Significant miniaturization of high-Q supercavity systems with planar technology requires novel coupling structures that excite the desired set of resonant modes. We review the physics of bound states in the continuum (BICs) of open, high-index dielectric resonators, excited by new complex sources that enable a controlled interference in the system. We show that, in avoided-crossing regimes associated with quasi-BICs, the controlled retardation of inducing currents can bring up the Q-factors beyond the state-of-the-art levels in optimized, fully-symmetric systems. We illustrate our theory with proof-of-concept experiments in microwaves, comparing high-index dielectric resonators excited by microstrip structures with different mode complexity.
Zinc manganese oxide (ZnMnO) grown by metal-organic chemical vapor deposition (MOCVD) and atomic layer deposition (ALD) exhibit absorption band edge tunability with Mn incorporation. ZnMnO with good crystal quality oriented in the (002) direction was grown using MOCVD. ALD-grown ZnMnO was amorphous but exhibited high crystallinity after annealing at 800 °C for 1 hour. ZnMnO using both growth techniques showed an overall reduction in band edge with Mn incorporation, but the trend was scattered. The band edge reduction is influenced by energy states and oxidation states of Mn incorporated in ZnMnO rather than the cumulative Mn incorporation. Incorporation of Mn with oxidation states favorable to achieve bandgap tunability could be controlled with growth techniques and growth conditions. Control over energy states introduced by Mn in ZnMnO could enable application of ZnMnO for various areas of interest including spintronics, photovoltaics, photodiodes, and sensing.
Nickel-doped zinc oxide (ZnNiO) was grown on sapphire by metal organic chemical vapor deposition (MOCVD) with varying Ni content under two growth conditions of 400°C/100 Torr and 450°C/30 Torr. Elemental composition indicated that Ni could occupy Zn and O/interstitial sites in ZnNiO. Ni-doping in ZnO resulted in shifts in X-ray diffraction (002) peak, and introduced a (111) phase. Absorption spectrum showed a reduction in near band edge with Ni content in both the samples’ sets. Samples grown at 400°C/100 Torr had a band gap reduction from 3.276 eV to 3.269 eV, while those synthesized at 450°C/30 Torr showed reduction from 3.287 eV to 3.260 eV. The bandgap reduction rate was influenced by growth conditions, and sites activated for Ni incorporation during the growth. Nickel could introduce shallow energy states near the valence band in ZnNiO, and result in a reduction in the bandgap. A potential for bandgap tunability, and controllable introduction of energy states in zinc oxide with transition metal doping by MOCVD, could widen the application range of zinc oxide-based materials for energy harvesting and electronics.
Optical antennas are known as components that enhance interaction between energy of guided modes of optical waveguides and optical free space modes to grow the efficiency of optoelectronic devices. In optical wireless communications, radiation specifications such as efficiency and directivity, and impedance matching are crucial parameters of optical antennas. In addition, compatibility between optical antennas and waveguides that feed them is significant consideration. In some works, optical antennas are designed to transfer energy to/from plasmonic waveguides based on leaky wave concept. In some investigations, hybrid plasmonic leaky-wave optical antennas were designed and optimized to radiate efficiently in conventional plasmonic hybrid structures (a material with low refractive index (SiO2) is located between a metal, and another material with higher refractive index (Si)). For further improvement, by perturbing conventional structures and adding an extra layer such as silicon carbide (SiC) or nickel silicide (NiSi2) between SiO2 and Si, controlling radiation confinements were improved. In this work, a novel structure of hybrid plasmonic leaky-wave optical antenna is proposed that has improvement in impedance matching and directivity between 192 and 197 THz compare with previous works. Here, Electron Beam Lithography (EBL) nanopatterning procedure is suggested for fabrication process to achieve multicomponent-multilayer hybrid plasmonic leaky-wave optical antenna.
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