Band Gap Parameters Research Articles

A novel analytical model for scattering limited electron transport in nano-dimensional InAlAs/InGaAs heterostructure for cryogenic applications

This paper models the scattering limited electron transport in a nano-dimensional In0.52Al0.48As/In0.53Ga0.47As/InP heterostructure. An analytical model for temperature dependent sheet carrier concentration and carrier mobility in a two dimensional electron gas, confined in a triangular potential well has been developed. The model accounts for all the major scattering process including ionized impurity scattering and lattice scattering. Quantum mechanical variational technique is employed for studying the intrasubband scattering mechanism in the two dimensional electron gas. Results of various scattering limited structural parameters such as energy band-gap and functional parameters such as sheet carrier concentration, scattering rate and mobility are presented. The model corroborates the dominance of ionized impurity scattering mechanism at low temperatures and that of lattice scattering at high temperatures, both in turn limiting the carrier mobility. Net mobility obtained taking various scattering mechanisms into account has been found in agreement with earlier reported results, thus validating the model.

Band-Gap Nonlinearity in Lead Chalcogenide (PbQ, Q = Te, Se, S) Alloys.

Narrow band-gap lead chalcogenides have been developed for several optical and electronic applications. However, band-gap energies of the ternary and quaternary alloys have received little attention compared with the parent binary phases. Here, we have fabricated single-phase ternary (PbTe)1–x(PbSe)x and quaternary (PbTe)0.9–y(PbSe)0.1(PbS)y and (PbTe)0.65–z(PbSe)0.35(PbS)z alloys and shown that although lattice parameters follow Vegard’s law as a function of composition, the band-gap energies exhibit a substantial bowing effect. The ternary (PbTe)1–x(PbSe)x system features a smaller bowing parameter predominantly due to the difference in electronegativity between Se and Te, whereas the larger bowing parameters in quaternary alloys are generated from a larger crystal lattice mismatch and larger miscibility gap. These findings can lead to further advances in tuning the band-gap and lattice parameters for optical and electronic applications of lead chalcogenides.

On the dual role of halogen in magnesium oxyhalide bismuth borate glasses: Insight through optical absorption

The present research communication deals with some significant outcomes related to the compositional dependence of optical absorption in magnesium oxyhalide bismuth borate glasses. These vitreous materials have been synthesized over very wide composition range of xMgX2·(30–x)MgO·20Bi2O3·50B2O3 (X=Cl, F, Br and x=0, 2, 5, 7, 10mol%) via convenient melt-quench route. The analysis of fundamental absorption edge (from UV–Vis spectroscopy data) has been carried out in order to obtain optical band gap (Eopt) and band tailing parameter (B) corresponding to indirect allowed and forbidden Mott’s transitions. The non-linear compositional variations of Eopt have predicted a dual role (network former and modifier) of halogen ions in the magnesium bismuth borate matrix. Moreover, evaluation of Urbach’s energy has been done and order of its values indicates the presence of phonon-assisted indirect transitions in each synthesized composition.

Structural and luminescence studies of Eu3+: TeO2[sbnd]B2O3[sbnd]AO[sbnd]AF2 (A = Pb, Ba, Zn, Cd, Sr) glasses

Eu3+ doped oxyfluoro boro-tellurite (TBXFE) with molar composition 29 TeO230B2O320AO20AF21Eu2O3 (where A = Pb, Ba, Zn, Cd, Sr) glasses were prepared and investigated by XRD, FTIR, UV–Vis–NIR, luminescence and decay measurements. XRD patterns confirm the glassy nature of the prepared glasses. The influence of metal ions on the structure of boro-tellurite glasses were investigated through FTIR spectra. The intra band (4f-4f) transitions of Eu3+ ions are discussed through UV–Vis–NIR absorption spectra. The covalent nature around the Eu3+ ions with ligands are discussed using the bonding parameter (δ) and nephelauxetic ratio (β). The fundamental absorption edge, direct, indirect band gap, Urbach energy and band tailing parameters are reported. A bright red emission at 616 nm corresponding to the 5D0 → 7F2 transition of Eu3+ ions could be observed in the title glasses. Judd-Ofelt parameters were estimated from the emission spectra of Eu3+ ions. The dependence of these parameters on the composition of the glass is discussed. Judd-Ofelt parameters were used to derive the radiative parameters such as transition probabilities (A, s−1), branching ratios (βR), radiative lifetime (τrad) and stimulated emission cross-section (σPE) for the 5D0 → 7FJ (J = 0, 1, 2, 3 and 4) transitions. The luminescence intensity ratio (LIR) of 5D0 → 7F2/5D0 → 7F1 transitions was estimated to analyze the local site symmetry around the Eu3+ ions in the present glasses. The chromaticity coordinates and colour purity were calculated from the emission spectra and analyzed with Commission International de I'Eclairage (CIE) 1931 diagram. The experimental lifetime of 5D0 level could be fitted to a single exponential indicating the absence of energy transfer between the Eu3+ ions in the present glasses.

