Semiconductor Energy Gap Research Articles

Optoelectronic and photocatalytic properties of GaN, GeS and SiS monolayers and their vdW heterostructures

Using first principles calculations the optoelectronic and photocatalytic properties of GaN, GeS, SiS monolayers, and GaN-GeS/SiS, GeS-SiS van der Waals (vdW) heterostructures are studied for the first time. Initially, it is confirmed that all monolayers and their vdW heterostructures are stable in energy and phonon vibrations, respectively. GaN, GeS, and SiS monolayers are found an indirect energy gap semiconductor with energy gap values are 2.17, 2.25, 2.17 eV, respectively. Type-II band alignment has been observed in GaN-GeS/SiS and GeS-SiS vdW heterostructures which represent application into photovoltaic and energy harvesting devices. Furthermore, charge transfer at the interface of GaN-GeS/SiS and GeS-SiS vdW heterostructures generates an inbuilt electric field which in turn pushing electrons and holes in opposite direction, this can avoid recombination of photogenerated electron-hole pairs. Charge carrier separation inside the materials is the prime criteria for optoelectronic and photocatalytic applications. Upgraded optical features of vdW heterostructures reveal their remarkable absorption of visible light which hold promise for future high-performance photocatalysts and optical devices. Moreover, the suitable band edge positions of GaN, GeS, SiS monolayers, and GaN-GeS/SiS, GeS-SiS van der Waals (vdW) heterostructures relative to the standard electrode potentials at PH = 0, indicates that these materials can be used as a photocatalyst.

Modeling optical energy gap of strontium titanate multifunctional semiconductor using stepwise regression and genetic algorithm based support vector regression

Strontium titanate semiconductor is multi-functional metallic oxide with perovskite structure and wide range of applications in oxygen gas sensors (in storage batteries), superconductivity, ferro-electricity, dielectric constant materials, dye-sensitized solar cells photo-electrodes, optoelectronics applications and photocatalysis. The wide band gap of strontium titanate metal oxide constrains its response to ultraviolent light with light harvesting capacity of 5% for incoming solar energy in generating photocatalytic activity. Anions and cations incorporation into the parent strontium titanate compound strongly break the semiconductor symmetry and ultimately influence the energy gap with stretches as well as distortions in perovskite structural architecture. This work develops genetic algorithm based support vector regression (GABSVR) hybrid model and stepwise regression algorithm (SRA) for modeling the energy gap of distorted strontium titanate semiconductor using structural lattice constants and the size of its nano-particles as model descriptors. The developed GABSVR model performs better than SRA model with performance improvement of 62.98%, 79.12% and 81.05% using coefficient of correlation (CC), mean absolute error (MAE) and root mean square error (RMAE) metrics, respectively. The developed model investigates the influence of preparation method, silver dopants, nitrogen dopants and sulfur incorporation on energy gap of strontium titanate photocatalytic activity. The developed GABSVR model was further validated externally for determining the significance of cobalt dopants on the activity of strontium titanate and the obtained energy gaps agree well with the measured values. High level of precision demonstrated by the developed hybrid model is of enormous significance for strengthening light harvesting capacity of the semiconductor for optoelectronics and photocatalysis applications.

Band gap engineering in blended organic semiconductor films based on dielectric interactions.

Blending organic molecules to tune their energy levels is currently being investigated as an approach to engineer the bulk and interfacial optoelectronic properties of organic semiconductors. It has been proven that the ionization energy and electron affinity can be equally shifted in the same direction by electrostatic effects controlled by blending similar halogenated derivatives with different energetics. Here we show that the energy gap of organic semiconductors can also be tuned by blending. We use oligothiophenes with different numbers of thiophene rings as an example and investigate their structure and electronic properties. Photoelectron spectroscopy and inverse photoelectron spectroscopy show tunability of the single-particle gap, with the optical gaps showing similar, but smaller, effects. Theoretical analysis shows that this tuning is mainly caused by a change in the dielectric constant with blend ratio. Further studies will explore the practical impact of this energy-level engineering strategy for optoelectronic devices.

