Function Of Photon Energy Research Articles

Gamma radiation shielding studies on highly dense barium bismuth borate glasses

AbstractTransparent dense barium bismuth borate (BBB) glasses in ternary x(BaO–Bi2O3)–(1–x)B2O3 system, with x = .15, .25, .35, and .45, were prepared by the melt‐quenching process. Density of the glasses increased to 7.145 g/cm3 with increasing BaO–Bi2O3 content. Gamma radiation shielding performance of the glasses was estimated by studying mass attenuation coefficients (MAC) and effective atomic numbers, using XCOM software as a function of photon energy. Subsequently, experimental MAC values of the glasses were measured using 152Eu and 60Co sources by the radiation transmission method. Measured and calculated MAC values of the glasses were in close agreement. Equivalent atomic numbers, exposure, and energy absorption buildup factors were analyzed at different mean free paths and photon energies using Phy‐X software. Dense glasses exhibited large effective atomic numbers and radiation shielding characteristics comparable with the dense heavy metal oxide glasses. Effective atomic numbers of the glasses were found to be close to the heavy metallic elements (Pb, W, and Hf) at low gamma energies. Radiation shielding ability of the glasses is discussed by comparing with the recently reported radiation shielding glasses and conventional shielding materials. Lead‐free and dense transparent BBB glasses in the present study can be effective in radiation shielding for radiological applications.

Empirical formulation of broadband complex refractive index spectra of single-chirality carbon nanotube assembly

Abstract Assemblies of single-walled carbon nanotubes with a specific chiral structure are promising future optofunctional materials because of their strong light–matter coupling arising from sharp optical resonances of quasi-one-dimensional excitons. Their strong optical resonances, which lie in the infrared-to-visible wavelength region, can be selected by their chiralities, and this selectivity promises a wide range of applications including photonic and thermo-optic devices. However, the broadband complex optical spectra of single-chirality carbon nanotube assemblies are scarce in the literature, which has prevented researchers and engineers from designing devices using them. Here, we experimentally determine broadband complex refractive index spectra of single-chirality carbon nanotube assemblies. Free-standing carbon nanotube membranes and those placed on sapphire substrates were fabricated via filtration of the nanotube solution prepared by the separation method using gel chromatography. Transmission and reflection spectra were measured in the mid-infrared to visible wavelength region, and the complex refractive indices of nanotube assemblies were determined as a function of photon energy. The real and imaginary parts of the refractive indices of the nanotube membrane with a bulk density of 1 g cm−3 at the first subband exciton resonance were determined to be approximately 2.7–3.6 and 1.3i–2.4i, respectively. We propose an empirical formula that phenomenologically describes the complex refractive index spectra of various single-chirality nanotube membranes, which can facilitate the design of photonic devices using carbon nanotubes as the material.

The electronic structure of the metal-organic interface of isolated ligand coated gold nanoparticles.

Light induced electron transfer reactions of molecules on the surface of noble metal nanoparticles (NPs) depend significantly on the electronic properties of the metal–organic interface. Hybridized metal–molecule states and dipoles at the interface alter the work function and facilitate or hinder electron transfer between the NPs and ligand. X-ray photoelectron spectroscopy (XPS) measurements of isolated AuNPs coated with thiolated ligands in a vacuum have been performed as a function of photon energy, and the depth dependent information of the metal–organic interface has been obtained. The role of surface dipoles in the XPS measurements of isolated ligand coated NPs is discussed and the binding energy of the Au 4f states is shifted by around 0.8 eV in the outer atomic layers of 4-nitrothiophenol coated AuNPs, facilitating electron transport towards the molecules. Moreover, the influence of the interface dipole depends significantly on the adsorbed ligand molecules. The present study paves the way towards the engineering of the electronic properties of the nanoparticle surface, which is of utmost importance for the application of plasmonic nanoparticles in the fields of heterogeneous catalysis and solar energy conversion.

