Structural and optical properties of wurtzite InN grown on Si(111)

We report the structural and optical properties of InN films on Si(111) prepared by ion-beam-assisted filtered cathodic vacuum arc technique. X-ray diffraction and Raman spectroscopy measurements indicated that all the InN films were hexagonal crystalline InN. The InN films deposited at substrate temperature of 475 °C exhibited highly (0001) preferred orientation and texturing (cratered) surface morphology. The oxygen incorporated in the InN films was segregated in the form of amorphous indium oxide or oxynitride phases at the grain boundaries. Photoluminescence emission of ∼ 1.15 eV was observed at room temperature from the InN films.     

Improvement of InN layers deposited on Si(111) by RF sputtering using a low-growth-rate InN buffer layer

We investigate the influence of a low-growth-rate InN buffer layer on structural and optical properties of wurtzite nanocrystalline InN films deposited on Si(111) substrates by reactive radio-frequency sputtering. The deposition conditions of the InN buffer layer were optimized in terms of morphological and structural quality, leading to films with surface root-mean-square roughness of ~ 1 nm under low-growth-rate conditions (60 nm/h). The use of the developed InN buffer layer improves the crystalline quality of the subsequent InN thick films deposited at high growth rate (180 nm/h), as confirmed by the narrowing of X-ray diffraction peaks and the increase of the average grain size of the layers. This improvement of the structural quality is further confirmed by Raman scattering spectroscopy measurements. Room temperature PL emission peaking at ~ 1.58 eV is observed for InN samples grown with the developed buffer layer. The crystal and optical quality obtained for InN films grown on Si(111) using the low-growth-rate InN buffer layer become comparable to high-quality InN films deposited directly on GaN templates by RF sputtering.     

Structure and bandgap determination of InN grown by RP-MOCVD

InN thin films are grown on sapphire substrates by remote plasma-assisted metal organic chemical vapor deposition while varying the indium pulse length and substrate temperature. The effects of the indium pulse length and temperature on the structural, morphological, electronic, and optical properties of the thin films are studied. The structural parameters are determined by X-ray diffraction and X-ray photoelectron spectroscopy and the effects of incorporating oxygen atoms in the structure is described. The N K-edge X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) measurements are used to determine the band gap and it is found to be 1.80?±?0.25 eV for all samples. A complementary measurement namely, X-ray excited optical luminescence measurement is performed to confirm the band gap value obtained from XAS and XES measurements. O K-edge XAS measurements are performed to determine the presence of oxygen impurities in the samples. Meanwhile, we carry out the density functional theory calculations for Wurtzite InN, hypothetical Wurtzite-type InO_0.5N_0.5, and InO_0.0625N_0.9375 structures. We find that the measured N-edge spectra agree well with our Wurtzite InN calculations and the measured O K-edge spectra agree better with hypothetical Wurtzite-type InO_0.0625N_0.9375 than Wurtzite-type InO_0.5N_0.5.

     

Growth of InN layers on Si (111) using ultra thin silicon nitride buffer layer by NPA-MBE

Indium nitride (InN) epilayers have been successfully grown by nitrogen-plasma-assisted molecular beam epitaxy (NPA-MBE) on Si (111) substrates using different buffer layers. Growth of a (0001)-oriented single crystalline wurtzite-InN layer was confirmed by high resolution X-ray diffraction (HRXRD). The Raman studies show the high crystalline quality and the wurtzite lattice structure of InN films on the Si substrate using different buffer layers and the InN/β-Si₃N₄ double buffer layer achieves minimum FWHM of E₂ (high) mode. The energy gap of InN films was determined by optical absorption measurement and found to be in the range of ~ 0.73-0.78 eV with a direct band nature. It is found that a double-buffer technique (InN/β-Si₃N₄) insures improved crystallinity, smooth surface and good optical properties.     

Raman scattering and Rutherford backscattering studies on InN films grown by plasma-assisted molecular beam epitaxy

A series of InN thin films was grown on sapphire substrates via plasma-assisted molecular beam epitaxy (PA-MBE) with different nitrogen plasma power. Various characterization techniques, including Hall, photoluminescence, Raman scattering and Rutherford backscattering, have been employed to study these InN films. Good crystalline wurtzite structures have been identified for all PA-MBE grown InN films on sapphire substrate, which have narrower XRD wurtzite (0002) peaks, showed c-axis Raman scattering allowed longitudinal optical (LO) modes of A₁ and E₁ plus E₂ symmetry, and very weak backscattering forbidden transverse optical (TO) modes. The lower plasma power can lead to the lower carrier concentration, to have the InN film close to intrinsic material with the PL emission below 0.70 eV. With increasing the plasma power, high carrier concentration beyond 1 × 10²⁰ cm^− 3 can be obtained, keeping good crystalline perfection. Rutherford backscattering confirmed most of InN films keeping stoichiometrical In/N ratios and only with higher plasma power of 400 W leaded to obvious surface effect and interdiffusion between the substrate and InN film.     

