ... D. Wasserman.Applied Physics Letters, 111(9):091105, 2017.

Long-Wave Infrared Topological Phonon Chain

R: Detectors and Narrow Bandgap Materials

technical paper

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(EMC) C: Plasmonics, Strong-Coupling and Resonant Optical Structures

The Electronic Materials Conference (EMC) is the premier annual forum on the preparation, characterization and use of electronic materials. This year’s event will feature a plenary session, topical sessions, a poster session and more.

EMC is coordinated with the Device Research Conference (DRC), which will be held during the same week, from June 20-23. This recognizes the strong interaction between device and electronic materials research and provides fruitful exchange of information between attendees of both Conferences.

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Abhilasha Kamboj

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Guided-Mode Resonance Enhanced Room-Temperature Infrared Detectors

Long-Wave Infrared Topological Phonon Chain

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