Increase In Optical Band Gap Research Articles

Explication of the luminescent and optically active RE3+ triply-doped silica phosphate glass films for photonic applications

The multi-component silicate glass films triply-doped with Er3+/Yb3+/Nd3+ were fabricated by spin coating technique. X-ray diffraction revealed a cristobalite phase in the glasses doped above 0.6 mol% of Nd3+. The transparency of the films increases with the addition of the co-dopant, due to the increase in optical band gap by the Burstein-Moss shift. The high value of the correlated color temperature of the blue emission indicates enhanced visual perception, suggestive of cool blue film lasers. The red emission from upconversion exhibits potentiality for flat display panels. The gain cross-section of the glass with 0.6 mol% of Nd3+ was 13.54 ×10−20 cm2 which makes it ideal for NIR film lasers in the S-band region. The Inokuti-Hirayama model predicts luminescence quenching due to dipole-dipole interactions in the glasses co-doped beyond 0.6 mol% of Nd3+. The 4F9/2→4I13/2 transition observed in the films, suggests their suitability for O + E + S band NIR film lasers in telecommunication sectors.

Carbon-doped ZnO thin films: A transparent conductive oxide for application in solar-blind photodetectors

Transparent conductive oxide (TCO) films are crucial in optoelectronic devices, such as photodetectors, due to their unique blend of transparency and electrical conductivity. ZnO is a top choice for TCOs owing to its excellent properties, non-toxicity, and cost-effectiveness. In this work, we explore the potential of carbon doping to enhance the electrical properties of ZnO films for transparent conductive applications. Our findings reveal that C-doped ZnO (ZnO:C) films retain the pristine high quality and surface morphology despite an increase in defects with higher C doping. Notably, C doping does not compromise the visible light transmittance of ZnO films, while inducing a gradual increase in optical bandgap, indicative of the typical Burstein–Moss effect. As carbon doping increases, the ZnO:C films exhibit improved carrier concentration, lower resistivity, and sustained high mobility, achieving optimal performance with an electron concentration of 3.73 × 1019 cm−3, resistivity of 3.69 × 10−3 Ω cm, and mobility of 46.08 cm2 V−1 s−1. Finally, we utilized ZnO:C films as a transparent electrode material in ε-Ga2O3-based photodetector, achieving the development of transparent device and attaining high-performance solar-blind detection capabilities. This work provides a strategy for developing a transparent conductive oxide, with ZnO:C emerging as a promising rival to IIIA-doped ZnO for optoelectronic applications.

Nonlinear optical properties of zinc oxide thin films

This study reports the influence of deposition temperature (573 K-773 K) on the microstructural, linear and nonlinear optical properties of zinc oxide nano thin films synthesized using the chemical spray pyrolysis method. Synthesized films are polycrystalline, exhibiting a dominant (101) orientation, for which the crystallite size is found to increase with deposition temperature up to 723 K followed by a decrease. Concurrently, the deposit prepared at 723 K showed improved electrical properties, i.e. higher charge carrier concentration and mobility. Optical studies reveal increased transmittance in the visible region and a gradual increase of optical bandgap with deposition temperature. The photoluminescence studies show a near-white light emission for all thin films, however, the density of defect states was comparatively higher for thin films deposited at lower temperatures. A saturable absorption behaviour was observed due to the presence of defects. The thin films show a negative refractive index with self-defocusing phenomena. The total nonlinear susceptibility is found to decrease with increasing deposition temperature, and the solution-processed functional thin films thus have potential implications for nonlinear optical applications such as nonlinear optical switching, optical memory management, and saturable absorbers.

