Optical Band Gap Of Thin Films Research Articles

Tailoring of charge carriers with deposition temperature in pulsed laser deposited BiFeO3 thin films

This research investigates the structural, topological, electrical and optical properties of pulsed laser deposited polycrystalline BiFeO3 thin films on silicon and glass substrate at varying deposition temperatures ranging from 400 °C to 700 °C. X-ray diffraction confirm rhombohedral phase and X-ray photoelectron spectroscopy reveals stoichiometric BiFeO3 films. The optical bandgap of thin films obtained from absorption spectra increases with the substrate temperature. Photoluminescence emission spectrum reveals the defects and Atomic Force Microscopy analysis bring out the surface topography and crystallinity improvement with temperature. The charge transport studies reveal a transition in conductivity from n-type at lower deposition temperature to p-type at higher deposition temperature, attributed to oxygen and bismuth vacancies respectively. The intricate understanding of conductivity tuning and the leaky nature of BiFeO3 thin film opens avenues for applications in non-volatile memories, particularly neuromorphic devices.

Structural, Electrical and Optical Properties of Mg-Ni Thin Films for Hydrogen Storage Applications

Using the magnetron sputtering technique, Mg-Ni (150nm) bilayer thin films were deposited onto the simple, and ITO coated glass substrates. To obtain proper mixing and inter diffusion of thin film structure, annealing of the prepared thin films was made at constant temperature 523 K. The surface morphology of thin films confirms the uniform deposition of the Mg-Ni thin films on substrates. The Raman spectroscopy of thin films shows that the intensity of Raman peaks is decreased as the hydrogen pressure increases and variation in the intensity peak confirms the existence of hydrogen in the prepared film. The d.c. conductivity of thin films were observed at different hydrogen pressure (10 - 40 psi) for both the as-deposited and annealed thin films and the variation in the conductivity after hydrogenation was found out. In Uv-Vis spectroscopy, it was found that the optical bandgap of thin films increases with the increase of hydrogen pressure. The deviations in the structural, electrical and optical properties after hydrogenation indicate that Mg-Ni thin films may be used for solid state hydrogen storage applications. HIGHLIGHTS Preparation of Mg-Ni bilayer thin films using magnetron sputtering technique Finding the opportunity to use Mg-Ni bilayer thin film as solid-state hydrogen storage materials Raman spectroscopy for confirming the presence of hydrogen in Mg-Ni bilayer thin films Effect of hydrogen on conductivity and optical energy bandgap of Mg-Ni bilayer thin films GRAPHICAL ABSTRACT

A NOVEL METHOD FOR PRODUCING NANOSTRUCTURED CdSe THIN FILM

In this study, we produced Cadmium selenide (CdSe) crystalline thin film on commercial glass substrates via chemical bath deposition. Transmittance, absorbance, refractive index and optical bandgap of thin films were examined by UV/vis spectrum. XRD revealed a hexagonal form. The pH level of the baths in which CdSe thin films were deposited varied and optical and structural properties of the resulting thin films were analyzed. SEM analysis was used for surface analysis. Some features of the films were supposed to change with pH and these properties were investigated by testing different pH levels, which were 8, 9, 10 and 11. The variation of the optical bandgap changed between 1.60 and 1.75[Formula: see text]eV, according to the pH of deposition bath. Film thickness varied from 60[Formula: see text]nm to 93[Formula: see text]nm, with the variation of deposition bath’s pH. Moreover, it has been found that refractive index values were also changed with film thickness; these were calculated as 2.28, 2.19, 2.22 and 2.36 for 93.27, 60.97, 61.09 and 60.18[Formula: see text]nm, respectively. Dielectric constant also varied with refractive index, taking values 0.85, 0.75, 0.78, 0.93 for refractive indexes 2.28, 2.19, 2.22 and 2.36, respectively.

Validation of a Terminally Amino Functionalized Tetra‐Alkyl Sn(IV) Precursor in Metal–Organic Chemical Vapor Deposition of SnO2 Thin Films: Study of Film Growth Characteristics, Optical, and Electrical Properties

AbstractTin(IV) oxide is a promising semiconductor material with leading‐edge properties toward chemical sensing and other applications. For the growth of its thin films, metal–organic chemical vapor deposition (MOCVD) routes are advantageous due to their excellent scalability and potential to tune processing temperatures by careful choice of the reactants. Herein, a new and highly efficient MOCVD process for the deposition of tin(IV) oxide thin films employing a terminally amino alkyl substituted tin(IV) tetra‐alkyl compound is reported for the first time. The liquid precursor, tetrakis‐[3‐(N,N‐dimethylamino)propyl] tin(IV), [Sn(DMP)4], is thermally characterized in terms of stability and vapor pressure, yielding highly pure, polycrystalline tin(IV) oxide thin films with tunable structural and morphological features in the presence of oxygen. Detailed X‐ray photoelectron spectroscopy (XPS) analysis reveals the presence of oxygen vacancies and high amounts of chemisorbed oxygen species. Based on these promising features, the MOCVD process is optimized toward downscaling the thickness of tin(IV) oxide films from 25 to 50 nm to study the impact of incipient surface morphological changes occurring after initial thin‐film formation on the electrical properties as investigated by van der Pauw (vdP) resistivity measurements. Optical bandgaps of thin films with varying thicknesses are estimated using ultraviolet–visible (UV–vis) spectroscopy.

