Papers by Keyword: Optical Band Gap

Abstract: In this study, zinc telluride (ZnTe) thin films were deposited using radio frequency (RF) sputtering at various powers ranging from 100 to 250 W for 60 minutes. Structural and optical properties were investigated as a function of RF power. X-ray diffraction (XRD) analysis revealed that increasing the RF power led to a growth in the crystallite size from 3 to 9.4 nm, while dislocation density and microstrain decreased. The ZnTe films exhibited a cubic crystal structure with a lattice parameter of 6.08 Å. Scanning Electron Microscopy (SEM) showed that the film surfaces are uniform and free of cracks. Optical measurements using UV-Vis-NIR spectrophotometry indicated that both transmittance and optical band gap increased from 1.82 to 1.94 eV with increasing RF power. The modulation of the optical and structural properties of ZnTe thin films by RF power, as demonstrated in this study, opens perspectives for optimizing these materials in real device architectures, particularly for more efficient solar cells or high-performance sensors.

Abstract: The review article focuses on the growth of thin film and its characterization by UV-Vis-NIR spectroscopy. For UV-Vis-NIR spectroscopy of thin films, they are usually deposited on translucent quartz glass surfaces. The article reports the extraction of various thin film optical parameters viz., absorption coefficient (α), Urbach energy (E_u), optical band gap (E_g), refractive index (n), extinction coefficient (k), dielectric constants, dissipation factor (tanδ) and optical conductivity (σ_optical) by using optical spectra (absorption(A)/transmittance (T)/reflectance (R)). Furthermore, the effect of thin film substrate temperature (T_s) and/or thickness (d) and/or post-deposition annealing temperature (T_a) on various optical parameters is discussed in detail.

Abstract: Among the numerous metal oxide semiconductors, zinc oxide (ZnO) is one of the most widely used materials in various fields due to its non-toxic nature, tunable electric and optical properties, and good thermal and chemical stability. This research aims to study the tuning of optical, electrical, and surface properties of ZnO film treated with dielectric barrier discharge (DBD) plasma produced at atmospheric pressure. The result revealed a significant decrease in its optical band gap, but there was an increase in conductivity. The results of contact angle measurement clearly showed the change of surface nature from hydrophobic to hydrophilic for DBD-treated ZnO film.

Abstract: Ti doped Cu₂O thin films were prepared at distinct Argon/Oxygen gas flow ratio of 34/1, 33/2,32/3 and 31/4 with net flow (Ar+O₂) of 35 sccm by using DC magnetron sputtering system on glass substrates at room temperature. The gas mixture influence on the film properties studied by using X-ray diffraction, Field emission scanning electron microscopy and UV-Visible spectroscopy. From XRD results, it is evident that, with a decrease in oxygen content, the amplitude of (111) peak increased, peak at a 35.67^o scattering angle and the films shows a simple cubic structure. The FESEM images indicated the granularity of thin films was distributed uniformly in a homogenous model and also includes especially pores and cracks. The film deposited at 31/4 showed a 98% higher transmittance in the visible region.

Abstract: In the present work, reactive DC magnetron sputtering method is used to deposit TiO₂ thin films on glass substrates. The structural, surface morphology and optical studies of TiO₂ thin films were discussed by varying the oxygen flow rates from 1 to 4 sccm. X-ray diffraction patterns of TiO₂ thin films show amorphous nature. The surface morphological and elemental composition of TiO₂ thin films were examined by field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. From the optical absorption spectra, the shifting of absorption edge towards the longer wavelength leads to the decrement of optical bandgap from 3.48 to 3.19 eV with an increase of oxygen flow rate from 1 to 4 sccm.

Abstract: Multiferroics, with two or more coexisting ferroic orders (ferroelectric, ferro (antiferro)-magnetic) in a single phase, display promising photovoltaic characteristics which can be utilised in solar energy harvesting. However, the efficacy is seriously challenged due to their wide band gap, far from the ideal value of ~1.52 eV for photovoltaic applications, resulting in overall unimpressive performance. In the present work, an approach towards imparting multiferroism in an otherwise non-ferroic system was adopted through strain engineering. Bulk SrMnO₃ (SMO) is antiferromagnetic-paraelectric. However, our previous first-principles studies predicted high-pressure phase transformation from bulk non-polar phase to a tetragonal polar phase. In light of the above, SMO was synthesised hydrothermally at 200°C for 96 h using water-soluble nitrate salts of strontium and manganese. FESEM study reveals the formation of hexagonal bipyramid shaped SMO crystals with elongated 1-D features. Powder x-ray diffraction studies and subsequent Rietveld refinement confirm the presence of hexagonal (P6₃/mmc) as well as tetragonal (P4mm) phases. Energy dispersive x-ray analysis (EDAX) confirms Sr/Mn ≈ 1, the stoichiometric ratio. UV-VIS spectroscopy was utilised to estimate the optical bandgap of the as-grown sample which was found to be in the range of 1.4-1.5 eV. Temperature-dependent magnetisation plot indicates the magnetic transition temperature, ~275K.

