Carrier Optical Absorption Research Articles

Effect of Li Doping on Structural, Optical, and Optoelectrical Characteristics of ZnSnO3 Thin Films Prepared by Nebulizer Spray Pyrolysis

In this work, ZnSnO3 (ZTO3) and Li-doped ZTO3 thin films were synthesized on glass slides by a cost-effective nebulizer spray pyrolysis procedure. The X-ray diffraction analysis revealed that the ZTO3 and Li-doped ZTO3 thin films possessed a rhombohedral structure. The structural indices (grain size, dislocation density, lattice strain) of the ZTO3 and Li-doped ZTO3 thin films were computed. The morphology characteristics of the ZTO3 and Li-doped ZTO3 thin films were observed by field emission scanning electron microscopy. The inspected films display uniform and homogeneous surfaces. The optical transmittance, T, and reflectance, R, of the ZTO3 and Li-doped ZTO3 thin films were recorded using a double-beam spectrophotometer to investigate the optical characteristics of these layers. The refractive index of the ZTO3 and Li-doped ZTO3 thin films was enhanced via the Li content increase. Moreover, Tauc’s plots demonstrated that the energy gap of the ZTO3 and Li-doped ZTO3 thin films was reduced from 3.85 eV to 3.08 eV by boosting the Li doping content. Moreover, the increase in Li content produces an enhancement in the optoelectrical indices (optical resistivity, optical carrier concentration, optical mobility, plasms frequency, and optical conductivity) of the ZTO3 and Li-doped ZTO3 thin films. The nonlinear optical indices of the ZTO3 and Li-doped ZTO3 thin films were deduced, and it was noted that Li content boosted the nonlinear optical indices of these layers. All the ZTO3 and Li-doped ZTO3 thin films displayed n-type semiconducting properties by the hot probe equipment.

Structural, Optical and Optoelectrical Properties of CuAlSnS4 Thin Films

The present study used chemical deposition to deposit thin copper aluminum tin sulfide (CATS4) layers onto clean glass substrates. X-ray diffraction analysis was utilized to explore the crystalline structure of the CATS4 films, which refers to the CATS4 films having a cubic crystal structure. Energy-dispersive X-ray analysis showed the presence of Cu, Al, Sn, and S peaks in the CATS4 films, and their atomic ratio is close to 1:1:1:4. Spectrophotometric measurements of optical transmittance and reflectance spanning the 400–2500 nm spectral range were performed to describe the optical properties of the CATS4 layers. The CATS4 films demonstrated a direct energy gap transition between 1.42 and 1.31 eV. Further, increasing the layer thickness enhanced the refractive index and Urbach energy of the CATS4 films. The inspected CATS4 films showed better optoelectrical properties with increasing thickness, including improved optical conductivity, optical resistivity, optical carrier concentration, relaxation time, and optical mobility. Increasing the thickness of the CATS4 films increased their nonlinear optical indices. Additionally, the hot probe apparatus verified the p-type semiconducting characteristics of CATS4 films.

Relationship between electrical and optical characterization of Ga-doped ZnO thin films deposited by magnetron sputtering

Introduction: Transparent conducting films have received much attention in energy conversion applications. To replace high-cost indium-tin-oxide (ITO), Ga-doped ZnO (GZO) film is considered due to its high conductivity, good transparency, low cost, and low toxicity. Methods: GZO and pure ZnO films were deposited on glass substrates by dc magnetron sputtering. The crystalline structure of the samples was verified by using X-ray diffraction. In particular, the relationship between the electrical and optical characterization of the GZO film was investigated through the plasma wavelength obtained from transmittance and reflectance spectra. Meanwhile, carrier transport was directly confirmed by Hall effect-based measurements. Results: The GZO film shows a hexagonal wurtzite structure, with successful incorporation of Ga into the ZnO lattice. Ga doping increases the carrier concentration, leading to a decrease in the resistivity of the film. This study also discusses the correlation of carrier transport obtained from Hall effect-based measurements and optical spectroscopies. Here, we extracted the optical carrier concentration and optical mobility from the plasma wavelength and compared them with the Hall data. Conclusion: The dependence of carrier transport on ionized impurity scattering can be pointed out. It proposes an effective way to qualitatively predict the electrical characteristics and transport properties of thin films via optical transmittance and reflectance analysis.