Ultraviolet and vacuum ultraviolet photo-processing of protonated benzonitrile (C6H5CNH+)

Context. The recent detection in pre-stellar sources of cyano-substituted and pure hydrocarbon cycles has emphasized the importance of aromatic chemistry in the earliest stages of star formation. Ultraviolet (UV) and vacuum-UV (VUV) radiation is ubiquitous in space and thus the photo-processing of small cyclic ions may open a window onto rich chemical networks and lead to the formation of larger aromatics in space. Aims. The aim is to investigate the fate of protonated benzonitrile species after UV and VUV photoexcitation and the subsequent potential impact on stellar and interstellar chemistry. Methods. Protonated benzonitrile was isolated in a linear ion trap prior to irradiation with UV and VUV radiation (4.5–13.6 eV) from the DESIRS beamline at synchrotron SOLEIL. The study was extended down to 3.5 eV using a cryogenic Paul ion trap coupled to an OPO laser at the PIIM laboratory. Photodissociation action spectra were obtained by monitoring the photofragment yields as a function of photon energy. Results. The UV/VUV photodissociation action spectra of protonated benzonitrile show structured bands from 3.8 to 9 eV. The primary dissociation channel of protonated benzonitrile corresponds to HCN/HNC loss and formation of the phenylium cation (C6H5+); whereas at high energies, a minor channel is observed that correlates with HC3N loss and formation of C4H5+. Conclusions. The UV and VUV photodestruction of protonated benzonitrile leads to the formation of a highly reactive cationic species, C6H5+, predicted to be an important precursor of larger aromatic molecules in space, such as polycyclic aromatic hydrocarbons. The inclusion of C6H5+ – a precursor of benzene and, by extension, of benzonitrile – as the result of formation via the photodissociation of protonated benzonitrile in current astrochemical models could improve the predicted abundance of benzonitrile, which is currently underestimated.

Photoionization and transient Wannier-Stark ladder in silicon: First-principles simulations versus Keldysh theory

Nonlinear photoionization of dielectrics and semiconductors is widely treated in the frames of the Keldysh theory whose validity is limited to small photon energies compared to the band gap and relatively low laser intensities. The time-dependent density functional theory (TDDFT) simulations, which are free of these limitations, enable to gain insight into non-equilibrium dynamics of the electronic structure. Here we apply the TDDFT to investigate photoionization of silicon crystal by ultrashort laser pulses in a wide range of laser wavelengths and intensities and compare the results with predictions of the Keldysh theory. Photoionization rates derived from the simulations considerably exceed the data obtained with the Keldysh theory within the validity range of the latter. Possible reasons of the discrepancy are discussed and we provide fundamental data on the photoionization rates beyond the limits of the Keldysh theory. By investigating the features of the Stark shift as a function of photon energy and laser field strength, a manifestation of the transient Wannier-Stark ladder states have been revealed which become blurred with increasing laser field strength. Finally, it is shown that the TDDFT simulations can potentially provide reliable data on the electron damping time that is of high importance for large-scale modeling.

Determination of optical bandgap energy and optical characteristics of Cd30Se50S20 thin film at various thicknesses

At room temperature, the Cd30Se50S20 ternary thin films with thicknesses ranging from 100 to 400 nm were synthesized using a vacuum evaporation process in an adequate atmosphere of pure nitrogen. X-ray and scanning electron microscopy techniques were used to validate the amorphous nature of the investigated thin films. Changing the thickness of the pristine thin film had a significant effect on controlling the linear and nonlinear optical properties. The optical absorption coefficient was determined using the optical measurements (the transmittance, the reflectance spectra and the film’s thickness) in the range of (300–2500 nm) and the thickness of the thin layer. The optical parameters were calculated in the linear path: the band tail energy and the optical bandgap energy determined in this work by several methods, including the first derivative of the transmittance, reflectance, and optical absorption coefficient curves as a function of wavelength, as well as the second derivative of the transmittance curves. The optical bandgap energy was also computed as a function of photon energy using Tauc formula, the relaxation time, and the portions of the optical conductivity curves. It turns out that the bandgap energy and the tail energy were affected by the increase in thickness so that the first decreases and the other increases in a harmonious behavior. The linear optical constants (the extinction coefficient, the refractive index), the linear dispersion parameters (the single oscillator energy, the dispersion energy), and the linear dielectric parameters were all affected by the increase in thickness of the thin layer. The phase velocity, the group velocity, and Kirchhoff functions were determined, as well as the linear optical dispersion coefficient. The Boling formula, on the other hand, was used to compute the nonlinear refractive index. Finally, the spectral distribution of molar parameters was discussed.

