Optical Band Gap Of Films Research Articles

Effect of annealing temperature on the structure and optical properties of ZnO thin films

The effect of annealing temperature on the microstructure, defects and optical properties of ZnO thin films are investigated using sol–gel based spin coating method for a range of annealing temperatures from 200 ∘C to 500 ∘C. The correlation among the microstructure, defects, impurity content and the optical band gap of films of thickness about 10–12 nm is elucidated. The particle size increases and the optical band gap reduces with the annealing temperature. At 200 ∘C, amorphous films were formed with particle size less than 10 nm with an optical band gap of about 3.41 eV. As the temperature increases the grain size increases and the defect, impurity content as well as the optical band gap reduces. This could be due to the reduction in the lattice strain. For an average grain size of about 35 nm and above, the band gap asymptotically approaches the theoretical value of ZnO (3.37 eV). The photoluminescence (PL) spectra show a systematic red-shift in the excitonic levels corresponding to the variation in the optical band-gap. The defect emission from Zn-vacancies is observed in the PL spectra and are further supported by the positron annihilation measurements.

Analysis of structural and optical properties in co doped Mn,Gd in bismuth ferrite (BiFeO3) thin films prepared by sol-gel technique

In this paper, we reported the structural and optical properties of co-doped bismuth ferrite (Bi0.99Gd0.01Fe0.99Mn0.01 O3) thin films that were fabricated on corning glass substrates by sol-gel spin coating technique. The thin films were deposited in different layers on the glass substrates(3,4,5-layers) and annealed at 550 °C in a muffle furnace for 2 hrs in air. The effect of co-doping and thickness on structural and optical properties of bismuth ferrite perovskite thin film was systematically studied and analyzed. The X-ray diffraction pattern of the sample films fabricated confirms the existence of a Rhombohedral structure with space group (RE). Transmittance spectra and absorption spectra were determined by Ultraviolet–visible (UV–Vis) spectrophotometer. The optical band gap of films with different coating layers was estimated from Tauc’s plot of the optical data.

Improvement of third-order NLO properties of vacuum deposited Cd1-xPbxS nanostructured thin films for optoelectronic device applications

A polycrystalline nanostructured cadmium lead sulfide thin film was deposited using the thermal evaporation (PVD) technique (Cd1-xPbxS with x = 0.00, 0.01, 0.05 and 0.1 wt.% of Pb). Structural parameters of as-prepared Cd1-xPbxS thin films have been studied through X-ray diffraction. The optical investigation demonstrates that Cd1-xPbxS film's optical band gap (Eg) may be adjusted from the visible to the near-infrared region. (2.64 - 2.42 eV). The film is substantially more appropriate for absorbing layers in solar cells and optoelectronic applications due to the large decrease in ‘Eg.’ The enhanced Pb doping was found to have altered the surface morphology, verified by Field Emission Scanning Electron Microscopy (FESEM) images. The doped films also showed a significant red shift in the band edge and increased transmittance in the visible and NIR regions. The third-order nonlinear optical (TONLO) parameters of the samples were determined from the Q-switched Nd: YAG laser with 65-ps pulse duration at 1064 nm. The investigated TONLO components such as nonlinear absorption coefficient (β), nonlinear refractive index (n2) and the susceptibility χ(3)were found to be in the range from 1.16 × 10−3 to 4.12 × 10−3 (cmW−1), 1.06 × 10−8 to 3.32 × 10−8 (cm2 W−1) and 1.23 × 10−4 to 5.62 × 10−4 (esu) respectively. The results indicate that Pb-doping on CdS nanostructures on surface morphology can be used to modify NLO characteristics.Cd1-xPbxS thin film is a potential and able material for optoelectronic device applications, as seen by these encouraging NLO results.

