We report the optical and magneto-optical properties of amorphous and crystalline Co60Fe20B20 films with thicknesses in the range of 10 nm to 20 nm characterized using spectroscopy ellipsometry (SE) and magneto-optical Kerr effect (MOKE) spectroscopy. We derived the spectral dependence of the dielectric tensor from experimental data for samples prior and after annealing in vacuum. The features of the dielectric function can be directly related to the transitions between electronic states and the observed changes upon annealing can be ascribed to an increase of the crystalline ordering of CoFeB.
Since their proposal by Esaki, superlattices have been observed to have fascinating features such as quantum size effects, negative differential resistance, and sequential resonant tunneling. However, the technology threshold for fabricating superlattices is high, requiring methods like molecular beam epitaxy (MBE) and atomic layer deposition (ALD), among others, even for amorphous materials. Thus, the desirable features from superlattices have not been extensively utilized. It is shown that superlattices of Se and As2Se3 (superlattice‐Se), fabricated using rotational evaporation, exhibit sequential tunneling, a typical superlattice feature. From current–voltage measurements of the superlattice deposited on n‐type Si, oscillations in the characteristics are observed. Using models of reverse‐biased Schottky barriers, the observations are explained as tunneling in sequence from superlattice minibands. The superlattice‐Se also shows carrier blocking, with a resistivity of the order of 1012 Ω cm in dark conditions at room temperature, despite the low resistivity (≈10 Ω cm) of the n‐type Si substrate. When the Si is illuminated, the device shows higher detectivity for weaker signals compared to higher illumination. The ease of fabrication, and the blocking and amplifying capabilities make superlattice‐Se an interesting “add‐on” structure to improve conventional photodetector materials such as Si or Ge, which have issues with dark currents at room temperature.
be tailored from semimetallic to semiconducting by opening the zero bandgap, e.g., by applying an electric field, [5] chemical doping, [6] and/or strain, [7] offering opportunities for engineering its optical properties. Recently, Wang et al. reported strong and layer-dependent optical transitions of graphene and the tunability of reflectance in mid-infrared (MIR) by back-gating. [8] Polat and Kocabas reported a transmittance modulation of up to 35% in graphene supercapacitors working with ionic electrolytes in the spectral range from 500 to 1200 nm. [9] The manipulation of the dielectric function of graphene in the visible to near-infrared (NIR) region of the electromagnetic spectrum has tremendous application potential in both industrial and fundamental research fields. For instance, graphene is a highly promising material for electro-optical modulators. [10] The application of such materials as antirefractive coatings can improve the performance of optical and optoelectronic devices by selectively eliminating unwanted reflections. [11] On the other hand, substrates with tunable optical properties are highly desirable for the detection of minute amounts of molecules by surface-enhanced Raman spectroscopy (SERS) [12] in disciplines ranging from physics to biomedicine. In this work, we present the influence of field-effect doping on the optical properties of back-gated bilayer graphene in air in a broad spectral range, from NIR to visible. We elucidate that The refractive index and the extinction coefficient are usually inherent (noncontrollable) material characteristics. Recently, it was reported that the reflectivity of graphene in the mid-infrared spectral range can be modified by an external bias. This report attracted much attention, but the controllable frequency/energy range is too narrow for possible applications. In this work, it is demonstrated that the potential of graphene is not limited to mid-infrared wavelengths, but spans a much wider range including the visible spectral range. Here, back-gated bilayer graphene is characterized in air using spectroscopic ellipsometry with a lateral resolution in the micrometer range. By applying a back-gate voltage, the dielectric function can be modified in a broad spectral range, including the visible spectrum. To explain the change in the dielectric function, a simplified phenomenological approach which assumes that the back-gating-induced change in the carrier density of graphene can be described by a modified 2D Drude model is introduced. The trend of increasing values for the dielectric function with increasing sheet charge carrier density is confirmed by theoretical calculations performed in the independent particle picture.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.