Dependence Of Band Gap Research Articles

Electrical and optical characterisation of InGaAsSb-based photodetectors for SWIR applications

Abstract The In x Ga 1 − x A s y Sb 1 − y alloy was studied in epilayers and photodiodes grown lattice matched to GaSb across a comprehensive composition range, 0 ⩽ x ⩽ 0.3 , as a promising technology to support the extended short-wave infrared region ∼ 1.7 − 3 µm. Low background carrier concentrations between 6 × 10 14 and 1 × 10 15 cm − 3 were achieved in all samples, reducing with In fraction. Both the absorption coefficient and external quantum efficiency were found to increase with indium fraction, up to ∼ 10 4 cm − 1 and 70% without an AR coating, respectively. Counter to the fundamental bandgap dependence, leakage current density initially reduced with the addition of low In and As fractions, before rising as the fractions increased and the bandgap reduced further. These properties resulted in specific detectivity reaching a maximum in the sample with x = 0.043, before decreasing towards higher alloy fractions. It is concluded that for moderate In fractions, the InGaAsSb alloy offers clear potential to improve on the disappointing material and photodiode properties of GaSb and support emerging SWIR sensing applications. However, development of fabrication and passivation technology is required to fully exploit this potential.

Modeling to study the shape, dimensionality and crystal structure dependence of energy band gap in nanosized semiconductors

Modeling to study the shape, dimensionality and crystal structure dependence of energy band gap in nanosized semiconductors

Linear and nonlinear optical studies on successfully mixed vanadium oxide and zinc oxide nanoparticles synthesized by sol–gel technique

Abstract In this study, V2O5, 5ZnO/10V2O5, and ZnO, 10ZnO/10V2O5 nanocomposites were synthesized by the sol–gel method. The sol–gel technique is an important process for the fabrication of advanced oxide materials with desirable catalytic, optical, and structural properties. The varieties and flexibilities of sol–gel techniques help in preparing materials with extremely specific properties. For the presented samples, three types of phases were assessed. The average crystalline size of V2O5, 5ZnO/10V2O5 and ZnO, 10ZnO/10V2O5 nanocomposites were found to be 25, 26, 14.5, and 15.5 nm, respectively. SEM images showed three different shapes of semi-tube, semi-spherical, and semi-flower. The pure samples of V2O5 and ZnO showed semi-tube shapes. 5ZnO/10V2O5 shows a spherical shape with average dimeter of 0.6 µm. Strong dependence of the direct optical band gap was observed on different compositions that varied within the range of (2.33–2.73 eV). Conversely, the indirect values varied within the range of 2.119–2.35 eV. On the other hand, 10ZnO/10V2O5 has semi flower shape with different layers. Optical parameters, such as optical band gap, extension coefficient, tails of localized states, and refractive index, were gauged for these nanocomposites. In addition, the mean refractive index of ZnO is lower than that of V2O5, with differences observed between 5ZnO/10V2O5 and 10ZnO/10V2O5 nanocomposites.

Control under optical, nonlinear optical and kinetic properties of two-dimensional gradient CdSe1-xSx nanocrystals

Peculiarities of photoluminescence (PL) and absorption spectra of gradient nanocrystals CdSe1-xSx colloidal solution were studied by pump and probe technique under stationary excitation of excitons by nanosecond laser pulses. The PL peaks and differential transmission peaks positions changing were revealed with the CdSe1-xSx nanocrystals composition variation. Bleaching of excitons transitions was observed for high pump intensities and explained by excitons space filling effect. The changing of the differential transmission peaks positions was explained by the nanocrystal band gap dependence on the chemical composition. Time-resolved PL measurements from the sub-picoseconds to tens of nanoseconds range demonstrated a strongly different behavior for gradient nanocrystals and pure CdSe nanocrystals. For pure nanocrystals two typical time-scales were resolved contrary to the gradient nanocrystals where (with the growth of sulfur concentration) only a single time scale was revealed. The observed modification of time-resolved PL for gradient nanocrystals is caused by the presence of traps in the gradient samples due to the chemical composition modification.

