Fundamental Band Gap Energy Research Articles

Impact of gamma irradiation on optical and nonlinear properties of Indium chloride phthalocyanine thin films

This study investigates the impact of gamma radiation on indium chloride phthalocyanine (lnPcCl) thin films, which were prepared via vacuum thermal evaporation. x-ray diffraction revealed the amorphous structure of the films, with increasing gamma doses causing more noticeable structural disorders. Optical analysis showed a slight decrease in the optical band gap energy and a significant reduction in the fundamental band gap energy. Additionally, higher gamma doses led to decreased transmittance and increased reflectance. The study also observed substantial enhancements in nonlinear optical parameters, such as third-order nonlinear susceptibility (χ(3)) and nonlinear refractive index (n 2). These findings suggest the potential of gamma-irradiated lnPcCl films for advanced optoelectronic and nonlinear optical applications.

Determination of the Complex Refractive Index of GaSb1−xBix by Variable‐Angle Spectroscopic Ellipsometry

Variable‐angle spectroscopic ellipsometry is used to determine the room temperature complex refractive index of molecular beam epitaxy grown GaSb1−xBix films with x ≤ 4.25% over a spectral range of 0.47–6.2 eV. By correlating to critical points in the extinction coefficient k, the energies of several interband transitions are extracted as functions of Bi content. The observed change in the fundamental bandgap energy (E0, −36.5 meV per %Bi) agrees well with previously published values; however, the samples examined here show a much more rapid increase in the spin‐orbit splitting energy (Δ0, +30.1 meV per Bi) than previous calculations have predicted. As in the related GaAsBi, the energy of transitions involving the top of the valence band are observed to have a much stronger dependence on Bi content than those that do not, suggesting the valence band maximum is most sensitive to Bi alloying. Finally, the effects of surface droplets on both the complex refractive index and the critical point energies are examined.

Carriers induced ferromagnetism in Co(II)-doped ZnO monolayers and their optical properties: First principles calculations

Diluted magnetic semiconductors are advantageous for magneto-electronic devices because they create ferromagnetism at high Curie temperatures and exhibit spin-dependent interactions. The complex microstructural and compositional aspects of optical emission dynamics and ferromagnetism are still unknown. Here, using first-principles calculations, we investigate the magnetic and opto-electronic characteristics of Co(II) mono-doped and (Co, Na) co-doped ZnO monolayers. The results show that Na co-doping can change the ground state of a Co(II)-doped monolayer from AFM to FM due to the exchange coupling between the Co-d spins and hole produced by Na. The observed room-temperature (RT) ferromagnetism in the co-doped monolayer below with 5 % Na doping is due to exchange coupling via electron trapping oxygen vacancies with the magnetic Co ions. The optical investigation reveals a red shift in the d-band to d-band transition of Co(II) and a blue shift in the fundamental energy gap with increasing Co concentration. Na co-doping results in mid-IR and near-infrared absorption peaks. Furthermore, the correlation between spin-spin coupling and optical absorption shows that the FM(AFM) systems exhibit a red-shift (blue-shift) in the fundamental band gap energy and spin-allowed d-band to d-band transition of Co ions. The enhanced optical and magnetic findings suggest that the (Co, Na);ZnO monolayer might be a suitable option for spin-photonic and spintronic devices in the future.

The effect of tin doping on physical properties of cobalt oxide thin films

This work deals with the effect of Sn doping at mole percentages of 1 %, 2 %, 3 % and 4 % on the structural, morphological, and optical properties of Co3O4 thin films. These physical properties were carried out by X-Ray Diffraction (XRD), Raman, Atomic Force Microscopy (AFM), scanning electron microscope (SEM), Ultraviolet-Visible-Near infrared spectroscopy (UV-Vis-NIR) and spectroscopic ellipsometry (SE). Co3O4 thin films were grown on amorphous glass substrates by spray pyrolysis technique. Experimental and modeling rigorous studies using these different techniques particularly SE were achieved in order to determinate the effect of tin doping on physical properties of cobalt oxide thin films. The incorporation of Sn into the Co sites affects drastically the optical transitions values as well as other optical properties such as the dielectric function, the band gap, the refractive index and the extinction coefficient. All doped samples exhibited a relatively higher absorption coefficient compared to the undoped ones, greater than 105 cm−1 over a wide energy range. SE analysis revealed a smaller transition of approximately 0.77 eV considered as fundamental band gap energy that was assigned to a 3d-d type within the Co2+ tetrahedral site.

