Plasmonics provides great promise for nanophotonic applications. However, the high optical losses inherent in metal-based plasmonic systems have limited progress. Thus, it is critical to identify alternative low-loss materials. One alternative is polar dielectrics that support surface phonon polariton (SPhP) modes, where the confinement of infrared light is aided by optical phonons. Using fabricated 6H-silicon carbide nanopillar antenna arrays, we report on the observation of subdiffraction, localized SPhP resonances. They exhibit a dipolar resonance transverse to the nanopillar axis and a monopolar resonance associated with the longitudinal axis dependent upon the SiC substrate. Both exhibit exceptionally narrow linewidths (7-24 cm(-1)), with quality factors of 40-135, which exceed the theoretical limit of plasmonic systems, with extreme subwavelength confinement of (λ(res)3/V(eff))1/3 = 50-200. Under certain conditions, the modes are Raman-active, enabling their study in the visible spectral range. These observations promise to reinvigorate research in SPhP phenomena and their use for nanophotonic applications.
An MOS transistor fabricated on (001) β-Ga 2 O 3 exfoliated from a commercial (−201) β-Ga 2 O 3 substrate is reported. A maximum drain current of 11.1 mA/mm was measured, and a non-destructive breakdown was reached around 80 V in the off state. Threshold voltage of +2.9 V was extracted at 0.1 V drain bias, and peak transconductance of 0.18 mS/mm was measured at V DS = 1 V, corresponding to a field effect mobility of 0.17 cm 2 /Vs. Hall effect and electron spin resonance data suggested that electron conductivity was due primarily to O vacancy donors (V O + ) with an estimated density of 2. The single-crystal monoclinic (β) phase of Ga 2 O 3 is an advantageous material for high-power, high-temperature electronic device applications due to its high energy gap (4.8-4.9 eV) and high breakdown field (8 MV/cm), yielding a nearly ten-fold higher Baliga figure of merit than that of 4H-SiC (BFOM Ga 2 O 3 = 3444, BFOM 4H-SiC = 300).1 Commercially available β-Ga 2 O 3 substrates enable the epitaxial growth of low defect density epitaxial β-Ga 2 O 3 by a number of methods, including chemical vapor deposition, hydride vapor phase epitaxy (HVPE), and molecular beam epitaxy (MBE), among others.2-6 Schottky barrier diodes (SBDs) based on Ga 2 O 3 have exhibited very low turn on voltage and reverse leakage current, suggesting that unintentionally doped Ga 2 O 3 has extremely low generation/recombination rates and thus a high photoconductive gain.7 Advances in doping control have enabled exceptional early reports of metal-and metal-insulatorgated field effect transistors (MOSFETs). Wong et al. demonstrated a field-plated β-Ga 2 O 3 MOSFET with a breakdown voltage of over 750 V using a Si-implanted channel.8 Most recently, Green and coworkers have reported a Ga 2 O 3 MOSFET with a Sn-doped channel and a 0.6 μm gate-drain spacing to operate at 200 V drain bias, experimentally demonstrating gate-drain fields in excess of 3 MV/cm. 9This excellent progress has positioned Ga 2 O 3 as a viable candidate for next generation material for power applications. However, no demonstration of normally-off operation, a key requirement for fail-safe operation of power switches, has been achieved or proposed to-date.From a practical perspective, development of Ga 2 O 3 transistors has been limited by the availability of device-quality epitaxial films. For this reason, early reports have exploited the relatively large a-plane lattice constant of β-Ga 2 O 3 (1.2 nm) in order to mechanically exfoliate thin films from the (001) plane of a substrate using the scotch tape method to fabricate back-gated devices. 10,11 We employed a similar method to transfer a thin (∼300 nm) Ga 2 O 3 flake onto a SiO 2 /Si substrate, 12 and performed a standard top-side insulated-gate process to fabricate a three-terminal device. We also utilized a high-k HfO 2 gate dielectric process, as only SiO 2 and Al 2 O 3 have been reported to-date. 13,14Experimental A thin sliver of Ga 2 O 3 was cleaved along the (001) face of an on-axis (−201), non-intentionally n-type doped (∼3 ×...
The sensitivity to water vapour of one-, two-, and three-layer epitaxial graphene (1, 2, and 3LG) is examined in this study. It is unambiguously shown that graphene's response to water, as measured by changes in work function and carrier density, is dependent on its thickness, with 1LG being the most sensitive to water adsorption and environmental concentration changes. This is furthermore substantiated by surface adhesion measurements, which bring evidence that 1LG is less hydrophobic than 2LG. Yet, surprisingly, it is found that other contaminants commonly present in ambient air have a greater impact on graphene response than water vapor alone. This study indicates that graphene sensor design and calibration to minimize or discriminate the effect of the ambient, in which it is intended to operate, are necessary to insure the desired sensitivity and reliability of sensors. The present work will aid in developing models for realistic graphene sensors and establishing protocols for molecular sensor design and development.
Optical limiting is desirable or necessary in a variety of applications that employ high-power light sources or sensitive photodetectors. However, the most prevalent methods compromise between on-state transmission and turndown ratio or rely on narrow transmission windows. We demonstrate that a metasurface-based architecture incorporating phase-change materials enables both high and broadband on-state transmission (−4.8 dB) while also providing a large turndown ratio (25.2 dB). Additionally, this design can be extended for broadband multiwavelength limiting due to the high off-resonance transmittance and readily scalable resonant wavelength. Furthermore, our choice of active material allows for protection in ultrafast laser environments due to the speed of the phase transition. These benefits offer a strong alternative to state-of-the-art optical limiters in technologies ranging from sensor protection to protective eyewear.
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