A Full‐Scale Analysis of Absorption Edges in Dye‐Doped Nonlinear Optical Polymers

AbstractA full‐scale analysis of the absorption edges by modified Tauc‐Lorentz models is essential in determining the optical bandgap and Urbach energy of semiconductors, transparent conductors, ionic compounds, and dielectric materials. This technique has not yet been applied to analyzing organic nonlinear optical (NLO) materials. This problem is tackled by preparing high‐quality films of guest–host NLO polymers with a wide thickness range from sub‐micron to 200 microns, allowing accurate measurement of full‐spectral absorption coefficients of NLO materials over four orders of magnitude by the UV‐VIS‐NIR spectroscopy. The Tauc model and a new Monolog–Lorentz model are used to study the optical absorption edge of guest‐host NLO polymers containing various push‐pull chromophores and the dependence of optical bandgap and Urbach edge on the structure and composition of materials is analyzed. The results reveal the critical transition of the Urbach exponential tail to a low energy tail that overlaps with vibrational overtones of materials at the telecom wavelengths. Determining the fundamental absorption region of organic NLO films in this study provides quantitative insight into the research to harness the resonance‐enhanced nonlinear coefficients of materials by operating at the wavelengths near the band edge with the control of optical loss.

Introduction of Local Resonators to a Nonlinear Metamaterial With Topological Features

Abstract Recent work in nonlinear topological metamaterials has revealed many useful properties such as amplitude dependent localized vibration modes and nonreciprocal wave propagation. However, thus far, there have not been any studies to include the use of local resonators in these systems. This work seeks to fill that gap through investigating a nonlinear quasi-periodic metamaterial with periodic local resonator attachments. We model a one-dimensional metamaterial lattice as a spring-mass chain with coupled local resonators. Quasi-periodic modulation in the nonlinear connecting springs is utilized to achieve topological features. For comparison, a similar system without local resonators is also modeled. Both analytical and numerical methods are used to study this system. The dispersion relation of the infinite chain of the proposed system is determined analytically through the perturbation method of multiple scales. This analytical solution is compared to the finite chain response, estimated using the method of harmonic balance and solved numerically. The resulting band structures and mode shapes are used to study the effects of quasi-periodic parameters and excitation amplitude on the system behavior both with and without the presence of local resonators. Specifically, the impact of local resonators on topological features such as edge modes is established, demonstrating the appearance of a trivial bandgap and multiple localized edge states for both main cells and local resonators. These results highlight the interplay between local resonance and nonlinearity in a topological metamaterial demonstrating for the first time the presence of an amplitude invariant bandgap alongside amplitude dependent topological bandgaps.

Determination of energy band gap of α-LiIO3 doped with L-Arginine and L-Nitroarginine amino acids using diffuse reflectance spectroscopy

An accurate determination of the band gap energy is crucial for predicting the photophysical and photochemical properties of investigated materials. In the present work, the dependence of the energy band gap (Eg ) of α-LiIO3 crystals doped with L-arginine and L-nitroarginine amino acids was obtained. The method, based on the simultaneous fitting of many absorption mechanisms to the spectral dependence of the Kubelka-Munk function estimated from diffuse reflection data, as well as Tauc's method, has been applied to determine the energy band gap. In the case of a small dopant concentration, additional electron states appear within the band gap of the crystals. As a result, a broad absorption band appears in the material spectrum. The optical transmittance spectra were recorded using an Agilent Cary 60 spectrophotometer in the spectral range 190–1100 nm.

