Band Gap Energy Of Semiconductor Research Articles

Synthesis of Ag and Gd Co-doped LaCoO3: Tuning the Optical Bandgap through Quantum Confinement Effect for Outstanding Photocatalytic Activity

Structural defects and tuning in bandgap energy of semiconductors can greatly enhance their catalytic performance as photocatalysts for the removal of various water contaminants. For this purpose, a series of perovskite materials were fabricated. Perovskites have chemical formula A+2B+4(X2-)3, where A site cation is generally an alkaline earth or rare earth metal and B site cation is 3d, 4d, or 5d transition metal. The present study includes the synthesis of LaCoO3, Ag@LaCoO3, Gd@LaCoO3, and Ag/Gd@LaCoO3 by simple co-precipitation route. The prepared materials were characterized using X-ray diffraction and Fourier transform infrared spectroscopy. The average crystallite size and % porosity of Ag/Gd@LaCoO3 were increased to 25 nm and 45% respectively as compared to LaCoO3 (15 nm and 5%) after doping of Ag and Gd in the crystal lattice of pristine LaCoO3. Moreover, the UV-Visible analysis was made to determine the bandgap energy and Urbach energy profiles of fabricated samples. The significant decrease in bandgap energy was noticed for co-doped LaCoO3 i.e. Ag/Gd@LaCoO3 as compared to pure LaCoO3. The calculated bandgap (Eg) values of LaCoO3, Ag@LaCoO3, Gd@LaCoO3, and Ag/Gd@LaCoO3 were 3.11 eV, 2.98 eV, 2.83 eV, and 2.44 eV respectively. The decrement in bandgap energy of Ag/Gd@LaCoO3 could be accredited to the increment in its crystallite size as compared to its other counter parts. The average crystallite size and bandgap energy are in good agreement with each other due to the production of quantum confinement effect in LaCoO3 after doping. Furthermore, the samples were tested for the photocatalytic degradation of bromocresol blue (BCB) and bromocresol green (BCG) under sunlight irradiation of about 60 min. The results of photocatalytic experiments showed 88% and 91% degradation of BCB and BCG respectively by Ag/Gd@LaCoO3 photocatalyst. The enhanced catalytic removal activity of Ag/Gd@LaCoO3 could be assigned to its small bandgap, large crystallite size, high Urbach energy, and high % porosity as compared to pure LaCoO3, Ag@LaCoO3, and Gd@LaCoO3. Hence, Ag/Gd@LaCoO3 can be an efficient photocatalyst for the removal of various industrial effluents.

High-temperature sensitivity complex dielectric/electric modulus, loss tangent, and AC conductivity in Au/(S:DLC)/p-Si (MIS) structures

Complex dielectric (ε* = ε′ − jε″)/electric modulus (M* = M′ + jM″), loss tangent (tanδ), and ac conductivity (σac) properties of Au/(S-DLC)/p-Si structures were investigated by utilizing admittance/impedance measurements between 80 and 440 K at 0.1 and 0.5 MHz. Sulfur-doped diamond-like carbon (S:DLC) was used an interlayer at Au/p-Si interface utilizing electrodeposition method. The capacitance/conductance (C/G) or (ε' ~ C) and (ε″ ~ G) values found to be highly dependent on both frequency and temperature. The increase of them with temperatures was attributed to the thermal-activated electronic charges localized at interface states (Nss) and decrease in bandgap energy of semiconductor. The observed high ε′ and ε″ values at 0.1 MHz is the result of the space/dipole polarization and Nss. Because the charges are at low frequencies, dipoles have sufficient time to rotation yourself in the direction of electric field and Nss can easily follow the ac signal. Arrhenius plot (ln(σac) vs 1/T) shows two distinctive linear parts and activation energy (Ea) value was found as 5.78 and 189.41 from the slope; this plot at 0.5 MHz is corresponding to low temperature (80–230 K) and high temperature (260–440 K), respectively. The observed higher Ea and ε′ (~ 14 even at 100 kHz) show that hopping of electronic charges from traps to others is predominant charge transport mechanism and the prepared Au/(S:DLC)/p-Si structure can be used to store more energy.