Growth of coherent BGaN films using BBr3 gas as a boron source in plasma assisted molecular beam epitaxy

Incorporating boron into gallium nitride to make BxGa1-xN solid solutions would create an avenue for extreme alloys due to the fact that wurtzite phase BN has a larger band gap and smaller lattice parameters compared to GaN. In this paper, the authors report the growth of high crystal quality, random alloy BxGa1-xN thin films with x up to 3.04% grown on (0001) Ga-face GaN on sapphire substrates using plasma assisted molecular beam epitaxy and BBr3 gas as a B source. High resolution x-ray diffraction was used to measure both the c plane spacing and the strain state of the films. It was determined that the films were fully coherent to the GaN substrate. Elastic stress-strain relations and Vegard's law were used to calculate the composition. Atom probe tomography was used to confirm that the BxGa1-xN films were random alloys. In addition to demonstrating a growth technique for high crystal quality BxGa1-xN thin films, this paper demonstrated the use of BBr3 as a novel B source in plasma assisted molecular beam epitaxy.

Erratum to: Fabrication of reduced graphene oxide nanosheets doped PVA composite films for tailoring their opto-mechanical properties

Laminar graphene nanosheets have raised passionate attention due to their incredible physico-chemical properties. Its wide-scale, high-yield production at low-cost has made it possible to produce top class promising versatile polymer nanocomposites. Reduced graphene oxide (RGO) nanosheets were incorporated to prepare optically tunable and high mechanical strength polymer nanocomposite films. RGO-doped poly(vinyl alcohol) (PVA) nanocomposite films were prepared via solution casting. Low level RGO doping significantly altered the structural, optical and mechanical properties of pure PVA films. Most of the band structure parameters like direct/indirect band gap, band tail, refractive index, dielectric constant, optical conductivity and dispersion parameters were investigated in detail for the first time. Tauc’s, Wemple–DiDomenico, Helpin–Tsai and mixture rule models were employed to investigate optical and mechanical parameters. The applied models reinforced the experimental results in the present study. Advanced analytical techniques were engaged to characterize the nanocomposites films.

Graphene oxides nanosheets mediation of poly(vinyl alcohol) films in tuning their structural and opto-mechanical attributes

Herein, we report successful incorporation of graphene oxide (GO) nanosheets into poly(vinyl alcohol) (PVA) matrix by employing solution casting method. The effect of GO loadings on structural, optical and mechanical properties of PVA films was investigated. Most of the optical properties of such films are reported for the first time in the present study. On incorporating GO nanosheets into PVA matrix, the properties of nanocomposites were changed entirely. The tensile strength and Young’s modulus of nanocomposites were enhanced. Alongside, a variation in absorption edge, direct/indirect band gap, Urbach energy, refractive index, optical dielectric constant, optical conductivity and dispersion parameters were noticed. The band gap and dispersion parameters were calculated using Tauc’s and Wemple–DiDomenico models, respectively. Helpin–Tsai and mixture rule models were employed to calculate Young’s modulus. The applied models reinforced the experimental results in the present study. Advanced analytical techniques were employed to characterize the nanocomposites films. The prepared nanocomposites might be used in designing the opto-electronic devices.

