Enhanced Band Gap Research Articles

First principal calculations of electronic, optical and magnetic properties of cubic K1−xYxNbO3(Y = Fe, Ni)

The First principle study based on Density Function Theory (DFT) was accomplished to explore the electronic bandgap configurations of KNbO3 by transition metal doping such as Iron [Fe], and Nickel [Ni] using PBE-GGA (Perdew–Burke–Ernzerhof- Generalized Gradient Approximation) for the exchange-correlation potentials. In the current study K1−xYxNbO3 doped with various percentages (12.5%, 25%, 50%, and 75%) of [Ni] and [Fe] metal ions. Different unique properties such as electronic, optical conductivity, and magnetic properties of cubic K1−xYxNbO3(Y = Fe, Ni) compounds have been calculated through the FP-LAW WEIN2k software within DFT. The bandgap of KNbO3 can be reduced by doping various metal ions such as [Ni] and [Fe]. The spin up band structures was observed semiconductor but spin down metallic behaviour. The bandgap structure of overall K1−xYxNbO3(Y = Fe, Ni) compound after doping [Fe] and [Ni] with various concentrations become half metallic compound. Under the DFT scheme, iron [Fe] and nickel [Ni] are reliable as dopants for reducing the bandgap of KNbO3. After substituting various impurity concentration (12.5%, 25%, 50%, and 75%) of [Fe] and [Ni] the energy absorption peaks are 8.2 to 8.43eV for K1−xYxNbO3(Y = Fe, Ni). It is also observed that optical conductivity starting points shift towards the large energy because of bandgap enhancement when the doping concentration (12.5%, 25%, 50%, and 75%) of [Fe] and [Ni] increased in K1−xYxNbO3(Y = Fe, Ni) compound. Magnetic moment was increasing 1.00153 to 3.02210 μB by the increment of doping [Fe] and [Ni] concentrations. K1−xYxNbO3(Y = Fe, Ni) compounds are appropriate perovskite oxides materials for promising optical, magnetic and photovoltaic device applications.

Investigations on the effect of swift heavy silicon ion irradiation on hydroxyapatite

The effect of swift heavy silicon ion irradiation on hydroxyapatite prepared by hydrothermal technique was analyzed. The physical and biological properties were studied using G1XRD, Micro-Raman, photoluminescence, AFM, SEM, EDX, in vitro bioactivity, antimicrobial activity and drug release. When compared with pristine the crystallinity increases with an increase in fluence. Slight reduction in crystallinity was noted for irradiated samples at higher fluence (1×1013 and 1×1014 ions/cm2) than lower fluence (1×1012 ions/cm2). After irradiation the υ4 O-P-O asymmetric bending mode peak at 583 cm−1 disappeared. The PL intensity increases with an increase in fluence and it had become narrow and showed red shift. This suggests the material could find application as phosphors. The enhancement in band gap was attained for irradiated samples than Hpris (5.38–5.5 eV). AFM studies revealed the enhancement of roughness, particle size and pores on irradiation. SEM exposed the creation of pores along with an increase in porosity (2 µm to 30 µm). Formation of platy crystals was noted for 1×1013 ions/cm2 sample. In vitro bioactivity results with the formation of spherical (2 µm) apatite deposition along with the presence of interconnected pores (2–10 µm) which could enhance osteointegration and osteoconduction. In addition, Ca/P ratio was found to increase after soaking in SBF. Initial burst release followed by sustained release was obtained upto 45 h. Therefore it could assist in the treatment of bone and joint infection. Hence, SHI had improved the material to be used in biomedical field as an implant due to its enhanced properties such as crystallinity, pore size, surface roughness, PL intensity, antimicrobial activity, drug release and bioactivity.

Effect of HCl and HNO3 on the synthesis of pure and silver-based WO3 for improved photocatalytic activity under sunlight