Weak oxidant fraction in the microwave plasma influencing the evolution of nanocrystalline-diamond–imbedded diamond–like carbon network at low temperatures and its orbital hybridization dependent wide optical band gaps

The diamond-like carbon (DLC) thin films having intrinsic nanocrystalline diamond (NCD) components were synthesized on bare glass substrates at 300 °C, employing a (C2H2/CO2/H2/) gas mixture in MW-PECVD. Relevant influence of the weak oxidant fraction [F = CO2/(CO2 + C2H2)] in the plasma on the specific hybridized constituents (sp3 and sp2) in the C-network, optical transmission characteristics of the film, and its accomplished degree of nanocrystallinity were investigated. A substantial segment of the NCD was achieved in the DLC matrix. An optimized diamond-phase component corresponding to the minimized bond angle disorder in the matrix was accounted from the manifestation of the maxima of IDia/IG and IDia/ID simultaneous to the minimum of ID/IG ratio in Raman response, along with an allied diamond peak appearing near 1332 cm−1. The optimal DLC film at F = 0.23 revealed a wide optical band gap (Eg) of ∼3.60 eV, ∼59% sp3-hybridized C component of the diamond phase, and a significant sp3/sp2 ratio of ∼2.1. The film microstructure seemed homogeneous with uniformly distributed NCDs of average diameter ∼7.5 nm and dominant 〈111〉 crystallographic orientation. The sp3/sp2 fraction in the film matrix has been correlated directly to the IDia/IG and IDia/ID, and inversely to ID/IG ratios of the Raman data. Atomic-O, including atomic-H, remains instrumental in chemical reactions, facilitating the etching of graphitic and a-C phases while preserving the superior sp3-hybridized NCD component growing uninterruptedly in the DLC network that subsists shielded from the high-energy ion impact within secondary plasma under the shadow mask.

Special role of indium nitride in the properties of related compounds and quantum structures

This Review provides a thorough description of the experimental progress on the InN family and other relevant compounds. Although InN is of great interest, many of its properties are not well understood and are still puzzling researchers with a number of unexpected effects. These include a surprisingly small energy gap, sensitivity to applied pressure in terms of lattice stability, and poor miscibility with compounds with smaller lattice parameters, such as GaN and AlN. Special features of InN under pressure are highlighted, such as the effect of conduction band filling and the strong pressure dependence of the effective mass. Several negative and positive effects due to the presence of In have been observed. We highlight their implications for InN-based alloys and quantum structures, which are crucial materials in modern optoelectronics (light emitting diodes and laser diodes). These effects include In clustering, large piezoelectricity resulting in strong internal electric fields that reduce the optical gain in nitride heterostructures, and difficulties in growing high-In superlattices and other quantum structures. All of these effects pose challenges that need to be addressed. We show that theoretical explanations allow for the clarification of puzzling experimental observations. Discussed are (i) a reformulation of the rule describing the bandgap dependence on pressure in all III–V semiconductors; (ii) the very large bandgap curvatures in nitride alloys; and (iii) the discrepancies between theory and experiment in the optical emission from InN/GaN superlattices, leading to the conclusion that epitaxial growth of high In content InxGa1−xN (x > 0.3) quantum wells on GaN is not possible.

Boron and carbon in two-dimensional nitrogene structures: Heterodoping, doping, and chemical functionalization

We perform density functional calculations to determine the effects of simultaneous doping with carbon (C) and boron (B) on the electronic properties of nitrogene. Our procedure substitutionally incorporates the two dopants into the nitrogen monolayer. We analyze the relative position between dopants by considering different configurations. Band structure, density of states, band gaps, magnetic stability energies (energy difference between states with total magnetization with spin S=1 and S=0), and energetic stability were examined. The codoped structures exhibit a spin−dependent band gap with a strength of 1.04–2.68 eV, which is reduced compared to that in nitrogene (3.80 eV). The B-C codoped nitrogene incorporated ferromagnetism with well-localized flat bands around the Fermi level. A spin−polarized ground state was exhibited by the systems with a total magnetization of S=1, in which magnetic moments were localized mainly at the C atom and its first neighbors. The systems displayed an antiferromagnetic ordering when the total spin was fixed to S=0. The valence band maximum (VBM) was dominated by spin−up, while the conduction band minimum (CBM) was dominated by spin−down. Dopants placed as second neighbors in the nitrogene structures exhibited the most prominent band gap and magnetic stability.

