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Item type:Publication, Thermally Tunable Bi-Functional Metasurface Based on InSb for Terahertz Applications(Multidisciplinary Digital Publishing Institute (MDPI), 2025)In this work, we propose and analyze a thermally tunable metasurface based on indium antimonide (InSb), designed to operate in the terahertz (THz) frequency range. The metasurface exhibits dual functionalities: single-band perfect absorption and efficient polarization conversion, enabled by the temperature-dependent permittivity of InSb. At approximately 280 K, InSb transitions into a metallic state, enabling the metasurface to achieve near-unity absorptance (100%) at 0.408 THz under normal incidence, independent of polarization. Conversely, when InSb behaves as a dielectric at 200 K, the metasurface operates as an efficient polarization converter. By exploiting structural anisotropy, it achieves a polarization conversion ratio exceeding 85% over the frequency range from 0.56 to 0.93 THz, while maintaining stable performance for incident angles up to 45°. Parametric analyses show that the resonance frequency and absorption intensity can be effectively tuned by varying the InSb square size and the silica (SiO₂) layer thickness, achieving maximum absorptance at a SiO₂ thickness of 16 μm. The proposed tunable metasurface offers significant potential for applications in THz sensing, imaging, filtering, and wavefront engineering.4 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Revisiting the optoelectronic properties of sputtered aluminium-doped zinc oxide: a study combining advanced optical dispersion models(Institute of Physics, 2025)Aluminium-doped zinc oxide (AZO) thin films with different aluminium (Al) concentrations were grown by RF-magnetron sputtering with substrate active cooling. Sputtering induced sample heating was aimed to be mitigated by the applied cooling, achieving films with electrical resistivities as low as 3.3 × 10 − 3 Ω ⋅ cm , in the as-deposited state. Subsequently, an annealing treatment was performed to enhance the electrical properties and assess the effect of the Al concentration. The absorption coefficient spectra of zinc oxide (ZnO) exhibits an excitonic absorption contribution to the fundamental absorption that is typically not considered in AZO when determining the optical bandgap. Nevertheless, here we show that this free exciton band remains visible in AZO even at Al concentrations greater than 4 at.%. Additionally, the doping-induced defect states increases the width of tail states. These two factors have a substantial effect on the absorption edge, and thus must be considered with adequate models when attempting to determine the optical bandgap. In this work, we use a recently developed Elliot-based optical dispersion model to accurately determine the optical bandgap, exciton binding energy and Urbach energy of AZO thin films. On the other hand, we assess the infrared free carrier absorption, typically modeled by the Drude dispersion formula, by considering a complex frequency-dependent dynamical resistivity and the polar nature of the ZnO lattice. Normally, the real part of the dynamical resistivity follows a power law dependence and the exponent is assumed to be −1.5 for highly-doped semiconductors. Notwithstanding, here we let this exponent as a free fitting parameter to assess the effect of distinct scattering mechanisms present in sputtered AZO thin films and its dependence with the Al doping concentration. We believe these results can be extended to other degenerated semiconductors and are relevant for the understanding and tailoring of their fundamental optoelectronic properties.1 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Description of excitonic absorption using the Sommerfeld enhancement factor and band-fluctuations(Institute of Physics, 2025)One of the challenges of excitonic materials is the accurate determination of the exciton binding energy and bandgap from optical measurements. The difficulty arises from the overlap of the discrete and continuous excitonic absorption at the band edge. Many researches have modeled the shape of the absorption edge of such materials on the seminal formulation proposed by Elliott in 1957 ( Phys. Rev. 108 1384–9) and its several modifications such as non-parabolic bands, magnetic potentials and electron–hole-polaron interactions. However, exciton binding energies obtained from optical absorption often vary strongly depending on the chosen ‘Elliott formula’. Here, we propose an alternative and rather simple approach, which has previously been successful in the determination of the optical bandgap of amorphous, direct and indirect semiconductors, based on the band-fluctuations (BFs) model. In this model, the fluctuations due to disorder, temperature or lattice vibrations give rise to the well known exponential shape of band tail states. The formulation results in an analytic equation for the fundamental absorption with 6 parameters only. To test it, the binding energy and optical bandgap of GaAs and the family of tri-halide perovskites ( MAPbX 3 ), X = Br , I , Cl , over a wide range of temperatures, are obtained by fitting the modified Elliott model. The results for the bandgap, linewidth and exciton binding energy are in good agreement with reports based on non-optical measurements. Moreover, due to the polar nature of perovskites, the retrieved binding energies can be compared with those computed with a model proposed by Kane (1978 Phys. Rev. B 18 6849). In the latter model, the exciton is surrounded by a cloud of virtual phonons interacting via the Frölich interaction. As a consequence, the upper bound for the binding energy of the exciton-polaron system can be estimated. These results are in good agreement with the optical parameters obtained with the proposed Elliott equation including BFs.1 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Significant Luminescence Enhancement of Ga-Doped WS₂ Monolayers Grown by CVD(American Chemical Society, 2025)Monolayer tungsten disulfide (WS₂) is a direct-band-gap semiconductor that has excellent luminescence properties, which are of great interest for optoelectronic applications. In this study, we investigated the effect of gallium (Ga) on WS₂ monolayers grown by chemical vapor deposition. Our results indicate that Ga-doped WS₂ exhibits a 3.6-fold increase in photoluminescence intensity for doped samples compared to pristine WS₂. To confirm the existence of Ga in the WS₂ structures, resonance Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were utilized as characterization methods. A redshift of the XPS spectrum was observed as well as an increase in the disorder-related Raman modes, which were attributed to the influence of Ga. XPS analysis and ab initio electronic structure calculations reveal the presence of substitutional Ga atoms as well as Ga atoms adsorbed on WS₂ surfaces.1 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Triboelectric Nanogenerators Based on Ulvan Biopolymer: Impact of Lithium Sulfate Doping on Electrical Output(John Wiley and Sons, 2025)The increasing demand for sustainable energy solutions has driven extensive research into energy harvesting devices, such as triboelectric nanogenerators (TENGs). Although various additives, including nanowires and salts, have been investigated to enhance the performance of biopolymer-based TENGs, the use of lithium salts in green algae-based TENGs remains unexplored. Herein, a series of TENGs are fabricated using ulvan, a biopolymer derived from the green algae Ulva nematoidea. To improve the output performance of these TENGs, the ulvan matrix is doped with lithium sulfate (Li2SO4) at concentrations of 0%, 10%, 20%, 30%, 40%, and 50% by weight. Dielectric permittivity measurements are conducted to calculate the surface charge density. The results show an increase from 0.94 nC cm−2 for the pristine film to 1.14 nC cm−2 at 30 wt% Li2SO4, beyond which further increases in salt concentration lead to a decrease in charge density. The incorporation of salts significantly enhances the electrical performance, with the 20% Li2SO4/ulvan device achieving a maximum power density of 0.156 W m−2, representing an 85.7% improvement compared to the pristine ulvan TENG. The open-circuit voltage (Voc) and short-circuit current also increase with salt concentration, with Voc reaching 87.71 V at 30% Li2SO4.1