The effective role of potassium doping in improving the structural, morphological optical, and electrical properties of CdO thin film for optoelectronic application

Aspiring to increase the electrical conductivity, enhance the electron mobility, and widen the band gap, potassium (K) was used as a substitutional dopant in the CdO matrix. Transparent cadmium oxide (CdO) and potassium-doped cadmium oxide (K–CdO) thin films with different K concentrations (0.02, 0.04, and 0.06 mol) were deposited on glass substrates via thermal evaporation technique. A remarkable shift of (111) peak towards high Bragg's angle was noticed as the potassium content was increased, which established the successful incorporation of K into the CdO matrix. The surface became more compacted and denser with a noticeably smaller particle size upon doping with K, as revealed by field emission scanning electron microscopy (FESEM)aand the Willmason-Hall plot. The optical band gap was boosted from 2.5 to 2.79 eV, when the K concentration was increased from 0.0 to 0.06 mol. Moreover, the optoelectronic features, such as transmittance, reflectance, skin depth, refractive index, tailing energy, optical dielectric constants, and optical conductivity were investigated in depth. The Hall experiment was used to determine the DC electrical properties of the K– CdO film including the resistivity (ρ), Carrier concentration, Carrier mobility, and Hall coefficient. The Hall measurement asserted that the film is an n-type semiconductor and electron mobility (μn) was boosted, as the K concentration was raised. The increased optical band gap and enhanced electron mobility achieved by potassium doping reflected the fact that K-doped CdO thin films are promising window layers in photovoltaic applications.

Cu2Te/CoTe nanoparticles with tuneable bandgaps: Implications for photovoltaic and optoelectronic devices

Herein, we report the structural, optical, and electrochemical response of Cu2Te/CoTe nanoparticles synthesized by the facile microwave synthesis method by varying Cu and Co concentrations. Various characterizations such as Rietveld-refined X-ray diffraction, Raman Spectroscopy, and Transmission electron microscopy analysis infer the two hexagonal phases Cu2Te and CoTe having space group p6/ mmc and P63/ mmc, respectively. The elemental Energy-dispersive X-ray and X-ray photoelectron spectroscopy confirm the composition of all the elements. Field emission scanning electron microscopy images exhibit nanoparticles that remain unaltered even after the essential concentration variation. However, the differential scanning calorimetry study analyses the phase change of the material from room temperature to higher temperatures. Meanwhile, from UV-Vis spectroscopy, the optical band gap increases, and the refractive index value decreases in both the cases, Tauc plot, as well as Kubelka-Munk plot by varying Cu and Co concentrations, which shows well-defined properties that enable the material for various solar cell and optoelectronic applications. In addition, the electrochemical impedance spectroscopy analysis of the as-prepared material reveals small kinetic at high-frequency regions that can be used as the charge transfer of the electrode-electrolyte interface. The tuneable structural, optical, and electrochemical response of the CuCoTe nanomaterial broadens the advanced optoelectronic application prospects.

Gamma radiation-induced modifications in the physiochemical features of ZnO nanoparticles synthesized using microwave technique

Zinc oxide nanoparticles (ZnO NPs) have a wide range of applications, and their properties can be significantly affected by gamma (γ) radiation, particularly in metal oxide semiconductor-based devices. This study investigates the impact of γ-irradiation on the physicochemical properties of ZnO NPs. The ZnO NPs were synthesized using a microwave method with zinc nitrate hexahydrate as a precursor and urea as a fuel. These synthesized ZnO NPs were exposed with γ rays emitted from 60Co radioactive source at different doses (0, 25, 50, and 75 kGy). We systematically examined the effects of γ irradiation on the structure, optical properties, and colloidal stability of the ZnO NPs using various techniques, including XRD, Raman spectroscopy, FTIR, SEM, UV–visible absorption, and zeta potential/particle size analysis (ZP/PSA). The characterization results revealed that γ irradiation caused significant alterations in the microstructure of ZnO NPs, resulting in reduced crystallite and grain sizes. Additionally, the optical properties and colloidal stability were found to be dose-dependent, with absorption spectra shifting towards the blue region, an increase in optical bandgap, and a decrease in zeta potential values as the dose rate of γ radiation increased.