DFT+U study of the structures and properties of the actinide dioxides

The actinide oxides play a vital role in the nuclear fuel cycle. For systems where current experimental measurements are difficult, computational techniques provide a means of predicting their behaviour. However, to date no systematic methodology exists in the literature to calculate the properties of the series, due to the lack of experimental data and the computational complexity of the systems. Here, we present a systematic study where, within the DFT+U formulism, we have parametrized the most suitable Coulombic (U) and exchange (J) parameters for different functionals (LDA, PBE, PBE-Sol and AM05) to reproduce the experimental band-gap and lattice parameters for ThO2, UO2, NpO2, PuO2, AmO2 and CmO2. After successfully identifying the most suitable parameters for these actinide dioxides, we have used our model to describe the electronic structures of the different systems and determine the band structures, optical band-gaps and the Bulk moduli. In general, PBE-Sol provides the most accurate reproduction of the experimental properties, where available.We have employed diamagnetic order for ThO2, PuO2 and CmO2, transverse 3k antiferromagnetic order for UO2 and AmO2, and longitudinal 3k antiferromagnetic order for NpO2. The Fm 3¯ m cubic symmetry is preserved for diamagnetic ThO2, PuO2 and CmO2 and longitudinal 3k NpO2. For UO2 and AmO2, the transverse 3k antiferromagnetic state results in Pa3¯ symmetry, in agreement with recent experimental findings. Although the electronic structure of ThO2 cannot be reproduced by DFT or DFT+U, for UO2, PuO2, NpO2, AmO2 and CmO2, the experimental properties are very well represented when U = 3.35 eV, 6.35 eV, 5.00 eV, 7.00 eV and 6.00 eV, respectively, with J = 0.00 eV, 0.00 eV, 0.75 eV, 0.50 eV and 0.00 eV, respectively.

Order–Disorder Phenomena and Their Effects on Bandgap in ZnSnP2

A ternary compound semiconductor ZnSnP2 has the order–disorder transition, where the ordered and disordered phases are chalcopyrite (I42d, a = 5.651 A, c = 2a) and sphalerite (F43m, a = 5.651 A), respectively. In this study, the quantitative relationship between bandgap and long-range order parameter η was investigated by analyzing ZnSnP2 bulk crystals obtained by various cooling rates in crystal growth. The Chipman and Warren method was used to evaluate the long-range order parameters from X-ray difffaction profiles. The results showed that the long-range order parameter η decreases from 0.94 to 0.54 with the increase in cooling rates, and the bandgap gradually reduced from 1.60 to 1.37 eV, corresponding to the η value. It was also demonstrated that bandgap tuning of ZnSnP2 was possible by controlling the long-range order parameter through annealing process. This study clarified the effects of the order–disorder phenomena on bandgap in a model material, ZnSnP2, based on the evaluation of long-range ord...

A simple and distinguished nebulizer approach to prepare CdS thin films

In this paper, we report the substrate temperature induced change in structural, optical, morphological, luminescence and photoelectrochemical properties of CdS films deposited by a simple and facile approach called nebulized spray pyrolysis technique. X-ray diffraction study confirmed the deposited CdS films belong to hexagonal wurtzite structure, with preferential orientation along c-axis, (002) direction perpendicular to the substrate plane. The crack free, uniform, and homogeneously distributed spherical particles are witnessed from AFM image. Various optical parameters like energy band gap, optical conductivity, refractive index, extinction coefficient, dielectric constants, and dispersion energy parameters of the films were evaluated. The strong band edge emission observed in the PL study may be attributed to the recombination of excitations and/or shallowly trapped electron-hole pairs. The first and second overtone of LO modes of CdS at 302 and 600cm−1 are observed in the Raman study. The photoelectrochemical properties of the films were also tested.

Effect of Fe doping on the electronic structure, optical and electrical properties of ZnO compound: Ab initio insights

By means of first-Principe method within TB-mBJ approach and Boltzmann transport equations, the electronic structure, optical and electrical properties of zinc oxide doped with Iron are investigated. Both calculated band gap and lattice parameters of pure ZnO are found to be in reasonable agreement with the experimental measurements. Furthermore, the doping ZnO with Fe leads to the appearance of some deep impurity levels in the band gap arisen from Fe-3d states. Indeed, these deep level donors enhance the infrared and visible-light absorption. Besides, we notice that the electrical conductivity is enhanced while the carrier mobility is decreased after Fe doping.

Effect of energy band gap in graphene on negative refraction through the veselago lens and electron conductance

A remarkable property of intrinsic graphene is that upon doping, electrons and holes travel through the monolayer thick material with constant velocity which does not depend on energy up to about 0.3eV (Dirac fermions), as though the electrons and holes are massless particles and antiparticles which move at the Fermi velocity vF. Consequently, there is Klein tunneling at a p–n junction, in which there is no backscattering at normal incidence of massless Dirac fermions. However, this process yielding perfect transmission at normal incidence is expected to be affected when the group velocity of the charge carriers is energy dependent and there is non-zero effective mass for the target particle. We investigate how away from normal incidence the combined effect of incident electron energy ϵ and band gap parameter Δ can determine whether a p–n junction would allow focusing of an electron beam by behaving like a Veselago lens with negative refractive index. We demonstrate that there is a specific region in ϵ−Δ space where the index of refraction is negative, i.e., where monolayer graphene behaves as a metamaterial. Outside this region, the refractive index may be positive or there may be no refraction at all. We compute the ballistic conductance across a p–n junction as a function of Δ and ϵ and compare our results with those for a single electrostatic potential barrier and multiple barriers.

