Photoluminescence and optical dispersion parameters of N-doped ZnO nano-fiber thin films

N-doped ZnO (NZO) nanocrystalline thin films were successfully synthesized via sol–gel method. The structural and optical properties of the films were characterized by various techniques including X-ray diffraction, atomic force microscopy (AFM), UV–vis absorption and photoluminescence. The UV–vis absorption edge was changed with increasing N-doping concentration. X-ray diffraction (XRD) results clearly showed that the zinc oxide doped with nitrogen (5 to 20 wt.%) were identified with phases of hexagonal ZnO and N-doped ZnO nanocrystalline thin films. The refractive index dispersion mechanism obeys the Single oscillator model. The dispersion parameters E _o and E _d of the thin films were determined. The dispersion parameters were changed by N dopant. It is evaluated that the structural, optical constants, photoluminescence properties of Zinc oxide film can be controlled by N dopants.     

Effects of Mg doping concentration on the band gap of ZnO/Mg x Zn1−x O multilayer thin films prepared using pulsed laser deposition method

Epitaxial ZnO/Mg _x Zn_1-x O multilayer thin films (x?=?0~0.15) were prepared on c-Al₂O₃ substrates by pulsed laser deposition and their crystallinity and optical properties were investigated using X-ray diffraction, TEM, and UV-Vis spectroscopy. ZnO/Mg _x Zn_1-x O multilayer thin films were grown by stacking alternate layers of ZnO and Mg _x Zn_1?x O with laser fluence of 3 J/cm², repetition rate of 5 Hz, substrate temperature of 600 °C, and oxygen partial pressure of 5?×?10^–4 Torr. The thickness of individual ZnO and Mg _x Zn_1?x O layers was maintained at 3 and 6 nm, respectively, and the total thickness of the films was kept in 300 nm. X-ray diffraction results showed that the multilayer thin films were grown epitaxially on c-Al₂O₃ substrates with an epitaxial orientation relationship of $\left. {\left( {0001} \right)\left[ {10\bar 11} \right]_{{\text{multilayer}}} } \right\|\left( {0001} \right)\left[ {10\bar 11} \right]_{{\text{Al}}_{\text{2}} {\text{O}}_{\text{3}} } $ . Cross-sectional TEM micrographs showed alternating layers of bright and dark contrast, indicating the formation of ZnO/Mg _x Zn_1?x O multilayer thin films. The 2θ value of Mg _x Zn_1?x O (0002) peak increased from 34.30° at x?=?0 to 34.67° at x?=?0.15 with increasing Mg doping concentration in the multilayer thin films. The absorption edge in the UV-Vis spectra shifted to shorter wavelength from 360 at x?=?0 to 342 nm at x?=?0.15 and the band gap energy increased from 3.27 eV at x?=?0 to 3.54 eV at x?=?0.15.     

Electrical and optical properties of fluorine-doped tin oxide (SnOx:F) thin films deposited on PET by using ECR–MOCVD

The electrical, optical, structural and chemical bonding properties of fluorine-doped tin oxide (SnO_x:F) films deposited on a plastic substrate prepared by Electron Cyclotron Resonance–Metal Organic Chemical Vapor Deposition (ECR–MOCVD) were investigated with special attention to the process parameters such as the H₂/TMT mole ratio, deposition time and amount of fluorine-doping. The four point probe method, UV visible spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic emission spectroscopy (AES), X-Ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were employed to characterize the films. Based on our experimental results, the characteristics of the SnO_x:F thin films were significantly affected by the process parameters mentioned above. The amount of fluorine doping was found to be one of the major parameters affecting the surface resistivity, however its excess doping into SnO₂ lead to a sharp increase in the surface resistivity. The average transmittance decreased with increasing film thickness. The lowest electrical resistivity of 5.0?×?10^?3 Ω^.cm and highest optical transmittance of 90% in the visible wavelength range from 380 to700 nm were observed at an H₂/TMT mole ratio of 1.25, fluorine-doping amount of 1.3 wt.%, and deposition time of 30 min. From the XRD analysis, we found that the SnO_x:F films were oriented along the (2 1 1) plane with a tetragonal and polycrystalline structure having the lattice constants, a?=?0.4749 and c?=?0.3198 nm.     

