Publications

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Here, we review the progress and most recent advances in phonon-polaritonics, an emerging and growing field that has brought about a range of powerful possibilities for mid- to far-infrared (IR) light. These extraordinary capabilities are enabled by the resonant coupling between the impinging light and the vibrations of the material lattice, known as phonon-polaritons (PhPs). These PhPs yield a characteristic optical response in certain materials, occurring within an IR spectral window known as the reststrahlen band. In particular, these materials transition in the reststrahlen band from a high-refractive-index behavior, to a near-perfect metal behavior, to a plasmonic behavior - typical of metals at optical frequencies. When anisotropic they may also possess unconventional photonic constitutive properties thought of as possible only with metamaterials. The recent surge in two-dimensional (2D) material research has also enabled PhP responses with atomically-thin materials. Such vast and extraordinary photonic responses can be utilized for a plethora of unusual effects for IR light. Examples include sub-diffraction surface wave guiding, artificial magnetism, exotic photonic dispersions, thermal emission enhancement, perfect absorption and enhanced near-field heat transfer. Finally, we discuss the tremendous potential impact of these IR functionalities for the advancement of IR sources and sensors, as well as for thermal management and THz-diagnostic imaging.

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We demonstrate a top-down fabrication strategy for creating a III-nitride hole array photonic crystal (PhC) with embedded quantum wells (QWs). Our photoelectrochemical (PEC) etching technique is highly bandgap selective, permitting the removal of QWs with well-defined indium (In) concentration. Room-temperature micro-photoluminescence (μ-PL) measurements confirm the removal of one multiple quantum well (MQW) while preserving a QW of differing In concentration. Moreover, PhC cavity resonances, wholly unobservable before, are present following PEC etching. Our results indicate an interesting route for creating III-nitride membranes with tailorable emission wavelengths. Our top-down fabrication approach offers exciting opportunities for III-nitride based light emitters.

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We demonstrate a new route toward the integration and deterministic placement of quantum dots (QDs) within prepatterned nanostructures. Using standard electron-beam lithography (EBL) and inductively coupled plasma reactive-ion etching (ICP-RIE), we fabricate arrays of nanowires on a III-nitride platform. Next, we integrate QDs of controlled size within the prepatterned nanowires using a bandgap-selective, wet-etching technique: quantum-size-controlled photoelectrochemical (QSC-PEC) etching. Low-Temperature microphotoluminescence (μ-PL) measurements of individual nanowires reveal sharp spectral signatures, indicative of QD formation. Further, internal quantum efficiency (IQE) measurements reveal a near order of magnitude improvement in emitter efficiency following QSC-PEC etching. Finally, second-order cross-correlation (g(2)(0)) measurements of individual QDs directly confirm nonclassical, antibunching behavior. Our results illustrate an exciting approach toward the top-down integration of nonclassical light sources within nanophotonic platforms.

The goal of this LDRD is to develop a quantum nanophotonics capability that will allow practical control over electron (hole) and photon confinement in more than one dimension. We plan to use quantum dots (QDs) to control electrons, and photonic crystals to control photons. InGaN QDs will be fabricated using quantum size control processes, and methods will be developed to add epitaxial layers for hole injection and surface passivation. We will also explore photonic crystal nanofabrication techniques using both additive and subtractive fabrication processes, which can tailor photonic crystal properties. These two efforts will be combined by incorporating the QDs into photonic crystal surface emitting lasers (PCSELs). Modeling will be performed using finite-different time-domain and gain analysis to optimize QD-PCSEL designs that balance laser performance with the ability to nano-fabricate structures. Finally, we will develop design rules for QD-PCSEL architectures, to understand their performance possibilities and limits.

Topological photonic structures in analogy to their electronic counterparts can provide new functionalities in nanophotonics. In particular, they can possess topologically protected photonic modes that can propagate unidirectionally without scattering and can have an extreme photonic density of states (PDOS). These unique properties can directly impact many photonic systems in optical communications and in quantum information processing applications such as single photon transport. In analogy to spin Hall effect in electronics, photonic systems can exhibit helicity or pseudo-spin dependent light transport. Below we describe such a system in a honeycomb two-dimensional hole-array photonic crystal. Enabling such properties at optical frequencies and on chip-scale will be very important for practical applications of such phenomena.

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