Interband Transition Strength Research Articles

Optimized structural, optical, and electrical properties of spin-coated Pt(II) octaethylporphyrin thin films for optoelectronic applications

Octaethylporphyrin (PtOEP) is an organic molecule that has unique optical properties, such as high fluorescence quantum yields, strong light absorption, etc. Here we investigate the structural, optical, and electrical characteristics of spin-coated PtOEP thin film. X-ray diffraction (XRD) patterns indicated an increase in the crystallite of the annealed film. Field emission-scanning electron microscope (FESEM) images clearly showed agglomeration and an increase in the nanoparticle size of the annealed film. The Raman spectra of the thin films revealed symmetrical peak positions and improved peak strength for the annealed film. UV-Vis-NIR and photoluminescence (PL) spectroscopy were used to examine optical characteristics. The findings demonstrated that energy gap and PL peak emission were significantly influenced by the grown crystallite size as well as a decrease in lattice defect concentration at the grain boundary during annealing. The optical constant and interband transition strength spectra (Jcv) were estimated and addressed. Based on the linear refractive index and optical gap, third-order nonlinear susceptibility χ(3), nonlinear refractive index n2, and two-photon absorption coefficient, βc of spin-coated PtOEP thin films were calculated and discussed. Finally, the dark current-voltage (J-V) curves were utilized to assess the diode parameters, specifically the zero-bias barrier height (ΦB) and the ideality factor (n), for the ITO/PtOEP/Al diode using thermionic emission theory. Additionally, an investigation was conducted to examine the conduction mechanism of the ITO/PtOEP/Al diode under both forward and reverse bias voltage conditions. On the basis of these findings, spin-coated PtOEP thin films were concluded to be helpful in producing cutting-edge optoelectronic devices.

AgSbTe2 semi-nanocrystalline thin films as a multifunctional platform for optoelectronic and diode applications

The synthesis of the nanosized multifunctional thin film provides new solutions for many technological issues and consider a great step for miniaturized technology. Toward these goals, AgSbTe2 semi-nanocrystalline thin films of different thicknesses were synthesized by the thermal evaporation technique. The structural features were investigated by X-ray diffraction, and selected area electron diffraction (SAED) yielding a semi-nanocrystalline thin film of grain size ranging from 9.98 to 21.38 nm. The energy-dispersive X-ray spectroscopy (EDAX) verified the high purity and stoichiometry of the deposited films. For optoelectronic application, many optical parameters, including band gap (Eg), Urbach energy (Eu), Refractive index (n), dispersion energy (Ed), electronic polarizability (αe), and interband transition strength (JCV) were extensively discussed. The optical band gap reduced from 1.41 to 1.04 eV upon increasing the thickness from 150 to 550 nm. The temperature dependence of the electrical resistivity (ρ) of nanosized thin film was measured and the activation energy was estimated and it was found that the resistivity increased up to 450 K asserting the semiconductor behavior of the films. As for diode application, The Ag/2D-MoS2/p-AgSbTe2 (550 nm)/n-Si/Al heterostructure diode was constructed by thermal evaporation and all the diode parameters alongside conduction mechanism were studied in detail. AgSbTe2-based diode showed a low rectification ratio; however, the ideality factor (n) and zero bias barrier height (Φb) had optimal values of about 1.40 and 0.75 at room temperature, respectively.

Structural, linear/non-linear optical, optoelectrical, and electrical properties of novel crystalline antimony-doped tin oxide thin films synthesized by the chemical deposition method

Antimony-doped tin oxide thin films (Sb-doped Sn–O) have been synthesized via the chemical bath deposition (CBD) procedure and annealed at 450 °C for different annealing times of 1, 2, 3, 4, and 5 h. The morphological, linear/non-linear optical, dispersion, optoelectrical, and electrical properties were examined and discussed. The energy band gap (Eg) values fell in the range of 2.70–2.83 eV for annealing times of 1–3 h and decreased to 2.78 and 2.15 eV for annealing times of 4–5 h, respectively. Optical and optoelectronic properties were directly derived from the results of transmittance and reflectance. The theoretical Wemple-DiDomenico single oscillator model was employed to calculate various dispersion parameters of the Sb-doped Sn3O4 films. Furthermore, the non-linear optical properties were calculated via simple semi-empirical relations. Meanwhile, inter-band transition strength, optical surface resistance, and thermal emissivity were also obtained for optical/optoelectronic systems, non-linear optical devices.