Heterogeneous photocatalysis have been considered an important and efficient alternative water and wastewater treatment process. In this area, different semiconductors, such as tungsten trioxide, have been investigated aiming to enhance photocatalytic performance. WO3 is known to be an efficient material with high stability in acidic conditions. In the present work, pure and Ag/AgCl-doped WO3 photocatalysts were synthesized by a simple hydrothermal method. A discussion of the effects of two pH-controlling agents, HCl and HNO3, in the final properties of the catalyst is reported for the first time. The materials were characterized by XRD, BET, SEM, EDS and UV–vis DRS. All catalysts showed similar or enhanced band gap values compared to a standard photocatalyst benchmark (TiO2 P25). The type of acid did not lead to significant differences in morphology or photocatalytic activity of undoped catalysts. In contrast, doped catalysts prepared using HCl resulted in particles of flower-like morphology, with higher uniformity and slightly narrower band gap values. Furthermore, the use of HCl in the synthesis of silver-doped WO3 resulted in catalysts containing AgCl, while Ag0 was the major dopant species when HNO3 was used. All materials exhibited good photocatalytic activity, with a maximum of 75.4% acetaminophen degradation under simulated sunlight achieved by the catalyst prepared with HCl and doped with 5% Ag-equivalent. For this catalyst, the degradation kinetics was found to be consistent with the Langmuir-Hinshelwood (L−H) model, and reusability tests showed no significant decrease in the degradation efficiency after four cycles. Finally, the effects of different scavengers suggest that O2•− species play a major role in acetaminophen degradation with the material containing WO3, Ag and AgCl.

Advances in tuning band gap of graphene by potential doping using DFT: a review

Graphene: a sp2 carbon system is a zero band gap semiconductor. In spite of having extraordinary properties, opening of band gap is the bottleneck in the path of graphene for becoming the heart of all modern electronics. Chemical doping can prove itself to be the fastest solution to this problem as it is one of the most informal approaches to induce band gap in pristine. Due to tiny nanostructures and dimensions of graphene, modelling and simulative study of graphene is more effective and confirmative than experimental results. In this study we have compared our results with the previous works, our simulation matches well with the previous works. The main concern is on the substitution and pair doping of BN, B and N open up an energy band gap up to (0.379eV) and (0.386eV). Codoping of B-N create a band gap up to (0.712eV) and pair doping shows that 1BN(0.616eV), 2BN(0.386eV), 3BN pair create a sharp increase in band gap up to (1.457eV) when substitute on graphene, while the substitution doping and increased in the super cell models with the same doping concentration of silicon induced a band gap of 1.019eV, where Si doping on different super cell shows a band gap enhancement from 0.57eV at (6x6) model to 1.90eV at (5x5) model and change its nature from semimetal to semiconductor. The present review article focuses on the alteration of electronic and optical properties by adding different dopants on to the graphene sheets, using density functional theory (DFT) calculations. Doping can improve the electronic properties of graphene by producing a small band gap in it, resulting in the appropriateness of this interesting material for modern electronics. Different codes and approximations have been applied to tune the band structure of graphene that has been discussed in the article.

Strain modulation for enhancing Cu–Zn ordering in CZTS absorber layer using seed layer assisted growth for efficient carrier transport

Cu2ZnSnS4 (CZTS) solar cells suffer from lower power conversion efficiency relative to its fellow copper indium gallium selenide thin-film technology, which have been asserted on the existence of non-stoichiometry and high degree of Cu–Zn disorder. Huge disparity among the lattice constants of Mo and CZTS is one of the causes of inducing strain in the film, which often creates defects in the CZTS structure. This work focused on investigating the effect of strain modulation using seed layer (SL) assisted growth on the structural and optoelectronic properties of CZTS films. The results indicate that SL growth of CZTS reduces strain in the film and improves the crystallinity and overall quality of the CZTS absorber, as indicated by SEM and x-ray diffraction studies. Raman shifts to higher wavenumber and photoluminescence (PL) energy shift corresponding to dominant band-to-band transition in SL CZTS correlate perfectly with the high value of order parameter. Bandgap enhancement and reduction in the Urbach energy of SL CZTS implicate higher ordering (reduction in Cu–Zn disorder) due to strain modulation. Consequently, substantial improvement from 2.13 to 13.5 cm2/V s in hole mobility is achieved. Finally, the faster response of the photodetector based on SL CZTS compared to without SL growth supports all the findings. Our results imply that SL assisted growth of CZTS could be critical to obtain a high-quality CZTS absorber layer.

Strain-Induced Bandgap Enhancement of InSe Ultrathin Films with Self-Formed Two-Dimensional Electron Gas.

