Band Gap Of Thin Films Research Articles

Optical, structural and electrochromic behavior studies on nanocomposite thin film of aniline, o-toluidine and WO3

In the field of materials for electrochromic (EC) applications much attention was paid to the derivatives of aniline. We report on the optical, structural and electrochromic properties of electrochromic thin film based on composite of WO3 nanoparticles and copolymer of aniline and o-toluidine prepared by electrochemical polymerization method on fluorine doped tin oxide (FTO) coated glass. The thin film was studied by X-ray diffraction (XRD) and Fourier transforms infrared (FTIR) spectroscopy. The morphology of prepared thin film was characterized by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and the thermal gravimetric analysis (TGA) as well. The optical spectra of nanocomposite thin film were characterized in the 200–900 nm wavelength range and EC properties of nanocomposite thin film were studied by cyclic voltammetry (CV). The calculation of optical band gaps of thin film exhibited that the thin film has directly allowed transition with the values of 2.63 eV on first region and 3.80 eV on second region. Dispersion parameters were calculated based on the single oscillator model. Finally, important parameters such as dispersion energy, oscillator energy and lattice dielectric constant were determined and compared with the data from other researchers. The nonlinear optical properties such as nonlinear optical susceptibility, nonlinear absorption coefficient and nonlinear refractive index were extracted. The obtained results of nanocomposite thin film can be useful for the optoelectronic applications.

Band engineering of amorphous silicon ruthenium thin film and its near-infrared absorption enhancement combined with nano-holes pattern on back surface of silicon substrate

Silicon is widely used in semiconductor industry but has poor performance in near-infrared photoelectronic devices because of its bandgap limit. In this study, a narrow bandgap silicon rich semiconductor is achieved by introducing ruthenium (Ru) into amorphous silicon (a-Si) to form amorphous silicon ruthenium (a-Si1-xRux) thin films through co-sputtering. The increase of Ru concentration leads to an enhancement of light absorption and a narrower bandgap. Meanwhile, a specific light trapping technique is employed to realize high absorption of a-Si1-xRux thin film in a finite thickness to avoid unnecessary carrier recombination. A double-layer absorber comprising of a-Si1-xRux thin film and silicon random nano-holes layer is formed on the back surface of silicon substrates, and significantly improves near-infrared absorption while the leaky light intensity is less than 5%. This novel absorber, combining narrow bandgap thin film with light trapping structure, may have a potential application in near-infrared photoelectronic devices.

Effects of Concentration of Triethanolamine and Annealing Temperature on Band Gap of Thin Film of Tin Sulphide Prepared by Chemical Bath Deposition Method

<p>Thin films of Tin Sulphide (SnS) were deposited by chemical bath deposition technique using a precursor solution of stannous chloride (SnCl<sub>2</sub>.2H<sub>2</sub>O), thioacetamide (TA), triethanolamine (TEA), ammonia (NH<sub>3</sub>), and distilled water. The effects of concentration of triethanolamine and annealing temperature on the growth of SnS films were studied to optimize the growth conditions. X-ray diffraction study shows the deposited films were polycrystalline in nature and orthorhombic in structure. The optical direct and indirect band gap values of SnS films prepared with 15ml of TEA were found to be 1.76 eV and 0.89 eV respectively. Annealing the sample prepared with 12ml of TEA results increase in band gap from 1.79eV to 3.32eV.</p><p>Journal of Nepal Physical Society, 2015, Vol. 3(1): 1-5</p>

Effect of film thickness and texture morphology on the physical properties of lead sulfide thin films

Lead sulfide (PbS) thin films were prepared onto ultra-clean quartz substrate by the electron beam gun (EBG) evaporation method. The thicknesses of the thin films were 50, 100, 150 and 200 nm. They were annealed at 423 K for 2 h. Field emission scanning electron microscopy (FESEM) images of the thin films showed their texture morphology at the surface of the quartz substrate. X-ray diffraction (XRD) patterns of the thin films showed that they have a cubic phase and rock-salt structure after annealing. The average crystallite size for the thin films was in the range of 32–100 nm. Optical measurements confirmed that crystalline thin films have a direct band gap that increases by decreasing the film thickness. This blue shift of the band gap of thin films compared to the bulk structure can be attributed to the quantum confinement effects in the nanoparticles. A decrease in conductivity by increasing the temperature confirmed the positive temperature coefficient of resistance in the thin films that showed the dominant conduction mechanism is via a band-like transition. The density of localized states at the Fermi level increases by increasing the film thickness. Current–voltage behavior of the thin films showed an increase in both dark current and photocurrent by increasing the crystallite size which is discussed, based on the presence of trap states and barriers in nanostructures.