The Case Studies of PtX2 (X = As, P) as High Thermo-power Materials

For thermoelectric applications, semiconductors are generally better than metals and insulators. PtAs2 and PtP2 are indirect energy gap semiconductors that have been predicted with high thermo-powers (PtP2 having higher thermopower than PtAs2). The crystal structure and the electronic structure of PtAs2 and PtP2 are similar except for the energy band gap of PtP2 that is wider than that of PtAs2. The generalized gradient approximation of the Density Functional Theory (DFT), the Density Functional Perturbation Theory (DFPT) were used to explore the full elastic tensors, phonon dispersion and the thermodynamics of PtP2 and PtAs2. This was done to understand the link, if any, between high thermo-power materials and the results. The two compounds are dynamically and elastically stable with higher mechanical properties recorded for PtP2 over PtAs2. The calculated entropy, vibration free energy and the heat capacity at constant volume for PtAs2 (PtP2) were 354.51 (264.18) J/K; -9.21 (27.84) kJ and 276.04 (250.36) J/K at 300 K respectively. The low frequency acoustic modes are between 100 - 170 cm-1 for PtAs2 while it is between100 - 190 cm-1 for PtP2. The calculated high frequency transverse optical (TO) mode for PtP2 is 410 cm-1 while it is 250 cm-1 for PtAs2. Further analysis of the phonons spectrum showed that additional bond-bending modes can be created in PtP2 than in PtAs2. All the results points toward PtP2 as better material over PtAs2 for thermoelectric application and these, with or without the knowledge of the energy bandgap can serve to guide material selection/modelling.

Doped ZnO Nanostructured and their application as photocatalytic: as Review

There are two types of methods of synthesis of several different kinds of doped ZnO nanomaterials for photocatalytic applications, gas phase methods, include pulsed laser deposition and chemical vapor deposition and wet chemical methods such as sol–gel, electrospinning, hydrothermal, spray pyrolysis, thermomechanical .doping with metal ions is make local energies levels within the semiconductor energy gap, which results in prolongation of the light absorbance to the visible light region. Several studies have that metaldoped ZnO, such as N, S, and C, using Co, Fe, Cu, Eu, Ce, Ag, Mn, and Al and non-metal doping, ZnO to the reducing Energies and enhancement of photocatalytic behavior in the region of visible light.

Empirical Relation for Electronic and Optical Properties of Binary Tetrahedral Semiconductors

The concept of ionicity has been developed by Phillips and Van Vechten from the dielectric analysis of the semiconductors and insulators to evaluate various bond parameters of binary tetrahedral (AIIBVI and AIIIBV) semiconductors. In this paper, an advance hypothesis of average atomic number of the elements in a compound has been used to evaluate intrinsic electronic and optical parameters such as ionic gap (Ec), average energy gap (Eg), crystal ionicity (fi) and dielectric constant (ϵ) of binary tetrahedral semiconductors.

Structural and elastic properties of binary semiconductors from energy gaps

In the present work, we have calculated the structural and mechanical properties of II–VI and III–V tetrahedral semiconductors using some empirical relations. The calculated properties are then correlated with the optical energy gap of respective semiconductors. We carried out a comparative analysis between the predictions obtained from different empirical relations. An exponential relationship is proposed to obtain plasmon energy of binary tetrahedral semiconductors directly from their energy gap. The plasmon energy have been correlated with some of the semiconductor properties. The predicted values of the structural and elastic properties of the semiconductors from a recently proposed Tripathy relation are found to be compatible with those from many other established empirical formulae.

The Role of Oxide Traps Aligned With the Semiconductor Energy Gap in MOS Systems

This work demonstrates that when inelastic tunneling between oxide traps and semiconductor bands is considered, the traps with energy aligned to the semiconductor bandgap play a significant role in the frequency dispersion of the capacitance–voltage ( C–V ) and conductance–voltage ( G–V ) characteristics of metal–oxide–semiconductor (MOS) systems. The work also highlights that a nonlocal model for tunneling into interface states is mandatory to reproduce experiments when carrier quantization in the inversion layer is accounted for. A model, including these ingredients, is used to evaluate the energy and depth distribution of oxide traps in a n-In0.53Ga0.47As/Al2O3 MOS system and is able to accurately fit the C–V frequency dispersion from depletion to weak inversion. The oxide trap distribution determined from the C–V response predicts the corresponding G–V dispersion with frequency.