Modified Sol-Gel Processing of NiCr2O4 Nanoparticles; Structural Analysis and Optical Band Gap

Abstract Nickel Chromite nanoparticles were successfully synthesized via a modified sol-gel method using nickel acetate and ammonium dichromate in melted stearic acid as a complexing agent. The diffractograms of the nanoparticles confirmed a pure formation of NiCr2O4 spinel without any minor phase. The coordination structure of as prepared nanoparticles shows a series of absorption bands below 1,000 cm−1 were evidenced the M-O (Cr-O, Ni-O) bond in the sample. Optical band gap, magnetic properties and color parameters (L*.a*.b*) indicates that the final nanoparticles are optically and magnetically active. The particle size of NiCr2O4 was calculated using Scherrer equation at about 24 nm. Optical band gap obtained at 1.7 eV indicating that NiCr2O4 nanoparticles are semiconductor material and can be used in electrical devices.

Thickness-dependent electrical and optical properties of Ge8Sb2Te11 thin films

ABSTRACTThe amorphous Ge8Sb2Te11thin films with varying thickness are thermally deposited on well-cleaned glass substrate from its polycrystalline bulk. Absence of any sharp peak confirms the amorphous nature of deposited films. Thickness-dependent electrical and optical properties including dc-activation energy, sheet resistivity, optical band gap, band tailing parameter, etc. of Ge8Sb2Te11thin films have been studied. The optical parameters have been calculated from transmission, reflection and absorbance data in the spectral range of 200–1100 nm. It has been found that optical band gap and band tailing parameter decreases with the increase in Ge8Sb2Te11thin films thickness. The dc-activation energy and sheet resistivity decreases while the crystallization temperature of the amorphous Ge8Sb2Te11 films increases with the increase in thickness of the films. The decrease of the sheet resistivity has been substantiated quantitatively using the classical size-effect theory. These results have been explained on the basis of rearrangements of defects and disorders in the amorphous chalcogenide system.

Structural, optical and device characteristics of 1-(2-(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)-2-oxoethyl)pyridinium chloride

1-(2-(1,5-Dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)-2-oxoethyl)pyridinium chloride (DOPC) was chemically synthesized and showed thermal stability up to 220 °C. DOPC powder has polycrystalline structure and crystallizes in triclinic structure with space group, $$ P\bar{1} $$ . Miller indices for each diffraction plan in X-ray diffraction spectra are determined. DOPC films have been prepared via spin-coating technique onto quartz and silicon single crystal substrates. The optical properties of the films are investigated by spectrophotometric measurements of the transmittance and reflectance over the spectral range 200–2500 nm. The absorption coefficient and the refractive index of the films are calculated in which the optical band gap and single oscillator parameters are estimated. Hybrid Au/DOPC/p-Si/Al heterojunction is constructed, and the dark current–voltage characteristics are recorded. The device exhibited rectification behavior and the basic parameters such as ideality factor, barrier height, series resistance and charge carrier mobility are evaluated.

Influence of Ti Doping on the Properties of Ge-Sb-Te Thin Films for Phase Change Memory

The influence of Ti doping on the resistivity, activation energy of conductivity, energy band gap, Urbach energy, crystallization temperature, heat effect and crystallization kinetic parameters in Ge2Sb2Te5 thin films for phase change memory was investigated. It was shown that introduction of Ti influences on the thermal properties, and kinetics of crystallization process. Results of analyzes showed that Ti doping affects crystallization time, and probability of spontaneous crystallization at room temperature, which must be taken into consideration at designing PCM cells with Ti electrodes.