Effect of γ-radiations on the optoelectrical parameters of coumarin-poly vinyl alcohol composite thin films

This work aims to study the effect of γ-radiations on the optoelectrical parameters of coumarin-poly vinyl alcohol composite thin films at room temperature prepared by solution casting method. For these polymer composite films, the various parameters calculated from the refractive index and extinction coefficient were obtained from transmittance and reflectance spectra. The effect of radiations on the optical band gap, Urbach energy, tangent loss factor, volume and surface energy loss functions were studied. The effect of γ-radiations on the optoelectrical parameters like high-frequency dielectric constant, optical carrier concentration, relaxation time, optical mobility and optical resistivity derived from Drude theory were also discussed. Moreover, other parameters of interest under the investigation were optical conductivity, electronic polarizability, optical electronegativity, nonlinear optical susceptibility, optical, and chemical hardness. The impacts of γ-radiations on dispersion parameters like oscillator energy, dispersion energy, oscillator wavelength and oscillator strength were also studied by using Wemple-DiDomeenico single oscillator model.

Dielectric properties, Optoelectrical parameters and electronic polarizability of thermally evaporated a-Pb-Se-Ge thin films

This article is devoted to the study of various dielectric and optoelectrical parameters, besides electronic polarizability, and metallization parameter of amorphous Pb10Se90-xGex (0.0≤x≤10.0at.%) thin films. These studies are based on the calculated values of refractive and extinction coefficient. The thin films were prepared using the conventional thermal evaporation technique. All samples were previously investigated by XRD, EDX, and UV–Vis–NIR spectrophotometric measurements. Using refractive index and extinction coefficient spectra, the dielectric constant (real and imaginary parts), dissipation and quality factors are discussed. Also, many optoelectrical factors of Pb–Se-Ge films have been studied. The energy loss functions, high-frequency dielectric constant and optical carrier concentration are also deduced and studied. The plasma frequency and some other optoelectrical parameters, such as scattering time, optical mobility, and optical resistivity are studied and discussed. From the computed results it can be said that these films can be used in many optoelectronic applications, IR photodetectors, and sensors.

Enhancement of elastic, optical and opto-electrical properties of Ni-Substituted CoFe2O4 nanoparticles with different concentrations

This study examined the influence of the addition of Ni ions to nano-ferrite with general formula; Ni x Co 1-x Fe 2 O 4 (where, x = 0.0, 0.3, 0.5, 0.7 and 1.0), which was synthesized using the coprecipitation technique. The analysis of XRD and FTIR analyses suggest the formation of the single-phase cubic structure for all samples. The average crystallite size of the prepared specimen was computed at 36 nm using the Scherer equation. The force constants for the tetrahedral and octahedral sites were well-estimated using FTIR data. Hence, longitudinal, transverse (shear), mean elastic sound wave velocities were calculated. Thus, Elastic moduli such as Young's modulus, stiffness constant, bulk modulus, modulus of rigidity, Poisson ratio and Debye temperature were determined. The variation of these parameters for all synthesized samples has been explained in terms of binding forces between ions of the spinel lattice. In addition, reflectance and transmittance have been used to investigate the optical properties. Both calculated refractive index, n , and the absorption index, k , have been used to estimate, the high-frequency dielectric constant, lattice dielectric, complex dielectric constant, volume and surface energy loss functions, dielectric relaxation time and complex optical conductivity as well as optical electronegativity. Moreover, Drude theory was applied to investigate the opto-electrical parameters, such as optical carrier concentration, optical mobility, optical resistivity, and the non-linear optical parameters. Finally, the electronic transitions of all studied concentrations were estimated. The goal of this work is to investigate the structure, elastic modulus and optical and opto-electrical properties of Ni x Co 1-x Fe 2 O 4 . • FTIR spectroscopy technique was used to locate the position bands of vibration and the elastic modules. •The linear and nonlinear optical properties were investigated using spectrophotometric measurements of reflectance and transmittance. •The Calculated refractive index, n , and the absorption index, k , have been used to estimate, the optical parameters. •The Drude theory was applied to investigate the opto-electrical parameters, such as optical carrier concentration, optical mobility and optical resistivity