Criteria of the electron pumping in electron-hole quantum plasma

The degradation of quantum semiconductor plasma during electron pumping is an important problem since it has several applications in the technological industry. Moreover, the identification of such a problem cannot be accomplished by experiment alone and a further theoretical investigation is required. Owing to the energy gap of semiconductors, electrons should acquire energy in order to move from the valence band to the conduction band. Therefore, to employ the quantum fluid model that includes the exchange-correlation potentials, Bohm potential, and the degenerate pressure, the electron-hole lifetime should be greater than the plasma oscillation time. If the latter condition is not satisfied, the quantum fluid model failed to describe the system and it is convenient to use the density functional theory. As a result of that, we apply the quantum fluid model to GaN where the plasma oscillation has a time of 0.002 ps while the electron-hole lifetime is 1 ps. The modified Kadomtsev-Petviashvili (mKP) equation had been obtained using a new set of stretched coordinates as the Kadomtsev-Petviashvili (KP) equation had been derived in (Afify et al 2019 Chaos Soliton Fract 124, 18–25). Our findings determine whether the quantum fluid model is valid or not in the case of semiconductor plasma. Studying exchange effects in a dynamic context has certain limitations. Thus, we stressed that the more accurate approaches introduced in the literature are hard to apply for nonlinear issues. Further, the applicability of our results is discussed, but not this much. Moreover, the numerical results showed that the electron beam parameters and quantum effects have significant effects on the growth of the solitary waves.

Realization of noble heterobilayers with enhanced optoelectronic properties

First-principles calculations were performed to investigate the materials properties such as structural, electronic, optical and vibrational of PdS2/PtS2 and PdSe2/PtSe2 noble heterobilayers. The energetic and dynamic stability of the noble heterobilayers have been confirmed in term of binding energy and phonon vibrations, respectively. The phonon spectra show that the interlayer coupling in the noble heterobilayers is comparatively stronger than that in the transition metal dichalcogenide heterobilayers. The electronic band structure analysis reveals that PdS2/PtS2 and PdSe2/PtSe2 noble heterobilayers are indirect energy gap semiconductor materials. We have observed spin-orbit coupling effect in the electronic band structure of PdS2/PtS2 and PdSe2/PtSe2 noble heterobilayers, which make them prospective materials for nanospintronic devices. The charge carrier separation in PdSe2/PtSe2 noble heterobilayer indicates its application in the photovoltaic and energy harvesting devices. The PdS2/PtS2 and PdSe2/PtSe2 noble heterobilayers exhibit intrinsic type-II band alignment which is required in the photovoltaic and photocatalytic devices. Furthermore, PdS2/PtS2 and PdSe2/PtSe2 noble heterobilayers reveal enhanced optical absorption both in the ultraviolet and visible regions as compared to their respective monolayers.

Optical and Structural Characterization of CdTe Nanoparticles Synthesized Using Chemical Bath Deposition Technique

The purpose of this research is the elaboration of cadmium telluride nanoparticles by using the chemical bath deposition technique. The formulation procedure consists of preparing tellurium ions (Te−2) and combination of tellurium ion solution with deionized water, cadmium chloride, and polyethyleneimine (PEI). The nanoparticles were synthesized at three different concentrations denoted C1, C2, and C3. Furthermore, for each CdTe, nanoparticles were obtained with absorption edges at 404.02 nm, 428 nm and 452.66 nm related to C1, C2, and C3, respectively. Also, the direct energy gaps of CdTe nanoparticle semiconductors were: Eg(C1) = 3.07 eV, Eg(C2) = 2.9 eV, and Eg(C3) = 2.74 eV. Transmission electron microscopy (TEM) indicated three different average diameter sizes of a single nanoparticle: D(C1) = 3.23 nm, D(C2) = 6.46 nm, and D(C3) = 7.73 nm with average sizes of 6.11 nm, 5.29 nm, and 9.76 nm, respectively. The fast Fourier transform of TEM contrast micrographs corresponded with a hexagonal structure. The presence of Cd, Te, and TeO2 was identified by x-ray photoelectron spectroscopy. Raman spectroscopy was used to identify three peaks at 122 cm−1, 140 cm−1 and 165 cm−1 that proved the formation of CdTe nanoparticles.

Experimental investigation of sandwich glazed solar photovoltaic module

The light and heat energies from the sun are directly converted into electricity either by directly using solar photovoltaic (SPV) module or indirectly using concentrated solar technology system. Photovoltaic (PV) cells is a semiconductor device which is sensitive to temperature. The energy gap of the silicon material reduces when its temperature increases. The decrease in the energy gap of the silicon semiconductor with increasing working temperature can affect the performance of the PV cell. In this article, the working temperature of commercial grade silicon-based solar photovoltaic module as well as sandwich glazed solar photovoltaic module and its impact upon the electricity delivered is discussed. The significant effects of operating temperature, irradiation and wind speed on the PV module temperature were presented. These parameters were used to estimate the electrical performance of the commercial and sandwich glazed PV modules.