The Study of Optical and Electrical Properties of Nanostructured Silicon Carbide Thin Films Grown by Pulsed-Laser Deposition

In this paper, nanostructured silicon carbide (SiC) thin films are deposited onto glass substrate using pulsed laser deposition technique. Electrical and optical characterizations such as conductivity, resistivity, transmission, Seeback effect, absorption, absorption coefficient, energy band gap, and extinction coefficient as a function of photon energy, and the effect of thin films thickness on transmission are carried out to characterize the prepared samples. Results showed that the prepared SiC thin film is an n-type semiconductor with an indirect bandgap of ~3 eV, 448 nm cutoff wavelength, 3.4395 × 104 cm−1 absorption coefficient and 0.154 extinction coefficient. The surface morphology of the SiC thin films is studied using scanning electron microscope at a substrate temperature of 400 °C and it is found that the grain size of the prepared SiC thin film is about 30 nm. As such, the nano thin films optical and structural characteristics enable the films to be used as gases sensors in many optoelectronic devices such as the environment and ultraviolet photodiode.

Measurements of natCd(γ, x) reaction cross sections and isomer ratio of 115m,gCd with the bremsstrahlung end-point energies of 50 and 60 MeV * *Supported by the National Research Foundation of Korea (NRF) through a grant provided by the Ministry of Science and ICT (NRF-2017R1D1A1B03030484, NRF-2013M7A1A1075764, NRF-2018R1A6A1A06024970)

The flux-weighted average cross sections of natCd(γ, xn)115g,m,111m,109,107,105,104Cd and natCd(γ, x)113g,112,111g,110mAg reactions were measured at the bremsstrahlung end-point energies of 50 and 60 MeV. The activation and off-line γ-ray spectrometric technique was carried out using the 100 MeV electron linear accelerator at the Pohang Accelerator Laboratory, Korea. The natCd(γ, xn) reaction cross sections as a function of photon energy were theoretically calculated using the TALYS-1.95 and the EMPIRE-3.2 Malta codes. Then, the flux-weighted average cross sections were obtained from the theoretical values of mono-energetic photons. These values were compared with the flux-weighted values from the present study and were found to be in general agreement. The measured experimental reaction cross-sections and integral yields were described for cadmium and silver isotopes in the natCd(γ, xn)115g,m,111m,109,107,105,104Cd and natCd(γ, x)113g,112,111g,110mAg reactions. The isomeric yield ratio (IR) of 115g,mCd in the natCd(γ, xn) reaction was determined for the two bremsstrahlung end-point energies. The measured isomeric yield ratios of 115g,mCd in the natCd(γ, xn) reaction were also compared with the theoretical values of the nuclear model codes and previously published literature data of the 116Cd(γ, n) and 116Cd(n, 2n) reactions. It was found that the IR value increases with increasing projectile energy, which demonstrates the characteristic of excitation energy. However, the higher IR value of 115g,mCd in the 116Cd(n, 2n) reaction compared to that in the 116Cd(γ, n) reaction indicates the role of compound nuclear spin alongside excitation energy.

Direct Measurement of Helicoid Surface States in RhSi Using Nonlinear Optics.