Optical and temperature-dependent electrical and dielectric properties of ultrasound-synthesized CdS quantum dots

CdS quantum dots (QDs) were synthesized by the ultrasound-assisted chemical precipitation technique. The structure analysis revealed the presence of bi-structural cubic and hexagonal phases with an average crystallite size of 3 nm. The N2-adsorption isotherm exhibited the evolution of meso-/macro-porous interfaces with a pore size of 7.56 nm and a surface area of 44.41 m2·g−1. The improvement of the quantum size effect in CdS QDs resulted in the increase of optical bandgap to 2.52 eV compared with the corresponding bulk phase. However, the analysis of long-tail states absorption revealed a very small Urbach energy of about 76 meV compared with CdS QDs prepared by other techniques. The as-synthesized CdS QDs revealed high room-temperature DC conductivity of 2.56 × 10–6 Ω−1 · m−1 and very small activation energy of 268 meV facilitating tunnelling of the thermionically excited carrier through the high bandgap of CdS QDs. The frequency-dependent behavior of AC conductivity (σ AC) and dielectric constant (ε r) of CdS QDs were investigated at different temperatures in the range from 303 K to 453 K. It was observed that both σ AC and ε r were improved with increasing temperature up to 363 K followed by a sudden decrease at higher temperatures.

Study of the annealing effect in optical properties for phosphorus-doped a-Si x C1− x :H films deposited by PECVD

The optical properties of phosphorus-doped hydrogenated amorphous silicon carbide (P-doped a-Si x C1−x :H) thin films are studied. Films were deposited by plasma-enhanced chemical vapor deposition at 110 kHz of frequency and pressure of 1.5 Torr, with silane (SiH4) and methane (CH4) as precursor gases. Hydrogen (H2) and phosphine (PH3) were used as diluent and dopant gases, respectively. The impact of the gases flow rate and thermal annealing on the optical properties is evaluated. A concordance is observed between the atomic content of Si, C, and P in films, determined by Energy Dispersive X-ray Spectroscopy, as gases flow rate increases. The composition of the films is established by identifying the vibrational bonding modes using Fourier transform infrared spectroscopy measurements. Si−H, Si−C, and C−H bonds were identified and their density was obtained. Characterization with UV–Vis spectroscopy shows that the optical band gap (E gopt), oscillation energy (Eo ), Urbach energy (EU ), and iso-absorption energy (E 04) increase with the doping level but decrease with the annealing treatment. However, values of dispersion energy (Ed ), dielectric constant (ϵ) and the refractive index (n) generally become smaller as the phosphorus and carbon content grows, but with a tendency to fall during the annealing. The refractive index by UV–Vis is compared with measurements made with ellipsometry, resulting in a similarity between both techniques. High values of E gopt obtained in P-doped a-Si x C1−x :H films can be related to better values of the temperature coefficient of resistance for flow sensor applications.

Structure and electronic properties of thin Ge2Sb2Te5 films produced by DC ion-plasma spattering

The optical properties of Ge2Sb2Te5 thin films were studied as a function of thickness. An increase in optical band gap with decreasing film thickness has been observed. The current– voltage characteristics measured in Ge2Sb2Te5 thin films in the current mode are studied. A decrease in switching time and threshold voltage with decreasing film thickness is established.

Nucleation and quantum confinement of nano-platelet Bi2–Bi2Se3

The nucleation, nano-platelet growth, and optical properties under quantum confinement are investigated in the topological semimetal superlattice Bi2–Bi2Se3 as a function of thickness and Ar + ion pressure in sputtered growths. Quantum confinement and evolution of the band structure with a series of reduced dimensionality and surface terminations are studied by density functional theory corroborating the observed optical properties. An initial Volmer–Weber growth mode of nano-platelets is observed until a pressure-dependent critical thickness, where a transition to Frank–van der Merwe growth occurs. Nucleation statistics characterized using atomic force microscopy find the nearest-neighbor ordering of nano-platelets. Optical properties using ultraviolet to visible light spectroscopy measurements in transmission mode reveal a marked increase in optical bandgap below a nano-platelet critical volume reaching a maximum of 2.21 eV. Raman vibrational spectroscopy is performed, revealing softening of vibrational modes as the nano-platelet volume decreases.