Optical investigations on PVA capped SnS nanocrystalline films deposited by CBD process

Tin monosulphide (SnS) nanocrystalline films, capped by polyvinyl alcohol (PVA) were successfully deposited on glass substrates using chemical bath deposition (CBD). The films were deposited at different deposition times that vary in the range, 45–90 min The XRD spectra indicated that PVA capped SnS layers were polycrystalline in nature and exhibiting orthorhombic structure. The average crystallite size was evaluated using W-H plots. Cross section view of SEM micrographs were used to determine the thickness of the films. The optical behaviour of all the deposited layers was investigated in relation to deposition time. The studies revealed a very high optical absorption coefficient of ∼105 cm−1 for all the deposited layers and the optical band gap varied from 1.79 eV to 1.55 eV with increase of deposition time. The band gap values obtained were higher than the bulk value of 1.3 eV, which is attributed to quantum confinement effect. The size of particles, calculated using Brus equation, varied marginally in the range, 5.8–8.4 nm with increase of growth time. The optical parameters such as refractive index, extinction coefficient, high frequency dielectric constant, optical carrier concentration, relaxation time and optical conductivity were also determined.

Growth, structure, optical and optoelectrical characterizations of the Cu2NiSnS4 thin films synthesized by spray pyrolysis technique

Earth-abundant Kesterite materials are very important to fabricate low-cost solar cells. Here, good quality Cu2NiSnS4 (CNSS) thin films were successively manufactured on a glass substrate at 350 °C using a simple spray pyrolysis system. The structural characterization of the sprayed Cu2NiSnS4 thin films was examined by the FE-SEM and XRD techniques. X-ray diffraction patterns indicate that the sprayed Cu2NiSnS4 films are single phase and having polycrystalline structure. The elemental composition analysis of the sprayed Cu2NiSnS4 thin films confirmed that the Cu2NiSnS4 film is near stoichiometric in compound. Our optical observations indicate that the refractive index (n) of the sprayed Cu2NiSnS4 films was increased by increasing the film thickness. Moreover, the sprayed Cu2NiSnS4 films exhibit a direct optical transition and the magnitudes of the energy gap have been decreased from 1.28 to 1.14 eV with the increase of thickness. The optoelectrical parameters of the Cu2NiSnS4 films, like optical conductivity, optical mobility, optical resistivity, optical carrier concentration and relaxation time were estimated with different thickness. Additionally, the nonlinear optical parameters of the Cu2NiSnS4 films were estimated. The fabricated CNSS/n-Si heterojunction achieved a conversion efficiency of 11.34%.

The lead selenide photoconductive sensitization via oxygen ion implantation with enhanced optical absorption and carrier mobility

We demonstrate a lead selenide material sensitization method using O+ beam implantation at 50 keV. A nano-polycrystalline material with ~29 nm grain size is synthesized, which is completely different with the currently diffused material in submicron scale. This nano-material exhibits high carrier mobility and optical absorption with an Urbach energy as low as 29.5 meV, indicating a well-ordered microstructure. The responsivity of up to ~2 A/W at 4 μm is achieved for sample with implantation dose of 1 × 1018 cm−2. It is revealed that the high responsivity may be attributed to the high optical absorption and carrier mobility.

Near-infrared (1 to 4 μ m ) control of plasmonic resonance wavelength in Ga-doped ZnO

The plasmonic resonance wavelength λres in ZnO doped with 3 wt.% Ga2O3 can be controlled over the range 1 to 4 μm by simple furnace annealing in flowing Ar. For each annealing temperature TA, the reflectance Rm and transmittance Tm are measured over a wavelength range, λ=185 to 3200 nm, (energy range, E=6.7 to 0.387 eV), and the reflectance coefficient R is calculated from Rm and Tm. The value of λres is then determined from a Drude-theory analysis of R versus E that yields fitting parameters nopt (optical carrier concentration), μopt (optical mobility), high-frequency dielectric constant ϵ∞, and thickness d at each annealing temperature TA. The validity of this process is confirmed by comparison of ϵ∞ with literature values and comparison of nopt and μopt with analogous quantities n and μH measured by the Hall effect.