Despite the fundamental nature of the edge state in topological physics, direct measurement of electronic and optical properties of the Fermi arcs of topological semimetals has posed a significant experimental challenge, as their response is often overwhelmed by the metallic bulk. However, laser-driven currents carried by surface and bulk states can propagate in different directions in nonsymmorphic crystals, allowing for the two components to be easily separated. Motivated by a recent theoretical prediction G. Chang et al., Phys. Rev. Lett. 124, 166404 (2020)PRLTAO0031-900710.1103/PhysRevLett.124.166404, we have measured the linear and circular photogalvanic effect currents deriving from the Fermi arcs of the nonsymmorphic, chiral Weyl semimetal RhSi over the 0.45-1.1eV incident photon energy range. Our data are in good agreement with the predicted spectral shape of the circular photogalvanic effect as a function of photon energy, although the direction of the surface photocurrent departed from the theoretical expectation over the energy range studied. Surface currents arising from the linear photogalvanic effect were observed as well, with the unexpected result that only two of the six allowed tensor element were required to describe the measurements, suggesting an approximate emergent mirror symmetry inconsistent with the space group of the crystal.

Phonon-Trapping-Enhanced Energy Resolution in Superconducting Single-Photon Detectors

A noiseless, photon counting detector, which resolves the energy of each photon, could radically change astronomy, biophysics and quantum optics. Superconducting detectors promise an intrinsic resolving power at visible wavelengths of $R=E/\delta E\approx100$ due to their low excitation energy. We study superconducting energy-resolving Microwave Kinetic Inductance Detectors (MKIDs), which hold particular promise for larger cameras. A visible/near-infrared photon absorbed in the superconductor creates a few thousand quasiparticles through several stages of electron-phonon interaction. Here we demonstrate experimentally that the resolving power of MKIDs at visible to near-infrared wavelengths is limited by the loss of hot phonons during this process. We measure the resolving power of our aluminum-based detector as a function of photon energy using four lasers with wavelengths between $1545-402$ nm. For detectors on thick SiN/Si and sapphire substrates the resolving power is limited to $10-21$ for the respective wavelengths, consistent with the loss of hot phonons. When we suspend the sensitive part of the detector on a 110 nm thick SiN membrane, the measured resolving power improves to $19-52$ respectively. The improvement is equivalent to a factor $8\pm2$ stronger phonon trapping on the membrane, which is consistent with a geometrical phonon propagation model for these hot phonons. We discuss a route towards the Fano limit by phonon engineering.

Anion Resonances and Photoelectron Spectroscopy of the Tetracenyl Anion.

The photoelectron spectroscopy of the tetracenyl anion using slow electron velocity-map imaging (SEVI) of cryogenically cooled ions is presented. The total photodetachment yield as a function of photon energy is used to reveal a rich manifold of anion excited states above the detachment threshold. The lowest energy anionic resonance has a sufficiently long lifetime to yield a vibrationally resolved absorption spectrum that can be directly compared with theoretical predictions. Excitation of this state mostly results in electron detachment via thermionic emission. The total photodetachment yield spectrum is used to select photon wavelengths that minimize the indirect detachment signal to allow acquisition of vibrationally resolved photoelectron spectra that can inform on the neutral tetracenyl radical. Assignment of spectral features corresponding to the ground and first excited state of the neutral 12-tetracenyl isomer is made with the aid of Franck-Condon simulations. This yields adiabatic electron affinity and term energies that differ significantly from the previously reported values. Weak features corresponding to the ground state of the minor 2-teracenyl and 1-tetracenyl isomers are also identified, which allows for the experimental determination of their electron affinities for the first time.