Blueshift of absorption edge and photoluminescence in Al doped ZnO thin films

ABSTRACT

Pure and Al doped ZnO thin films are fabricated on quartz substrates by sol–gel method, and then analyzed by X-ray diffraction (XRD), transmittance spectra, and photoluminescence (PL) measurements respectively. XRD results reveal that all the thin films have a preferential c-axis orientation. With the increase of Al doping, however, the peak position of the (002) plane is shifted to a low 2θ value. On the other hand, the data of spectrometer transmittance are obtained, with which the band gap energies of Al doped ZnO films are calculated by a linear fitting method. The band gap is found to be broadening, and the absorption edge has an obvious blueshift to the shorter wavelength with increasing dopant concentration. PL measurement is also conducted, and deep-level (DL) emission and near band edge (NBE) emission are observed in pure ZnO thin films. But DL emissions are depressed when Al is doped into thin films. And the peak of NBE emission has a blueshift to the region of higher photon energy as the Al concentration increases, a performance which tallies with observations through the optical transmittance data. The study demonstrates that the blueshift of optical properties in the ZnO:Al films, can nevertheless be easily manipulated and managed by controlling dopant concentration, a big plus to the said films in their applications in broadband UV photodetectors with highly tunable wavelength resolution.     

Optical properties of RF-sputtered Ba0.65Sr0.35TiO3 thin films

Ba_0.65Sr_0.35TiO₃ (BST) thin films have been prepared by radio frequency magnetron sputtering on fused quartz at different substrate temperatures. Optical constants (refractive index n, extinction coefficient k) were determined from the optical transmittance spectra using the envelope method. The dispersion relationship of the refractive index vs. substrate temperature was also investigated. The refractive index of BST thin films increased from 1.778 to 1.961 (at λ?=?650 nm) as deposited temperature increases from 560°C to 650°C. The extinction coefficient of as-deposited BST thin films increased with the increase of the oxygen-to-argon ratio, which was due to the change of the film stoichiometry, structure, and texture of BST thin films. The oxygen-to-argon ratio also affected the fluorescence spectra. The fluorescence peaks intensity was greatly increased, apparent frequency shift was detected, and the linewidth became narrow as the ratio of oxygen to argon increased from 1:4 to 1:1. The fluorescence spectra also indicated the band transition of BST thin films was an indirect gap transition.     

Optical properties of epitaxial plzt thin films

In the epitaxial (Pb_1?x , La _x )(Zr_1?y , Ti _y )_1?x/4O₃ [PLZT] films, the composition dependence of the refractive index and electric-optic (EO) coefficient near the morphotropic phase boundary (MPB) composition was investigated. A (100/001)-oriented PLZT 10/65/35 epitaxial film is found to have isotropic optical properties. Highly (100/001)-oriented epitaxial PLZT films with compositions near the MPB on Nb–SrTiO₃ substrates were fabricated using a sol–gel process. The value of birefringence from 4?×?10^?3 to 5?×?10^?4 in PLZT epitaxial film was smaller than that of lithium niobate single crystal. The refractive index decreases with increasing lanthanum content. The difference in the refractive index obtained depended upon the lanthanum content up to 2%. This value is adequate for fabrication of waveguide structures. The EO coefficient of PLZT 9/65/35 thin films was 45 pm/V, which is larger than that of lithium niobate single crystal. A very small polarization dependence of the EO coefficient was also observed.     

Fabrication and electrical characterization of solution-processed all-oxide transparent NiO/TiO2 p-n junction diode by sol–gel spin coating method

Solution-processed all-oxide transparent NiO/TiO₂ p-n junction was fabricated using sol–gel spin coating method. The optical properties of the NiO and TiO₂ films were studied by transmittance and absorbance spectra. The optical band gaps of NiO and TiO₂ films were determined by optical absorption method and found to be 3.83 eV and 3.74 eV, respectively. The current–voltage characteristics of the oxides based p-n junction showed a rectifying behavior. The junction parameters such as ideality factor and barrier height were calculated using thermionic emission model, Chenug, and Norde method. The barrier height and ideality factor values of the diode were obtained to be 0.59 eV and 9.8, respectively.     

Determination of optical band gap of ZnO:ZnAl2O4 composite semiconductor nanopowder materials by optical reflectance method

ZnO:ZnAl₂O₄ composite semiconductor nanopowder materials were synthesized by sol gel method. X-ray diffraction results reveal that Al doped ZnO samples have a polycrystalline hexagonal structure with a?=?3.2506 Å, c?=?5.2079 Å lattice parameters. The crystallite size of the ZnO samples is decreased with increasing Al content. Atomic force microscope results indicate the presence of micro/nanohexagons with different sizes from 128 to 166 nm. Optical band gap of the ZnO samples is decreased and reaches a low value of 2.82 eV for 20 % Al. The electrical conductivity dependence of temperature confirms that ZnO:ZnAl₂O₄ composite semiconductor nanopowder materials exhibit semiconductor behavior.     