Atomic layer deposition of copper sulfide thin films

Atomic Layer Deposition (ALD) of copper sulfide (CuxS) thin films from Cu(acac)2 (acac=acetylacetonate=2,4-pentanedionate) and H2S as Cu and S precursors is reported. Typical self-saturated reactions (“ALD window”) are obtained in the temperature range Tdep=130–200°C for an average growth per cycle (GR)=0.25Å/cycle. The morphology, crystallographic structure, chemical composition, electrical properties and optical band gap of thin films were investigated using scanning electronic microscopy (SEM), X-ray diffraction under Grazing Incidence conditions (GI-XRD), X-ray reflectivity (XRR), energy dispersive spectrometry (EDS), Hall effect measurements, and UV–vis spectroscopy. The obtained copper sulfide films are heavily p-doped (charge carrier concentration~1021–1022cm−3) with optical band gaps in the range of 2.2–2.5eV for direct and 1.6–1.8eV for indirect band gaps. Depending on the number of ALD cycles, multiphase compounds (made of digenite Cu1.8S, chalcocite Cu2S, djurleite Cu31S16 and covellite CuS) or single-phase digenite Cu1.8S films are obtained via a growth mechanism that involves in-situ copper reduction and loss of sulfur by evaporation.

The Influence of Thickness and Annealing Temperature on Some Physical Properties of Cu2snse3 Films

Copper Tin Selenide Cu2SnSe3 (CTSe) alloy have been prepared from their elements with high purity. The composition and microstructure of this alloy was determined by energy dispersive x-ray spectroscope (EDS) and scanning electron microscope (SEM) respectively. CTSe thin film have been deposited onto well-cleaned glass substrates by flash thermal evaporation method with different thicknesses (500, 750 and 1000) nm.The as-deposited films were annealed in vacuum at 473 K for 1h.The structure of asdeposited and annealed films has been studied by X-ray diffraction technique, these studies revealed that the films crystallizes in the monoclinic phase. The crystallite size were determined from scherrer calculation method. Atomic force microscopy (AFM) showed that the grain size of the films was increases with increasing thickness ,but decrease with annealing temperature. The optical properties of thin films has been measured by UV-VIS spectrometer. The result showed that the energy band-gap of thin films decreased from 2.21 to 1.60 eV with increasing thickness and increased with annealing temperature.

Synthesis of MAPbBr3‐iYi (Y=I, Cl and i=0, 1, 2, 3) thin film perovskites

AbstractMethylammonium lead halide perovskites with different halides (iodide, bromide and chloride) have been synthetized from methylamine, lead nitrate and the corresponding hydroX acid (X = I, Br, Cl) precursors. Subsequently MAPbBr3‐iYi (Y = I, Cl; i=0, 1, 2, 3) perovskites were deposited as thin films onto FTO substrates by spin coating or dipping. Thin film perovskites were then characterized by X‐Ray Diffraction, elemental analysis and optical spectrometry. Crystallites' sizes are between 100‐600 nm depending on the synthesis temperature. All synthetized MAPbX3‐iYi perovskites crystallized in the same cubic phase irrespective of the X and Y components and a unique phase is observed. Elemental analysis shows that in all cases the atomic components meet the expected stoichiometric formulae. The bandgap of thin film MAPbX3‐iYi perovskites were inferred from transmittance and reflectance spectral measurements. It is found that the onset of the absorption edge for thin film MAPbX3 perovskites is about 1.66, 2.55 and 3.37 eV for X= I, Br, Cl, respectively and it reaches intermediate values for mixed MAPbX3‐iYi perovskites. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Characteristics of Al-doped ZnO:Ni films grown on glass by sol–gel dip coating technique

Al-doped NiZnO thin films were fabricated by dip coating and annealed at various temperatures (250–550°C) and their properties were evaluated. With increasing annealing temperature, the Al contents in the thin films were continually increased, because of the rapid increase in the incorporation efficiency of the Al–O layer with respect to the NiZn–O layer. Polycrystalline nature of the thin films was confirmed by the X-ray diffraction technique. All films have a perfect wurtzite structure without any recordable variation in the ZnO lattice produced by replacing Zn with Ni and Al. The absorption edge shifted to a higher wavelength (red shift) with the increase of annealing temperature indicating that the shrinkage of the optical band gap was induced. The optical band gaps of thin films decreased from 3.5 to 2.5eV. All films showed ferromagnetic behavior. The annealing process provided a reduced resistivity due to the improved crystal structure of films.