Atomically thin indium selenide (InSe) is a representative two-dimensional (2D) family that have recently attracted extensive interest for their intriguing emerging physics and potential optoelectronic applications with high-performance. Here, by utilizing molecular beam epitaxy and scanning tunneling microscopy, we report a controlled synthesis of InSe thin films down to the monolayer limit and characterization of their electronic properties at atomic scale. Highly versatile growth conditions are developed to fabricate well crystalline InSe films, with a reversible and controllable phase transformation between InSe and In2Se3. The band gap size of InSe films, as enhanced by quantum confinement, increases with decreasing film thickness. Near various categories of lattice imperfections, the band gap becomes significantly enlarged, resulting in a type-I band alignments for lateral heterojunctions. Such band gap enhancement, as unveiled from our first-principles calculations, is ascribed to the local compressive strain imposed by the lattice imperfections. Moreover, InSe films host highly conductive 2D electron gas, manifesting prominent quasiparticle scattering signatures. The 2D electron gas is self-formed via substrate doping of electrons, which shift the Fermi level above the confinement-quantized conduction band. Our study identifies InSe ultrathin film as an appealing system for both fundamental research and potential applications in nanoelectrics and optoelectronics.

Nano synthesis of ZnO–TiO2 composites by sol-gel method and evaluation of their antibacterial, optical and photocatalytic activities

85ZnO–15TiO2, 75ZnO–25TiO2, and 65ZnO–35TiO2 nanocomposites were prepared by the sol-gel method. The structural, morphological, antibacterial, optical and photocatalytic performances were analyzed. Three phases, i.e., hexagonal wurtzite, anatase, and hexagonal ZnTiO3 were detected for each of the specimens. The crystallite size reduced as the TiO2 content increased, whereas the corresponding values for 65ZnO–35TiO2 were 39.02 nm (ZnO), 20.40 nm (anatase) and 34.89 nm (ZnTiO3). A particle size reduction phenomenon was observed as approaching from 85ZnO–15TiO2 (66 nm) to 65ZnO–35TiO2 (47 nm). The antibacterial activity was measured through the inhibition of the growth of Escherichia coli bacteria by ZnO–TiO2. The maximum inhibition zone for bacterial growth was achieved for 65ZnO–35TiO2 (19.7 mm). Two types of absorption bands were obtained within the UV–Visible region. However, the blue shifting of these bands resulted in the enhanced band gap. Moreover, 65ZnO–35TiO2 demonstrated the highest photodegradation efficiency of methylene blue dye backing the reason for the lowest particle size (47 nm). The photodegradation efficiency values of 85ZnO–15TiO2, 75ZnO–25TiO2 and 65ZnO–35TiO2 at 100 min were 72.9%, 80.2%, 90.7% respectively.

Optimized Omnidirectional High-Reflectance Using Octonacci Photonic Crystal for Thermographic Sensing Applications

The transmittance of waves through one-dimensional periodic and Octonacci photonic structures was studied using the theoretical transfer matrix method for both wave-polarization-modes. The first structures were made up of the SiO2 and TiO2 materials. The objective here was to obtain a broad omnidirectional high reflector covering the infrared spectrum of a thermographic camera [1–14µm] and, especially, to prevent the transmission of emitted human body peak radiation λmax = 9.341 µm. By comparing the periodic and Octonacci structures, we found that the last structure presented a main and wide photonic band gap near this human radiation. For that, we kept only the Octonacci structure for the rest of the study. The first structure did not give the aspired objective; thus, we replaced the TiO2 layers with yttrium barium copper oxide material, and a significant enhancement of the omnidirectional photonic band gap was found for both TE and TM polarization modes. It was shown that the width of this band was sensitive to the Octonacci iteration number and the optical thickness (by changing the reference wavelength), but it was not affected by the ambient temperature. The number of layers and the thickness of the structure was optimized while improving the omnidirectional high reflector properties.

Phosphorus-doped nanocrystalline silicon-oxycarbide thin films

P-doped nc-SiOxCy:H films are grown at moderately low substrate temperature ~250°C and rf power ~200 W via controlled incorporation of C and O from CH4 and CO2 precursor gases by PECVD. The optoelectronic and structural properties of the films have been studied in detail. On gradual increase in CH4 flow rate (F) in the plasma, systematic formations of the Si-C and Si-O-C bonds in a-SiOxCy:H network are evident from the gradual shift of the Si-H wagging and Si-O-Si stretching vibrational modes towards higher and lower wavenumbers, respectively. XPS studies have confirmed on the presence of Si-O-C bonds and the P-atoms as dopants in the network. The Si-C bond density has increased from 1.56×1021 to 4.1×1021 cm−3 and the grain size of the nanocrystals has reduced from 6 to 3.2 nm with the increase in F from 0 to 0.3. An enhancement in the optical band gap is accomplished via the addition of stronger Si-C bonds in the a-SiOxCy:H matrix and also due to quantum confinement effect arising from the reduced size of the nanocrystals, together. The optimum n-type nc-SiOxCy:H film possessing ~50.5% crystallinity with nanocrystal grain size ~5 nm has demonstrated an optical band gap ~1.96 eV and high dark conductivity ~6.41 × 10−1 S cm−1, which altogether appear promising for the window layer of all-Si tandem solar cells. A switching of the electrical characteristics from the degenerate-like crystalline network to its non-degenerate amorphous-like configuration is identified at higher C incorporation in the P-doped SiOxCy:H complex network, corresponding to the CH4 flow rate above 0.2sccm.