Physical properties of very thin SnS films deposited by thermal evaporation

SnS films with thicknesses of 20-65 nm have been deposited on glass substrates by thermal evaporation. The physical properties of the films were investigated using X-ray diffraction (XRD), scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and ultraviolet-visible-near infrared spectroscopy at room temperature. The results from XRD, XPS and Raman spectroscopy analyses indicate that the deposited films mainly exhibit SnS phase, but they may contain a tiny amount of Sn₂S₃. The deposited SnS films are pinhole free, smooth and strongly adherent to the surfaces of the substrates. The color of the SnS films changes from pale yellow to brown with the increase of the film thickness from 20 nm to 65 nm. The very smooth surfaces of the thin films result in their high reflectance. The direct bandgap of the films is between 2.15 eV and 2.28 eV which is much larger than 1.3 eV of bulk SnS, this is deserving to be investigated further.     

Effect of annealing in a various oxygen atmosphere on structural,optical, electrical and gas sensing properties of MoxOy thin films

Molybdenum oxide thin films were thermally evaporated on a glass substrate and monitored by an annealing process in a variable oxygen atmosphere. The effects of post annealing condition on the microstructural, morphological, optical and electrical properties were investigated using X-ray diffraction, Raman spectroscopy, atomic force microscope, spectroscopic ellipsometry and impedance spectroscopy. As-deposited amorphous films crystallized into tetragonal metastable phase of Mo₅O₁₄ on annealing at 500 °C in vacuum and air. This structure transformed to stable orthorhombic of MoO₃ with annealing in oxygen environment. The optical parameters such as the refractive index, extinction coefficient, optical band gap energy and the Urbach energy were calculated from Cauchy formalism. Ellipsometric measurements reveal that the samples present optical gap located between 3.24 and 3.90 eV when the atmosphere becomes rich on oxygen. The variation of the conductivity in terms of the temperature shows an electrical behavior with oxygen environment. Finally, it has been found that MoO₃ thin films had high sensitivity to ethanol, which made them as a good candidate for the ethanol sensor.     

Influence of O2 pressure on the properties of heavily-doped ZnO:Sb thin films grown by pulsed laser deposition

Heavily Sb-doped ZnO films were deposited on the glass substrates by pulsed laser deposition (PLD). X-ray diffraction (XRD) and photoelectron spectroscopy (XPS) were employed to characterize their microstructures and chemical valence states. Transmittance spectra and Hall measurements were used to evaluate their optical and electrical properties. It was found that the as-prepared ZnO:Sb thin films showed a single-hexagonal-phase structure, with the optical band gap tuning from 3.33 to 3.11 eV. The variation in the band gap was attributed to a large co-axis strain in the alloy films induced by Sb incorporation. Besides, the alloy films showed a semi-insulated characteristic with high resistivity of ~10⁴ Ω cm, which was possibly related to a compensation of intrinsic defects.     

Synthesis and optical properties of CeO<Subscript>2</Subscript> nanocrystalline films grown by pulsed electron beam deposition

The nanocrystalline cerium dioxide (CeO₂) thin films were deposited on soda lime (SLG) and Corning glass by pulsed e-beam deposition (PED) method at room temperature. The structure of the produced CeO₂ thin films was investigated by X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), and micro Raman spectroscopy. The surface topography of the films was examined by atomic force microscopy (AFM). Film thickness and growth morphologies were determined with FEG-SEM from the fracture cross sections. XPS studies gave a film composition composed of +4 and +3 valent cerium typical to nanocrystalline ceria structures deficient in oxygen. The ceria films were polycrystalline in nature with a lattice parameter (a) of 0.542 nm. The Raman characteristics of the source material and the films deposited were very similar in character. Raman lines for thin film and bulk CeO₂ was observed at 465 cm⁻¹. The optical properties of the CeO₂ films were deduced from reflectance and transmittance measurements at room temperature. From the optical model, the refractive index was determined as 1.8–2.7 in the photon energy interval from 3.5 to 1.25 eV. The optical indirect band gap (E _g) of CeO₂ nanocrystalline films was calculated as 2.58 eV.     