Effect of annealing temperature on bismuth vanadate nano thin films for solar cell applications

Bismuth vanadate (BiVO4) has been used as the photoanode electrodes in ferroelectric solar cells owing to its unique combination of properties: a narrow bandgap among ferroelectrics, economic viability, negative conduction band edge, and remarkable stability. The present work explores the fabrication and characterization of BiVO4 thin films prepared via spin coating, with a specific focus on elucidating the influence of the annealing temperature (400–550 °C) on their structural, optical, and photovoltaic properties. From X-ray diffraction (XRD) analysis, it is observed that higher annealing temperatures have promoted the formation of larger grains, enhanced crystallinity, and induced a preferred crystal orientation characteristic of the monoclinic scheelite structure. Tauc plot analysis shows the dependence of the optical band gap on the annealing temperature for BiVO4 thin films. The band gap values have decreased slightly from 2.50 eV at 400 °C to 2.44 eV at 550 °C. This is indicated by the slightly narrowed bandgap, which influences the structure of the material or defect states at higher annealing temperatures. A narrower bandgap allows for the absorption of lower-energy light, potentially improving the light absorption efficiency of BiVO4 thin films in photoanode applications. The influence of annealing temperature on BiVO₄ thin film solar cell performance was investigated further through the analysis of open-circuit voltage (Voc), short-circuit current (Isc) and power conversion efficiency.

Colloidal‐Doped Semiconductor Nanocrystals Embedded in One‐Dimensional Photonic Crystals for Ultrafast Photonics

The optical properties of strongly doped semiconductor nanocrystals depend strongly on the carrier density of the nanocrystals. These characteristics can be exploited for the design of innovative optical devices based on ultrafast switching potentially in the THz modulation bandwidth. In this study, the optical response of one‐dimensional photonic crystals incorporating colloidal nanoparticles of a highly doped semiconductor such as indium tin oxide (ITO) is investigated, taking into consideration the angular dependence of the photonic band gap and the position dependence of the photonic band gap on the light‐induced tunability of the ITO doping.

Influence of temperature on bandgap shifts, optical properties and photovoltaic parameters of GaAs/AlAs and GaAs/AlSb p–n heterojunctions: insights from ab-initio DFT + NEGF studies

The III–V group semiconductors are highly promising absorbers for heterojunctions based solar cell devices due to their high conversion efficiency. In this work, we explore the solar cell properties and the role of electron–phonon coupling (EPC) on the solar cell parameters of GaAs/AlSb and GaAs/AlAs p–n heterojunctions using non-equilibrium Green function method (NEGF) in combination of ab-initio density functional theory (DFT). In addition, the band offsets at the heterointerfaces, optical absorption and bandgap shifts (BGSs) due to temperature are estimated using DFT + NEGF approach. The interface band gaps in heterostructures are found to be lower than bulk band gaps leading to a shift in optical absorption coefficient towards lower energy side that results in stronger photocurrent. The temperature dependent electronic BGS is significantly influenced by the phonon density and phonon energy via EPC. The phonon influenced BGS is found to change the optical absorption, photocurrent density and open-circuit voltage. In case of GaAs/AlSb junction, the interface phonons are found to have significantly higher energies as compared to the bulk phonons and thereby may have important implications for photovoltaic (PV) properties. Overall, the present study reveals the influence of EPC on the optical absorption and PV properties of GaAs/AlSb and GaAs/AlSb p–n heterojunctions. Furthermore, the study shows that the DFT + NEGF method can be successfully used to obtain the reasonable quantitative estimates of temperature dependent BGSs, optical absorption and PV properties of p–n heterojunctions.

