Determination Of Band Gap Research Articles

Influence of Bi substitution on structural, optical and photoluminescence behaviour of Sb2S3 nanoparticles

Pure and doped semiconductor nanoforms are explored extensively due to their unique properties. Here, we synthesized Sb2-x BixS3 (x = 0.0, 0.004, 0.008.) nanoparticles by chemical route using SbCl3, CH3CSNH2 and Bi (NO3)3.5H2O. The purity of Sb2-x BixS3 (x = 0.0, 0.004, 0.008.) nanoparticles is confirmed by energy dispersive analysis of X – Rays (EDAX). From X- Ray diffractrogram, we determined the orthorhombic structure of all samples with Pnma space group and also evaluated lattice parameters. Transmission electron microscope (TEM) images gave the size of nanoparticles ranging from 8 nm to 35 nm. Room temperature UV – VIS, Raman, FTIR and PL spectra led to the determination of band gap, various stretching modes, vibrations mode and emission bands respectively. The detailed results are presented in the paper.

Band gap determination in multi-band-gap CuFeO2 delafossite epitaxial thin film by photoconductivity

The photoconductivity within a wavelength range of 450–1100 nm was determined for a sample of epitaxial delafossite CuFeO2 film grown by pulsed laser deposition. The film thickness was estimated to be 75 nm. The resistance of the films was determined with four-contact van der Pauw’s method and using monochromatic illumination of the film. The most significant change in resistance resulted in three rapid lineal conductivity increases at photon energies of ~ 1.5 eV (gap-1), ~ 2.1 eV (gap-2) and ~ 2.5 eV (gap-3). The conductivity properties are well correlated with prior optical absorption results obtained in the NIR-VIS region using transmittance spectroscopy.

Optical Characterization of III-V Multijunction Solar Cells for Temperature-Independent Band Gap Features

A recently developed method to characterize the band gap energies of III-V optosemiconductors was utilized to determine temperature-invariant band gap features of multijunction solar cells. The method is based on measuring electroluminescent spectra of the solar cells at different temperatures. The normalized spectra reveal temperature-invariant energy values of the different junctions which are further converted to band gap energies. The method utilization requires a calibrated spectroradiometer and a temperature controlled mounting base for the solar cell under test, however, no knowledge about the absolute temperature of the cell under measurement. The method was tested on GaAs and GaInP solar cells that consist of single and dual junctions. The band gap energies were also derived from spectral response measurements. The differences of the determined band gap energies from the literature values were smaller than 1.1%. Compared with other band gap determination methods, the developed method yields temperature-invariant band gap characteristics; with a known uncertainty, that separated the different junctions in a multijunction device without individual biasing for the different junctions. In addition, a temperature-independent characterization parameter ensures that the operating conditions of the device under test do not affect the results.

On the determination of alloy composition using optical spectroscopy in MOVPE grown InGaN layers on Si(111)

Abstract Alloy composition of InxGa1-xN layer is investigated using photoluminescence (PL), and photoluminescence excitation (PLE) techniques. InGaN layers were grown on Si(111) substrates using metal organic vapour phase epitaxy (MOVPE) technique under variable flow of either ammonia (NH3) or trimethyl gallium (TMGa) with corresponding V/III ratios in the range of 3.6 × 103 to 1.2 × 104. We observed that though room temperature PL measurements give an indication about the growth of InGaN, it doesn't help in the estimation of band gap or alloy composition of layer. It is restricted mainly by the presence of multiple peaks in the PL spectra which is rather severe at low temperature. A comparison of PL and reflectivity spectra confirmed that such peaks are attributed to interference oscillations and are not related with multiple compositions of InGaN. Further, in such a scenario PLE is found to be quite effective where the measured PLE spectrum is consisted of a clear onset related to InGaN layer in the sub band gap region of GaN. It is quite helpful in a precise determination of band gap and hence the alloy composition of InGaN layer. The indium composition is estimated to be in the range of 3.5% ≤ x ≤ 20.5%, however its trends with respect to V/III ratio as a function of NH3 or TMGa flow are found to be rather opposite.