Analysis of mixed optical transitions in dilute magnetic AlAs/GaAs/GaMnAs quantum wells grown on high substrate index by molecular beam epitaxy

In this study, we report the influence of high-index substrate orientation on the optical properties of dilute Mn containing a single quantum well (QW) structure grown by molecular beam epitaxy (MBE). The electronic band structure of the samples is calculated with finite element methods (FEM). Photomodulated reflectance (PR) spectroscopy is employed to determine the optical transition energies at room temperature. PR experimental results are analyzed with the Third Derivative Functional Form (TDFF) signal function. TDFF fitting shows that the optical transition starts below the fundamental GaAs bandgap energy for the samples grown on (311) B and (411) B-oriented substrates. Comparing TDFF fitting and calculated optical transition energies with FEM show that the optical transition occurs in type-I and type-II as direct and indirect transitions, respectively. Type-I and -II optical transitions are addressed concerning the electronic band structure of the sample grown on oriented substrates.

Electronic and thermoelectric properties of the layered Zintl phase CaIn2P2: first-principles calculations

ABSTRACT We have studied the doping concentration dependence of the thermoelectric (TE) properties for the n- and p-doped CaIn2P2 layered Zintl phase at two fixed temperatures: T = 600 and 900 K through first-principles electronic band structure calculations combined with Boltzmann's transport theory within charge-carrier relaxation time and rigid band approximations. The band structure calculated using the Tran-Blaha modified Becke–Johnson potential shows a fundamental indirect energy band gap (E g) of 1.10 eV that comes from the polyanion (In2P2)−2. CaIn2P2 exhibit a mixture of flat and dispersive energy bands in the energy window from to eV, which is a required characteristic for high electrical transport coefficients. The computed lattice thermal conductivity for CaIn2P2 is equal to at 900 K and at 1250 K. This relatively low lattice thermal conductivity of CaIn2P2 can be mainly attributed to its layered crystalline structure. The highest value of the figure of merit of CaIn2P2, viz. ZT = 0.73 (0.71), is obtained for an optimal electron (hole) concentration of () at 900 K.

Influence of gamma irradiation on linear and nonlinear optical properties of nanocrystalline manganese(III) chloride tetraphenylporphine thin films

90 nm thickness of MnTPPCl thin films were deposited by thermal evaporation technique on glass and quartz substrates under vacuum. The examined thin films were irradiated by 60Co γ-rays with 150 kGy. XRD and FTIR techniques are used to comprehend the structure of MnTPPCl thin films. The results confirmed that the structure of pristine thin films is nanocrystallites dispersed in the amorphous matrix and the irradiated films have an amorphous structure. Refractive index, oscillator's parameters (dispersion energy, Ed, oscillator energy, Eo), the absorption coefficient, optical energy gap, and Urbach energy were estimated before and after exposure to γ-irradiation by using spectrophotometric measurements. All mentioned parameters were influenced by the γ-irradiation process. The type of electronic transition was classified as a direct allowed transition. The gamma irradiation process was caused an increase in the fundamental band gap energy from 2.48 to 2.52 eV (blue shift) which is good for solar cells window. Third-order nonlinear optical susceptibility χ(3) and the nonlinear refractive index n2 of MnTPPCl thin films were studied before and after γ-irradiation. An increase in χ(3) and n2 with γ-irradiation is observed, so it is recommended to be used as optical switching applications.