Pressure dependence of band gap of (0 4 0) oriented TlI films

Perfectly (040) oriented Thallium iodide films grown by vacuum thermal evaporation were found to have strain and band gap uncorrelated with their film thicknesses. Band structure of orthorhombic TlI was calculated using Density functional Theory (DFT) with appropriate functional. Elastic constants were calculated for determining the residual stress from strain. Band gaps of films linearly correlate with their residual stress. Experimental stress free direct band gap 2.92 eV determined from band gap-residual stress correlation matches quite closely with calculated 2.88 eV. Pressure coefficient of band gap −1 eV/GPa was determined from the residual stress dependence of band gap.

Wave dispersion in a phononic metaplate with Boater-like cells

Meta-structure based on acoustic-mismatch among different materials shows distinct properties and also leads potential damage at the multi-material interfaces under complex loading conditions. In this paper, a phononic metaplate with Boater-like cells is proposed based on the concept of acoustic black hole and vibrator-plate models with the aim to explore the possibility of multi-acoustic meta-phenomena in a mono metaplate. Firstly, the proposed model is introduced and the governing equations for wave dispersion are formulated. Then the band structures are investigated. The wave dispersion at the double degeneracy points, Dirac-like cone, as well as bi-refraction are explored. At last, parameter dependence of band gaps is analyzed. The results indicate that multi-acoustic meta-phenomena could be realized in this phononic metaplate with Boater like cells, including bi-refraction and formation of band gaps. Considering low-cost and easily manufactured, the prototype in this paper provides a simpler but effective pattern for the metaplate design.

Dielectric, electrical and optical properties of a Ni-substituted double perovskite ceramic

In this report, iron based double perovskite oxide Ca2Fe0.85Ni0.15NbO6 was successfully synthesized adopting the solid state reaction method. The structure and microstructure along with the purity, frequency and temperature dependent dielectric properties, energy storage and band gap modulation properties of the ceramic is also discussed. The ceramic shows a small band gap with a high remnant polarization which aligns it toward ferroelectric photovoltaic device applications. The temperature stable dielectric constant of the material up to a high temperature range is useful for MLCC applications. The energy storage density of the material is calculated from room temperature hysteresis loop. The frequency variation of ac conductivity refers Jonscher’s law. The temperature variation of frequency exponent term n indicates CBH (correlated barrier hopping), model of the conduction mechanism in the sample. The presence of room temperature M-H loop with negligible magnetization and coercive value indicates the soft ferromagnetic behavior of the ceramic.

Local Structural Distortions and Thermochromic Properties in Cs2NaFeCl6 Halide Double Perovskite

The enhanced structural stability of halide double perovskites compared to hybrid perovskite has aided their use in photovoltaic research. In the present study, we explored the temperature dependent band gap...

Strained AlGaInAs on InP: Bandgap dependence on composition—Model benchmark and optimization

Influence of chemical composition on the bandgap of AlGaInAs deposited on InP is often calculated using models for unstrained composition and then corrected for strain-induced bandgap energy changes using deformation potentials. This method relies on up to 25 coefficients, many of which are burdened with large uncertainty. In this paper, a large set of experimental data is used to verify the accuracy of existing approaches and to search for optimal deformation potentials. It is shown that the main source of inaccuracy is not the deformation potentials, but the unstrained bandgap formulas. Additionally, a novel model is proposed, yielding the highest accuracy on our dataset. For the first time, composition determination of a quaternary alloy on InP is reported using inductively coupled plasma-optical emission spectrometry, which is used as a benchmark for modeling.