Investigation the optical band gap of self-assembled monolayer of tin selenide synthesized by chemical solution deposition

In this study, the fabrication and characterization of the thin layer of SnSe self-assembled were investigated by control of the preparation parameters. SnSe binary nanoparticles semiconductor were prepared using chemical solution deposition technique. The deposition time and temperature and the solution concentration that govern the evolution of the configuration films and optical band gap in chemical deposition processes was explored. We benefited from Rutherford Backscattering Spectrometry with 2 MeV 4He ions to determine the depth profile of the elements in tin selenide. UV–visible spectroscopy was used for energy band gap determination. Also, the nanostructured and the morphologies of the thin films were analyzed by scanning electron microscopy. We were able to achieve a broad optical band gap ranging from 5.82 to 3.06 eV of SnSe thin films appropriate for solar cell and photovoltaic applications.

Homogenization Approach and Bloch-Floquet Theory for Band-Gap Prediction in 2D Locally Resonant Metamaterials

This paper provides a detailed comparison of the two-scale homogenization method and of the Bloch-Floquet theory for the determination of band-gaps in locally resonant metamaterials. A medium composed by a stiff matrix with soft inclusions with 2D periodicity is considered and the equivalent mass density of the homogenized medium is explicitly obtained both for in-plane and out-of-plane wave propagation through two-scale asymptotic expansion. The intervals of frequency where the effective mass is negative identify the band-gaps of the material. The Bloch-Floquet problem is then considered and, through an asymptotic analysis, its is shown that it leads to the same prediction of the band-gaps. The results are confirmed by some examples and the limits of the asymptotic approach are explicitly given and numerically verified.

Large-Scale Benchmark of Exchange-Correlation Functionals for the Determination of Electronic Band Gaps of Solids.

We compile a large data set designed for the efficient benchmarking of exchange–correlation functionals for the calculation of electronic band gaps. The data set comprises information on the experimental structure and band gap of 472 nonmagnetic materials and includes a diverse group of covalent-, ionic-, and van der Waals-bonded solids. We used it to benchmark 12 functionals, ranging from standard local and semilocal functionals, passing through meta-generalized-gradient approximations, and several hybrids. We included both general purpose functionals, like the Perdew–Burke–Ernzerhof approximation, and functionals specifically crafted for the determination of band gaps. The comparison of experimental and theoretical band gaps shows that the modified Becke–Johnson is at the moment the best available density functional, closely followed by the Heyd–Scuseria–Ernzerhof screened hybrid from 2006 and the high-local-exchange generalized-gradient approximation.

Exciton Binding Energy of Two-Dimensional Highly Luminescent Colloidal Nanostructures Determined from Combined Optical and Photoacoustic Spectroscopies.

Reduced dimensionality of structures such as 0D quantum dots, 1D nanorods, and 2D nanoplatelets is predicted to favor the creation of tightly bound excitons stable at room temperature, making experimental determination of the exciton binding energy ( R x) crucial for evaluating the performance of semiconductor nanoparticles. We propose a fully optical approach for R x determination based on a complementary combination of photoacoustic and transmission spectra, using 5.5, 4.5, and 3.5 ML CdSe nanoplatelets as a benchmark system. The absence of excitonic features in photoacoustic spectra allows for probing the band-to-band transition, leading to the band gap determination. Such an unusual effect is explained by efficient re-emission of the absorbed radiation typical for high quantum yield structures, keeping the crystal lattice from excess phonon generation. The determined exciton binding energy for CdSe nanoplatelets ranges from 130 to 230 meV, confirming the presence of robust excitons in highly confined 2D systems.

Bandgap and Electronic Structure Determination of Oxygen-Containing Ammonothermal InN: Experiment and Theory

The electronic structure and band gap of InN synthesized by the ammonothermal method are studied by synchrotron-based soft X-ray absorption spectroscopy (XAS), emission spectroscopy (XES), X-ray ex...