Optical characteristics of Bi4-xEuxTi3O12 ferroelectric thin films on fused silica substrates

Bi_4-xEu_xTi₃O₁₂ (BEuT) ferroelectric thin films were prepared on fused silica substrates by using chemical solution deposition technique. The attained samples had a polycrystalline bismuth-layered perovskite structure, and their optical properties were composition dependent. The thin film samples had good optical transmittance above 500?nm wavelength. A blue shift of the optical absorption edge was observed in the BEuT thin films with increasing Eu³⁺ concentration. The optical band gaps of BEuT thin films were estimated to be about 3.57, 3.60, 3.61, 3.63, and 3.69?eV for the samples with x?=?0.25, 0.40, 0.55, 0.70, and 0.85, respectively. Photoluminescence measurements showed that two emission peaks of BEuT thin films originated from two transitions of ⁵ D ₀????⁷? F ₁ (594?nm) and ⁵ D ₀????⁷? F ₂ (617?nm) had maximum intensities when Eu³⁺ concentration was x?=?0.40. The relatively high quenching concentration of Eu³⁺ content was thought to be related to the layered structure of BEuT thin films. These results suggested that multifunctional BEuT thin film materials could have promising applications in optoelectronic devices.     

A first-principles study of the structural,elastic, electronic,vibrational, and optical properties of BaSe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The structural, elastic, electronic, vibrational, and optical properties of BaSe_1?xTe_x alloys are investigated by means of the full-potential linearized augmented plane wave method. The exchange–correlation effects are treated with the local density approximation, as well as the GGA-PBE, GGA-PBEsol, and GGA?+?mBJ schemes of the generalized gradient approximation. Ternary BaSe_1?xTe_x compounds have not yet been synthesized. Improved predictions of the structural parameters are obtained using the GGA-PBEsol approach. Calculations of the electronic and optical properties with the GGA?+?mBJ approach yield accurate results. Ternary BaSe_1?xTe_x alloys are wide-band-gap semiconductors with a direct gap Γ–Γ. The upper valence band is mainly due to Se p and Te p states, while the bottom of the conduction band results essentially from Ba d states. The dielectric function, refractive index, reflectivity, absorption coefficient, and energy-loss function are calculated in the range 0–35 eV. The increase in x gives rise to a redshift of the optical spectra. BaSe_1?xTe_x alloys exhibit reflective properties of metals in some energy ranges. The static dielectric constant ?₁(0) and the static refractive index n₀ are calculated. The investigation of the elastic and vibrational properties shows that ternary BaSe_1?xTe_x should be mechanically and dynamically stable, elastically anisotropic, brittle, and relatively soft.     

Fabrication and characterization of Au/SBT/LZO/Si MFIS structure

Ferroelectric SrBi₂Ta₂O₉ (SBT) films on a p-type Si (100) wafer with a LaZrO _x (LZO) buffer layer have been fabricated to form a metal-ferroelectric-insulator–semiconductor (MFIS) structure. The LZO thin film and SBT films were deposited by using a sol–gel method. The equivalent oxide thickness (EOT) value of the LZO thin film was about 8.83 nm. Also, the leakage current density of the LZO thin film is about 3.3?×?10^?5 A/cm² at bias sweeping voltage of ±5 V. SBT films were crystallized in polycrystalline phase with highly preferred (115) orientation. Also, the intensity of each pick slightly increased as thickness of SBT films increased. The C–V characteristics of Au/SBT/LZO/Si structure showed clockwise hysteresis loop. The memory window width increased as the thickness of SBT films increased. The leakage current density of Au/SBT/LZO/Si structure decreased as thickness of SBT films increased.     

Preparation of TiO<Subscript>2</Subscript> thin films deposited from highly dense targets with multi-oxide glass doping