Synthesis, spectral, thermal, optical dispersion and dielectric properties of nanocrystalline dimer complex (PEPyr–diCd) thin films as novel organic semiconductor

Dimer complex PEPyr–diCd (5a) has been prepared by reacting CdCl2⋅2.5H2O with 1,1′-bis(diphenylphosphino)ethyl-6-methyl-3-(pyridin-2-yl)-1,4-dihydro-pyridazine tungsten tetracarbonyl PEPyr (4a) as bipyridine ligand. The structural properties of PEPyr–diCd complex were characterized on the basis of elemental analysis (EA), Fourier transform infrared spectra, fast atom bombardment-mass spectrometry, thermogravimetric/differential thermal analysis, and 1H nuclear magnetic resonance spectroscopy. The crystal is orthorhombic, space group Pbca. Cd(II) metal in PEPyr–diCd organic semiconductor complex coordinated with two N of the PEPyr and three Cl − (one terminal and two bridging). The micro-structural properties of the films were studied via X-ray diffraction, and scanning electron microscopy. The as-deposited films were annealed in air for 1 h at 150, 200, and 250 ∘C. An average transmittance ≥ 70% for PEPyr–diCd complex at higher wavelength ≥ 800 nm was observed. In UV spectrum, the transmittance increases followed by a sharp decrease at wavelength 700–750 nm within visible range. The results of the absorption coefficient were determined to find the binding energy (E B ) of PEPyr–diCd organic semiconductor complex as 0.242 and 0.47 eV, respectively. Refractive index (n) and absorption index (K) of PEPyr–diCd complex were calculated. Moreover, the dispersion parameters such as dispersion energy, oscillator energy, dielectric constant, and dissipation factor were determined. The oxidation of the imino-phosphine derivatives were examined using cyclic voltammetry in methylene chloride solvent. The cyclic voltammogram of PEPyr–diCd (5a) organic semiconductor appears to have two quasi-reversible oxidations at 543 and 441 mV. The obtained results indicate that the PEPyr–diCd organic semiconductor thin film is a good candidate in optoelectronic devices based on its band gap and dispersion parameters.

New dispersion model for band gap tracking

The spectroscopic ellipsometry (SE) is known as the best in-situ non-invasive method suitable for thickness and composition measurements of the Si/oxide gates. However, a composition measurement performed by the SE is indirect and it needs a reference. Moreover, thickness and composition cannot be directly related to the relevant device performance parameters. On the other hand, a dielectric function, another optimized parameter of the SE metrology, has a direct relation to the bandgap parameter which is a major factor determining electrical performance of the Si/oxide gates. In this paper we develop and demonstrate a new optical model suitable for band gap tracking. The optical model developed is based on continuous version of the Cody–Lorentz model. This model can intrinsically define a physically meaningful value of the band gap. We show that developed model can be used for device process monitoring.

Parametrized dielectric functions of amorphous GeSn alloys

We obtained the complex dielectric function of amorphous Ge1−xSnx (0 ≤ x ≤ 0.07) alloys using spectroscopic ellipsometry from 0.4 to 4.5 eV. Amorphous GeSn films were formed by room-temperature implantation of phosphorus into crystalline GeSn alloys grown by molecular beam epitaxy. The optical response of amorphous GeSn alloys is similar to amorphous Ge and can be parametrized using a Kramers-Kronig consistent Cody-Lorentz dispersion model. The parametric model was extended to account for the dielectric functions of amorphous Ge0.75Sn0.25 and Ge0.50Sn0.50 alloys from literature. The compositional dependence of band gap energy Eg and parameters associated with the Lorentzian oscillator have been determined. The behavior of these parameters with varying x can be understood in terms of the alloying effect of Sn on Ge.

Optical and thermal investigations on vanadyl doped zinc lithium borate glasses

Using standard melt-quench technique, transition metal oxide (2 mol% of V2O5) doped glasses having composition xZnO·(30 − x)Li2O·70B2O3 (x = 0, 2, 5, 7 and 10) are prepared. The density (D) is measured using buoyancy and found to be lying between 2.21 and 2.45 g/cm3 with an increasing trend on substituting ZnO contents in place of Li2O. The theoretical optical basicity (Λth) is calculated and found to increase with increasing inclusion of ZnO indicating an increase in the ionic character. The molar refraction (Rm), refractive index (nr) and molar polarizability (αm) are calculated and explained on the basis of structural changes. The optical absorption spectra have been used to evaluate the values of optical band gap (Eopt) and band tailing parameter (B). It is observed that Eopt decreases with the increasing contents of ZnO in base glass matrix. The decrease in Eopt is an evidence of enhancement in the number of non-bridging oxygen atoms (NBOs) thereby increasing the four-coordinated boron atoms. The as-quenched samples in bulk form are subjected to differential thermal analysis (DTA) to assess the glass transition temperature (Tg), which is 476 °C for pure lithium borate glass. The variations suggest that the structure is being modified by the substitution of ZnO.