Design of a novel series of small molecule donors for application in organic solar cells

In an effort to study high-efficient electron donor materials for application in organic solar cells (OSC), density functional theory (DFT) calculations were performed to predict a variety of small molecules (SMs) with terminal acceptor-π bridge-central donor-π bridge-terminal acceptor (A-π-D-π-A) framework. An interesting A-π-D-π-A-type SM containing phenothiazine as D unit has been recently synthesized and applied to in the OSC. Motivated by this study, here, we have systematically predicted 10 SM donor materials based on the phenothiazine as the central D unit as well as several A and π units that have been used into materials representing excellent SC as well as charge transport characteristics. Then, the structural, electronic, and optical properties of the predicted SM donors have been investigated. The fundamental band gap energies, orbital spatial distributions, and intrinsic dipole moments were calculated using DFT while the optical band gap energies were obtained using time-dependent density functional theory (TD-DFT). Several SC properties of the predicted SMs were then computed and compared with the available experimental results of OSCs. Our suggested SMs represented the enhancement in the open circuit voltage (VOC) and charge transport properties which may lead to OSCs with improved power conversion efficiency (PCE) compared to the previously synthesized SMs. Moreover, small reorganization energies, large transfer integrals, and high intra-molecular coupling obtained from dense π-stacking give rise to increased electron mobility in the predicted SMs. However, this strategy can be helpful for further improving the performance of SMs in OSCs.

Tailoring optical and electrical properties of thin-film coatings based on mixed Hf and Ti oxides for optoelectronic application

In this work multi-magnetron sputtering stand was used for the deposition of the mixed oxides thin films based on HfO2 and TiO2. In order to obtain various material composition the power released to each magnetron (containing metallic hafnium and titanium targets) was precisely selected. Structural, surface, optical, electrical and mechanical properties of as-deposited coatings were analyzed. Depending on the hafnium content in the deposited thin films various types of the microstructure was obtained, i.e. HfO2-monoclinic, amorphous and TiO2-rutile. Increase of Ti content above 28at. % in the as-prepared mixed oxides coatings caused their amorphization. It was found that with an increase of Ti content in prepared coatings their surface roughness and simultaneously water contact angle decreased. Performed measurements of electrical properties revealed that the lowest leakage current density in the range of 10−7–10−8A/cm2 was obtained for amorphous coatings. Moreover, the tailoring of the dielectric constant was possible by a proper selection of material composition and microstructure of the deposited thin films. Average transparency in the visible wavelength region was in the range of ca. 79–86%. The influence of material composition and structure on shifting of the fundamental absorption edge and optical band gap energy was also observed. The refractive index increased with an increase of Ti content, while extinction coefficient was the lowest for amorphous coatings. Additionally, hardness values were dependent on the material composition and optical packing density and were in the range from 7.6GPa to 10.1GPa.

Electronic structure and optical response for Zn1−xBexSe

Abstract The electronic structures and optical properties of the Zn1−xBexSe semiconductor ternary alloys have been investigated by using the full-potential linear augmented plane wave (FP-LAPW) method. From this study, the energy band gap has a value of about 1.2 eV for zinc-blende ZnSe. However, for Zn0.50Be0.50Se and BeSe, the fundamental band gap energy is found to occur at the highly symmetric X point in the Brillouin zone and has values of about 2.3 eV and 2.8 eV, for Zn0.50Be0.50Se and BeSe, respectively. Optical parameters, such as dielectric constant, refractive index and reflectivity are calculated and analyzed. The results demonstrated that the compounds Zn1−xBexSe have the potential to be used for optoelectronic applications.

Accurate, First-Principle Study of Electronic and Related Properties of the Ground State of Li<sub>2</sub>Se

We present results from ab-initio, self-consistent calculations of electronic and related properties for the ground state of cubic lithium selenide (Li2Se). We employed a local density approximation (LDA) potential and performed computations following the Bagayoko, Zhao, and Williams (BZW) method, as enhanced by Ekuma and Franklin (BZW-EF). This method verifiably leads to the ground state of materials without employing over-complete basis sets. We present the calculated electronic energies, total and partial densities of states, effective masses, and the bulk modulus. The present calculated band structures show clearly that cubic Li2Se has a direct fundamental energy band gap of 4.065 eV at the Γ point for the room temperature experimental lattice constant of 6.017 A. This result is different from findings of previous density functional theory (DFT) calculations that uniformly reported an indirect band gap, from Γ to X, for Li2Se. We predicted a direct band gap of 4.363 eV, at the computationally determined equilibrium lattice constant of 5.882 A, and a bulk modulus of 35.4 GPa. For the first time known to us, we report calculated electron and hole effective masses for Li2Se. The experimental confirmation of the large, direct gap we found will point to a potential importance of this material for ultraviolet technologies and applications. Due to a lack of experimental results, most of our calculated ones in this paper are predictions for Li2Se.