Analysis of Photonic Bandgap Extension in One-Dimensional Quasiperiodic Superconducting Photonic Slabs

One-dimensional superconducting photonic slabs made of alternated layers of isotropic dielectric (SiO2) and a high-Tc superconductor (YBCO) are theoretically investigated by the Gorter Casimir two fluid model (GCTFM) and the transfer matrix method (TMM). The proposed photonic quasicrystals are built according to the inflation rule of quasiperiodic sequences. The enhancement of the photonic band gap is theoretically investigated. Extending photonic band gap (E-PBG) is achieved for suitable quasiperiodic chains. The bandwidth of the photonic band gap can be enhanced by changing the temperature of superconductor, parameter of quasiperiodic sequence. An overall photonic band gap is obtained in the visible frequency range and can be enhanced by applying a typical thickness’ deformation along the superconducting photonic sample.

Proposal of graphene band-gap enhancement via heterostructure of graphene with boron nitride in vertical stacking scheme

Since the discovery of graphene and other two-dimensional (2D) materials in recent years, heterostructures composed of multilayered 2D materials have attracted immense research interest. This is mainly due to the potential prospects of the heterostructures for basic and applied applications related to the emerging technology of energy-efficient optoelectronic devices. In particular, heterostructures of graphene with 2D materials of similar structure have been proposed to open up the band gap to tune the transport properties of graphene for a variety of technological applications. In this paper, we propose a heterostructure scheme of band-gap engineering and modification of the electronic band structure of graphene via the heterostructure of graphene–boron nitride (GBN) based on first-principles calculations. For a comparative analysis of the properties of the proposed GBN heterostructure, we employ Kohn–Sham density functional theory (DFT) using local density and generalized gradient approximations within Perdew–Burke–Ernzehof parameterization. To account for weak interlayer van der Waals interactions, we employ the semi-empirical dispersion-corrected DFT scheme of Grimme, called the DFT-D2 approximation. In the vertical stacking arrangement of boron-nitride-doped graphene with hexagonal boron nitride, we predict a band-gap opening of 1.12 eV which, to our knowledge, is the largest value attained for this kind of system. The impact of interlayer spacing on the band-gap opening arising from the interlayer coupling effect is also analyzed. The band-gap enhancement supports the widely proposed promise of GBN heterostructure in design of high-performance optoelectronic devices such as field-effect transistors for potential applications.

Defect states and grading induced bandgap variability analysis of CIGS solar cells through device simulations

Copper-indium-gallium-diselenide (CIGS) is one of the promising absorbing material in thin film solar cells. It is a direct band gap material with the band gap (Eg) ranging from 0.98 to 1.68 eV. The band gap of this material is dependent on the composition of the material. The band gap enhancement leads to significant reduction in the extent of exciton recombination but on the other hand it also reduces the absorption in the absorber layer. We simulated and analyzed the effect of band gap variations in CIGS layer, induced by grading of doping concentration profile and defect states over the performance of solar cell. The performance analysis has been done using SCAPS-1D (Solar Cell Capacitance Simulator) simulator. It is intended to develop specially to simulate the AC and DC characteristics of hetero-junction thin film solar cells, especially CIGS and CdTe solar cells. By the introduction of grading in the CIGS material, an enhancement of 2.48% has been observed in the overall efficiency. This enhancement can be attributed to the reduction in recombination and increase in the exciton generation.