Glass doped TiO₂ (GTO) thin films were deposited by radio frequency (RF) magnetron sputter at room temperature and annealed in a reductive atmosphere containing 90 % N₂ and 10 % H₂. Highly dense TiO₂ ceramic mixed with glass consisting of multi-metal oxides (as a sintering aid) was used as the sputtering target. This sintering aid allows low temperature densification of TiO₂ target through a liquid phase wetting mechanism, and also works as a doping resource. XRD and FESEM were carried out to characterize the microstructure of the GTO films and the results reveal that the doping of multi-metal ions enhances the crystallization and increases the grain size of TiO₂ films. TEM analysis also showed that these metal ions were dissolved into TiO₂ lattices. The electrical and optical properties of TiO₂ thin films at different glass concentrations were evaluated and compared to the films merely doped with MoO₃. The electrical resistivity of the GTO films reaches 9.1 × 10^–4 Ω·cm at 2 wt% glass doping, corresponding to a carrier density of 8.9 x 10²⁰ cm^-3 and a mobility of 7.1 cm²/Vs. Meanwhile, the electrical resistivity of the TiO₂ film doped with glass was found to be lower than that of MoO₃-doped film. This was mainly attributed to the increase in carrier concentration by double doping effect of glass. The optical band gap of the GTO films ranged from 3.34 to 3.42 eV, which is greater than that of the un-doped TiO₂ film. This blue shift of approximately 0.18 eV was due to the Burstein-Moss effect.     

Effect of Mg doping on dielectric properties of sol-gel derived (Pb0.7Sr0.3)Mg x Ti1–x O3–x thin film

(Pb_0.7Sr_0.3)Mg _x Ti_1–x O_3–x (x?=?0?～?0.3) thin films were successfully prepared on ITO/glass substrate by sol-gel technique. The crystalline phase structures were measured through X-ray diffraction (XRD). The dielectric properties were measured by a precision impedance analyzer. Results show that the perovskite phase was stable in (Pb_0.7Sr_0.3)Mg _x Ti_1–x O_3–x thin film. Its lattice constant was found to decrease with the increase of x when x?<?0.1 and increase when x?>?0.1.The crystalline phase formation and the dielectric properties of the (Pb_0.7Sr_0.3)Mg _x Ti_1–x O_3–x thin film depend on Mg doping content. The phase formation ability was decreased below x?=?0.1 and then increased above x?=?0.1 with the increase in x. The dielectric constant of the thin film is correspondingly changed. The tunabilities of about 35%?～?63% were obtained at 10 kHz. The highest tunability and the lowest dielectric loss of the thin films appeared at x?=?0.2. The FOM of the thin film with Mg doping of x?=?0.2 is about three times higher than that of x?=?0.1 under applied frequency of 10 kHz.     

Effects of temperature on structural and optical properties of ZnMgO films fabricated by pulsed laser deposition

ZnMgO thin films have been deposited on Si(111) substrates by pulsed laser deposition (PLD) technique at growth temperature from 300 to 700°C in nitrogen ambient of 1.0 Pa. The effects of growth temperature on structural and optical properties of deposited ZnMgO thin films have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared absorption (IR) spectra and photoluminescence (PL) spectra. The results of XRD and SEM analyses show that the film fabricated at 400°C possesses good crystallinity with hexagonal wurtzite structure and surface morphology. The Mg has been incorporated into ZnO in the form of substitutional Zn. The IR spectra reveal the typical absorption peaks of ZnMgO. The band-gap values have been obtained from 2.96 to 4.23 eV with increasing growth temperature. The PL spectra show that the highest UV emission is obtained at growth temperature of 600°C, and the obvious blue-shift is observed. This may be assigned as the change of the band-gap due to the increasing incorporation of Mg²⁺ ions with the increasing growth temperature.     

Effect of band parameters on interband optical absorption in quantum wire structure of low band gap III–V semiconductors

A generalized theory is presented to study the effect of band parameters on inter band optical absorption in quantum wire structure of III–V compound semiconductors considering the wave-vector ( $\vec{k}$ ) dependence of the optical transition matrix element (OME). The band structures of these low band gap semiconducting materials with sufficiently separated split-off valance band are frequently described by the three energy band model of Kane. This has been adopted to calculate the inter band optical absorption coefficient (IOAC) for a wide range of III–V compound semiconductors like, InAs, InSb, Hg_1?x Cd _x Te and In_1?x Ga _x As _y P_1?y lattice matched to InP, having varied split-off energy band compared to their energy band gap. It has been found that IOAC for quantum wires (QWRs) increases in oscillatory manner with increasing incident photon energy and the positions of peaks of oscillation of the coefficient are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of band energy constants. This effect of band parameters is better revealed from the study of light polarization dependence of the absorption coefficient.     