Structural and optoelectrical properties of nanostructured LiNiO2 thin films grown by spray pyrolysis technique

Abstract LiNiO2 thin films of different thicknesses (200–354 nm) have been synthesized using conventional pyrolysis technique. Systematic investigations of the structure, morphology, optical, and optoelectrical properties have been made using X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, High-resolution scanning electron microscopy (HR-SEM), and spectrophotometric analysis. XRD patterns of the as-synthesized LiNiO2 films have revealed the polycrystalline nature of films under study with the rhombohedral crystal structure. HR-SEM micrographs have shown an evolution in films morphology from a rugged to a smooth surface with the increase in the film thickness. The change in morphology has been interpreted to the orientation and/or crystalline phase. Remarkable changes in the crystalline and surface properties of the films have been noticed with increasing film thickness. The optical constants of the studied films have been extracted from both transmittance and reflectance spectra. The films band gap was found to decrease with the increase of film thickness. The dispersion of the refractive index has been analyzed in the view of Wemple-DiDomenico model which enable the determination of linear and nonlinear optical parameters. Among the investigated films, the 354 nm film demonstrated the highest nonlinear optical parameters. This finding could shed lights of the possibility of using LiNiO2 in nonlinear devices. In addition, the real and imaginary parts of the dielectric constants have been utilized to determine various optoelectrical parameters such as the dissipation factor tan δ , relaxation time τ , the optical carrier concentration N o p t , optical mobility μ o p t , optical resistivity ρ o p t , plasma frequency ω p , and damping frequency ω d . Good correlations have been established between the optical and optoelectrical parameters of the investigated films.

Studies on dielectric properties, opto-electrical parameters and electronic polarizability of thermally evaporated amorphous Cd50S50−xSex thin films

The objective of this work is to study the influence of the addition of more Se on dielectric properties, opto-electrical parameters and electronic polarizability of amorphous chalcogenide Cd50S50−xSex thin films (30 ≤ x ≤ 50 at%). Thin films of thickness 200 nm were synthesized by vacuum deposition at ≈8.2×10−4 Pa. Both refractive index and extinction coefficient were used to obtain all the studied parameters. The high frequency dielectric constant, real and imaginary parts of dielectric constant were discussed. Drude theory was applied to investigate opto-electrical parameters, like optical carrier concentration, optical mobility and optical resistivity. Moreover, other parameters were investigated and studied, e.g. Drude parameters, volume and surface energy loss functions, dielectric loss factor, dielectric relaxation time, complex optical conductivity and electronic polarizability as well as optical electronegativity and third-order nonlinear optical susceptibility. Values of electronic polarizability and nonlinear optical susceptibility were found to be decreased while optical electronegativity increased as Se-content was increased. Increment of Se-content in amorphous Cd50S50−xSex thin films has also led to minimize the energy losses when electromagnetic waves propagate through films as well as optical conductivity and the speed of light increased. The other studied properties and parameters of Cd50S50−xSex films were found to be strongly dependent upon Se-content.

Extracting the effective mass of electrons in transparent conductive oxide thin films using Seebeck coefficient

A method is proposed that combines Seebeck coefficient and carrier concentration to determine the electron effective mass of transparent conductive oxide (TCO) thin films. Experiments were conducted to test the validity of this approach on the transparent conductive Ga-doped ZnO thin films deposited by magnetron sputtering. An evident agreement of the calculated electron effective mass of the films is observed between the proposed approach and the previous studies. Besides, the optical carrier concentration and mobility derived from the calculated electron effective mass and spectroscopic ellipsometry using a complex dielectric function are consistent with those from direct Hall-effect measurement. The agreements suggest that Seebeck coefficient can serve as an alternative tool for extracting the effective mass of electrons in TCO films.