In-situ growth of CuI/Porphyrin-based graphdiyne (PDY) p-n heterojunction for high-performance cathodic photoelectrochemical sensing

Cathodic photoelectrochemical (PEC) bioanalysis has been attracting great interest due to its excellent anti-interference capability. As a p-type wide energy band gap semiconductor, CuI is regarded as an ideal material for the construction of photocathodes, while its poor stability and narrow light absorption range limit its application as a photoelectrode in PEC sensing. Herein, we report a simple in-situ growth strategy to synthesize CuI/Porphyrin-based graphdiyne (PDY) p-n heterojunction as a photocathode. CuI crystals were firstly deposited on the ITO glass surface via the electrochemical deposition, and CuI could catalyze the in-situ Glaser coupling reaction of 5,10,15,20-tetra(4-ethynylphenyl) porphyrin (TEPP), allowing the growth of PDY film on the CuI crystal surface and forming the p-n heterojunction photocathode. The as-prepared PDY film plays a crucial role in the significant enhancement of PEC performance because of its intense light absorption, and the formation of CuI/PDY p-n heterojunction can efficiently promote the transportation of photogenerated carriers between CuI and PDY thanks to the excellent electrical conductivity and high carrier mobility of highly π-conjugated PDY. After the growth of PDY, the photocurrent response of PDY/CuI/ITO is almost seven folds higher compared to that of CuI/ITO. Owing to the selective Cu–S bond interaction between l-cysteine (L-Cys) and Cu+, a PEC sensor for the L-Cys determination is developed with a broad linear range from 0.05 to 1.2 μM and a limit of detection (LOD) of 0.03 μM.

Effect of Temperature Variation on Band Gap Value in Thin Layers of Nano Photocatalyst Fe2O3/CuO/MnO2

Water is one of the primary needs of all living things in daily life. However, the availability of clean water is currently starting to decrease along with the decline in the quality and quantity of water in the environment. Industrialization and rapid economic development have caused concern due to the habit of disposing of waste without proper management. Attempts to get clean water free from pollution are to utilize technology with photocatalytic properties that can reduce liquid pollutants with Infra-Red light. The purpose of this study was to determine the optimum conditions of the band gap to photocatalyst by temperature variation. Fe2O3, CuO, and MnO2 are doped semiconductor materials for the application of photocatalyst properties. The materials were milled using a High Energy Milling (HEM-3ED) to obtain nanoparticle sizes. The synthesis was carried out by sol-gel and spin-coating methods to make a thin film in enhancing photocatalytic activity in industrial applications. Characterization was conducted using ultraviolet-visible (Uv-Vis) spectrophotometry analysis. The results showed that temperature affects photocatalyst properties and the band gap value obtained at a temperature variation of 400°C is 1.36 eV which is the most optimum semiconductor band gap energy.

Ultrasound-Assisted Mineralization of 2,4-Dinitrotoluene in Industrial Wastewater Using Persulfate Coupled with Semiconductors.

Oxidative degradation of 2,4-dinitrotoluenes in aqueous solution was executed using persulfate combined with semiconductors motivated by ultrasound (probe type, 20 kHz). Batch-mode experiments were performed to elucidate the effects of diverse operation variables on the sono-catalytic performance, including the ultrasonic power intensity, dosage of persulfate anions, and semiconductors. Owing to pronounced scavenging behaviors caused by benzene, ethanol, and methanol, the chief oxidants were presumed to be sulfate radicals which originated from persulfate anions, motivated via either the ultrasound or sono-catalysis of semiconductors. With regard to semiconductors, the increment of 2,4-dinitrotoluene removal efficiency was inversely proportional to the band gap energy of semiconductors. Based on the outcomes indicated in a gas chromatograph-mass spectrometer, it was sensibly postulated that the preliminary step for 2,4-dinitrotoluene removal was denitrated into o-mononitrotoluene or p-mononitrotoluene, followed by decarboxylation to nitrobenzene. Subsequently, nitrobenzene was decomposed to hydroxycyclohexadienyl radicals and converted into 2-nitrophenol, 3-nitrophenol, and 4-nitrophenol individually. Nitrophenol compounds with the cleavage of nitro groups synthesized phenol, which was sequentially transformed into hydroquinone and p-benzoquinone.