Intrinsic magnetism and thermoelectric applicability of novel halide perovskites Cs2GeMnX6 (X = Cl, Br): Route towards spintronics and energy harvesting technologies

Novel halides becomes a point of prestige due to their intriguing multi-dimensional applications. In this work, strict and highly accurate spin-polarized Density Functional Theory (DFT) combined with Boltzmann transport scheme has been applied to extract the properties of new class of Pb-free prototypical halide semiconductors Cs2GeMnX6 (X = Cl, Br). The structural composition of these alloys suitably prefers their cubic crystalline geometry not only at room temperature but at higher temperatures also. The electronic properties were executed by Pedrew-Burke and Ernzerhof (PBE-GGA) in addition with the strong on-site Hubbard-parameter (U) implemented on Mn-partially filled d states to designate the complete understanding regarding their electronic structures. The inclusion of two calculation schemes claims p-type indirect semiconducting band profiles with the enhancement of band gap follows the trend GGA < GGA + U. The semiconducting nature at different symmetric points with ultra-spin splitting results ferromagnetic magnetic character of 5μB leads to the promising route towards spintronics. Elastically and mechanically these alloys are characterized to show brittle/ductile capability. Conservative estimates of Seebeck coefficient gears its extending application stand in thermoelectric energy harvesting technologies. The compact overview on these FM halide perovskites can develop into other highly dynamic research fields with vast implications for high-performance spin optoelectronics, spintronics, thermoelectrics and topological devices.

Rapid microwave-assisted fabrication of Al-doped zinc oxide nanorods on a glass substrate for photocatalytic degradation of phenol under visible light irradiation

A rapid microwave-assisted process was used to synthesize a quasi-aligned Al-doped ZnO nanorods on a glass substrate. X-ray diffraction and scanning electron microscopy were used to investigate the crystal structure and morphological properties while the optical properties of the prepared materials have been examined by UV–visible and photoluminescence spectroscopy. Two different Al concentrations, 1% and 5%, were used to dope ZnO nanorods. The prepared Al-doped ZnO samples were annealed at 350 °C–550 °C temperature range. 1% AZO sample annealed at 550 °C showed the highest visible light absorption. Synthesized NRs surface chemistry have been characterized using X-ray photoelectron spectroscopy. Samples morphology, NRs density and diameter significantly changed with Al doping. Results show that the crystal orientation and surface oxidation states are dependent on Al content. Overall, Al-doping of ZnO NRs enhanced the photocatalytic degradation of phenol, especially at 1% Al due to bandgap narrowing and enhancement of visible light absorption.

Novel rare earth yttrium doping effect on physical properties of PbS nanostructures: facile synthesis and characterization

The dielectric properties of pure and yttrium-doped PbS nanoparticles synthesized by the coprecipitation chemical synthesis route have been studied by several characterizations. X-ray diffraction patterns of samples were employed to estimate the crystallite sizes and intrinsic microstrains using Williamson–Hall (W–H) plot analysis. The crystallite size and intrinsic macrostrain values were evaluated in the range of 13.7–15.9 nm and 1.09 × 10–3–1.72 × 10–3, respectively, using W–H plots. The formation of nanoparticles, nanoflakes, sponge, and nanosheets were seen via scanning electron microscope (SEM). Energy dispersive spectroscopy (EDS) of 5.0 wt% confirms the Y: PbS sample elements' chemical composition and stoichiometry. The optical band gaps increase in the range of (0.93–1.17 eV) with an increase in the dislocation density. The higher values of dielectric constant (23.6–28.0), dielectric loss (37.6–176.8), loss tangent (2.7–8.6), and electrical conductivity [ 10.2 to ( 11.7) S/m] have been reported at the lower frequency. The highest electrical conductivity values were obtained in the range of [ 4.71 to ( 4.81) S/m] for as-prepared samples. The greater capacitance and impedance values were found at 3 kHz and decrease with increasing the frequency up to 10 MHz. The current–voltage characteristic curves of undoped and Y: PbS NPs were performed under biased voltage. The space charge current density was noticed in the range of (8.7 × 10–4–4.2 × 10–4 amp/cm2) at 1.0, 2.5, and 5.0 wt% of Y: PbS samples. The enhancement in the optical band gap and dielectric and electric properties on yttrium doping in PbS compared to pristine PbS NPs makes them suitable for optoelectronic applications.

Comparative DFT study of vibrational, electronic, and optical properties of energetic alkali metal salts based on nitrogen-rich 5-aminotetrazole.