Electron dynamics in α -quartz induced by two-color 10-femtosecond laser pulses

The time dependent density functional theory (TDDFT) is used to study the femtosecond laser induced excitation dynamics of electrons in bulk $\ensuremath{\alpha}$-quartz, and evaluate the laser energy deposition into this material. In order to properly distinguish the contributions of ionization (electron transitions from the valence band to the conduction band) and laser heating (electron transitions in the conduction band), two 10-femtosecond laser pulses exhibiting different wavelengths are used. Short wavelengths are expected to enhance the ionization rate, whereas longer wavelengths should be more suitable for excitation in the conduction band, thus providing a possible control of the whole electron dynamics. The influence of the pulse-to-pulse delay and intensities is studied. A significant enhancement of the interaction efficiency, in terms of excited electron density and their energy density, is observed for zero pulse-to-pulse delay. It is attributed to the opening of new ionization pathways involving various combinations of both photon energies ensuring the energy conservation, i.e., the sum of photon energies bridges the bandgap. This analysis is supported by a semi-analytical quantum model in the multiphoton absorption regime. The role and strength of direct interband transitions for the electron dynamics in the conduction band are highlighted. The associated laser energy deposition into the material is shown to be as efficient as collisional processes.

Structural analysis, FTIR study and optical characteristics of graphene doped Bi2O3 thin film prepared by modified sol–gel technique

Bismuth oxide(Bi2O3) and Graphene doped bismuth oxide thin films were synthesized using modified Sol-gel technique at a temperature about 180–220 °C in a cost effective procedure. In this experiment, self synthesized graphene was used as dopant. The effect of graphene doping on the microstructure and crystalline nature of bismuth oxide were studied after the samples had been subjected to XRD. The prepared graphene was found to be in hexagonal crystal structure and the bismuth oxide was monoclinic in structure. A increase in lattice parameters and decrease in crystallite size and an increase in microstrain and dislocation density was also resulted in this work for graphene doped bismuth oxide (Bi2O3). A detailed structure study from rietveld refinement was carried out in terms of atomic position of various partipating atom, their bond angles and lengths. Finally, a simulated structure was also generated for Bi2O3 and graphene doped Bi2O3. Obtained bandgap of doped Bi2O3 was low. Also the optical properties like refractive index, SELF, interband transition strength etc. were studied.

Structural, microstructural and optical properties of perovskite CCNbxTi1−x O (x = 0.02) thin film explored for photovoltaic applications

CCNbxTi1−xO(CCTO-Nb) thin film was prepared by modified sol-gel route owing to its obvious benefit over traditional sol-gel process. The prepared gel was used for preparing film by doctor’s blade technique. The material was observed to be crystallized in perovskite phase in space group no. Im3. The rietveld refinement confirms its phase and the morphological study reveal the formation of transformation of microstructure from grain to bead to rod like structure and then to fibrous form. From mapping it is seen that the grains are uniformly distributed. Mean surface roughness and RMS surface roughness were estimated from atomic force microscopy (AFM) study. The different optical properties like, band gap, optical conductivity, interband transition strength, oscillation energy etc. are estimated in this study. This shall throw an insight to the applicability of the material in photovoltaic applications.

Tin telluride quantum dot thin films: Size dependent structural, optical and electrical properties

In the current study, efforts have been made to acquire tin telluride quantum dot (QD) thin films that work at room temperature and in the region of visible and near-infrared (NIR). SnTe ingot and thin films were formed using the solid solution and inert gas condensation (IGC) techniques respectively. A cubic polymorph structure was identified using XRD for the prepared SnTe ingot, while grazing incident in-plane X-ray diffraction (GIIXD) and HR-TEM electron diffraction was used for identifying the thin films. The average particle size was found to increase from 2.3 to 9.6 nm with increasing film thickness from 5 to 25 nm. The optical gap of thin film QDs is wider than those of bulk samples; this is attributable to the quantum confinement effect. As a result of quantum confinement, SnTe thin films have optical gap values in the visible and NIR region (2–0.85 eV) instead of being in the infrared region (0.19 eV) of their bulk materials counterpart. The electronic transition was described by studying various important optical parameters such as optical conductivity (σop), interband transition strength (JCV), and surface and volume energy loss functions (SELF, VELF). Electrical conductivity shows a degenerate semiconductor performance. I–V characteristic show symmetric nonlinear behavior for 10 and 15 nm film thickness.