Preparation and characterization of Sn doped NiO thin films by sol–gel spin coating technique

Nickel Oxide (NiO), being a wide energy bandgap semiconductor, exhibit excellent optical, electrical and magnetic characteristics and show great application potential in various technological applications. Doping with suitable dopant is known to further enhance the intrinsic properties of NiO. Pristine and Sn-doped (2, 4, 6 and 8 mol%) nano-crystalline NiO films are deposited onto the substrates (glass) using conventional sol–gel spin coating technique. Detailed structural, optical, and photoluminescence properties are examined to comprehend the consequences of Sn doping in NiO host matrix. The XRD results reveal the formation of single phased, polycrystalline films that have cubic face-centered structure of NiO. The crystallinity and size of crystal found decreasing as increasing the Sn doping concentration. The vibrational stretching modes of Ni-O absorption band are observed from the FTIR spectra with wave number of 550–750 cm−1. The UV–visible transmittance results show that, the prepared samples of pure, 2 mol% and 4 mol%Sn doped NiO exhibit 75%transmittance within the visible region and which decreases with raise in concentration of Sn. Further, the optical bandgap of the films is evaluated using the Tauc’s relations and the optical energy bandgap values are found to be 3.47, 3.51, 3.52, 3.50 and 3.44 eV for pristine, 2 mol%,4 mol%, 6 mol%, and 8 mol% Sn doped films, respectively. The results offered that the structural and optical properties can be tailored by varying concentration of dopant; these films are the potential candidates for gas sensing and optoelectronic device applications.

Dispensability of the conventional Tauc’s plot for accurate bandgap determination from UV–vis optical diffuse reflectance data

The use of the conventional Tauc’s method to determine optical bandgap energy from UV–vis spectroscopy data has been overemphasized for decades. However, a misuse of the Tauc’s formula in conjunction with the Kubelka-Munk function to determine the bandgap energy of semiconductors from diffuse reflectance data can lead to erroneous estimates. Particularly, large errors can be associated with computing values of the ordinate using the Tauc-Kubelka-Munk relationship for diffuse reflectance to produce Tauc’s plot. To address this apparent error, the present paper shows that the reflectance versus photon energy plot for bandgap estimation from UV–vis diffuse reflectance data can be employed to obtain reasonable bandgap values, suggesting that the conventional Tauc’s plot is not indispensable for accurate bandgap energy determination. The relatively simple method can be best choice when a researcher is unsure about the accurate computations from diffuse reflectance data which lead to proper Tauc’s plot. Interestingly, the rarely reported (if at all it can be found elsewhere) step-by-step approach to Tauc’s plot from diffuse reflectance data is described in this paper to serve as a simple guide for emerging material scientists. The UV–vis optical diffuse reflectance data for β-Ga2O3, ZnO and TiO2 semiconductor films are used for this study.

Photocatalytic Reduction of CO2 with N-Doped TiO2-Based Photocatalysts Obtained in One-Pot Supercritical Synthesis.