Investigation of fast and slow traps in atomic layer deposited AlN on 4H-SiC

We investigated the electrical and interfacial properties of AlN/4H-SiC interfaces prepared by atomic layer deposition (ALD). The conductance–voltage (G/ω–V) characteristics were identified based on two types of traps: fast and slow. Fast traps located in the semiconductor energy gap close to the AlN/SiC interface showed both narrow and wide energy distributions. Slow traps with defects in the AlN layer exhibited a narrow energy distribution. According to X-ray photoelectron spectroscopy analysis, the formation of AlN during the initial ALD deposition was unclear and some of the oxygen atoms present on the SiC surface were converted into Al2O3. Both O 1s and Al 2p core level spectra shifted to lower energies as the AlN thickness increased. This was associated with the strain relaxation originating from the lattice mismatch between AlN and SiC.

Rigid-band electronic structure of scandium nitride across the n -type to p -type carrier transition regime

Intentional doping and unintentional impurities in intrinsic semiconductors generate carriers that enable device operations. Fundamental to the electronic activity of dopants and impurities is the introduction of defect states inside the forbidden energy gap of semiconductors having shallow and/or deep characteristics, which fundamentally define the ability to engineer its physical properties and associated device performance. Here we demonstrate that unintentional electron doping by oxygen (${\mathrm{O}}_{\mathrm{N}}$) impurities and intentional magnesium hole doping ($\mathrm{M}{\mathrm{g}}_{\mathrm{Sc}}$) in scandium nitride (ScN) do not introduce any defect states inside its fundamental bandgap and that the rigid-band electronic structure remains unchanged. Employing a combination of spectroscopic techniques as well as first-principles density functional theory analysis, we show that the ${\mathrm{O}}_{\mathrm{N}}$ and $\mathrm{M}{\mathrm{g}}_{\mathrm{Sc}}$ defect states in ScN are located inside the bands, which leaves behind the virgin ScN bandgap as well as the valence and conduction band edges that are important for electronic transport. The rigid-band electronic structure of ScN with respect to the electron and hole doping results in high electron and hole concentrations due to the free movement of Fermi level and results in tunable electronic and thermoelectric properties necessary for device applications.

Giant values obtained for first hyperpolarizabilities of methyl orange: a DFT investigation

Advances in photonics and optoelectronics depend on proposing new materials with well-defined nonlinear optics properties. Based on the foundations of density functional theory, this work presents a systematic investigation of linear and nonlinear optical properties of methyl orange, a well-known azo dye. Structural changes from alkaline to acidic structures drastically boost all investigated properties. For instance, the material dipole polarizability starts from an isotropic condition ( $$\alpha _{\mathrm{iso}}>\varDelta \alpha $$ ) to an anisotropic behavior ( $$\alpha _{\mathrm{iso}}<\varDelta \alpha $$ ). The first hyperpolarizabilities are also strongly tuned varying from 18.9 $$\times\, 10^{-30}$$ to 171.7 $$\times\, 10^{-30}$$ esu. A careful analysis of frontier molecular orbitals indicates proper wide-bandgap semiconductor energy gap (3.22 eV) and associates the highest hyperpolarizabilities to the lowest energy gap, which means semiconductor molecules with intense nonlinear optical activity.

Molecular spectroscopy in a solid-state device

The quantification of the electronic transport energy gap of a molecular semiconductor is essential for pursuing any challenge in molecular optoelectronics.

Temperature dependence of the energy band gap of CuSi2P3 semiconductor using PSOPW method

Abstract Theoretical formalism based on the orthogonalized plane wave method supplemented by a potential scaling scheme was used to predict the temperature dependence of energy gap of CuSi2P3 semiconductor. A computer code in Pascal was used to perform the variation of fundamental energy gap with temperature in the range of 150 K to 800 K. The dependence of energy gap on temperature for lattice dilation contribution, lattice vibration contribution and total temperature effect were performed separately. The results revealed that, as temperature increases, the top of the valence band and the bottom of the conduction band increase, while the energy band gap decreases. Generally, at low temperatures, the energy gap varies slowly and exhibits a nonlinear dependence and approaches linearity as temperature increases. The calculated energy gap of CuSi2P3 at T = 300 K is 0.4155 eV. The temperature coefficients in the linear region due to lattice dilation contribution, lattice vibration contribution and total temperature effect were calculated as –1.101 × 10−5 eV/K, –1.637 × 10−4 eV/K and –1.7523 × 10−4 eV/K, respectively. Also, the ratio of temperature coefficient of the energy gap due to LV contribution to its value and LD contribution in the linear region is equal to 14.868. That ratio is compared to those of CuGe2P3 and III-V compounds, where those of the latter show a systematic change with Eg. Moreover, the Eg of all the compounds shows a quadratic dependence on the inverse of mean bond length.