Comparative investigation of linear and nonlinear optical properties of As–70 at% Te thin films: influence of Ga content

Thin films (~ 150 nm) of amorphous As30Te70−xGax (where x = 0, 1, 3, 6, and 10 at%) are prepared through thermal evaporation of As30Te70−xGax bulk samples on glass substrates. X-ray powder diffraction (XRD) analysis reveals the amorphous nature of the as-prepared As30Te70−xGax thin films. The influence of Ga content on the As30Te70−xGax thin films’ linear and nonlinear optical properties is determined based on the optical reflectance and transmittance spectra. The estimated (direct or indirect) optical bandgap decreases with an increase in Ga content up to 3 at% and then increases, whereas the Urbach energy exhibits an opposite trend. The linear and nonlinear refractive indices, extension coefficient, optical conductivity, electrical conductivity and nonlinear susceptibility, optical density, inter-band transition strength, etc., are found to be significantly influenced by Ga content and the energy of incident waves. The As30Te67Ga3 composition can be considered as a puzzling compound as most of the investigated parameters in As30Te70−xGax alloys demonstrate opposite behaviors around that composition. Moreover, the optical surface resistance and thermal emission of As30Te70−xGax thin films are estimated from the investigated optical parameters and it was found that they are dependent on Ga content. The obtained results enhanced basic understanding and showed that the As–Te–Ga system qualifies for various optoelectronic applications.

EFFECTS OF Co CONCENTRATION ON THE STRUCTURAL AND OPTICAL PROPERTIES OF Zn1−xCoxS FILMS

Amorphous and crystalline Zn[Formula: see text]CoxS ([Formula: see text], 0.3, 0.5) thin films were grown on sapphire (Al2O3) substrates by pulsed laser deposition at substrate temperature of 25∘C and 800∘C, respectively. The X-ray diffraction results show that the crystalline film has a cubic zinc blende structure and the crystalline quality decreased with increasing Co-doping concentration. The X-ray diffraction and X-ray photoelectron spectroscopy spectra reveal that the samples reached an overdoping state at Co-doping concentration of [Formula: see text]. The absorbance of films increases and the absorption edge shifts to longer wave length direction with increasing Co-doping concentration. The redshift of the band gap energy depends on the Co composition associating with the Urbach energy. Furthermore, the refractive index and dielectric constant increase with increasing Co-doping concentration. The dispersion parameters, such as dispersion energy ([Formula: see text]), oscillator energy ([Formula: see text]), static refractive index ([Formula: see text]), static dielectric constant ([Formula: see text]), interband transition strength moments ([Formula: see text] and [Formula: see text]), oscillator strength [Formula: see text] and oscillator wavelength [Formula: see text], have been analyzed by Wemple–DiDomenico single oscillator model. All these parameters were found to be dependent upon the Co-doping concentration in the Zn[Formula: see text]CoxS thin films.

Single photon emission from droplet epitaxial quantum dots in the standard telecom window around a wavelength of 1.55 μm

We study the luminescence dynamics of telecom wavelength InAs quantum dots grown on InP(111)A by droplet epitaxy. The use of the ternary alloy InAlGaAs as a barrier material leads to photon emission in the 1.55 μm telecom C-band. The luminescence decay is well described in terms of the theoretical interband transition strength without the impact of nonradiative recombination. The intensity autocorrelation function shows clear anti-bunching photon statistics. The results suggest that our quantum dots are useful for constructing a practical source of single photons and quantum entangled photon pairs.

Electromagnetic properties in 160-170Dy nuclei: A microscopic description by the pseudo- SU(3) shell model

The large collectivity observed in the rare-earth region of the nuclear landscape is well known. The microscopic studies are difficult to perform in this region due to the enormous size of the valence spaces, a problem that can be avoided by means of the use of symmetry-based models. Here we present calculations for electromagnetic properties of 160-170Dy nuclei within the pseudo-SU(3) scheme. The model Hamiltonian includes the preserving symmetry \( Q\cdot Q\) term and the symmetry-breaking Nilsson and pairing terms, systematically parametrized for all members of the chain. The model is used to calculate B(E2) and B(M1) inter-band transition strengths between the ground state, \( \gamma\) and \( \beta\) -bands. In addition, we present results for quadrupole moments and g factors in these rotational bands. The results show that the pseudo-SU(3) shell model is a powerful microscopic theory for a description of electromagnetic properties of states in the normal parity sector in heavy deformed nuclei.