Optical, Dielectric and Ferroelectric Characteristics of Gel Grown Erbium Tartrate Hexahydrate Crystals

With an aim of finding a material suitable for microelectronic applications, experiments were performed to grow erbium tartrate crystals by gel encapsulation. The crystals grow with very well-developed and remarkably flat habit faces as revealed by micro-structural studies, using optical and scanning electron microscopy. The study reveals that the most prominent faces include {001}, {100} and {010}. The crystallographic data analysis of x-ray diffraction results, supplemented by trial-and-error software, shows that the compound crystallizes in a tetragonal crystal system with non-centrosymmetric space group. The high resolution x-ray diffraction results indicating the perfection of the grown crystals are presented. Results of ultraviolet–visible near infra-red (UV–Vis–NIR) spectra leading to determination of energy band gap of 5. 56 eV are described and discussed. The refractive index of the grown material comes out to be 1.40. Comparative analysis of dielectric characteristics of the grown material is made, both for the single crystal and powder form. The material is shown to be ferroelectric with low value of dielectric constant. Behaviour of dielectric constant, dielectric loss and alternating current (ac) conductivity on frequency of the applied ac field at different temperatures is described and discussed. The results are correlated with those of optical and high resolution x-ray diffraction. The material characteristics as revealed by the study suggest that the compound has the basic qualities of a promising material for microelectronic device applications.

Development of a particle swarm optimization based support vector regression model for titanium dioxide band gap characterization

Energy band gap of titanium dioxide (TiO2) semiconductor plays significant roles in many practical applications of the semiconductor and determines its appropriateness in technological and industrial applications such as UV absorption, pigment, photo-catalysis, pollution control systems and solar cells among others. Substitution of impurities into crystal lattice structure is the most commonly used method of tuning the band gap of TiO2 for specific application and eventually leads to lattice distortion. This work utilizes the distortion in the lattice structure to estimate the band gap of doped TiO2, for the first time, through hybridization of a particle swarm optimization algorithm (PSO) with a support vector regression (SVR) algorithm for developing a PSO-SVR model. The precision and accuracy of the developed PSO-SVR model was further justified by applying the model for estimating the effect of cobalt-sulfur co-doping, nickel-iodine co-doping, tungsten and indium doping on the band gap of TiO2 and excellent agreement with the experimentally reported values was achieved. Practical implementation of the proposed PSO-SVR model would further widen the applications of the semiconductor and reduce the experimental stress involved in band gap determination of TiO2.

Superior photocatalytic activity of tungsten disulfide nanostructures: role of morphology and defects

Tungsten disulphide (WS2) nanostructures, WS2 nanosheets (WNS) and WS2 nanorods (WNR), were synthesized by varying the surfactant, N-cetyl-N, N,N-trimethyl ammonium bromide (CTAB), concentration using facile hydrothermal technique. Samples were characterized by high-resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM) for morphology, X-ray diffraction (XRD) to confirm their phase and crystal structure, photoluminescence (PL) and Raman studies for the determination of defect density, Tauc plot for the determination of band gap, Fourier transform infra red (FTIR) spectroscopy for functional groups and bonds, and Brunauer–Emmett–Teller (BET) isotherms for the determination of pore size and surface area. A comparative study using WS2 nanostructures (WNS and WNR) was conducted to observe the photocatalytic degradation efficiency (ƞ) and degradation kinetics on methylene blue (MB) and 4-chlorophenol (4-CP). The superior photocatalytic performance of WNS over WNR is attributed to enhanced pore size and reduced defect density. High-performance liquid chromatography was carried out for the determination of intermediate products during photocatalytic degradation.

Synthesis and optical band gap determination of CuO nanoparticles from salen-based infinite coordination polymer nanospheres

A symmetric bi-carboxylic acid functionalized salen-type ligand was used as organic linker to prepare a Cu-based infinite coordination polymer. The analytical data demonstrated that the proposed structure contains one bi-carboxylic acid salen type ligand and two copper cations in each monomeric unit. One of the Cu2+ cations is coordinated by N2O2 site of salen ligand and the other one acts as node to connect metal-organic linkers to each other. The reasonable formation mechanism for coordination polymer formation proposed which shows the formation of nanoparticles from intertwined oligomer chains. The prepared coordination polymer was used as a good precursor to synthesis copper oxide nanoparticles with larger band gap relative to bulk CuO.