Room temperature chemical bath deposition of cadmium selenide, cadmium sulfide and cadmium sulfoselenide thin films with novel nanostructures

A simple, convenient and low cost chemical synthesis route has been used to deposit nanostructured cadmium sulfide, selenide and sulfoselenide thin films at room temperature. The films were deposited on glass substrates, using cadmium acetate as cadmium ion and sodium selenosulfate/thiourea as a selenium/sulfur ion sources. Aqueous ammonia was used as a complex reagent and also to adjust the pH of the final solution. The as-deposited films were uniform, well adherent to the glass substrate, specularly reflective and red/yellow in color depending on selenium and sulfur composition. The X-ray diffraction pattern of deposited cadmium selenide thin film revealed the nanocrystalline nature with cubic phase; cadmium sulfide revealed mixture of cubic along with hexagonal phase and cadmium sulfoselenide thin film were grown with purely hexagonal phase. The morphological observations revealed the growth and formation of interesting one, two and three-dimensional nanostructures. The band gap of thin films was calculated and the results are reported.

The effects of inorganic surface treatments on photogenerated carrier mobility and lifetime in PbSe quantum dot thin films

We used flash-photolysis, time-resolved microwave conductivity (TRMC) to probe the carrier mobility and lifetime in PbSe quantum dot (QD) thin films treated with solutions of the metal salts of Na2Se and PbCl2. The metal salt treatments tuned the Pb:Se stoichiometry and swept the Fermi energy throughout the QD thin film bandgap. A stoichiometric imbalance favoring excess Se heavily p-doped the QD thin film, shifted the Fermi energy toward the valence band, and yielded the highest TRMC mobility and lifetime. Introducing Pb first compensated the p-doping and shifted the Fermi level through mid-gap, decreasing the TRMC mobility. Further Pb addition created an excess of Pb, n-doped the QD thin film, moved the Fermi level to near the conduction band, and again increased the TRMC mobility. The increase in TRMC mobility as the Fermi energy was shifted toward the band edges by non-stoichiometry is consistent with the QD thin film density of states.

Electrochromic performance of sol–gel derived amorphous MnO2–ZnO nanogranular composite thin films

In this work, the MnO2–ZnO thin films with nominal molar ratios of 8%, 16% and 25% of Zn to Mn were deposited on glass and Indium Tin Oxide (ITO) substrates by dip-coating sol–gel method and annealed in air at 300°C. The films were characterized by Cyclic Voltammetry measurement (CV), X-ray Diffraction spectroscopy (XRD), Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray spectroscopy (EDX) and UV–Visible spectrophotometry. The XRD patterns indicated the amorphous structure for all samples. The CV measurements were performed in the potential window between −2V and 2V at a potential scan rate of 20mV/s and 50mV/s. The results of CVs at a scan rate of 20mV/s in the first cycle showed that the sample with 25% of Zn content with the maximum anodic and cathodic charge density has a better performance compared to other samples and the capacitance decreases with increasing cycle number of all samples at 50mV/s. Optical constants and optical band gaps of thin films were investigated by transmission and reflection. The AFM images revealed that roughness increases with increasing Zn concentration. The FE-SEM images showed nearly similar morphology for all thin films.

Analytical Study of the Band GAP and Optical Characteristics of Copper Sulphide Thin Film: Experiment and Computation

In this work, the analytical study of optical properties and band gap of copper sulphide thin film were carried out comparatively using two different but related depositional techniques done at room temperature. The techniques were (a) successive ionic layer adsorption and reaction and (b) chemical bath deposition. The film was characterized with emphasis on the optical properties within the spectral range of ultraviolet -infrared region of electromagnetic spectrum, Absorption coefficient depicts a maximal value of the band gap ranging from 1.45eV to 3.33 eV. Theoretically, scalar wave equation was used to analyze the behavior of wave propagated through the copper sulphide thin film for which computation of the optical properties such spectral transmittance, reflectance were computed. The band gap of the thin film was also computed for which all the computation was carried out within the same spectral range. In the analysis, it was observed that there was no significant deviation between the band gap obtained from the two different depositional techniques and the computed band gap Keywords;Analytical study, copper Sulphide, optical properties, band gap, Scalar wave, deposition, computation, wave propagation.