The objective of this work was to analyze the effect of carbon support on the activity and selectivity of N-doped TiO2 nanoparticles. Thus, N-doped TiO2 and two types of composites, N-doped TiO2/CNT and N-doped TiO2/rGO, were prepared by a new environmentally friendly one-pot method. CNT and rGO were used as supports, triethylamine and urea as N doping agents, and titanium (IV) tetraisopropoxide and ethanol as Ti precursor and hydrolysis agent, respectively. The as-prepared photocatalysts exhibited enhanced photocatalytic performance compared to TiO2 P25 commercial catalyst during the photoreduction of CO2 with water vapor. It was imputed to the synergistic effect of N doping (reduction of semiconductor band gap energy) and carbon support (enlarging e−-h+ recombination time). The activity and selectivity of catalysts varied depending on the investigated material. Thus, whereas N-doped TiO2 nanoparticles led to a gaseous mixture, where CH4 formed the majority compared to CO, N-doped TiO2/CNT and N-doped TiO2/rGO composites almost exclusively generated CO. Regarding the activity of the catalysts, the highest production rates of CO (8 µmol/gTiO2/h) and CH4 (4 µmol/gTiO2/h) were achieved with composite N1/TiO2/rGO and N1/TiO2 nanoparticles, respectively, where superscript represents the ratio mg N/g TiO2. These rates are four times and almost forty times higher than the CO and CH4 production rates observed with commercial TiO2 P25.

Comparative Study of High-Temperature Annealed and RTA Process β-Ga2O3 Thin Film by Sol–Gel Process

As a wide energy band gap semiconductor, a Ga2O3 thin film was prepared by the sol–gel process with different annealing processes. Since Ga2O3 is a type of metal oxide structure, an oxygen annealing process can be considered to remove oxygen defects. An effective oxygen annealing process can help form a β-Ga2O3 structure with reduced defects. In this study, different types of annealing effects for β-Ga2O3 were investigated and compared. An electric furnace process using thermal effect characteristics of and an Rapid Thermal Annealing (RTA) process applied with an infrared radiation light source were compared. Two and 4 h thermal annealing processes were conducted at 900 °C in the furnace. Meanwhile, to study the optical annealing effects, 2 h furnace at 900 °C + 15 min in rapid thermal annealing and only 15 min in rapid thermal annealing effects were compared, respectively. Through increasing the thermal annealing temperature and time, β-Ga2O3 can be formed even though a sol–gel process was employed in this experiment. An annealing temperature of at least 900 °C was required to form β-Ga2O3 thin film. Moreover, by introducing an RTA process just after the spinning process of thin film, a β-Ga2O3 thin film was formed on the sapphire substrates. Compared with the electric furnace process applied for 2 h, the RTA process performed in 15 min has a relatively short process time and results in similar structural and optical characteristics of a thin film. From the X-ray diffraction patterns and UV spectrometer analysis, optically annealed β-Ga2O3 thin films on the sapphire substrate showed a highly crystalized structure with a wide energy band gap of 4.8 eV.

Optimum matching of photovoltaic–thermophotovoltaic cells efficiently utilizing full-spectrum solar energy

The production of redundant waste heat limits the performance of photovoltaic cells, so removing waste heat and converting it back into electricity is a promising way to improve the utilization of solar energy. A new concentrated solar spectrum photovoltaic-thermophotovoltaic hybrid system mainly is proposed. Full-spectrum solar energy is split into different parts according to specific requirements. Expressions for the efficiency and power output of the system are derived. The effects of the voltage output and area ratio of the two subsystems, the bandgap energy of semiconductor in the photovoltaic cell, and the solar concentration factor on the system performance are analyzed comprehensively. By optimizing several key parameters, the problem of the optimal matching between two subsystems is solved. The performance characteristics of the system are revealed, and the maximum efficiency and corresponding power output density of the hybrid system are calculated numerically, reaching 47.74% and 31.13W cm−2, respectively, which are 9.190% and 19.25% higher than those of a single photovoltaic cell. The optimal selection criteria of several key parameters are provided. By comparison with other PV-based systems, the proposed system not only maintains a high energy conversion efficiency but also produces a relatively larger power output density.