Liquid deposition modelling 3D printing of semiconductor tin sulphide (SnS) thin film for application in optoelectronic and electronic devices

This study is focused on the investigation of three-dimensional (3D) printed SnS thin film and the optimisation of SnS thin film thickness by additive layer deposition of the film using three-dimensional printing system based on liquid deposition modelling (LDM). Voids in separate island-like state and traps associated with certain film thickness affect charge carriers due to the presence of large grain boundaries associated with small grains which acts as electron trap thus affecting SnS thin film's optical band gap energy and electrical conductivity among others. SnS thin films were printed on glass substrate using LDM-3D printing. Surface Profilometer, Energy dispersive X-ray spectroscopy, X-ray diffractometer, Scanning electron microscope, Uv-vis spectrophotometer and four point probe were used to characterise the SnS thin films. The conductivity of 0.002987 (Ωm)-1 and optical energy band gap of 1.37 eV of 0.6 μm 3D printed SnS thin film was optimum and favours the attainment of the threshold voltage for optoelectronic and electronic application. The results demonstrate the potential of the LDM-3D printing of thin film for materials deposition and application which provides a new way of layer thickness variation and levelling of semiconductor thin film.

Improved opto-nonlinear and emission properties of spray pyrolysis grown Nd:PbS nanostructured thin films

Present work reported the development of PbS nanostructured thin films with different (0.0, 0.5, 1.5 and 2.5 wt %) novel Nd doping concentrations via spray pyrolysis method. Structural parameters of films were calculated from X-ray diffraction (XRD) patterns. Raman spectroscopy showed 131.73 cm−1 and 427.90 cm−1 characteristics vibrational mode of PbS. Grain shapes and size of films were analysed from SEM micrographs and showed compact morphology of films and well-covered substrate. The optical band gaps of films were found in order of 1.38–1.77 eV. Absorption index (k), refractive index (n), optical dielectric constant and optical conductivity were calculated and correlated with Nd doping concentrations. In addition, nonlinear optics of films also were examined as a function of Nd doping concentrations. The χ(3) and n2 values were found in order of ∼1.55 × 10−10-1.27 × 10−8 esu and 1.34 × 10−9-7.8 × 10−8 esu; respectively. Films possess better opto-nonlinear properties hence may be used in optoelectronics.

Ion beam sputtering-deposited thermally annealed h-BN transferred film for improving GaN crystal quality

In this article, we focus on the effect of high-temperature annealing (HTA) on ion beam-sputtered hexagonal boron nitride (h-BN)/sapphire samples with different thicknesses. Using atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet–visible (UV–vis) spectroscopy, and other test methods, the changes in the properties of the h-BN material after HTA were compared and discussed in depth. The experimental results showed that HTA can reduce the B/N ratio and carbon in the h-BN film, increasing the film's optical bandgap. In addition, based on the annealed h-BN/sapphire template, high-quality GaN film epitaxy on h-BN was achieved by the metal-organic chemical vapor deposition (MOCVD) method. The method of HTA for h-BN grown by IBSD has huge potential for large size, low cost, and safe production.

Sol–gel spin coating derived cadmium oxide semiconductor thin films: Effect of Lutetium contribution

Continuously developing optoelectronic technology requires alternative transparent conductive oxide (TCO) materials. Due to their high optical transmittance and conductivity, TCO materials have many application areas. Cadmium oxide (CdO) thin films, one of the most important TCO materials, are frequently used in optoelectronic technology. In this study, pure and Lu doped CdO semiconductor thin films with 1, 2, 3, 4, and 5 at% concentrations were produced using the sol- gel spin coating technique. The changes in the optical, structural and surface properties of the films were examined as a function of the doping and it was determined that the doping process caused significant changes in the properties of the films. The XRD results showed that the samples were polycrystalline cubic and the average crystallite size varied between 13.42 nm and 26.39 nm with Lu contribution. To examine the optical properties of CdO: Lu thin films, the transmittance and absorption spectra of the films were taken in the UV–VIS region. The optical absorption coefficient, refractive indexes, dielectric constants, optical-electrical conductance, and optical band-gap of films were calculated by using the obtained transmittance and absorption spectra, and the effect of doping on the optical properties of the films was investigated. Depending on the amount of Lu, some fluctuations are observed in Eg values. It was determined that Lu doping from the changes in SEM is effective in changing the properties of CdO and these films are suitable materials for sensor and display applications. SEM images revealed that the Lu contribution rate caused the surface change of thin films. With this study, the effect of Lu doping on structural, optical, and superficial properties of CdO films was investigated and it was determined that Lu doping of CdO films were suitable materials for optoelectronic applications.