Hydrogenated Amorphous Silicon-Based Thin Film Solar Cell: Optical, Electrical and Structural Properties

Hydrogenated amorphous silicon (a-Si:H) has been developed as an important materials in thin film-based photovoltaic technologies because of considerable cost reduction as a result of low material consumption and low-temperature process. Among the materials used for thin film solar cells, amorphous silicon is the most important material in the commercial production. Despite of these benefits, the efficiency limit for a single band gap thin film based solar cell predicted by Shockley and Queisser (i.e. ~31%) has become a matter of challenge for current research community. Considering the thermodynamic behavior of a single threshold absorber in generating electricity from solar irradiance, this limit seems inevitable, and thus a tremendous investigation is now being carried out in different dimensions such as hot carrier generation, rainbow solar cell, multiple exciton generation, multiband absorber etc. Nonetheless, so far reported efficiency (ηlab~12%) provide enough room to improve and take challenge to reach to the highest value for a-Si:H based solar cell design. Further to improve architectural design as well as engineer the materials, it is indispensable to understand the optical, electrical and structural properties of aSi:H as an active layer. Here in this article, an attempt was taken into account to focus on such characteristics that affect the overall cell efficiency.

ALD NiO Thin Films As a Hole Transport-Electron Blocking Layer Material for Photo-Detector and Solar Cell Devices

A thin layer of a wide bandgap material disposed between an electrode and an absorber material in a photo-detector or solar cell can play important transport and optical roles in enhancing device performance. When the energy band edges of the materials are properly aligned, the thin layer can control the flow of photo-generated carriers preferentially: i.e., it can permit the transport of one type of carrier while blocking the other type.1 Further such wide band gap materials can affect light trapping.2 NiO is a p-type conductive oxide, and has, due to its band edge positions, a high potential as a hole transport-electron blocking layer (HT-EBL) material. Due to its wide bandgap, it is also a transparent material. Both the potential transport and the optical roles of wide bandgap thin film materials in opto-electronic devices require the ability to precisely control film deposition thickness and conformality. In the case of HT-EBL candidate materials, atomic layer deposited (ALD) NiO has proven to have the material properties and excellent deposition control potential needed for hole transport and electron blocking optical layers. Because of this ALD NiO has become a subject of research in many research groups.3-6 In this report, we demonstrated the usefulness of ALD NiO thin films as HT-EBL/optical material by using it in very thin CdTe solar cells with a superstrate configuration. The CdTe cells were fabricated on a soda-lime glass substrate, and configured with layers of 200nm of SnO2:F/ 50 nm CdS/ 500nm CdTe/4nm Cu and 20nm Au. In test samples, a 3nm thick ALD NiO layer was deposited on the CdTe layer before the Cu/Au deposition. The resulting test and control cells were characterized under AM 1.5G (100mW/cm2) spectrum. The results of the device performance are summarized in Table 1. As may be noted, the CdTe cells with the ALD NiO layer on the anode showed better Voc and FF, and resulted in 15% higher power conversion efficiency (PCE) than that of the control cells. The enhancement of the Voc and FF were ascribed to the enhanced control of the photo-generated carriers. It remains to be determined if the reduction of. Jsc in the test samples is due to optically non-optimized NiO thickness and therefore reflection loss at the back contact or to non-optimized hole collection at the back contact. References S. J. Fonash, Solar cell device physics, 2nd ed., Elsevier, (2010).S. J. Fonash, Introduction to light trapping in solar cell and photo-detector devices, Elsevier, (2014).S. Lattante, Electronics, 3, 132, (2014).E. Thimsen, et., al., J. Phys. Chem. C., 116(32), 16830, (2012).T. S. Yang, et., al., J. Vac. Sci. Technol. A., 23(4), 1238, (2005).H. L. Lu, et., al., J. Crystal Growth, 310, 5464, (2008). Figure 1

Deposition of ultra thin CuInS2 absorber layers by ALD for thin film solar cells at low temperature (down to 150 °C)

Two new processes for the atomic layer deposition of copper indium sulfide (CuInS2) based on the use of two different sets of precursors are reported. Metal chloride precursors (CuCl, InCl3) in combination with H2S imply relatively high deposition temperature (Tdep = 380 °C), and due to exchange reactions, CuInS2 stoechiometry was only achieved by depositing In2S3 layers on a CuxS film. However, the use of acac- metal precursors (Cu(acac)2, In(acac)3) allows the direct deposition of CuInS2 at temperature as low as 150 °C, involving in situ copper-reduction, exchange reaction and diffusion processes. The morphology, crystallographic structure, chemical composition and optical band gap of thin films were investigated using scanning electronic microscope, x-ray diffraction under grazing incidence conditions, x-ray fluorescence, energy dispersive spectrometry, secondary ion mass spectrometry, x-ray photoelectron spectroscopy and UV–vis spectroscopy. Films were implemented as ultra-thin absorbers in a typical CIS-solar cell architecture and allowed conversion efficiencies up to 2.8%.