Abstract: Borate glass system of composition (100-x)B₂O₃-15Al₂O₃-20CaO-0.4Fe₂O₃-xCeO₂ with x = 0, 0.25, 0.50, 0.75, and 1.0 mol% were prepared using conventional melt-quenching method. Optical measurements were carried out at room temperature to determine the Cerium (Ce³⁺) ions concentration dependent absorption and luminescence emission properties of such glass system. Optical energy band gap of the glass system were evaluated as a function of Ce³⁺ ions content. Indirect band gap energy was found to be lower than the direct band gap energy. Urbach energy was ranged between 0.12-0.17 eV. An increased broad absorption is observed in the UV region with increasing Ce³⁺ ions concentration. The emission spectra of the glass system recorded with 380 nm excitation wavelength revealed prominent cyan-green emission.

Abstract: Aluminium (Al) doped Zinc oxide (ZnO) thin films of different thicknesses were prepared on glass substrates by sol-gel spin coating method. The effect of thicknesses on micro-structural and optical properties was investigated for transparent conducting oxide (TCO) application in solar cells and other optoelectronic applications. Grazing incidence x-ray diffraction (GIXRD) showed maximum orientation along (002) plane of c-axis. The variation of different structural parameters like crystallite size, micro-strain, c-axis strain, dislocation density as a function of film thickness was investigated. The FTIR spectra confirmed the formation of Al-doped ZnO film. FESEM images showed spherical shaped nanosized grains and formation of micro pores. The optical absorption increased and absorption peak shifted towards longer wavelength (red shift) with increase in the thickness of the film respectively. The optical transmittance of all the films has a transparency of more than 75% in the visible region. The optical band gap (E_g) decreased with increase in the film thickness. The diffused reflectance (DRS) showed very low reflectance in the region of 400-800 nm, but increased in the 800-900 nm region. Photoluminescence (PL) spectra of the prepared films showed intense band edge UV and low intense visible emissions respectively. The effect of thickness of Al-doped ZnO film on micro-structure, surface morphology, optical absorption and transmittance, diffused reflectance and PL have been investigated and the results are reported.

Abstract: Zinc Oxide thin films were prepared for different precursor solution molarities from 0.025M to 0.1M by spray pyrolysis deposition technique. A comprehensive study was carried out to realize the effect of concentration of precursor on ZnO thin films. The optimized temperature of the glass substrate was 300°C. From the XRD data it is inferred that the films are polycrystalline and hexagonal wurtzite structure . The degree of preferred orientation were along diffraction planes (100), (002) and (101) for all the ZnO films. The intensity of the diffraction peak prepared with 0.1M concentration is higher than those prepared at lower concentrations. The grain size (D) was calculated using Debye-Scherrer formula. It was found that the average grain size increases, when the molar concentration increases. As the solution concentration increases, the band gap decreases. The films are transparent in the visible region (85%), and the transmittance decreases as the molar concentration increases, which is caused by optical scattering at grain boundaries.

Abstract: In this study, pure nickel oxide thin films were prepared by a sol-gel dip coating method with different withdrawal speeds, onto glass substrates and their structural, optical and morphological properties were investigated. The structural properties of NiO films were characterized by X-ray diffraction (XRD), Polycrystalline structures of the prepared films were detected. The optical properties of the films were studied by UV–visible spectrophotometer and the optical transmittance of the films within the visible and near infrared region was found to be more than 75% and decrease when the withdrawal speed increase. The surface morphology of the films was observed by atomic force microscopy and it was found that the root mean square (RMS) roughness increases from 3.78 to 15 nm when the withdrawal speed increased from 30 to70 mm/min. Thus, the withdrawal speed is a key factor to change the NiO thin films properties.