Optical and morphological properties of the CdO thin films as a function of film thickness

It has been investigated the effect of film thickness on the optical and morphological properties of cadmium oxide (CdO) thin film. For this reason, transparent and conducting CdO thin films were deposited on glass substrates at 200 °C temperature using DC magnetron sputtering method. The power of the sputter in the experiment was set up to 100 W. In order to determine the morphological properties of the films, X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) was used. Also optical band gap of the films was determined by using UV–VIS spectroscopy. The XRD results showed that the films were in polycrystalline cubic structure. It was concluding that the surface roughness values decrease with the increasing film thickness. The changes of optical band gap of the CdO thin films was stable for the thickness of 100 nm and 150 nm but the band gap value increase about 0.3 eV with the film thickness of 200 nm.

Optical and electrical characterization of organic solar cells obtained using gold and silver metal nanoparticles

Light absorption of metal nanoparticles and charge separation are two major factor for the efficiency improvement in organic solar cells. Metallic nanoparticles may exhibit surface plasmons when exposed to light. This special optical properties of metal nanoparticles make them useful in photonics, electronics and biomedical applications. In this study, gold and silver nanoparticles increased the surface roughness of the active layer. The absorption, SEM, AFM, XRD measurements of 1% ratio gold and silver nanoparticles doped active layers were carried out. Optical band gap of these films was calculated with using absorption measurements. Then, ITO/PEDOT:PSS/P3HT:PCBM:Au/LiF/Al and ITO/PEDOT:PSS/P3HT:PCBM:Ag/LiF /Al organic solar cells were obtained. It was calculated the solar cells parameters such as short -circuit current density (Jsc), open - circuit voltage (Voc), fill factor (FF) and power conversion efficiency (PCE) from current density–voltage (J-V) measurements at the room temperature. The experimental results revealed that the presence of Au and Ag nanoparticles (NPs) in the ITO/PEDOT:PSS/P3HT:PCBM/Al solar cell improved its performance with respect to undoped solar cells. For example, the power conversion efficiency was increased from 2.11% to 2.55% when doping 1 wt% of Au NPs to P3HT:PCBM and to 2.23% when doping of Ag NPs to P3HT:PCBM. This was attributed to increase of the light absorption in the presence of Au and Ag NPs doping. However, the optical band gap of films have not changed significiantly after the NPs doping.

Effects of Deposition and Annealing Temperature on the Structure and Optical Band Gap of MoS2 Films.

In this study, molybdenum disulfide (MoS2) film samples were prepared at different temperatures and annealed through magnetron sputtering technology. The surface morphology, crystal structure, bonding structure, and optical properties of the samples were characterized and analyzed. The surface of the MoS2 films prepared by radio frequency magnetron sputtering is tightly coupled and well crystallized, the density of the films decreases, and their voids and grain size increase with the increase in deposition temperature. The higher the deposition temperature is, the more stable the MoS2 films deposited will be, and the 200 °C deposition temperature is an inflection point of the film stability. Annealing temperature affects the structure of the films, which is mainly related to sulfur and the growth mechanism of the films. Further research shows that the optical band gaps of the films deposited at different temperatures range from 0.92 eV to 1.15 eV, showing semiconductor bandgap characteristics. The optical band gap of the films deposited at 200 °C is slightly reduced after annealing in the range of 0.71–0.91 eV. After annealing, the optical band gap of the films decreases because of the two exciton peaks generated by the K point in the Brillouin zone of MoS2. The blue shift of the K point in the Brillouin zone causes a certain change in the optical band gap of the films.