Thermoluminescent relative efficiency of TLD-100 glow peaks after exposure to X-rays of 20 kV–300 kV, 137Cs and 60Co gamma

Thermoluminescent dosimeter LiF:Mg, Ti (TLD-100) has been considered as the “gold standard” to measure absorbed dose from low-energy photon fields in medical applications. However, to calibrate the dosimeters, high energy beams (6 MV X-ray or 60Co gamma) are usually used since low photon energy beams are not always available. Thus, knowledge of the relative efficiency, RE, is necessary in order to convert the absorbed dose calibration from high energy beams to low-energy photon fields like those used in brachytherapy and diagnostic. In this work, RE as a function of the photon energy, besides, the influence of the phantom material used to collocate the dosimeters during irradiation has been studied. Thermoluminescent glow curves were deconvolved into 9 individual glow peaks by using an algorithm developed in Matlab based on the Podgorsak approximation using the first-order kinetics model. The influence of the phantom material on the dosimeter response is observed in every glow peak, where RE values are lower in air compared to other materials such as polymethyl methacrylate. For all the glow peaks, RE as a function of the mean photon energy shows a region with a minimum and a maximum.

First principle study of Er, co-doped Fe and Yb of NaBiF6; a promising materials for optoelectronic and transport properties; probed by DFT

Despite of getting higher efficiencies from hybrid perovskite solar cells, it is necessary to investigate stable and desirable bandgap materials. We introduced new promising class of double perovskites (DPs) materials using density functional theory predictions, for solar cells applications. The results of band structure show that Er along with the co-doped Fe and Yb of NaBiF6 with intermetallic nature. The optical properties have studied by considering interband transitions, where many levels of optical transitions is observed. We calculated optical dispersions e.g real and imaginary parts of complex dielectric function, energy loss function, reflectivity, absorption coefficient, refractive index and optical conductivity as function of photon energy from 0 to 14 eV for both spins up and down polarizations. The investigated materials contains high spin symmetry except at low energies, weakly photons reflected in IR and visible regions and absorb photons strongly in the UV region. These optical properties may be used for applications in optoelectronic devices.

Effect of manganese on electronic and optical properties of Ba2ZnS3: A DFT study

The structural, electronic, and optical properties of pristine Ba2ZnS3 and Mn4+ doped Ba2ZnS3 at Ba-site have been carried out by employing the first-principles calculations based on density functional theory (DFT). For the calculation of exchange and correlation interactions, the modified Becke Johnson (TB-mBJ) potential and generalized gradient approximation with the Hubbard parameter (GGA ​+ ​U) were used for pristine and Mn4+ doped Ba2ZnS3 respectively. The defective states due to Mn4+ doping are introduced below the conduction band which produces n-type conductivity in both spin-up and spin-down states. The direct band gaps are observed for Ba2ZnS3 and Ba2ZnS3:Mn4+ (spin up and spin down) with bandgap values 3.157 ​eV, 1.582 ​eV, and 2.176 ​eV respectively. For spin-up states, the intermediate states are induced due to the majority contribution of s-orbital of Mn atom, while minority contribution of p-orbital of Mn atom. For spin-down states, the defective states are produced as a result of the prominent contribution of d-orbital of Mn atom and minor contribution of s-orbital of Mn atom. The optical properties such as the real and imaginary parts of the dielectric function, reflectivity, electron energy loss spectrum, extinction coefficient, refractive index, absorption coefficient, and optical conductivity as a function of photon energy are calculated. Our results revealed that Mn4+ doped Barium zinc sulfide emerged as a highly efficient luminescent phosphor material, and is more suitable for optical devices due to its direct bandgap nature and small bandgap value (1.582eV).

Udkm1Dsim – a Python toolbox for simulating 1D ultrafast dynamics in condensed matter