Fragmented lignin-assisted synthesis of a hierarchical ZnO nanostructure for ammonia gas sensing.

In the present study, we demonstrated the use of fragmented lignin in the synthesis of a hierarchical-type structure of ZnO nanorods. Lignin was isolated from bagasse by the microwave assisted method and its fragmentation was achieved in alkaline conditions along with hydrogen peroxide. Lignin and fragmented lignin were purified by crystallisation followed by column chromatography and characterized by UV-visible spectroscopy, Frontier infra-red spectroscopy (FTIR), 1H-NMR and high resolution mass spectroscopy (HRMS). Fragmented lignin was utilized as a template for the synthesis of ZnO nanorods, which were characterized by powder XRD, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-DRS for the determination of crystal structure, particle morphology and band gap. XRD of the ZnO samples revealed a hexagonal wurtzite structure. The morphology of ZnO without fragmented lignin showed agglomerated nanoparticles and with fragmented lignin, a self-assembled hierarchical nanostructure due to nanorods of 30 nm diameter and 200–500 nm length was observed. The fragmented lignin showed a pronounced effect on the particle size and morphology of ZnO nanoparticles. We measured the response of the hierarchical ZnO nanostructure (50 ppm) for sensing NH3 in terms of change in voltage across known resistance. We observed the response and recovery upon introduction of the analyte ammonia gas at 175 °C.

Temperature Dependent Spectroscopic Properties of Cu+ and Dy3+ Co-Doped Phosphate Glass: Band Gap Analysis and Cu Nanocluster-Enhanced Dy3+ Luminescence.

This paper reports on the effects of temperature on light absorption and emission in Cu+ and Dy3+ co-doped phosphate glass, which is of interest for photonic applications. First, the temperature dependence of the absorption edge of the glass in connection with Cu+ ions absorption was assessed. A thermally-induced red shift attributed to Cu+ ion-lattice interactions was observed and analyzed through optical band gap determinations in the context of indirect-allowed transitions. Application of the Varshni model for the dependence of the energy gaps with temperature allowed to estimate the 0 K energy gap at 2.87 (±0.01) eV. Furthermore, Dy3+ photoluminescence (PL) along with Cu nanoparticles (NPs) absorption was monitored in real-time during an isothermal treatment by the in situ concurrent PL and absorption microspectroscopy technique. Periods of enhancement and quenching of Dy3+ emission linked to bidirectional energy transfer processes involving non-plasmonic Cu clusters and plasmonic Cu NPs were revealed. The formation of Cu NPs was promoted by tin(II) used as reductant. It is the first time to the author's knowledge that the 0 K energy gap is estimated for a highly Cu+ -doped glass and that the enhancement of Dy3+ PL by Cu clusters is exposed.

Synthesis and crystal structure of a CdII-based 2D coordination polymer and determination of band gap

Synthesis and crystal structure of a CdII-based 2D coordination polymer and determination of band gap

In situ Bandgap Determination of the GaAsN Nanolayer Prepared by Low-Energy $${\text{N}}_{2}^{ + }$$ Ion Implantation

An approach to solving the problem of the in situ bandgap determination in the extremely thin and chemically active nitride nanolayers fabricated in high vacuum on the n-GaAs surface has been suggested. The approach is based on measuring the interband transitions involving the quantum well states by the method of electron energy loss spectroscopy. The bandgap of the nitride layer formed on the GaAs surface by low-energy $${\text{N}}_{2}^{ + }$$ ion implantation was determined to be 0.2 eV less than that of GaAs, which evidenced for creation of the GaAsN dilute alloy on the GaAs surface.