Effect of substrate bias voltage on the physical properties of dc reactive magnetron sputtered NiO thin films

Nickel oxide (NiO) thin films were prepared on glass substrates at various bias voltages using dc reactive magnetron sputtering technique. The influence of substrate bias voltage on structural, optical and electrical properties was systematically investigated using X-ray diffraction (XRD), SEM, EDS, spectrophotometer and Hall effect studies. The NiO films are crystalline with preferential growth along (2 0 0) plane. The NiO films exhibit optical transmittance of 55% and direct band gap of 3.78 eV at the substrate bias voltage of −75 V. The electrical resistivity decreases as substrate bias voltage increases from 0 to −75 V thereafter it was slightly increased.     

<Emphasis Type="Italic">h</Emphasis>-MoO<Subscript>3</Subscript> microrods grown on wood substrates through a low-temperature hydrothermal route and their optical properties

Molybdenum trioxide (MoO₃) films with optical properties were successfully grown on wood substrates using a low-temperature hydrothermal method. Scanning electron microscopy analysis shows that MoO₃ thin films were composed of rods-like microstructures and the rod sizes increased as the initial pH value of the solution increased. X-ray diffraction studies indicate crystallinity was greatly improved by increasing the pH value of the precursor solution. Raman spectrum, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy analysis further proves that pure MoO₃ films could be grown on a wood substrate. The UV–Vis analysis suggests that the films exhibited better in response to UV light. The band gap energy estimated from the Kubelka–Munk function was found to be in the range of 2.847–2.974 eV. The results from thermogravimetric analysis and differential scanning calorimetry experiments imply that the films possessed good thermal stability.     

Synthesis of nanocrystalline iron oxide ultrathin films by thermal decomposition of iron nitropruside: Structural and optical properties

Ultrathin films of nanocrystalline α-Fe₂O₃ have been deposited on glass substrates from an inorganic precursor, iron nitropruside. This is a novel route of synthesis for iron oxide thin films on glass substrates, by annealing the precursor thin film in air at 650 °C for 15 min. The films were characterized using TG-DTA analysis, X-ray diffraction, UV-visible, FESEM, AFM and Raman measurements. X-ray diffraction and Raman analyses revealed that the deposited films contain α-phase of Fe₂O₃ (hematite). The synthetic route described here provides a very simple and cost-effective method to deposit α-Fe₂O₃ thin films on glass substrates with band gap energy of about 2.75 eV. The deposited films were found to show catalytic effect for the photo-degradation of phenol.     

Electronic structure of p-type ultraviolet-transparent conducting CuScO2 films

We investigate the electronic structure of CuScO₂ thin films grown on sapphire and mica substrates by pulsed laser deposition. X-ray diffraction and microanalysis confirm that the films have the expected delafossite crystal structure and stoichiometric proportions. The electronic structure is investigated by means of X-ray and ultraviolet photoelectron spectroscopy. Electronic states in the range 0-1350 eV are identified, making reference to theoretical density-of-states calculations up to 80 eV. Photoelectron spectra near the Fermi energy confirm the p-character of the films. Optical absorption spectroscopy shows that the films are transparent up to 3.7 eV and exhibit an intense excitonic peak, with a direct gap energy of 4.24 ± 0.05 eV at room temperature. Ab initio band structure calculations confirm the direct character of CuScO₂ and allow for an assignment of the direct gap to an electronic transition at the L point of the rhombohedral Brillouin zone.     

Some studies on successive ionic layer adsorption and reaction (SILAR) grown indium sulphide thin films

Indium sulphide (In₂S₃) thin films were grown on amorphous glass substrate by the successive ionic layer adsorption and reaction (SILAR) method. X-ray diffraction, optical absorption, scanning electron microscopy (SEM) and Rutherford back scattering (RBS) were applied to study the structural, optical, surface morphological and compositional properties of the indium sulphide thin films. Utilization of triethanolamine and hydrazine hydrate complexed indium sulphate and sodium sulphide as precursors resulted in nanocrystalline In₂S₃ thin film. The optical band gap was found to be 2.7 eV. The film appeared to be smooth and homogeneous from SEM study.     

Structural and electrochromic properties of TiO2 thin films prepared by metallorganic chemical vapor deposition

Titanium dioxide thin films were deposited by Metallorganic Chemical Vapor Deposition at substrate temperatures ranging from 250 °C to 450 °C over soda lime glass and indium tin oxide coated glass substrates. X-ray diffraction studies show that films have a crystalline anatase structure at all the deposition temperatures. Particle size decreases and texture changes with the increase in substrate temperature. X-ray photoelectron spectroscopy confirms the appearance of a new well resolved state in the core level of Ti 2p spectrum shifted by 1.16 eV to lower binding energy due to the reduction of Ti^+ 4 to Ti^+ 3 upon litheation. Chronoamperometery, cyclic voltammetery and in situ UV-Vis spectrophotometeric studies were carried out on the prepared samples. Particle size and crystallinity control the electrochromic performance. The 350 °C film shows the highest ion storage capacity and the highest optical modulation along with an appreciable band gap broadening.     