Single oscillator model of undoped and co-doped ZnO thin films

Undoped and co-doped zinc oxide thin films were deposited on glass substrates using a chemical spray technique. The experimental Lorentz profiles of co-doped ZnO thin films were measured in the spectral region 720–1750nm. A single oscillator model of the resulted materials is constructed by calculation of: zero-frequency refractive index (no), average interband oscillator wavelength (λo), oscillator strength (So), dispersion energy (Ed), single-effective oscillator energy (Eo), plasma oscillation frequency (ωp) and interband transition strength moments (M−1, M−3).

Tunable optical properties in atomic layer deposition grown ZnO thin films

ZnO thin films with very low surface roughness and bulklike electron density were grown on Si and SiO2 by atomic layer deposition. The real and imaginary parts of the complex dielectric function of ZnO on Si show monotonically decreasing values with decreasing film thickness at and below a threshold of about 20 nm. On the other hand, x-ray reflectivity results show that the electron density of our ZnO films is close to that of bulk ZnO and does not vary considerably with film thickness. While the reduction of the dielectric function cannot be explained by the electron density of our ZnO films, the Tanguy–Elliott amplitude prefactor governing the strength of optical interband transitions can explain our results consistently through the lowering of the electron–hole overlap factor at the ZnO/Si interface. In the case of ZnO/Si, a staggered type-II (spatially indirect) quantum well, holes are scattered into the Si substrate, causing a lowering of the electron–hole overlap factor and thus the reduction of excitonic absorption, consequently a decrease in the real and the imaginary parts of the dielectric function. This hypothesis was confirmed with ZnO films grown on SiO2, where a thin type-I quantum well, consisting of a narrower-bandgap semiconductor grown on a wider-bandgap (insulator) substrate, in which both the electron and the hole are confined in the ZnO thin film, leads to an increase in the electron–hole overlap matrix element with decreasing film thickness due to confinement, resulting in enhancement of the excitonic absorption in thinner ZnO films on SiO2.

Effect of Zn/Cd ratio on the optical constants and photoconductive gain of ZnO–CdO crystalline thin films

Optical and photo-electrical properties of ZnO–CdO films with the ratio of Zn/Cd=1:0, 3:1, 1:1, 1:3 and 0:1 has been studied. XRD study confirms the combination of hexagonal ZnO and cubic CdO phase present in the polycrystalline sample. Atomic force microscopy results indicate that the crystal grains are agglomerated and surface roughness enhanced due to higher Cd concentration in ZnO. From optical studies, it is found that the transmittance and the band gap decreased as Cd content increased. Photoluminescence studies on ZnO–CdO films showed intense near-band edge emissions at room temperature and is attributed to recombination of excitons localized within band tail states likely caused by non-uniform Cd distribution in ZnO–CdO matrix. The dispersion of refractive index was analyzed by the Wemple–DiDomenico single-oscillator model. The third-order nonlinear polarizability is found high with higher concentration of cadmium at higher photon energies. Some other optical parameters such as dissipation factor, optical conductivity, interband transition strength, surface and volume energy loss have been calculated depending on dielectric constant evaluated from optical data. Finally, photoconductive gain and carrier lifetime have been calculated and found dependent on Zn/Cd ratio.

Inter-band B(E2) transitions strengths in 160-170Dy nuclei

The rare earth region of the nuclear landscape is characterized by a large collectivity observed. The microscopic studies are difficult to perform in the region due to the enormous size of the valence spaces. The use of symmetries based models avoids that problem, because the symmetry allows to choose the most relevant degrees of freedom for the system under consideration. We present theoretical results for electromagnetic properties in 160-168Dy isotopes employing the pseudo-SU(3) model. In particular, we study the B(E2) inter-band transition strengths between the ground state, γ and, β-bands. The model succesfully describes in a systematic way rotational features in these nuclei and allows to extrapolate toward the midshell nucleus 170Dy.

Self-consistent analysis of the band structure of doped lattice-matched GaNAsBi-based QWs operating at 1.55 μm

Band structures of n–i doped lattice-matched GaNAsBi/GaAs quantum wells are studied theoretically using a self-consistent calculation (based on the envelop function formalism) combined with the 16-band anti-crossing model. Operating at 1.55μm, these QWs can represent active zones of temperature-insensitive optoelectronic device applications intended for optical fiber communications. We have calculated physical parameters of the structures such as the confining potential profiles, the Fermi level, the subband energies and their corresponding wavefunctions as well as the oscillator strength of inter-band transitions, the subband occupations, and the confined electrons density distributions. Finally, the absorption coefficient spectra of GaNAsBi-based QWs are also computed.