Influence of 120 MeV Au Ion Irradiation on Phase Transition, Surface, and Optical Properties of Lead‐Free (K,Na)NbO3 Films

High energy ion beam irradiation is an important tool to engineer the properties of multifunctional materials for diverse applications. The present study reports the impact of 120 MeV Au ion beam irradiation on structural and luminescence properties of (K,Na)NbO3 (KNN) films. The increase in ion fluence has resulted in crystalline‐to‐crystalline and crystalline‐to‐amorphous phase transitions at room temperature. The dense grain‐like morphology of crystalline films gets transformed into clusters of nano‐sized grains after irradiation, and the grain boundaries are diffused at higher fluence. X‐ray photoelectron spectroscopy results indicate the evaporation of K‐species from the surface after irradiation. The relative elemental ratio and film's thickness were estimated using Rutherford backscattering spectrometry, and subsequently, KNN/Si interface analysis was also carried out. The increase in optical band gap after irradiation is correlated to the suppression of extended band tails. An intense photoluminescence emission in the UV region is observed, and the intensity increases abruptly after the crystalline‐to‐amorphous phase transition, where the grain boundaries merge with nearby ones. The impact of high electronic energy loss in KNN enhanced the probability of radiative recombination. The obtained results demonstrate the possible use of KNN for optoelectronic applications.

Exciton radiative lifetime in CdSe quantum dots

Colloidal CdSe quantum dots (QDs) are promising materials for solar cells because of their simple preparation process and compatibility with flexible substrates. The QD radiative recombination lifetime has attracted enormous attention as it affects the probability of photogenerated charges leaving the QDs and being collected at the battery electrodes. However, the scaling law for the exciton radiative lifetime in CdSe QDs is still a puzzle. This article presents a novel explanation that reconciles this controversy. Our calculations agree with the experimental measurements of all three divergent trends in a broadened energy window. Further, we proved that the exciton radiative lifetime is a consequence of the thermal average of decays for all thermally accessible exciton states. Each of the contradictory size-dependent patterns reflects this trend in a specific size range. As the optical band gap increases, the radiative lifetime decreases in larger QDs, increases in smaller QDs, and is weakly dependent on size in the intermediate energy region. This study addresses the inconsistencies in the scaling law of the exciton lifetime and gives a unified interpretation over a widened framework. Moreover, it provides valuable guidance for carrier separation in the thin film solar cell of CdSe QDs.

Investigation of Dysprosium‐Incorporated Potassium Boro‐Tellurite Glasses Toward Radiation Screening and Photonic Applications

A series of quaternary tellurite‐based glasses (72−x)TeO2 + 25B2O3 + 3K2CO3 + xDy2O3, where (x = 0, 0.5, 1, 1.5, 2, 2.5), are prepared using melt quenching technique. The effect of dopants on structural, physical, optical, and thermal properties of alkali boro‐tellurite glasses are studied using the differential thermal analysis (DTA) technique, UV–vis spectrometer, and photoluminescence technique. The density of as‐prepared samples has been obtained using the conventional Archimedes principle and other physical parameters, viz. molar volume and ion concentration, are also calculated using density. The optical absorption spectra exhibits different excited states of Dy3+ corresponding to 6H15/2→ 6F5/2(∼805 nm), 6F3/2(∼755 nm), 4F9/2 (∼473 nm), 4I15/2 (∼454 nm), 4G11/2 (∼427 nm), 4F7/2(389 nm), 4P3/2(∼366 nm). With the increase in Dy+3 concentration, an increase in optical bandgap, density, and molar volume as well as decrease in molar reflectivity, and reflection loss is evident from this study. The effect of Dy+3 ion concentration on Y/B intensity ratios and CIE chromaticity coordinates have been evaluated to understand the possible applications of aforementioned glass samples for white‐light‐emitting diodes (WLEDs). Moreover, various shielding parameters, viz. half value layer (HVL), mean free path (MFP), effective atomic number (Z eff), mass attenuation coefficient (MAC) have also been determined to understand the shielding characteristics of as‐prepared glass samples.