Effect of annealing processing on morphology, spectroscopy studies, Urbach disordering energy, and WDD dispersion parameters in Cu-Al doped zinc oxide films

In this article, a mosaic target made of ZnO and Al-Cu atoms were used for fabricating of the Cu-Al doped zinc oxide films (CAZO films) using RF magnetron co-sputtering. The CAZO films were deposited in room temperature on glass substrates with the sputtering gases O2 and Ar in proportion of 30%. Then, films were annealed at different temperatures of 400, 500, and 600 °C in a electrical furnace with Ar atmosphere. Atomic Force Microscopy images showed that the size of nanoparticles in films annealed at 600 °C have maximum value about of 18.8 nm. Atomic Force Microscopy data shown that the films annealed at 600 °C were rougher and they were about of 4.68 nm. Transmittance T(λ) and reflectance R(λ) measurements in the wavelength range (300–2500 nm) were used to calculate the absorption coefficient α (λ), the refractive index n(λ), the optical dispersion parameters according to Wemple and Didomenico, and the optical band gap of films. The optical band gap has been estimated and confirmed by five different methods. It can be seen that with increasing annealing temperature the optical band gap of films were decreased. Films annealed at 400°C have more disordered. It is found that the as films annealed at 500°C have minimum values of the dispersion energy E d and the oscillator strength fin about of 0.57 eV and 2.42 (eV)2, respectively. The as deposited films have minimum values of oscillator length strength S 0 in about of 5.5 μm−2.

The effect of Cu content in MWCNTs synthesized by Ni - Cu @ a-C:H catalyst on the optical constants and the optical loss

In this paper, Ni-Cu NPs @ a-C:H films with different Cu content, by co-deposition of RF-sputtering and RF-plasma enhanced chemical vapor deposition (RF-PECVD) were prepared using acetylene gas and Ni and Cu targets. We studied optical constants of MWCNTs synthesized, with constant Ni content and different percentages of 5, 40 and 75 % from Cu atoms. With increase of Cu content, the average diameter of MWCNTs were increased however the RMS roughness of films were decreased. It is found that the absorption coefficients of films deposited with 5% Cu have maximum value. Also it can be seen that the minimum values of the optical band gaps of films happen in films deposited with 5% Cu. With increase of Cu content, the values of energy loss by the free charge carriers were increased however the plasma frequency ωp and free charge carriers concentration N/m* of films were decreased. The free carriers electric susceptibility χc at in films deposited with 75 % Cu has maximum value. The values of the ratio of free charge carriers concentration to effective mass, N/m*, in films deposited with 5% Cu has maximum value about of 423.731048 m−3 kg−1.

Solution-processed amorphous Ga2O3:CdO TFT-type deep-UV photodetectors

Amorphous Ga2O3:CdO thin films and their thin-film transistor (TFT) photodetectors were fabricated via a simple and low-cost spin-coating method. The film optical bandgap and TFT electrical parameters can be effectively regulated via changing the Cd content. The optimized Ga2O3:CdO TFT photodetector exhibited a responsivity of 2.17 A/W and a high UV/vis. rejection of 1.88 × 104 under 260 nm at small working biases, which are comparable or even superior to the recently reported results. Systematic comparison between metal-semiconductor-metal- and TFT-type photodetectors further confirmed that our TFT photodetectors had superior detective performance and lower electrical power consumption.