Polymer nanocomposites comprising PMMA matrix and ZnO, SnO2, and TiO2 nanofillers: A comparative study of structural, optical, and dielectric properties for multifunctional technological applications

Abstract Polymer nanocomposite (PNC) films consisted of poly (methyl methacrylate) (PMMA) matrix and wide energy bandgap semiconductor nanocrystallite fillers viz. zinc oxide (ZnO), tin oxide (SnO2), and titanium dioxide (TiO2) were prepared by a sonicated suspension of nanoparticles in polymeric solutions followed by the casting method. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) characterization revealed successful nanocomposite formation of these hybrids. The ultraviolet–visible (UV–Vis) spectroscopic study explained that the absorbance and energy bandgap of these PNC films largely differed with the type of metal oxide nanofillers and their concentrations (i.e., 1–5 wt%). The UV-absorbance was found relatively high for the PMMA/TiO2 films and low for the PMMA/SnO2 films at the same concentration of the fillers. The film thickness dependent study confirmed that the increase of film thicknesses significantly enhanced the UV–Vis absorbance and reduced the energy bandgaps of the same composition PMMA/TiO2 composites. The dielectric permittivity of the ZnO and SnO2 containing PNC films was found to be appreciably increased with the increase of concentration of these nanocrystallite fillers, whereas the films bearing TiO2 nanoparticles exhibited a decrease in permittivity as compared to that of the host PMMA matrix film at the temperature of 30 °C. Further, a gradual decrease in the permittivity of these nanocomposite materials was noted with the increase of experimental electric field frequency from 20 Hz to 1 MHz range. The electric modulus spectra exhibited a single relaxation process in the lower frequency region which attribute to the ester group rotations of the PMMA chain repeat units and it was found to be largely influenced by the fillers and their concentrations in these nanocomposites. The AC electrical conductivities of all these PNC films were observed slightly increased and showed a linear behaviour with the frequency variation. The wide range tailorable behaviour of the optical and dielectric parameters with the change of nanofillers and their concentrations evidence that these PNCs could be promising multifunctional materials for UV-shielders, optical sensors, and bandgap tuners in developing various advanced optoelectronic and organoelectronic devices, and also their use as low permittivity nanodielectric insulators and substrates to architect the next-generation flexible-type electronic devices.

SrTiO3 nanocubes doped with ir as photocatalytic system for enhancing H2 generation from water splitting

Designing an effective photocatalyst for hydrogen (H2) performance under visible irradiation with a decrease the band gap energy of semiconductor has been considered as an essential aspect in boosting the performance of photocatalytic reactions. Herein, we focus on evaluating the role of doping with Ir into SrTiO3 structure fabricated by hydrothermal method for H2 generation. The crystalline characteristics the Ir-SrTiO3 photocatalyst were carried out via XRD and FE-SEM. The chemical composition and the optical properties of the Ir-SrTiO3 were classified by EDX and UV-Vis spectra, respectively. The results showcased that the dramatically improved absorbing performances of Ir/SrTiO3 specimen could be governed by the presence of Ir impurity states in the forbidden energy gap causing a decrease in energy gap of SrTiO3. This work also revealed that Ir doped into SrTiO3 exhibited excellent photocatalytic H2 evolution compared with pristine SrTiO3 (~454 and ~325 mmol.h-1.g-1 H2 production under UV and visible light irradiation, respectively). A rational photocatalytic mechanism is projected to be able provide significant awareness for further research.

Advanced NiMoO4/g-C3N4 Z-scheme heterojunction photocatalyst for efficient conversion of CO2 to valuable products