Material Properties of Nanocrystalline Silicon Carbide for Transparent Passivating Contact Solar Cells

Due to its high transparency, silicon carbide can replace amorphous silicon as a front contact material in crystalline silicon solar cells. Herein, first a look at doping in nc‐SiC:H with different deposition techniques is taken. Then, the influence of various deposition conditions for hot wire chemical vapor deposition‐prepared nc‐SiC:H is investigated. Both the electrical conductivity and the optical bandgap increase simultaneously for a multitude of deposition parameters. Combining a high filament temperature of the catalytic filament, a high hydrogen dilution of the precursor gas and an overall low total gas flow, conductivities of 0.38 S cm−1 in combination with an optical bandgap of 3.2 eV can be achieved. In the last section, a closer look into the dependencies of the layer thicknesses of the two different nc‐SiC:H layers applied in solar cells on the cell performance is taken. While the layer with conducting properties only has minor influences on cell properties, a trade‐off between passivation and fill factor is identified for the passivating nc‐SiC:H layer. For thicker layers, the passivating nc‐SiC:H layer achieves a very high implied open‐circuit voltage above 740 mV, but the fill factor starts to degrade due to a very low conductance of the layer.

Thermal, structural, optical, and photon shielding studies of cerium-doped barium tellurite glasses.

A series of tellurite-based glasses are prepared by using a melt-quenching method. The effect of cerium on the physical, thermal, structural, optical, spectroscopic, and shielding properties of barium tellurite glass samples is studied. It has been observed that the thermal stability factor increases with increasing cerium ion (Ce3+ ) concentration. The density and other physical parameters such as ion concentration and molar volume are calculated using the Archimedes principle. An increase in optical band gap and density suggests a decrement in non-bridging oxygens. These results are in accordance with Raman results. The blue emission in prepared glasses is studied in terms of International Commissionon Illumination chromaticity coordinates. Moreover, various shielding properties such as mass attenuation coefficient, linear attenuation coefficient, effective atomic number, half-value layer, and tenth-value layer have also been determined to understand the photon shielding characteristics of as-prepared glass samples.

Invesigation of the electronic structure and Optoelectronic properties of Si-doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> using GGA+U method based on first-principle

In this work, the formation energy, band structure, state density, differential charge density and optoelectronic properties of undoped and Si doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> are calculated using GGA+U method based on density functional theory. The results show that the Si-substituted tetrahedron Ga(1) is more easily synthesized in experiments, and the obtained <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> band gap and Ga 3d state peak are in good agreement with the experimental results, and the effective doping is more likely to be obtained under oxygen-poor conditions. After Si doping, the total energy band moves to the low-energy end, and Fermi level enters the conduction band, showing n-type conductive characterastic. Si 3s orbital electrons occupy the bottom of the conduction band, the degree of electronic coocupy is strengthened, and the conductivity is improved. The dielectric function ε2(ω) results show that with the increase of Si doping concentration, the ability to stimulate conductive electrons first increases and then decreases, which is in good agreement with the quantitative analysis results of conductivity. The optical band gap increases and the absorption band edge rises slowly with the increase of Si doping concentration. The results of absorption spectra show that Si-doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> has strong deep ultraviolet photoelectric detection ability. The calculated results provide a theoretical reference for the further experimental investigation and the optimization innovation of Si-doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> and relative device design.

Investigation of electronic structure and optoelectronic properties of Si-doped <i>β</i>-Ga<sub>2</sub>O<sub>3 </sub>using GGA+<i>U</i> method based on first-principle

In this work, the formation energy, band structure, state density, differential charge density and optoelectronic properties of undoped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> and Si doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> are calculated by using GGA+<i>U</i> method based on density functional theory. The results show that the Si-substituted tetrahedron Ga(1) is more easily synthesized experimentally, and the obtained <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> band gap and Ga-3d state peak are in good agreement with the experimental results, and the effective doping is more likely to be obtained under oxygen-poor conditions. After Si doping, the total energy band moves toward the low-energy end, and Fermi level enters the conduction band, showing n-type conductive characteristic. The Si-3s orbital electrons occupy the bottom of the conduction band, the degree of electronic occupancy is strengthened, and the conductivity is improved. The results from dielectric function <i>ε</i><sub>2</sub>(<i>ω</i>) show that with the increase of Si doping concentration, the ability to stimulate conductive electrons first increases and then decreases, which is in good agreement with the quantitative analysis results of conductivity. The optical band gap increases and the absorption band edge rises slowly with the increase of Si doping concentration. The results of absorption spectra show that Si-doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> has the ability to realize the strong deep ultraviolet photoelectric detection. The calculated results provide a theoretical reference for further implementing the experimental investigation and the optimization innovation of Si-doped <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> and relative device design.