Structural and Magnetic Properties of CoZnO Films

CoZnO thin film is deposited at withdrawal speed of 250mm/s on glass substrate by sol-gel dip coating process. Structural, optical and magnetic properties of these films are investigated by XRD, VSM, Ellipsometry, UV-Visible spectroscopy and SEM. XRD pattern shows that thin film displays crystalline behavior along with wurtzite structure. From the UV-Visible spectroscopy the optical band gap of thin film is found to be 3.55eV. VSM study shows that thin film exhibits ferromagnetic behavior. SEM results confirmed that CoZnO thin film has attained porous surface.

Effect of Annealing and Surface Passivation on Doped SnO2 Thin Films Prepared by Spray Pyrolysis Technique

In this study doped SnO2 thin films have been prepared by spray pyrolysis technique using an alcoholic precursor solution consisting of stannic chloride (SnCl4.5H2O), ammonium fluoride (NH4F) and palladium chloride (PdCl2). Optimization on the deposition parameters was done so as to obtain high quality thin films. The effect of varying the Fluorine content on the optoelectronic properties of F: SnO2 thin films was studied. Data for transmittance and reflectance in the wavelength range from 300nm – 2500nm was obtained using the solid spec 3700DUV spectrophotometer. Electrical characterization of the thin films was done using the four point probe method at room temperature. Post deposition treatment of the thin films by annealing in air then passivating in nitrogen gas environment was done in a tube furnace at 4500C. Sheet resistivity for the as prepared F: SnO2 was found to be 0.4599 Ωcm and 0.00075 Ωcm being the highest and lowest sheet resistivity at 22.74 at% F and 16.41at% F doping in SnO2 respectively. Low sheet resistivity of F: SnO2 thin films is due substitutional incorporation of F ions instead of oxygen ions into the crystal lattice of SnO2 thin films which increases free carrier concentration. The effect of annealing generally was found to improve on the electrical conductivity of the thin films which is due to increase in carrier mobility and density. Passivation on the other hand had a slight opposite effect. Effects of annealing and passivation on doped SnO2 thin films band gap energy and their transparency was insignificant, rendering the doped SnO2 thin films good choice for making a transparent thin film gas sensors.

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.

Monolithic Multichannel Ultraviolet Photodiodes Based on (Mg,Zn)O Thin Films With Continuous Composition Spreads

We report on the fabrication of monolithic multichannel metal-semiconductor-metal photodiode arrays based on ternary (Mg,Zn)O thin films in wurtzite modification. The narrow bandwidth and the wavelength-selectivity of the device operating in visible-blind spectral range have been realized by employing a novel continuous composition spread approach relying on a single segmented target of pulsed-laser deposition. The Mg-content and subsequently the bandgap of thin films vary linearly along the compositional gradient across the wafer allowing the tuning of cutoff energies of the photodiode. In our device, the Mg-composition gradient of the active and optical filter layer (resulting in the narrow bandwidth of the photodiode) are designedly deposited with an angle of 72 ° with respect to each other. Here the onset of absorption is tuned over 430 meV and the bandwidth of the photodiodes is controlled from 270 meV down to 29 meV.

Physical characterization of Cu2ZnGeSe4 thin films from annealing of Cu–Zn–Ge precursor layers

Cu2ZnGeSe4 (CZGeSe) can be considered as a potential alternative for wide band gap thin film devices. In this work, CZGeSe thin films were deposited on Mo-coated soda lime glass substrates by sequential deposition of sputtered Cu, Zn and e-beam evaporated Ge layers from elemental targets followed by annealing at high temperature using H2Se gas. We report on the effect of the precursor stack order and composition and the impact of the annealing temperature on the physical properties of CZGeSe thin films. The optimal layer morphology was obtained when using a Mo/Cu/Zn/Ge precursor stack annealed at 460°C. We have observed that the formation of secondary phases such as ZnSe can be prevented by tuning the initial composition of the stack, the stack order and the annealing conditions. This synthesis process allows synthesizing CZGeSe absorber with an optical band gap of 1.5eV.