Improved optical properties of ion beam irradiated (K,Na)NbO3 thin films

In the present study, we have demonstrated the effect of swift heavy ion (SHI) irradiation on photoluminescence (PL) and time-resolved photoluminescence (TRPL) properties of potassium sodium niobate (KNN) thin films deposited on Si and quartz substrates using RF magnetron sputtering. Ion beam irradiation of crystalline KNN films was carried out at room temperature using 100 MeV Ni ions with different fluences such as 1 × 1012, 5 × 1012 and 1 × 1013 ions/cm2. Various modes obtained in Raman spectra of films are related to NbO6 octahedron which confirms the crystalline phase of KNN. Moreover, the decrease in peak intensities with ion fluence is attributed to defects produced after SHI irradiation. X-ray photoelectron spectroscopy results show the increase in oxygen vacancies after irradiation. The optical properties of pristine and irradiated films were evaluated using UV–Vis–NIR spectroscopy and a significant improvement in optical transmittance upon irradiation was observed. The optical band gap of films is decreased to 3.14 eV upon irradiation at 1 × 1012 ions/cm2. PL spectra of films were obtained with excitation wavelength of 274 nm and, the results depict the emission wavelengths (band-to-band or near band edge) of KNN thin films in regime of 313–367 nm (3.96–3.38 eV). The origin of blue and green emission is due to defects created as a result of ion irradiation. The green luminescence evolved at higher fluence (i.e. 1 × 1013 ions/cm2) may be attributed to intrinsic defects such as oxygen vacancies. The obtained Commission Internationale de I’Elcairage (CIE) color coordinates are shifted towards white point in chromaticity diagram as a function of ion fluence. TRPL result reveals the decay lifetime of KNN films in nanosecond regime and, is varied with ion fluence. At fluence of 1 × 1013 ions/cm2, film exhibited the minimum average decay lifetime (1.75 ns) which suggests that KNN can be a potential candidate for optical switching, optical display and sensors, and opto-electronic device applications.

Irradiation induced modification of structural and optical properties of potassium sodium niobate thin films

In the present study, the effects of swift heavy ion induced modification on the structural, morphological and optical properties of potassium sodium niobate (KNN) thin films have been investigated. KNN thin films were deposited using RF magnetron sputtering onto Si and quartz substrates. Subsequently, as-deposited films were annealed at 700 °C in air ambience for crystallization. Eventually, these crystalline films were irradiated using 100 MeV Ag ions at various fluences ranging from 1 × 1012 to 1 × 1013 ions/cm2. The crystalline and irradiated films were characterized using various techniques such as X-ray diffraction (XRD), atomic force microscopy (AFM), Raman spectroscopy, and UV–Vis spectroscopy. XRD results reveal that the crystallinity of films decreases drastically upon irradiation and almost disappeared at 1 × 1013 ions/cm2. Raman spectra show the different vibration modes of NbO6 octahedra. Raman peaks intensity is decreased and the peaks get broadened due to irradiation which indicates the amorphous nature of films. Variation in surface morphology and roughness of films before and after irradiation is studied using AFM. The minimum value of roughness is observed at 5 × 1012 ions/cm2. Ion beam irradiation results in the variation of transmittance and optical band gap of the films. The optical band gap of crystalline KNN film is found to be 3.82 eV which decreased to 3.72 eV upon irradiation at 5 × 1012 ions/cm2. The monotonous decrease in the refractive index and packing density of films is also observed with ion fluence.

Relation between carriers hopping rate and structural constants in amorphous carbon nickel films with different nickel nanoparticles distributions

In this paper, the films were prepared by radio frequency magnetron co-sputtering technique. The effect of different mosaic targets made of nickel strips and graphite pure on the dielectric relaxation time, the carriers hopping rate, the fractal dimensions and the optical loss of films were studied. The values of the optical band gap of films using the cross-point between the tangent of the plot of lower and higher values of the photon energy were calculated. The films deposited at 4.64% have maximum hopping rate of about 8.6 × 1012 S−1. It can be seen that the films deposited at 3.92% have minimum value of fractal dimension of 2.27. With increasing Ni content of films a nonmetal–metal transition is observed which it is explainable by the power law of percolation theory. Critical metal content and the critical exponent of films were 87.25% and 1, respectively. With increasing Ni content, the carriers effective mass of films decreased and average lattice separation values of films increased. Films deposited at 3.92% have minimum value of Debye frequency νD of about 1.09 × 1012 Hz. The value of energy loss by free charge carriers when traversing the bulk and surface of films at 3.92% has maximum value and it has an increasing function behavior with energy.