Abstract Herein, g-C3N4 and NiMoO4, which are moderate energy band gap semiconductors, have been effectively hybridized to create Z scheme heterojunction for successful visible-light photocatalytic converting CO2 into valuable products including CH4, CO, O2 and HCOOH. Ni(NO3)2·6H2O and (NH4)6Mo7O24·4H2O were used as precursors to synthesize NiMoO4 photocatalyst, which was continuously mixed with melamine before calcinating at 520 °C for 6 h to get NiMoO4/g-C3N4 Z scheme heterojunction. We explored that NiMoO4 intimately contacted with g-C3N4. These band positions of the NiMoO4 were also perfectly matched with those of the g-C3N4. Therefore, these photo-induced e− on conduction band of the NiMoO4 could easily travel to h+ on valence band of the g-C3N4 (recombination); thereby, minimize h+ and e− recombination in each material. Therefore, the NiMoO4/g-C3N4 direct Z-scheme heterojunctions could produce significant available h+ on the valence band of the NiMoO4 and e− on the conduction band of the g-C3N4. These e−/h+ have suitable redox potential to effectively convert CO2. Finally, the optimized g-C3N4 mole ratio for maximum enhancing photocatalytic efficiency of the NiMoO4/g-C3N4 heterojunction was 60%. When the g-C3N4 content increased to 70%, the excess g-C3N4 amount would entirely cover NiMoO4 surface leaded to form dense and closed shell. The formed closed shell decreased contact between NiMoO4 and CO2 as well as the interface charge transfer, which reduced the e− and h+ separation and transfer leading to decrease in photocatalytic conversion efficiency.

Degradation of Diclofenac in Aqueous Solutions under Conditions of Combined Homogeneous and Heterogeneous Photocatalysis

The sorption and photocatalytic activities of metal–ceramic composites synthesized via self-propagating high-temperature synthesis (SHS) in the degradation of diclofenac (DCF) is studied. The phase composition and optical properties of the composites are studied, along with the bandgap energy of semiconductors that form part of a ceramic matrix were determined from electronic absorption spectra. The effects the phase composition, UV irradiation time, amount and nature of the added catalyst (H2C2O4, H2O2), and the composite’s weight have on the oxidative destruction of organic contaminant are studied to optimize the catalytic process. The combination of heterogeneous catalysis using composites based on boron and sialon with the homogeneous photo-Fenton system demonstrate the highest efficiency in the degradation of diclofenac.

Accurate Band Gap Predictions of Semiconductors in the Framework of the Similarity Transformed Equation of Motion Coupled Cluster Theory.

In this work, we present a detailed comparison between wave-function-based and particle/hole techniques for the prediction of band gap energies of semiconductors. We focus on the comparison of the back-transformed Pair Natural Orbital Similarity Transformed Equation of Motion Coupled-Cluster (bt-PNO-STEOM-CCSD) method with Time Dependent Density Functional Theory (TD-DFT) and Delta Self Consistent Field/DFT (Δ-SCF/DFT) that are employed to calculate the band gap energies in a test set of organic and inorganic semiconductors. Throughout, we have used cluster models for the calculations that were calibrated by comparing the results of the cluster calculations to periodic DFT calculations with the same functional. These calibrations were run with cluster models of increasing size until the results agreed closely with the periodic calculation. It is demonstrated that bt-PNO-STEOM-CC yields accurate results that are in better than 0.2 eV agreement with the experiment. This holds for both organic and inorganic semiconductors. The efficiency of the employed computational protocols is thoroughly discussed. Overall, we believe that this study is an important contribution that can aid future developments and applications of excited state coupled cluster methods in the field of solid-state chemistry and heterogeneous catalysis.

DC Arc discharge synthesized zirconia nanoparticles: shed light on arc current effects on size, crystal structure, optical properties and formation mechanism

In this study zirconia nanoparticles (NPs) were successfully synthesized via the direct current (DC) arc discharge method in water. Formation mechanism of NPs and the effect of arc current on morphological, structural and optical properties of NPs have been studied. The NPs were synthesized at four different currents in the 40–160 A range. SEM observations showed NPs are spherical in shape and their average size decrease from 40 to 22 nm by increasing the current from 40 to 160 A. XRD analysis revealed phase composition of NPs is a mixture of tetragonal and monoclinic for all the samples, and the phase fraction of NPs are arc current dependent in such a way that an increase in the current leads to an increase in the weight percent of the tetragonal phase. UV–vis spectroscopy indicated that the NPs exhibit optical characteristics of the wide energy band gap semiconductors with a significant amount of oxygen deficiency. Also the effect of the arc current on the energy band gap of NPs were investigated. An increase in the arc current decreases energy band gap of the NPs from 3.8 to 3.0 eV. Optical emission spectroscopy (OES) studies demonstrate formation of zirconia NPs at temperatures as high as 4953 K, thereby zirconium exited species react with some of oxygen containing species. Finally, Thermal radiation measurement is proposed as a nondestructive method to evaluate the active mechanisms in an arc discharge zone beside other methods such as OES.