Optical properties of nanocrystalline SnS2 thin films

Thin films of nanocrystalline SnS₂ on glass substrates were prepared from solution by dip coating and then sulfurized in H₂S (H₂S:Ar = 1:10) atmosphere. The films had an average thickness of 60 nm and were characterized by X-ray diffraction studies, scanning electron microscopy, EDAX, transmission electron microscopy, UV-vis spectroscopy, and Raman spectroscopy. The influence of annealing temperature (150-300 °C) on the crystallinity and particle size was studied. The effect of CTAB as a capping agent has been tested. X-ray diffraction analysis revealed the polycrystalline nature of the films with a preferential orientation along the c-axis. Optical transmission spectra indicated a marked blue shift of the absorption edge due to quantum confinement and optical band gap was found to vary from 3.5 to 3.0 eV with annealing temperature. Raman studies indicated a prominent broad peak at ∼314 cm⁻¹, which confirmed the presence of nanocrystalline SnS₂ phase.     

Preparation of anatase TiO2 thin films for dye-sensitized solar cells by DC reactive magnetron sputtering technique

Anatase titanium dioxide (TiO₂) thin films are prepared by DC reactive magnetron sputtering using Ti target as the source material. In this work argon and oxygen are used as sputtering and reactive gas respectively. DC power is used at 100 W per 1 h. The distance between the target and substrate is fixed at 4 cm. The glass substrate temperature value varies from room temperature to 400 °C. The crystalline structure of the films is determined by X-ray diffraction analysis. All the films deposited at temperatures lower than 300 °C were amorphous, whereas films obtained at higher temperature grew in crystalline anatase phase. Phase transition from amorphous to anatase is observed at 400 °C annealing temperature. Transmittances of the TiO₂ thin films were measured using UV-visible NIR spectrophotometer. The direct and indirect optical band gap for room temperature and substrate temperature at 400 °C is found to be 3.50, 3.41 eV and 3.50, 3.54 eV respectively. The transmittance of TiO₂ thin films is noted higher than 75%. A comparison among all the films obtained at room temperature showed a transmittance value higher for films obtained at substrate temperature of 400 °C. The morphology of the films and the identification of the surface chemical stoichiometry of the deposited film at 400 °C were studied respectively, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The surface roughness and the grain size are measured using AFM.     

Effect of substrate temperature on structural, morphological and optical properties of crystalline titanium dioxide films prepared by DC reactive magnetron sputtering

Titanium dioxide (TiO₂) thin films have been deposited with various substrate temperatures by dc reactive magnetron sputtering method onto glass substrate. The effects of substrate temperature on the crystallization behavior and optical properties of the films have been studied. Chemical composition of the films was investigated by X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD) analysis of the films revealed that they have polycrystalline tetragonal structure with strong (101) texture. The surface morphological study revealed the crystalline nature of the films at higher substrate temperatures. The TiO₂ films show the main bands in the range 400–700 cm^?1, which are attributed to Ti–O stretching and Ti–O–Ti bridging. The transmittance spectra of the TiO₂ thin film measured with various substrate temperatures ranged from 75 to 90 % in the visible light region. The optical band gap values of the films are increasing from 3.44 to 4.0 eV at growth temperature from 100 to 400 °C. The structural and optical properties of the films improved with the increase in the deposition temperature.     

Room temperature deposition of ZnSe thin films by successive ionic layer adsorption and reaction (SILAR) method

The zinc selenide (ZnSe) thin films are deposited onto glass substrate using relatively simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method. The films are deposited using zinc acetate sodium selenosulphate precursors. The concentration, pH, immersion and rinsing times and number of immersion cycles have been optimized to obtain good quality ZnSe thin films. The X-ray diffraction (XRD) study and scanning electron microscopy (SEM) studies reveals nanocrystalline nature alongwith some amorphous phase present in ZnSe thin films. Energy dispersive X-ray (EDAX) analysis shows that the films are Se deficient. From optical absorption data, the optical band gap ‘E_g’ for as-deposited thin film was found to be 2.8 eV and electrical resistivity in the order of 10⁷ Ω cm.     

Microstructure and gas-sensing properties of sol-gel ZnO thin films

The paper presents the properties of zinc oxide thin films deposited on glass substrate via dip-coating technique. Zinc acetate dehydrate, ethanol and monoethanol amine were used as starting materials and N₂ gas was used as thermal annealing atmosphere for film crystallization. The effect of withdrawal speed on the crystalline structure, morphology, zinc and nitrogen chemical states, optical, electrical and gas-sensing properties of the thin films has been investigated using X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, optical transmittance and photoreduction-ozone reoxidation data.