Influence of 120 MeV Si9+ ion irradiation on ZnTe semiconductor thin films

ABSTRACTZnTe (Zinc Telluride) is a potential semiconducting material for many optoelectronic devices like solar cells and back contact material for CdTe-based solar cells. In the present study, ZnTe thin films were prepared by thermal evaporation technique and then irradiated with 120 MeV Si9+ ions at different fluences. These films are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–Visible spectroscopy techniques. XRD study confirms increased crystallinity and grain growth for post-irradiated ZnTe thin films for fluences, up to 1 × 1011 ions cm−2. However, the grain size and crystallinity decreased for higher fluence-exposed samples. SEM images confirm the observed structural properties. Modification of the surface morphology of the film due to the ion irradiation with different fluences is studied. Optical band gap of film is decreased from 2.31 eV (pristine) to 2.17 eV after irradiation of Si9+ ions.

Rapid micro-analysis of Al-In-Sn-O thin film using laser induced breakdown spectroscopy with picosecond laser pulses

Laser induced breakdown spectroscopy (LIBS) based on picosecond laser pulses was used to achieve rapid micro-analysis of Al-In-Sn-O (AITO) thin films deposited by radio frequency (RF) magnetron sputtering at various sputtering powers. We calculated the plasma temperature of 5063 ± 150 K and electron density of 4.6 × 1016 cm−3 with single ablation crater diameter of 46 ± 1 μm. The content ratio of Al/(Al+In+Sn) in AITO thin film was closely related to the optical band gap of the film, and the ratio was exhibited by the spectral line intensity of LIBS for each corresponding element. The quantitative analysis of Al/(Al+In+Sn) with LIBS intensity ratio was achieved by plotting calibration curves according to the value of energy dispersive X-ray spectroscopy (EDS). It was found that the optical band gaps calculated were decreasing as the increase of the sputtering power in the exhibition of the transmittance spectra of AITO thin films deposited at various sputtering powers. In addition, we found the consistency of the evolutions of LIBS target line intensity ratio and optical band gap of AITO thin films. Therefore, the utilization of LIBS based on picosecond laser pulses is available and efficient in the rapid micro-analysis of AITO thin film.

The Effect of Geometry Characterizations and Annealing Processing on Dissipation Electrical Energy in ZnO Films

In this paper, optical constants, surface topology, and fractal dimensions of zinc oxide films under different post-annealing temperatures from 400 °C to 600 °C especially were investigated near optical band gap of films so that the maximum value of fractal dimension belongs to film annealed at 500 °C with the value of 2.07. In addition, the relaxation time of dielectric were estimated using their high-frequency dielectric constant while optical band gap were calculated through the cross-point between the tangent of lower and higher values of the photon energy in the plot of relaxation time-energy. The high-frequency dielectric constant has the maximum value of 21 for film annealed at 400 °C. It can be seen that the free carriers electric susceptibility of films near optical band gap were increased with temperature. Moreover, the film annealed at 400 °C has high dissipation factor.

Study of CuSbS2 thin films nanofibers prepared by spin coating technique using ultra pure water as a solvent

Nanofiber thin films of CuSbS2 were successfully grown by spin coating method using ultra-pure water as a solvent. In this work, we study the annealing temperature effect on the structural, morphological and optical properties of the synthesized films. The XRD results indicate the presence of pure CuSbS2 as major phase in chalcostibite structure. Microstructural results revealed that the sample heated at 250 °C showed a high quality with disordered self-assembly nanofibers with an average diameter about 50 nm. It was found that by increasing heating temperature from 150 to 250 °C, the CuSbS2 thin films optical band gap decreased from 1.80 to 1.35 ± 0.15 eV; while the sheet resistance dropped from 680 ± 34 Ω to 516 ± 25Ω. The fact that the energy band gap of this ternary material, synthesized using water as a solvent for the first time, can be adjusted to expect values that absorb the maximum of the solar spectrum, makes this material as a promise candidate as absorber in cheap, flexible and environmentally friendly solar cell applications.