Annealing-induced phase transformation in In10Se70Te20 thin films and its structural, optical and morphological changes for optoelectronic applications.

In2Se3 and In2Te3 have great importance in various device fabrications. The present report is based on the annealing-induced phase formation of both In2Se3 and In2Te3 from In10Se70Te20 thin films at different annealing temperatures as found from the XRD analysis and well supported by the Raman study. The average crystallite size increased with a decrease in the dislocation density. The surface morphology changed with annealing and increased in particle size as noticed from the FESEM images. The uniform distribution and presence of constituent elements in the film were verified using EDX data. The increase in transmittance is accompanied by a decrease in extinction coefficient, optical density and increase in skin depth with annealing. The increase in optical bandgap from 0.418 eV to 0.645 eV upon annealing at 250 °C is associated with a decrease in disorder. The steepness parameter increased and the Se-p value decreased with annealing. The refractive index decreased with an increase in oscillator energy and decrease in dispersion energy. The quality factor, dielectric loss, optical conductivity and electrical susceptibility decreased. The optical electronegativity and plasma frequency increased with annealing. There is a significant change in the non-linear susceptibility and non-linear refractive index with annealing. The observed changes in the film structure and optical behaviour are due to the annealing-induced phase formation from the In10Se70Te20 host matrix upon annealing. Such materials are suitable for optoelectronic and phase change devices.

Sputter Deposited Mn‐doped ZnO Thin Film for Resistive Memory Applications

AbstractTransition metal doped Zinc oxide (ZnO) thin films with wide band gap semiconducting nature have diverse range of applications including, gas sensors, optical and optoelectronic devices, electronics and spintronics spintronic devices etc. In the present study, Manganese (Mn)‐doped ZnO thin films deposited on glass substrates using RF‐magnetron sputtering have been investigated for their optical and electrical behavior aiming at resistive random access memory applications. To study the influence of Mn doping and correlation between the structural and the physical properties of the films, the samples were characterized by X‐ray Diffraction (XRD), Raman spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X‐ray Spectroscopy (EDS), UV‐VIS spectrophotometry and X‐ray photoelectron spectroscopy (XPS). The films are found to be crystalline and a decrease in lattice parameter from 2.6049 Å to 2.5845 Å, an increase in optical band gap from 3.27 eV to 3.35 eV and a decrease in Urbach energy from 0.222 eV to 0.171 eV, is observed with increase in Mn‐concentration. The electrical performance of the film with highest Mn‐content is found to be more suitable for resistive memory applications. Tailoring the electrical behavior of the film by incorporating Mn as dopant is an important approach to find suitable material combination for novel memory devices.

Defect-induced measurements of semi-organic ammonium hydrogen oxalate oxalic acid dihydrate single crystals using gamma irradiation

The structural, optical, mechanical and electrical properties of pure and 5—20-kGy gamma-irradiated semi-organic single crystals of ammonium hydrogen oxalate oxalic acid dihydrate (NH4H3(C4O8).2H2O) are presented. The crystals were synthesized at room temperature using facile solvent evaporation technique. Powder XRD measurements indicate gradual enhancement in crystallinity and lattice defect annihilation for low radiation dosage. Radiation-induced increase in optical band gap (4.01–4.16 eV) indicates high damage threshold of the crystals. Quenching of photoluminescence is attributed to the lowering of surface defect density with radiation. The influence of gamma radiation on the functional vibrations of the crystals is studied using FTIR-Raman spectroscopy. Vickers microhardness measurements show gradual enhancement in crystal hardness with the increase in radiation. An increase in forward resistance with irradiation is observed from I–V measurements and is attributed to high transparency of the crystals. These results indicate the viability of NH4H3(C4O8) 2H2O crystals in potential space optoelectronic applications.