Structural, electrical and optical properties of transparent conductive titanium–gallium–zinc oxide films by magnetron sputtering

The transparent semiconductors of titanium–gallium–zinc oxide (TiGa–ZnO) thin films were prepared on glass substrates by radio frequency (rf) magnetron sputtering. The dependence of the grain-growth orientation, structure, electrical and optical properties of thin films on rf power was investigated by X-ray diffractometer, UV–visible spectrophotometer and Hall effect measurement system. Experimental results show that all nanocrystalline TiGa–ZnO thin films possess preferential orientation along the (002) plane. The rf power strongly affects the crystal structure, electrical and optical properties of thin films. When the rf power is at 190 W, the thin film deposited on the glass substrates has the optimal crystal quality and optoelectronic properties, with the largest mean grain size (83.1 nm), the minimum lattice strain (6.287 × 10−4), the highest average transmittance in the visible range (84.62 %), the lowest electrical resistivity (9.68 × 10−4 Ω cm) and the maximum figure of merit (6.173 × 103 Ω−1 cm−1). The optical bandgaps of thin films were evaluated by extrapolation method and observed to increase firstly and then decrease with the increment of rf power. Furthermore, the optical parameters including refractive index, extinction coefficient, dielectric constant and dissipation factor of the thin films were determined by the pointwise unconstrained optimization method. The dispersion behaviour of refractive index was also analyzed using the Wemple–DiDomenico single-oscillator theory.

Growth of manganese sulfide (α-MnS) thin films by thermal vacuum evaporation: Structural, morphological and optical properties

MnS thin films have been successfully prepared by thermal evaporation method at different substrate temperatures using different masses of MnS powder. The prepared films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and UV–visible spectrophotometry. The XRD measurements show that the films crystallized in the pure α-MnS for substrate temperatures above 100 °C. The optical bandgap of thin films is found to be in the range of 3.2–3.3 eV. A factorial experimental design was used for determining the influence of the two experimental parameters on the films growth.

Optical, electrical and structural properties of aluminum-doped nano-zinc oxide thin films deposited by magnetron sputtering

Nano transparent conducting aluminum-doped zinc oxide (AZO) thin films were deposited on glass substrates by the magnetron sputtering technique. The thin films were characterized with X-ray diffractometer, scanning electronic microscopy, four-point probe and UV–Visible spectrophotometer. The dependence of structural, morphological, optical and electrical properties on substrate temperature was investigated. The results show that all the thin films have hexagonal wurtzite structure with highly c-axis orientation. The structural and optoelectrical properties of thin films are observed to be subjected to the substrate temperature. The AZO thin film deposited at the substrate temperature of 370 °C possesses the best optoelectronic properties, with the lowest resistivity of 6.12 × 10−4 Ω cm, the minimum microstrain of 0.92 × 10−3, the highest average visible transmittance of 85.1 % and the maximum figure of merit of 1.03 × 104 Ω−1 cm−1. The optical bandgap of thin films was estimated from Tauc’s relation and observed to be an increasing tendency with the increment of the substrate temperature. Furthermore, the optical constants such as refractive index, extinction coefficient, dielectric constant, dissipation factor and optical conductivity were determined by the pointwise unconstrained optimization method, and the dispersion behaviour was studied by the Wemple–DiDomenico single-oscillator model.

Synthesis and characterization of NiPcTSTNa(L) thin films

NiPcTSTNa(L) [L = ethylenediamine (EDA); 1,4-diaminobutane (BDA); and 2,6-diamineanthraquinone (AqDA)] thin films were deposited by thermal evaporation. Their surface morphology was studied by AFM and SEM, and their chemical composition determined by EDS. Optical absorption studies of NiPcTSTNa(L) films were performed in the 200–1150 nm wavelength range. The optical bandgap of thin films was determined from the (αh ν)1/2 vs hν plots for indirect allowed transitions. The temperature dependence of electrical conductivity shows a semiconducting behaviour. The amorphous semiconductor films show thermal activation energies of electrical conduction between 3·3 and 3·7 eV.

Effect of carrier concentration on optical bandgap shift in ZnO:Ga thin films

The Ga-doped ZnO thin films were deposited on glass substrate by sputtering and annealed at 350 °C in hydrogen atmosphere for 1 h. The optical bandgap of thin films showed the lower blueshift than the theoretical value of the Burstein–Moss (BM) effect. The shift of bandgap was dependent on the carrier concentration and acquired by combining the nonparabolic BM effect and bandgap narrowing (BGN). The modified BM effect equation was proposed to substitute the nonparabolic BM effect and BGN. The exponent in the modified BM equation was affected by carrier concentration and it was decreased with carrier concentration.

On measurement of optical band gap of chromium oxide films containing both amorphous and crystalline phases

A method to calculate the optical band-gap of thin films composed of both crystalline phase and amorphous phase is suggested. Chromium oxide films were taken for the optical band-gap measurement, and the results were compared with those obtained by the conventional method. There is discrepancy between the values calculated by two different methods. The discrepancy decreases as the deposition temperature increases to the point where crystalline peaks occur. It has been speculated that the simple Tauc's relation for pure amorphous film would lead to an underestimation of the fundamental band-gap of the film composed of both amorphous and crystalline phases. A modified Tauc's equation, δ= f 1 δ c+(1− f 1) δ a, approach suggested by Krankenhagen et al. [J. Non-Cryst. Solids 198–200 (1996) 923] yields optical band-gap of the Cr 2O 3 film in the range of 4.7~5 eV when the deposition temperature was varied from room temperature to 300°C.