Effect of Gamma Radiation Induced on Structural, Electrical, and Optical Properties of N, N′-Dimethyl-3,4,9, 10-Perylenedicarboximide Nanostructure Films

N,N′-Dimethyl-3,4,9,10-perylenedicarboximide (PTCDI-C1) thin films were first prepared by thermal evaporation technique. Then, the prepared films were irradiated with gamma rays at room temperature with different absorbed doses. The structure of PTCDI-C1 films at different doses of gamma radiation was elucidated by x-ray diffraction. The results confirmed that PTCDI-C1 film has a nanostructure morphology. The grain size was observed to decrease slightly with increasing the gamma radiation doses. The temperature dependence of the electrical conductivity was measured in the temperature range of 293–423 K. It was found that the obtained activation energy of PTCDI-C1 films decreased with increasing gamma radiation dose. The optical parameters were obtained using spectrophotometric measurements. The single oscillator model of Wemple–Didomenico was adopted to study the normal dispersion of refractive index. The optical dispersion parameters of PTCDI-C1 films such as dispersion energy, oscillator energy and the high frequency dielectric constant were calculated. Furthermore, the nonlinear susceptibility values of PTCDI-C1 films at different gamma radiation dose were calculated. Also, the dielectric constants of the films were investigated in a large range of frequencies. The fundamental band gap energy values (3.91 eV Eg2 > 50 kGy).

Phase transition in BaThO3 from Pbnm to Ibmm turn the fundamental energy band gap from indirect to direct

The influence of phase transition on the electronic structure and the optical properties of BaThO3 is investigated by means of density functional theory. At room temperature BaThO3 is stable in the Pbnm phase, whereas it is stable in the Ibmm phase at high temperature. The transition from the Pbnm to the Ibmm phase cause a change in the band gap (Eg) nature from indirect to direct and a reduction by around 0.3 eV. The calculated Eg is about 4.9 eV (Pbnm) and 4.6 eV (Ibmm). The phase transition influences the k-dispersion of bands around the Fermi level and, hence, the effective masses resulting in increasing the mobility of the charge carrier and enhancing the charge transfer mechanism. The obtained optical properties clearly show the influence of phase transition on the electronic structure. It was noticed that moving from Pbnm →Ibmm phase leads to shift the whole spectral structure towards lower energies by around 0.3 eV and increase the magnitudes of the optical components. It is found that the Pbnm and Ibmm phases exhibit negative uniaxial anisotropy and negative birefringence.

Gamma radiation effect on physical properties of 2,9-Bis [2-(4-chlorophenyl)ethyl] anthrax [2,1,9-def:6,5,10-d′e′f′] diisoquinoline-1,3,8,10 (2H,9H) tetrone films

Thermal evaporating technique was used to prepare 2,9-Bis [2-(4-chlorophenyl)ethyl] anthrax [2,1,9-def:6,5,10-d′e′f′] diisoquinoline-1,3,8,10 (2H,9H) tetrone (Ch-diisoQ) thin films. The studied films were irradiated with gamma rays in the air at room temperature with different absorbed doses (50–200 kGy). X-Ray diffraction was used to comprehend the structure of Ch-diisoQ thin films. The outcomes affirmed that Ch-diisoQ films have nanostructure nature. The optical parameters were obtained by using spectrophotometric measurements. It was found that the dispersion of the refractive index follows the trend of single oscillator model. The optical dispersion parameters of Ch-diisoQ thin films such as dispersion energy, oscillator energy were investigated. The nonlinear susceptibility values of Ch-diisoQ films at different gamma radiation dose were calculated. Furthermore, the investigation of the optical absorption mechanism verified that the value of fundamental band gap energy, Eg2, increased when Ch-diisoQ films were exposed to gamma radiation. However, the conductivity was observed to be increased as the gamma radiation dose increased, while the activation energy of Ch-diisoQ films decreased with the increasing of gamma radiation dose.

