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Linear Optical Properties of Semiconductors
Published in Inamuddin, Mohd Imran Ahamed, Rajender Boddula, Tariq Altalhi, Optical Properties and Applications of Semiconductors, 2023
Muhammad Rizwan, Asma Ayub, Bakhtawer Razaq, Aleena Shoukat, Iqra Ilyas, Ambreen Usman
Bandgaps are typically divided into two groups on the basis of momentum distribution. If the momentum of the material is the same in the maxima of VB and in the minima of CB, then it is referred to as the direct bandgap of the material. Otherwise, the material has indirect bandgap if both do not have the same momentum (Rizwan et al. 2021). For those materials that have direct band, a photon that has larger energy than the bandgap is required for the direct transition of electron from the VB to CB. But in other case, those materials that have indirect bandgap, both a photon and a phonon are required for the transition of electron from valence to CB (Gu et al. 2007). Both types of materials have some applications. The materials having direct bandgap are used in light emitting diodes (LEDs), photovoltaics (PVs) and laser diodes and the other materials having indirect bandgap are commonly utilized in PVs and LEDs if these materials have some other advantageous characteristics (Yuan et al. 2018).
Design and Analysis of Transition Metal Dichalcogenide-Based Feedback Transistor
Published in Ashish Raman, Deep Shekhar, Naveen Kumar, Sub-Micron Semiconductor Devices, 2022
Prateek Kumar, Maneesha Gupta, Kunwar Singh, Ashok Kumar Gupta, Naveen Kumar
TMDC materials are found in the form MX2, where M represents transition metals like molybdenum, tungsten, and so forth, and X denotes chalcogens like sulfur, selenium, etc. Most common TMDC materials are molybdenum disulfide (MoS2), tungsten disulfide (WS2), molybdenum ditelluride (MoTe2), molybdenum diselenide (MoSe2), and tungsten diselenide (WSe2). TMDCs are extremely promising for nanoscale devices as a single layer of TMDC materials is only 6.5 Å thick. In TMDC materials, each atom is bound to each other by the van der Waals force. TMDC materials can be fabricated using different techniques, the most common of which are exfoliation, chemical vapor deposition, and molecular beam epitaxy. These materials have a direct bandgap in a few-layered configuration, which make them suitable even for optoelectronic applications. In the work “2D Transition Metal Dichalcogenides,” Manzeli et al. thoroughly reviewed TMDC materials and put the limelight on spin orbiting and the behavior of material under high-frequency applications [25]. Although there are transistors designed using TMDC materials, most of them suffer from a poor ION/IOFF ratio because of poor mobility of charge carriers of TMDC materials.
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Published in Zbigniew Galazka, Transparent Semiconducting Oxides, 2020
From the absorption coefficient evaluation, the fundamental bandgap of 2.72 eV was found to be indirect, wherein a direct bandgap has a value of about 3.8 eV. The as-grown crystals (from the melt) show an extensive absorption in the visible spectral region due to the presence of In nanoparticles as the result of the In2O3 decomposition at high temperatures, and high absorption in the NIR region due to free carrier absorption. Annealing the crystals in an oxidizing atmosphere removes the absorption in the visible region and significantly reduces the absorption in the NIR region, making the crystals transparent in the visible region. The absorption edge that originates at about 440 nm becomes very steep. Annealing the transparent crystals in a reducing atmosphere increases the absorption in the NIR region and eventually in the red part of visible spectrum due to enhanced free carrier absorption. At RT the CL spectra show one broad emission peaking at about 630 nm, and at about 620 nm at 10 K under X-ray excitation. It is likely due to self-trapped excitons. Relative static and high-frequency dielectric constants are 8.9 and 4.08, respectively. The refractive index of In2O3 in the visible spectral region 500–800 nm is in the range of 2.122–2.043. Phonon modes of In2O3 have also been explored, but for thin films or nanostructures.
The electronic and optical properties of Cs2 Ti1-xBxI6(B=Sn, Te, Se) with first principle method
Published in Molecular Physics, 2022
Including with structures we got in the last section, then the band structure of the material is studied to describe electrical and optical properties of CsTiBI. The definition of band gap is the energy difference between the highest point of the valence band (VBM) and the lowest point of the conduction band (CBM). Under the influence of external environment, electrons in the valence band can be thermally excited to the conduction band. Then both electrons in the conduction band and holes in the valence band contribute to conductivity. During this transition, momentum and energy must keep conservation. In direct gap semiconductor materials, the bottom of the conduction band overlaps with the top of the valence band in the same momentum wave vector. So the electrons at the VBM can direct stimulate to the conduction band without additional momentum coupling. While in indirect gap materials, electrons need couple with phonon to get extra momentum in the progress of transition, meanwhile part of energy contained by phonons is lost. Therefore, direct bandgap semiconductors are widely applied in the photovoltaic field attribute to their ability of better complete the photoelectric conversion autonomously.
Enhanced visible-light photocatalytic activity and antibacterial behaviour on fluorine and graphene synergistically modified TiO2 nanocomposite for wastewater treatment
Published in Environmental Technology, 2022
Qiwen Jiang, Jialu Liu, Tiantian Qi, Yanhua Liu
The crystal structure of photocatalysts was investigated by X-ray diffractometer (XRD, Bruker D8 ADVANCE, German) consisting X-rays source of Cu Kα radiation λ = 1.5418 Ǻ at 40 kV and 40 mA. The surface morphology of the nanocomposite was observed by field emission scanning electron microscope (FESEM, GeminiSEM 500, Japan) and a high-resolution transmission electron microscopy (HRTEM, JEOL JEM-F200, Japan). The X-ray photoelectron spectroscopy (XPS, Thermo Fisher ESCALAB Xi+, USA, 0.48 eV) equipped with Mg Kα radiation as the excitation source, was used to detect the bond information of the composites. The binding energy values of XPS spectra were calibrated by setting the binding energy of C1s speak at 284.8 eV. Laser Raman spectrometer (Raman, HR Evolution, China) with a 633 nm He–Ne laser was carried out to determine the quality of carbon materials. The specific surface area and pore size distribution were measured by N2 adsorption–desorption at liquid nitrogen temperature in a physical adsorption instrument (BET, ASAP 2020 Plus HD88, China), after out-gassing in vacuo at 120°C for at least 6 h. The absorbance was measured by ultraviolet–visible-near infrared spectrophotometer (UV-VIS-NIR, PE Lambda 950, China) equipped with the integrating sphere. The corresponding bandgap energy was estimated by the Kubelka–Munk function αhν = A(h−Eg)n, where α is the absorption coefficient, A represents the proportionality constant, h is the Planck constant, ν is the frequency of the light, n = 1/2 corresponds to the dipole transition allowed by the direct bandgap semiconductor and Eg is the forbidden band energy [30].