The udkm1Dsim toolbox is a collection of Python classes and routines to simulate the thermal, structural, and magnetic dynamics after laser excitation as well as the corresponding X-ray scattering response in one-dimensional samples, such as multilayers. The toolbox provides the capabilities to define arbitrary layered structures on the atomic level including a rich database of element-specific physical properties. The excitation of dynamics is represented by an N-temperature-model which is commonly applied in ultrafast physics. Structural dynamics due to thermal stresses are calculated by a linear-chain model of masses and springs. The implementation of specific magnetic dynamics can be easily accomplished by the user employing a generalized magnetization interface class. The resulting X-ray diffraction response is computed by kinematical or dynamical X-ray theory which can also include polarization-dependent magnetic scattering. The udkm1Dsim toolbox is highly modular and allows for injecting user-defined inputs at any step within the simulation procedure. New version program summaryProgram Title: udkm1DsimCPC Library link to program files:https://doi.org/10.17632/bnzw823v6y.1Developer's repository link:https://github.com/dschick/udkm1DsimCode Ocean capsule:https://codeocean.com/capsule/8131941Licensing provisions: MITProgramming language: PythonJournal reference of previous version: Comput. Phys. Commun. 185 (2) (February 2014) 651–660Does the new version supersede the previous version?: YesReasons for the new version: The toolbox has been ported from MATLAB (MathWorks Inc.) to Python and is based exclusively on free and open-source components. Moreover, new features have been added that allow for a broader applicability of the toolbox.Summary of revisions: Porting to Python.Introduction of amorphous layers in the sample structures.Add magnetization property to atoms and layers.Multilayer formalism to calculate laser absorption.New magnetization class to allow for user-defined magnetization dynamics.New resonant magnetic X-ray scattering employing dynamical X-ray theory.Calculation of X-ray scattering as function of photon energy and scattering vector.Nature of problem: Simulate the thermal, structural, and magnetic dynamics of 1D layered sample structures due to an ultrafast laser excitation and compute the corresponding transient (magnetic) X-ray scattering response.Solution method: The program provides an object-oriented toolbox for building arbitrary layered 1D crystalline/amorphous sample structures including a rich database of element-specific parameters. The excitation, thermal transport, and lattice dynamics are simulated utilizing SciPy's ODE solver. Magnetization dynamics can be introduced by the user employing a magnetization interface class. The dynamical (magnetic) X-ray scattering is computed by a matrix formalism that can be parallelized.Additional comments including restrictions and unusual features: The program is restricted to 1D layered sample structures. Phonon dynamics only include longitudinal acoustic phonons (sound waves). Magnetization dynamics have to be defined by the user. X-ray scattering only allows for symmetrical and co-planar geometries due to the 1D nature of the toolbox. The program is highly modular and allows the inclusion of user-defined inputs at any time of the simulation procedure.

Optical Properties of Copper-Zinc Sulphide Network from Mixed Single Solid Source Precursors of Copper and Zinc Dithiocarbamates

Thin films of copper-zinc sulphide (CxZn1-xS) have been deposited by metal-organic chemical vapour deposition (MOCVD) technique at 400 °C on soda-lime substrates. The films contained copper dithiocarbamate and zinc dithiocarbamate of various concentrations. The effect of the precursor’s concentration was investigated using Fourier transforms infrared (FTIR) spectroscopy and UV-Vis Spectrophotometer. The precursors’ FTIR spectrums have the characteristics of copper sulphide and zinc sulphide absorption bands below 800 cm-1. The optical properties for all the samples were studied by reading the absorbance and transmittance spectra in the range of 300 - 900 nm. The results indicate direct bandgap energy that ranged between 2.20 to 3.42 eV. The films were found to have a very high transmittance in the visible and near-infrared regions and an average reflectance of about 0.14 in the same regions. Optical constants like refractive index, extinction coefficient, and optical conductivity were estimated as a function of photon energy. The various properties exhibited by the films indicate that the films can find application in various optoelectronic devices.

Computation of Refractive Index Values of Inert Gases at Near Infrared and XUV Region based on Mathematica Software

In this study, refractive indices in the visible, near infrared and extreme ultraviolet (XUV) region are calculated based on Mathematica software. Atomic scattering factors are simulated for high photon energy range (20-60eV). By using the atomic scattering factors, the real and imaginary part of index of refraction values are plotted as a function of photon energy. The aim of this work is to present a computational program, which calculates the index of refraction of the inert gases at different wavelength regions. The refractive indices of gases, namely helium (He), neon (Ne), argon (Ar) and xenon (Xe) in the near infrared and XUV region are computed by using a Mathematica software. The applications of the index of refraction are discussed through the paper. The Mathematica program calculating the refractive indices is presented in the Appendix.