Pressure effects on structural, electronic, elastic and lattice dynamical properties of XSi2(X = Cr, Mo, W) from first principles

First-principles calculations have been performed to study the structure, elastic and lattice dynamical properties of C40 XSi2(X=Cr, Mo, W) under hydrostatic pressure. The obtained structural parameters are in line with existing experimental and theoretical data. The evolutions of fundamental bandgap energies, elastic moduli, IR absorption spectra with pressure have been investigated in detail. Our results indicate that the energy gaps of XSi2(X=Cr, Mo, W) show different trends as the pressure increases. Larger BH/GHratio and Poisson’s ratio are achieved with pressure, suggesting an improved ductility for XSi2(X=Cr, Mo, W). Moreover, a large elastic anisotropy under pressure is exhibited in Young’s anisotropic factors. The infrared-active phonon frequencies exhibit substantial blueshifts under pressure.

Optical properties of InGaN thin films in the entire composition range

The optical properties of thick InGaN epilayers, with compositions spanning the entire ternary range, are studied in detail. High structural quality, single phase InxGa1-xN (0001) films were grown heteroepitaxially by radio-frequency plasma assisted molecular-beam epitaxy on freestanding GaN substrates. Their emission characteristics were investigated by low temperature photoluminescence spectroscopy, whereas variable angle spectroscopic ellipsometry was applied to determine the complex dielectric function of the films, in the 0.55–4.0 eV photon range. Photoluminescence lines were intense and narrow, in the range of 100 meV for Ga-rich InGaN films (x < 0.3), around 150 meV for mid-range composition films (0.3 < x < 0.6), and in the range of 50 meV for In-rich alloys (x > 0.6). The composition dependence of the strain-free emission energy was expressed by a bowing parameter of b = 2.70 ± 0.12 eV. The films' optical dielectric function dispersion was obtained by the analysis of the ellipsometric data employing a Kramers-Kronig consistent parameterized optical model. The refractive index dispersion was obtained for alloys in the entire composition range, and the corresponding values at the band edge show a parabolic dependence on the InN mole fraction expressed by a bowing parameter of b = 0.81 ± 0.04. The bowing parameter describing the fundamental energy bandgap was deduced to be equal to 1.66 ± 0.07 eV, consistent with the ab initio calculations for statistically random (non-clustered) InGaN alloys.

First-principles calculations of the stibnite at the level of modified Becke–Johnson exchange potential

The demand for cheaper, nontoxic and earth-abundant materials as absorbing layer for solar cell is immensely needed to replace scarce, toxic and expensive one. In this regard, chalcogenide materials have considerably attracted the attention of a lot of researchers because of showing a great potential for different applications. Stibnite (Sb2S3), a chalcogenide binary material is considerably investigated for exploiting its potential for different energy technologies being a less toxic, abundantly available, stable and efficient, which are the fundamentals for sustainability as well as to realize the dream of green energy. In this study, theoretical calculations of the structural, electronic and optical properties of stibnite (Sb2S3) crystal structure are presented using the full potential (FP) linearized augmented plane wave (LAPW) framed within density functional theory (DFT). To incorporate the exchange-correlation part in the total energy functional, besides the local density approximation (LDA), Wu-Cohen parameterized generalized gradient approximation (WC-GGA), Perdew–Burke–Ernzerhof parameterized generalized gradient approximation (PBE-GGA), and Perdew–Burke–Ernzerhof generalized gradient approximation for solids and surfaces (PBEsol-GGA) are used for the calculations of the structural parameters, where the Trans-Blaha approach of the modified Becke–Johnson (TB-mBJ) potential is used to get more reliable results for the fundamental band gap energy value. These calculations are performed by involving spin-orbit coupling (SOC) contribution. Additionally, optical properties, such as imaginary and real parts of the dielectric function, optical conductivity, absorption coefficient, refractive index, reflectivity, and electron energy loss function are analyzed. Our first-principles calculations show that Wu-Cohen GGA (WC-GGA) reproduces results for lattice parameters comparable to the experimental measurements. The obtained results of the band gap energy and optical properties with TB-mBJ potential are also closer to the experimental data and, endorse its potentiality for the photovoltaics applications.