Exploring low, moderate and heavy Al doping impacts on microstructure and optical attributes of nanostructured cadmium oxide thin films

Bandgap tuning of semiconductors can often lead to significant performance increases and new applications for electronic, optoelectronic, and photocatalytic devices. In this study, we investigate the bandgaps of pure and aluminum doped cadmium oxide thin films synthesized using the low-cost sol–gel dip-coating method. Aluminum concentration is varied from 0 to 15at.%, and the effects that this doping has on the microstructure, electronic and optical properties are analyzed. Using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, d.c. electrical measurements and Uv–vis spectrophotometery a comprehensive study was carried out on the prepared samples. Adding Al deteriorates the crystallinity and electrical traits of the films. Taken micrographs indicate an anomalous roughness increase for 10at.% Al and emersion of bright agglomerations on the surface. Three regimes of bandgap variation via Al doping are uncovered. For doping up to 1% Al, there is a strong increase in the gap and continued doping up to 5at.% reduces the gap, while adding 10% and 15% Al causes bandgap enhancement. By evaluating dielectric constant of the samples, the interband transition strength of the films was calculated and grew abruptly beyond 3.25eV.

Optical properties of excitons in strained Gax In1-xAs/GaAs quantum dot: ef fect of geometrical conf inement on exciton g-factor

Taking into account anisotropy, nonparabolicity of the conduction band, and geometrical confinement, we discuss the heavy-hole excitonic states in a strained GaxIn1-xAs/GaAs quantum dot for various Ga alloy contents. The strained quantum dot is considered as a spherical InAs dot surrounded by a GaAs barrier material. The dependence of the effective excitonic g-factor as a function of dot radius and Ga ion content is numerically measured. Interband optical energy with and without the parabolic effect is computed using structural confinement. The interband matrix element for different Ga concentrations is also calculated. The oscillator strength of interband transitions on the dot radius is studied at different Ga concentrations in the GaxIn1-xAs/GaAs quantum dot. Heavy-hole excitonic absorption spectra are recorded for various Ga alloy contents in the GaxIn1-xAs/GaAs quantum dot. Results show that oscillator strength diminishes when dot size decreases because of the dominance of the quantum size effect. Furthermore, exchange enhancement and exchange splitting increase as exciton confinement increases.

Optical TCAD on the Net: A tight-binding study of inter-band light transitions in self-assembled InAs/GaAs quantum dot photodetectors

A new capability of our well-known NEMO 3-D simulator (Ref. Klimeck et al., 2007 [10]) is introduced by carefully investigating the utility of III–V semiconductor quantum dots as infrared photodetectors at a wavelength of 1.2–1.5 μm. We not only present a detailed description of the simulation methodology coupled to the atomistic sp3d5s∗ tight-binding band model, but also validate the suggested methodology with a focus on a proof of principle on small GaAs quantum dots (QDs). Then, we move the simulation scope to optical properties of realistically sized dome-shaped InAs/GaAs QDs that are grown by self-assembly and typically contain a few million atoms. Performing numerical experiments with a variation in QD size, we not only show that the strength of ground state inter-band light transitions can be optimized via QD size-engineering, but also find that the hole ground state wavefunction serves as a control factor of transition strengths. Finally, we briefly introduce the web-based cyber infrastructure that is developed as a government-funded project to support online education and research via TCAD simulations. This work not only serves as a useful guideline to experimentalists for potential device designs and other modelers for the self-development of optical TCAD, but also provides a good chance to learn about the science gateway project ongoing in the Republic of Korea.

OSCILLATOR STRENGTHES OF INTERBAND TRANSITIONS IN MULTILAYER QUANTUM DOTS WITH IMPURITY

The theoretical investigation is performed using the variational method in the approximation of effective mass. The energies and wave functions of the electron and hole ground states are calculated as functions of the position of hydrogen-like donor impurity in multi-shell spherical quantum dots. The different potential profiles of spherical nanosystems are studied. The dependences of the oscillator strength of interband transitions in different spherical nanosystems are obtained as functions of impurity position. It is shown weak influence of central or external impurity on oscillator strengths of interband transitions. It is proven that the maximal influence of impurity on the intensity of interband quantum transitions in multi-shell quantum dots is observed in the case of their location inside the potential well in the system, the core of which creates the potential barrier. For such systems even outer charges essentially influence on the intensities of interband quantum transitions. The results are promising for new type of sensors creation.