Abstract
Semiconductor nanowire arrays have been demonstrated as promising candidates for nanoscale optoelectronics applications due to their high detectivity as well as tunable photoresponse and bandgap over a wide spectral range. In the infrared (IR), where these attributes are more difficult to obtain, nanowires will play a major role in developing practical devices for detection, imaging and energy harvesting. Due to their geometry and periodic nature, vertical nanowire and nanopillar devices naturally lend themselves to waveguide and photonic crystal mode engineering leading to multifunctional materials and devices. In this paper, we computationally develop theoretical basis to enable better understanding of the fundamental electromagnetics, modes and couplings that govern these structures. Tuning the photonic response of a nanowire array is contingent on manipulating electromagnetic power flow through the lossy nanowires, which requires an intimate knowledge of the photonic crystal modes responsible for the power flow. Prior published work on establishing the fundamental physical modes involved has been based either on the modes of individual nanowires or numerically computed modes of 2D photonic crystals. We show that a unified description of the array key electromagnetic modes and their behavior is obtainable by taking into account modal interactions that are governed by the physics of exceptional points. Such models that describe the underlying physics of the photoresponse of nanowire arrays will facilitate the design and optimization of ensembles with requisite performance. Since nanowire arrays represent photonic crystal slabs, the essence of our results is applicable to arbitrary lossy photonic crystals in any frequency range.
Highlights
Nanowires (NWs) and nanopillars have seen rapid evolution and many improvements in fabrication and materials over the past decade
We can generally divide the modes of a 2D photonic crystal consisting of high refractive index rods into two types based on the primary location of power flow as follows: (i) modes where most of the power flows along the rods/nanowires are referred to as fiber modes, and (ii) modes for which most of the power flows through the embedding medium surrounding the rods are referred to as photonic crystal modes
We emphasize that both types of modes are proper photonic crystal modes regardless of the terminology used
Summary
Nanowires (NWs) and nanopillars have seen rapid evolution and many improvements in fabrication and materials over the past decade. Semiconductor nanowire devices have garnered much interest in the field of optoelectronics, with ternary III-V semiconductor NWs such as GaAsxSb1-x NWs finding promising applications in photodetectors [1,2,3,4], photovoltaics/solar cells [5,6,7] and transistors [1,8] These NWs have different accessible pathways for light absorption and carrier transport and exhibit prominent features, such as reduced reflectance, enhanced absorption efficiency, spectral selectivity and high quantum efficiency for carrier collection. Since light harvesting in single nanowire systems is limited, research has converged on much more capable nanowire arrays, which improve light collection and absorption through a collective response Because of their geometry and periodic nature such structures naturally lend themselves to waveguide and photonic crystal mode engineering, leading to multifunctional materials and devices. We show a path to take advantage of their unique properties by developing the theoretical foundation to design, engineer and optimize multifunctionality in nanowire array detector devices enabling enhanced use in multicolor imaging, single-photon detection, LIDAR, room-temperature IR detection, etc
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