Capacitance methodology for investigating defect states in energy gap of organic semiconductor

Abstract Organic semiconductor materials have been applied diffusely in photoelectronic devices, such as solar cells, light emitting diodes, etc. Defect states in energy gap are one of most significant physical parameters affecting the charge transport in organic devices. Hence, investigating defect states plays a vital role for improving device performance. As one of the most widely applied method of investigating defect states in organic materials, capacitance measurements mainly include capacitance-voltage, capacitance-frequency, forward bias capacitance-voltage and so on, however these measurements have not been comprehensively interpreted and even have not been used properly in detection range. Therefore, in this review, the theory of each capacitance measurement and its application in organic semiconductor are compiled. The comparison of advantages and disadvantages among these different capacitance measurements and detailed description of their detecting range have been carried out. And a following outlook comprising the future developments of capacitance measurement is given. In the end, a table including characteristics for each capacitance measurement is created so as to be understood and used by researchers.

Electron transport within the wurtzite and zinc-blende phases of gallium nitride and indium nitride

Wide energy gap semiconductors are broadly recognized as promising materials for novel electronic and opto-electronic device applications. As informed device design requires a firm grasp on the material properties of the underlying electronic materials, the electron transport that occurs within the wide energy gap semiconductors has been the focus of considerable study over the years. In an effort to provide some perspective on this rapidly evolving and burgeoning field of research, we review analyzes of the electron transport within some wide energy gap semiconductors of current interest in this paper. In order to narrow the scope of this review, we will primarily focus on the electron transport that occurs within the wurtzite and zinc-blende phases of gallium nitride and indium nitride in this review, these materials being of great current interest to the wide energy gap semiconductor community; indium nitride, while not a wide energy gap semiconductor in of itself, is included as it is often alloyed with other wide energy gap semiconductors, the resultant alloy often being a wide energy gap semiconductor itself. The electron transport that occurs within zinc-blende gallium arsenide will also be considered, albeit primarily for bench-marking purposes. Most of our discussion will focus on results obtained from our ensemble semi-classical three-valley Monte Carlo simulations of the electron transport within these materials, our results conforming with state-of-the-art wide energy gap semiconductor orthodoxy. A brief tutorial on the Monte Carlo electron transport simulation approach, this approach being used to generate the results presented herein, will also be provided. Steady-state and transient electron transport results are presented. The evolution of the field, a survey of the current literature, and some applications for the results presented herein, will also be featured. We conclude our review by presenting some recent developments on the electron transport within these materials. This review is the latest in a series of reviews that have been published on the electron transport processes that occur within the class of wide energy semiconductor materials. The results and references have been updated to include the latest developments in this rapidly evolving field of study.

Integrating Down-Shifting and Down-Conversion into Metal–Organic Frameworks to Enhance the Spectral Conversion for Solar Cells

Luminescent spectral conversion, including down-conversion (DC) and down-shifting (DS) is a potential route to overcome the spectral mismatch between solar photons and the semiconductor energy gap. Here, we introduce metal organic frameworks (MOFs) that integrate DC and DS processes into one system. Three different MOFs (Gd(BTC)(1), Gd(BPT)(2), and Gd(OBT)(3)) were synthesized doped with lanthanide ions couples. The DS–DC synergistic fluorescent processes were observed in all the MOFs. The overall absorption and near-infrared (NIR) emission intensity are dramatically enhanced (by factors of ∼4 800 and 550) due to the DS-sensitized effect for DC. As for DS process, the DC-bridge effect is quantified for the first time by comparing the NIR quantum yield (QYNIR). Benefiting from the bridge effect, QYNIR (5.30%) of Dy0.01Yb0.10-3 is increased around 3 times greater than the system without DC process, and it is close to the highest value reported for the C–H bond containing Yb3+ emitter. Our study demonstrated...