Ellipsometry characterization of polycrystalline ZnO layers with the modeling of carrier concentration gradient: Effects of grain boundary, humidity, and surface texture

Spectroscopic ellipsometry (SE) has been applied to study the effects of grain boundary, humidity, and surface texture on the carrier transport properties of Al-doped ZnO layers fabricated by dc and rf magnetron sputtering. In the SE analysis, the variation in the free carrier absorption toward the growth direction, induced by the ZnO grain growth on foreign substrates, has been modeled explicitly by adopting a multilayer model in which the optical carrier concentration (Nopt) varies continuously with a constant optical mobility (μopt). The effect of the grain boundary has been studied by comparing μopt with Hall mobility (μHall). The change in μHall/μopt indicates a sharp structural transition of the ZnO polycrystalline layer at a thickness of d ∼ 500 nm, which correlates very well with the structure confirmed by transmission electron microscopy. In particular, below the transition thickness, the formation of the high density grain boundary leads to the reduction in the μHall/μopt ratio as well as Nopt. As a result, we find that the thickness dependence of the carrier transport properties is almost completely governed by the grain boundary formation. On the other hand, when the ZnO layer is exposed to wet air at 85 °C, μHall reduces drastically with a minor variation of μopt due to the enhanced grain boundary scattering. We have also characterized textured ZnO:Al layers prepared by HCl wet etching by SE. The analysis revealed that the near-surface carrier concentration increases slightly after the etching. We demonstrate that the SE technique can be applied to distinguish various rough textured structures (size ∼ 1 μm) of the ZnO layers prepared by the HCl etching.

Optical/electrical correlations in ZnO: The plasmonic resonance phase diagram

The Drude equation for dielectric constant ϵ(E) depends on four parameters: ϵ∞, effective mass m*, optical mobility µopt, and optical carrier concentration nopt. By solving this equation at ϵ(Eres) = 0, we obtain a relationship between µopt and nopt at constant plasmonic resonance energy Eres [or wavelength λres (µm) = 1.2395/Eres (eV)]. A family of µopt versus nopt curves covering a range of λres values (including the limiting wavelength λres = ∞) constitutes a plasmonic resonance phase diagram (PRPD) for a semiconductor defined by only ϵ∞ and m*. The PRPD is a convenient instrument that allows an immediate prediction of λres from Hall‐effect measurements of µH and nH. We apply the PRPD analysis to a series of ten ZnO samples grown by pulsed laser deposition at 200 °C in an ambient of 33%H2:67%Ar and annealed in 25 °C steps for 10 min in air at various temperatures from 400 to 600 °C. For the samples annealed at 550 °C or lower, the µH/nH points yield predicted values of λres that range from 1.07 to 2.80 µm; however, the 575 and 600 °C samples are predicted to have no resonance at all. Reflectance curves for the eight samples annealed up to 550 °C decrease slowly from 6 eV down to about Eres = 0.5–1.15 eV, and then increase rapidly for E < Eres. In contrast, there is no such resonance‐related increase for the 575 and 600 °C samples. Satisfactory agreement is found between the reflectance minima and the Hall‐effect‐predicted values of λres.

Characterization of textured SnO2:F layers by ellipsometry using glass-side illumination

Spectroscopic ellipsometry (SE), in which the probe light is illuminated from a glass substrate side, has been applied for the characterization of textured SnO2:F layers formed on glass substrates. This approach can basically be employed for the non-destructive characterization of the component layers in silicon thin-film solar cells formed on large-area glass substrates, even when the backside metal electrodes are present. To perform the accurate characterization of the SnO2:F textured structure, the SE spectra obtained from the glass-side and conventional film-side illuminations are analyzed simultaneously by using the identical dielectric functions and optical models. In this study, the layer thickness and optical carrier concentration of the textured SnO2:F layer have been deduced from the SE analysis using the Drude model, and the estimated values from SE show excellent agreement with those obtained by other techniques. From the SE results, we demonstrate that the SE analysis using the glass-side illumination can be performed even for the textured structures.