Sulfide oxide XZnSO (X = Ca or Sr) as novel active photocatalytic water splitting solar-to-hydrogen energy conversion

The photocatalytic, structural and transport properties of the newly synthesized sulfide oxide CaZnSO and SrZnSO compounds are comprehensively investigated by means of first and second-principles calculation in order to explain the semiconductor's ‘photo-excitation' state mechanism in CaZnSO and SrZnSO. At the same time, the influence of the substitution of Ca2+ by Sr2+ on the structural properties and, hence, on the photocatalytic properties, are investigated. The optical conductivity and the absorption level exhibit an obvious enhancement from the ultraviolet to the visible light region when we move from Ca to Sr. This shows that the absorption edge moves from λ=387.4→λ=442.7nm, which corresponds to the direct optical band gap of 3.2eV→2.8eV, which is well matched with the solar spectrum and the sufficient negative conduction band potential for reduction of H+/H2. The calculated electronic band structure and the angular momentum character of various structures confirm that CaZnSO and SrZnSO possess a direct fundamental energy band gap of about 3.7eV (CaZnSO)→3.1eV (SrZnSO), and the electronic charge distribution reveals a clear map of the electronic charge transfer and the chemical bonding. Furthermore, the carrier concentration (n) as a function of chemical potential at three constant temperatures (T) and n as a function of T at fixed chemical potential were calculated. It was found that n increases exponentially with increasing T and reveals that the CaZnSO and SrZnSO are p-type semiconductors. Based on these results, one can conclude that CaZnSO and SrZnSO satisfied all requirements to be an efficient photocatalyst. This will greatly improve the search efficiency and greatly help experiments to save resources in the exploration of new photocatalysts with good photocatalytic performance.

Band structure and optical properties of polyaniline polymer material

The present contribution reports on the electronic structure and optical properties of the polyaniline polymer material. The calculations are performed using ab initio total energy calculations within the full-potential linearized augmented plane wave method in the framework of the density functional theory. The generalized gradient approximation is used to treat the effects of exchange and correlation. The fundamental band-gap energy and static and high-frequency dielectric constants of the polymer of interest are predicted. The optical spectra against the photon incident energy along both the x- and z-axis are presented and examined.

Photophysical, transport and structure properties of Tl10Hg3Cl16 single crystals: Novel photocatalytic water-splitting solar-to-hydrogen energy conversion

The photocatalytic, transport, photophysical, and structural properties of Tl10Hg3Cl16 single crystals are investigated by means of density functional theory in order to investigate its suitability to be used as an active photocatalyst. The calculation show that this compound possesses a narrow direct band gap. The obtained values of the fundamental energy band gap are about 0.82eV (LDA), 0.88eV (PBE-GGA), and 0.97eV (mBJ). The absorption edge of Tl10Hg3Cl16 occurs at λ=742.3nm, and the optical band gap is estimated to be 1.67eV. For use in photocatalytic water splitting, the optical band gap of the photocatalyst material must be sufficiently large to overcome the endothermic character of the water-splitting reaction, i.e., higher than 1.23eV therefore, Tl10Hg3Cl16 (Eg=1.67eV) is expected to be an active photocatalyst. The calculated density of states reveals the orbitals that form the conduction band minimum and the valence band maximum, and the existence of hybridization. The transport properties are calculated to investigate the suitability of Tl10Hg3Cl16 as a thermoelectric power generator, as an active photocatalyst for clean energy resources, and as an ultrafast scintillator for medical imaging.