Effect of Manganese-Doping on the chemical and optical properties of cobalt ferrite nanoparticles

We report on the effect of manganese (Mn) doping on the structural, chemical and optical properties of cobalt ferrite (CFO) nanoparticles (NPs). The Mn(II)-substituted CFO NPs with variable chemical composition (Co1-xMnxFe2O4; x = 0.0–0.5; CMFO) were synthesized by an eco-friendly hydrothermal route. The CMFO NPs produced were with a crystallite size varying in the range of 8–14 nm, where the chemical valence state, chemical bonding, electronic structure and optical properties are strongly influenced by the Mn-substitution. The X-ray diffraction (XRD) studies revealed the Mn-substitution induced changes in CFO crystal structure. The Mn-substitution in CFO causes the lattice parameter enhancement (a), crystallite size increase, and micro-strain (ε) as evident in the XRD studies. The chemical composition driven direct, functional relationship reflected in a-D-ε correlation, which suggests the Mn-substitution allows the ability to control the size and strain in CFMO NPs. Chemical bonding analyses using Fourier transform infrared spectroscopy (FTIR) corroborates with structural assessment made with XRD studies. The MTd–O (MTd = metal ions in tetrahedral locations) absorption bands shifting to higher wavenumbers in FTIR studies indicate that, Mn-substitution induce changes in the metal cation distribution between the tetrahedral and octahedral locations of the ferrite lattice. The X-ray photoelectron spectroscopic (XPS) analyses indicate the presence of iron as Fe+3, cobalt as Co+2, and manganese in Mn+2 chemical state. With increasing Mn-content, the XPS revealed that the binding energy (BE) separation of Fe, as well as Mn, does not change compared to Co, indicating the chemical stability and valence state of Fe+3 and Mn+2 cations maintained well in the CMFO samples. While the overall chemistry of CFO is maintained, and is not influenced by the increasing Mn-concentration, the remarkable effect of Mn-substitution is seen on the optical properties of CFO NPs. The optical studies indicate that the band gap of CFO NPs exhibits a direct, functional dependence on Mn-concentration; the band gap varies in a wide range of 2.38–3.12 eV. The analyses indicate the exponential dependence of CFO optical band gap with Mn-content which provide a roadmap to engineer the materials with tunable band gap for desired technological applications.

Threshold bandgap of lead halide hybrid perovskites for making stable single crystal by NIR laser trapping

The remarkable optoelectronic properties of hybrid halide perovskites position them as pivotal materials for the next generation of electronic devices, LEDs, lasers, and solar cells, potentially revolutionizing these technological domains. In this study, we harness the capabilities of contemporary laser trapping technology—a non-contact method for manipulating particles—to elucidate the conditions necessary for stable perovskite crystal formation. Using a 1064 nm near-infrared (NIR) continuous-wave (CW) laser, commonly selected for trapping experiments, we establish the threshold bandgap essential for the stable crystallization of MAPbX3 perovskite crystals. Our research reveals that MAPbI3, with a bandgap of 1.59 eV, undergoes rapid explosive crystallization when subjected to the 1064 nm laser, making it unsuitable for stable crystal growth. In contrast, MAPbBr3 with a bandgap of 2.26 eV forms stable single crystals within 6 min at the air-solution interface, when exposed to the same 1064 nm NIR laser at 1.0 W output power. Notably, a minor reduction in bandgap to 2.23 eV in the mixed halide MAPbBr2.75I0.25 results in an abrupt transition to explosive crystallization. These findings introduce a novel insight into the bandgap dependency for the crystallization process, delineating a threshold bandgap of 2.26 eV for MAPbBr3, below which the crystal growth becomes unstable under a 1064 nm laser. The study provides a significant advancement in the field by defining the precise bandgap necessary for the formation of robust, stable perovskite crystals using laser trapping techniques. This threshold bandgap knowledge is crucial for developing controlled synthesis protocols for perovskites, optimizing their optoelectronic properties for application in modern technologies. Moreover, the investigation suggests that to achieve stable crystallization of perovskites with a bandgap below 2.26 eV, laser trapping with wavelengths longer than 1064 nm may be required, opening new avenues for material processing and device fabrication.