This article presents a thorough density functional theory based comparative study on nitrogen-rich 5-aminotetrazole alkali metal salts M 5-At (M = Li, K, Rb, Cs). The calculated structural parameters using plane-wave pseudopotential method are consistent with the experimental results. The computed vibrational frequencies at ambient pressure show that vibrational modes in high energy region are due the NH bond of NH2 group. Pressure variation IR spectra of these materials show clear frequency shifts where Li 5-At shows an overall red shift below 900 cm-1 contrary to the blue shift seen in other materials in this range. The born effective charge values reveal the presence of strong covalency between N, H, and C atoms whereas an increased ionic nature is seen as the atomic number of metal atoms increases. Furthermore, we used full potential linear augmented plane wave (FP-LAPW) method for calculating electronic structure and optical properties with TB-mBJ potential which provides an enhanced band gap for all materials compared to standard GGA functional. Electronic structure calculation reveals that all the compounds are indirect band gap insulators with the exception of Li 5-At. The computed partial density of states show mixed ionic-covalent nature in metal-N/C bonds and covalent nature in NC bonds. In addition, we are also presenting the optical properties such as real and imaginary dielectric constant, absorption, refraction, reflection, loss spectrum as functions of photon energy. From the optical properties we can conclude that all the studied compounds are optically anisotropic in nature and are good absorbers in the ultraviolet (UV) region.

Shunted piezoelectric patches on auxetic microstructures for the enhancement of band gaps

Certain frequency ranges where waves do not propagate, and thus, vibrations are suppressed, are called band gaps. In the present paper, the appearance and the behavior of such areas are investigated on star-shaped auxetic microstructures, which are equipped with shunted piezoelectric elements. The optimal position of the piezoelectric patches is found using genetic algorithms, considering the maximization of the electromechanical coupling coefficient. A genetic algorithm is also used for the calculation of the values of the electrical parameters of the resonant shunt circuit, with objective the maximization of certain band gaps. The results indicate that the proposed technique can be used for the maximization of band gaps at certain frequency ranges, as well as at frequency bands which have not been considered in the optimization problem of the mechanical microstructure.

An extensive investigation of structural, electronic, thermoelectric and optical properties of bi-based half-Huesler alloys by first principles calculations

Half Huesler (HH) alloys have been a hot topic of research due to their fascinating properties and applications in several fields. There are several HH alloys been studied and this work is based on three Bismuth based HH alloys, ZrRhBi, ZrIrBi and HfRhBi, of which we have presented an extensive study on the structural, electronic, thermoelectric (TE) and optical properties using ab-initio density functional theory (DFT) calculations. The previous work on these alloys reported their stability and electronic properties stating that they possess good TE response which was done using DFT with PBE-GGA functional (J. Mater. Chem. A,5(13), 2017). In our study, we have used different exchange functionals to investigate these properties and observed that using nmBJ (new modified Becke–Johnson) potential, we can obtain enhanced band gap and TE response (high figure of merit, ZT and power factor, PF) of these alloys as compared to previous report and fascinating optical properties as well. Our results show that ZrIrBi and HfRhBi are narrow-gap and ZrRhBi is a moderate gap semiconductor. All of these alloys have excellent ZT values of around 0.7 at room temperature. The optical properties show that these compounds have low absorbance, moderate reflectivity and low optical conductivity in visible region. The contrasting behaviour of their optical properties with respect to the regions of electromagnetic spectrum and their electronic properties suggests that they can be effectively used in optoelectronics and various optical devices. Also, their high ZT values both in low and high temperatures open up a possibility to use them for various TE applications.

Size-dependent nonlinear optical absorption in SnO2 quantum dots

Using a Z-scan technique, we report size-dependent changeover from reverse saturable absorption to saturable nonlinear optical absorption properties of as-deposited and annealed stannic oxide semiconductor quantum dot thin films, prepared by a sol-gel technique on a quartz substrate. The average size of quantum dots, as obtained from grazing incident x-ray diffraction, was found to be in the range of the exciton Bohr radius. Atomic force microscopy data confirmed the spherical shape of quantum dots. The UV-Vis data of the films displayed bandgap enhancement due to the combined effect of Coulombic and confinement potentials. A density matrix analysis was conducted to obtain the transition energy-dependent nonlinear optical absorption coefficient in the cw excitation regime. We found a qualitative agreement between the experimental observations and theoretical calculations.

Influence of Al content on the optical band-gap enhancement and lattice structure of (Ga1-xAlx)2O3 single crystal

Abstract Single crystals of undoped, 4.8, 9.3 and 14.1 at.% Al substituted β-Ga2O3 have been grown by optical floating zone technique. It has been observed that it is not possible to grow good quality single crystal with higher Al content unlike the thin film grown by pulsed laser deposition [Appl. Phys. Lett. 105 (2014) 162107]. It has been found that the incorporation of Al in β-Ga2O3 has resulted a shrinkage in the lattice parameters and volume. This leads to a systematic increase in the band gap of the material and broadens the transmission window in the deep UV range up to 5.08 eV for 14.1 at.% of Al substitution in the lattice.