Photoelectrochemical Hydrogen Evolution Driven by Visible-to-Ultraviolet Photon Upconversion

Activation of ultraviolet (UV) energy bandgap semiconductors for solar fuel production using visible light as energy source is one of the most challenging tasks in the artificial photosynthesis fie...

Highly Stable Plasmon Induced Hot Hole Transfer into Silicon via a SrTiO3 Passivation Interface

AbstractExtracting plasmon‐induced hot carriers over a metal–semiconductor Schottky barrier enables photodetection below the semiconductor bandgap energy. However, interfacial carrier recombination hinders the efficiency and stability of this process, severely limiting its implementation in telecommunication. This study proposes and demonstrates the use of epitaxially grown lattice‐matched SrTiO3 for interfacial passivation of silicon‐based plasmonic Schottky devices. The devices are activated by an electrical soft‐breakdown of the interfacial SrTiO3 layer, resulting in reproducible rectified Schottky characteristics. The transition to a low resistance state of the SrTiO3 layer boosts the extraction efficiency of hot holes upon resonant plasmonic excitation, giving rise to a two orders of magnitude higher photocurrent compared to devices with a native oxide layer. Photoresponse, tunability, and barrier height studies under reverse biases as high as 100 V present superior stability with the incorporation of the SrTiO3 layer. The investigation paves the way toward plasmon‐induced photodetection for practical applications including those under challenging operating conditions.

Optoelectronic Structure and Related Transport Properties of Ag2Sb2O6 and Cd2Sb2O7

Using the full-potential linearized augmented-plane wave method, the electronic structure and thermoelectric properties of Ag2Sb2O6 and Cd2Sb2O7 compounds have been explored. The modified Becke–Johnson potential was applied to treat the exchange–correlation energy term. The electronic band structures reveal that the valence-band maximum and conduction-band minimum occur at Γ point, indicating that Ag2Sb2O6 and Cd2Sb2O7 are direct energy bandgap semiconductors. Strong hybridization appeared between Ag (Cd)-s/p and O-s/p states. The optical properties, i.e., complex dielectric function, reflectivity, refractive index, and energy loss function, reveal high reflectivity in the ultraviolet energy range, indicating usefulness of these materials in shields from high-energy radiation. Combining transport theory and the outputs from the full-potential linearized augmented-plane wave calculations, the thermoelectric properties were analyzed as functions of temperature. Due to their high thermopower and narrow bandgap, Ag2Sb2O6 and Cd2Sb2O7 are suitable materials for application in optoelectronic and thermoelectric devices.

A novel theoretical model for the temperature dependence of band gap energy in semiconductors

We report a novel theoretical model without any fitting parameters for the temperature dependence of band gap energy in semiconductors. This model relates the band gap energy at the elevated temperature to that at the arbitrary reference temperature. As examples, the band gap energies of Si, Ge, AlN, GaN, InP, InAs, ZnO, ZnS, ZnSe and GaAs at temperatures below 400 K are calculated and are in good agreement with the experimental results. Meanwhile, the band gap energies at high temperatures (T > 400 K) are predicted, which are greater than the experimental results, and the reasonable analysis is carried out as well. Under low temperatures, the effect of lattice expansion on the band gap energy is very small, but it has much influence on the band gap energy at high temperatures. Therefore, it is necessary to consider the effect of lattice expansion at high temperatures, and the method considering the effect of lattice expansion has also been given. The model has distinct advantages compared with the widely quoted Varshni’s semi-empirical equation from the aspect of modeling, physical meaning and application. The study provides a convenient method to determine the band gap energy under different temperatures.