Experimental studies on photoabsorption by endohedral fullerene ions with a focus on Xe@C60 + confinement resonances

A brief overview on the status of experimental investigations into photoionization and fragmentation of fullerenes and endohedral fullerenes by absorption of a single short-wavelength photon is presented. The focus of this paper is on the endohedral Xe@C60 + molecular ion in which a xenon atom is centrally encapsulated inside a fullerene cage. Confinement resonances that result from the interference of Xe photoelectron matter waves emerging from the cavity were studied by exposing Xe@C60 + ions to synchrotron radiation of 60 to 150 eV energy which is the region of the well-known giant atomic Xe excitation resonance. Photoions Xe@C n q+ (with final charge states of the product ions and numbers of carbon atoms left in the cage) were recorded as a function of photon energy and cross sections for the individual reaction channels were determined. In addition to previous work, new final channels ( and ) were observed, and thus, about 70% of the oscillator strength expected for the encapsulated Xe atom in the investigated energy range could be recovered. The present results establish the first and, so far, only conclusive experimental observation of confinement resonances in an endohedral fullerene. The data are in remarkable agreement with relativistic R-matrix calculations that accompanied the previous experimental work.

Analysis of optical band gap and urbach tail of zinc sulphide coated with aqueous and organic dye extracts prepared by chemical bath deposition technique

Detailed analysis of the optical band gap of zinc sulphide (ZnS) film coated with organic dye extract was conducted in this research. The chemical bath deposition technique was used in the deposition of ZnS coated with aqueous and alkanone dye extracts on glass substrate, annealed at different temperatures (100OC, 150OC and 200OC). Transmittance measurements were taken at room temperature in the wavelength range 300–1000 nm. The plots of the square of the product of absorption coefficient and photon energy were used to estimate the optical band gap energy of the film samples. The band gap exhibited red shift for some of the films and blue shift for other samples. Increasing the concentration of the precursor (Zn2+), increased the band gap of some film samples and decreased for others. The Urbach tail estimated from the plot of natural logarithm of the absorption coefficient as a function of photon energy, depicted a linear relationship for some of the film samples with respect to post-deposition temperature. In terms of the effect of concentration, the Urbach rule did not show a trend. The optical band gaps obtained in this study are in the range suitable for use in optoelectronics and solar photovoltaic applications.

Electronic band structure and optical properties of GaAsSb/GaAs for optoelectronic device applications: A 14 band k.p study

The band structure of GaAsSb/GaAs material is calculated along a crystallographic direction using a 14-band model approach. This model captures the reduction of bandgap by 13.5 meV/%Sb and provides a tool for device-level design under a range of wavelength ~ 0.9 μ m to 1.3 μ m for antimony composition limit 0.1%<Sb<35%, respectively. The analysis extends to calculating the outcome of the antimony composition on electron and hole effective mass. We have found that the electron effective mass (0.057 m o , 35% Sb) decreases by ~ 1.2 compared to GaAs (0.067 m o ). Which is responsible for improving the optical gain. So, from the obtained effective mass we determined intrinsic carrier concentration, which seems monotonic with antimony composition. Furthermore, due to uncertainty in VB and CB offset values a lateral variation of 160 nm between type I and type II QWs was observed in the optical gain spectrum. While for use in solar cells, the interband absorption coefficient was also examined as a function of photon energy with a fundamental absorption edge observed at 0.96 eV. The results obtained are well consistent with the literature result previously reported. • GaAs 1 − x Sb x band structures have been calculated by 14 band k.p hamiltonian. • Observed bandgap reduction of GaAs 1-x Sb x by 13.5 meV/%Sb. • Incorporation of Sb (35%) into the host GaAs leads to a decrease in electron effective mass by ~ 1.2 times. • Intrinsic carrier concentration analysis revealed that GaAsSb material pushes towards the p-type base. • Lateral variation by 160nm in optical gain spectrum between type-I and type-II QWs is observed.