Precise determination of electron-affinity and band gap via optical response and optical spectra

In order to obtain both the band gap and affinity of semiconductor by photoelectric effect and optical spectra, Lee A. DuBridge`s formula which describes the mathematical relationship between photocurrent and photon energy in metal is extended in semiconductor. Thus cut-off energy of photon can be figured out via this formula, at the same time, the affinity of semiconductor can be determined from the difference between cut-off energy and band gap detected by optical spectra in semiconductor. The results of application on five semiconductors prove that the method proposed in this paper is credible, the good agreements between experimental light energy-photoelectric yield curves and theoretical curves demonstrate that the classic Lee A. DuBridge`s theory of surface photoemission does an excellent job of fitting the photo absorption profile shapes of semiconductor as an earlier application on metals, these results suggest that the Lee A. DuBridge`s formalism, which is straightforward and physical, may be of significant utility in semiconductor spectroscopy. It is hoped also that the results will encourage a comprehensive theoretical analysis of the applicability of semiconductor. Beside, how the band gap of Cr3+ doped n-type TiO2 is controlled by composition of Ti is express with mathematical way.

Gallium clustering and structural effects of hydrogenation in InGaN/GaN nanostructures

We addressed the issue of atomic ordering in a series of In-rich InxGa1−xN epilayers grown on a GaN/AlN/sapphire(0001) epitaxial template by quantitatively measuring the Ga-cation coordination in the second atomic shell of Ga. We used Diffraction Anomalous Fine Structure Spectroscopy (DAFS) at the Ga K-edge to select the signal coming from the Ga atoms in the epilayer and eliminate any contribution from the buffer layer. DAFS measurements were also performed on hydrogenated epilayers in order to investigate the possible formation of Ga-H complexes. We find that deviation from cation random distribution in the form of Ga clustering is present in both untreated and hydrogenated samples and that in the latter ones the second atomic shell around Ga is modified, suggesting an additional perturbation of the cation sublattice related to hydrogen. However, comparing the present results with In K-edge x-ray absorption spectra previously reported, we conclude that the formation of Ga-H complexes vs. In-H ones is unlikely. Cation clustering has to be anyway taken into account as a possible channel playing in the determination of the optical bandgap of these technology-oriented semiconductors.

Quantitative Analysis and Band Gap Determination for CIGS Absorber Layers Using Surface Techniques.

Recently, Cu(InXGa(1−X))Se2 (CIGS) absorber layers have been extensively studied by many research groups for thin-film solar cell technology. CIGS material is particularly promising due to its exceptionally high absorption coefficient and large band gap range, which is adjustable as a function of alloy stoichiometry. To enhance the conversion performance of CIGS solar cells, understanding the CIGS structure and composition is a crucial challenge. We conducted a quantitative study to determine the bulk composition of the major elements such as Cu, In, Ga, and Se of four different CIGS photovoltaic cells. The compositional information was obtained by X-ray fluorescence (XRF), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and femtosecond laser ablation inductively coupled plasma mass spectrometry (fs-LA-ICP-MS). Then, the XRF concentration ratio was compared with the intensity ratio of fs-LA-ICP-MS to investigate the potential of accurate and rapid analysis using the fs-LA-ICP-MS technique. In contrast to the bulk information, the surface techniques can supply detailed information about the chemical composition across the depth profile. Here, elemental depth distributions of CIGS thin films were investigated using magnetic sector secondary ion mass spectrometry (SIMS) and Auger electron spectroscopy (AES). The atomic distributions of four different CIGS absorber layers exhibited a good agreement although they were obtained using two different surface instruments, AES and SIMS. Comparative analysis results of different CIGS absorber layers using SIMS, AES, and fs-LA-ICP-MS provide us with the appropriate technique for the information of accurate composition in a rapid analysis time. Thanks to a simple approach using the Ga/(In + Ga) ratio, the optical band gap energy of the Cu(InXGa(1−X))Se2 quaternary layer was monitored in the entire CIGS layer. The elemental distribution and the band gap determination were then used to elucidate their relationship to the corresponding CIGS cell efficiency result.