Nanostructured TiO2 thin films: synthesis and characterisations

In the present study, TiO2 thin film was fabricated by sol–gel dip coating technique, and the structural, optical and dielectric characteristics of the film have been investigated to identify the basic characteristics. By the help of the X-ray diffraction spectrum, the structural parameters of the nanostructured TiO2 thin film, such as lattice constants, texture coefficient and crystallite size, were analysed. The value of crystallite size has been evaluated by the Debye–Scherrer and Williamson–Hall methods and also estimated from the field emission SEM images. There was a consistency for the values of crystallite size obtained from all the methods. Swanepoel’s method and transmittance measurements were used to analyse the optical parameters of the TiO2 thin film. Film thickness, refractive index n, extinction coefficient k, band gap energy Eg and Urbach energy Eu have been determined as 264·03 nm, 2·67, 0·067, 3·22 eV and 0·127 eV respectively. It is seen that the real and imaginary parts of the static dielectric constants follow the same pattern and have the values of the real part (7·436 at 655 nm) higher than the imaginary parts (0·038 at 655 nm). Moreover, the Spitzer–Fan model was used for investigation of the values of high frequency dielectric constant ϵ∞ and free optical carrier concentration Nopt. Furthermore, the dissipation factor and optical conductivity of the TiO2 thin film were examined. These results show that understanding the fundamental characteristics of this structure may be of great help in improving the quality of TiO2 for the future of the optoelectronic device technology.

Optical characterization of textured SnO2:F layers using spectroscopic ellipsometry

The SnO2:F transparent conductive oxide (TCO) layers with submicron-size textured structures have been characterized using spectroscopic ellipsometry (SE). By applying the Drude model to the SE analysis, the optical carrier concentration, mobility, and sheet resistance of the textured SnO2:F layers have been estimated, in addition to the detailed layered structures. The excellent agreement has been observed between the results obtained from SE and other characterization techniques including scanning electron microscope, atomic force microscope, and Hall measurements, confirming that SE is a reliable measurement technique even for the textured structures. Nevertheless, the electron mobility obtained from SE is lower than that deduced electrically from the Hall measurement, although the carrier concentrations estimated from these techniques are quite similar. From the SE analysis, the optical constants of the textured SnO2:F layers have been extracted, and the free carrier absorption in the SnO2:F layers increases drastically with decreasing optical mobility. The SE technique developed in this study can be applied further to perform the nondestructive mapping characterization of large-area TCO textures incorporated into thin-film solar cell modules.

Mapping Characterization of SnO2:F Transparent Conductive Oxide Layers by Ellipsometry Technique

The mapping characterization for the structural and optoelectronic properties of textured SnO2:F transparent conductive oxide (TCO) layers has been performed by spectroscopic ellipsometry (SE). From the SE analysis of the free carrier absorption in the SnO2:F layer, the optical carrier concentration and mobility are extracted by using the Drude model. As a result, in the textured SnO2:F substrate with a size of 9×9 cm2, we have confirmed slight non-uniformities in the carrier concentration as well as the layer thickness. Moreover, in order to investigate the effect of the TCO inhomogeneity on hydrogenated amorphous silicon (a-Si:H) and microcrystalline silicon (µc-Si:H) tandem solar cells, we have simulated short-circuit current density (Jsc) in the a-Si:H and µc-Si:H layers by taking the TCO inhomogeneity into account using the optical admittance method. From this procedure, we have quantitatively estimated the variation of Jsc by the TCO inhomogeneity assuming a non-textured flat structure.

Extracting reliable electronic properties from transmission spectra of indium tin oxide thin films and nanocrystal films by careful application of the Drude theory

Analysis of the transmittance and reflectance of transparent conducting oxide thin films and nanocrystal films can be accurately modeled using the Drude free electron theory to extract electrical transport properties if enough care is taken. However, several fits starting from different initial guesses are needed before confidence in the extracted Drude parameters can be obtained. Film thickness, optical carrier concentration, and optical carrier mobility can be reliably derived when using either a fully empirical or semiempirical model for the ionized impurity scattering. The results are in good agreement with those based on more arduous spectroscopic ellipsometry measurements. Furthermore, fitting the reflectance along with the transmittance reduces the uncertainty, but does not significantly affect the values of the extracted parameters.