Analysis of saturation currents and barrier height of Ta2O5 doped based on Ba0,5S0,5TiO3 photodiode

Ba_0,5Sr_0,5TiO₃ (BST) thin films have been prepared on Si (100) p-type substrates using a chemical solution deposition (CSD) method and doped with 0%, 2.5%, 5%, 7.5%, 10% tantalum pentaoxide (Ta₂O₅). Chemical Solution Deposition Method (CSD) used the spin coating techniques with a rotational speed of 3000?rpm for 30?seconds. BST thin films annealed at a temperature 850?°C. Various electrical parameters such as saturation current, series resistance and barrier height have been calculated from the analysis of experimental I–V results and discussed in detail. The series resistance was found from the experiment of 42.8 MΩ, 7.9 MΩ, 7.2 MΩ, 2.03 MΩ, 1.2 MΩ for variation doping content. The saturation current of 22.3 μA, 2.7 μA, 9.7 μA, 4.82 μA, 4.50 μA was obtained in BST thin film with variation doping content. Then, the barrier height of 0.56?eV, 0.62?eV, 0.58?eV, 0.54?eV, 0.60?eV was obtained in BST thin film with variation doping content. The optical characterization and analysis microstructure such as XRD, EDX were discussed in detail.     

Effect of heat treatment of sputter deposited ZnO films co-doped with H and Al

ZnO films co-doped with H and Al (HAZO) were prepared by sputtering ZnO targets containing Al₂O₃ dcontent of 1 (HA₁ZO series) and 2 wt.% (HA₂ZO series) on Corning glass (Eagle 2000) at substrate temperature of 150 °C with Ar and H₂/Ar gas mixtures. The effects of hydrogen addition to Al-doped ZnO (AZO) films with different Al contents on the electrical, optical and structural properties of the as-grown films as well as the vacuum- and air-annealed films were examined. For the as-deposited films, the free carrier number in both series of HAZO films increased with increasing H₂ content in sputter gas. HA₂ZO film series prepared from target containing 2 wt.% Al₂O₃ showed better crystallinity and higher carrier concentration than HA₁ZO film series deposited using target containing 1 wt.% Al₂O₃. The crystallinity and the Hall mobility of HA₂ZO film series decreased with increasing H₂ content in sputter gas, while those of HA₁ZO film series showed a reversed behavior. Although HA₂ZO film series yielded lower resistivity than HA₁ZO film series due to higher carrier concentrations, the higher figure of merit (expressed as 1?/?ρα, where ρ and α represents the resistivity and absorption coefficient, respectively) was observed for HA₁ZO film series because of substantially low absorption loss in these films. When annealed in air ambient, HA₁ZO film series showed much stronger stability than HA₂ZO film series. Vacuum-annealing resulted in drop of the carrier concentrations as well as large shrinkage in lattice constant, which indicated that the hydrogen dopants are in relatively volatile state and can be removed easily from the films upon annealing.     

Electrical and optical studies of transparent conducting ZnO:Al thin films by magnetron dc sputtering

Transparent conducting aluminium-doped Zinc oxide (ZnO:Al) films have been deposited on glass substrates by magnetron dc sputtering using a ceramic target (ZnO with 2 wt% Al₂O₃). The dependence of the electrical and optical properties of these films on substrate temperature, sputtering pressure of Ar and location of substrates were investigated in detail. Target is perpendicular with substrate and we controlled the distance ‘x’ of target and substrate. Optimized films with resistivity of 3.7?×?10^?4 Ω cm, an average transmission in the visible range (300–800 nm) of greater than 85% and the reflectance in the infrared range being greater than 85% have been formed. Substrate temperature, distance ‘x’, and working pressure are optimized for lower resistivity and high concentration of carriers.     

Photoresponse and electrical properties of Al/nanostructure NiFe2O4/p-Si/Al photodiode

The electrical characterization of Al/NiFe₂O₄/p-Si/Al photodiode was investigated by current–voltage and capacitance-voltage characteristics. The barrier height and ideality factor magnitudes of the Al/NiFe₂O₄/p-Si/Al diode were found to be 0.82 and 5.2 eV, respectively. The optical properties of the NiFe₂O₄ film have been investigated and the optical band gap was found to be 2.66 eV. The photoresponse results indicate that the diode exhibits a photodiode behavior, and the photocurrent of the diode increases by increasing illumination intensity. The density of interface states of the diode was determined by conductance method. The obtained results show that the series resistance of the diode is decreased with increasing frequency. The obtained results indicate that NiFe₂O₄ spine oxide material can be used in diode applications.     

Effects of the O2/Ar gas flow ratio on the electrical and transmittance properties of ZnO:Al films deposited by RF magnetron sputtering

ZnO:Al thin films for transparent conductors were deposited on sapphire (0001) substrates by using an RF magnetron sputtering technique. Effects of the O₂/Ar flow ratio in the sputtering process on the crystallinity, carrier concentration, carrier mobility, and transmittance of the films were investigated. The FWHM of the (002) XRD intensity peak is minimal at the O₂/Ar flow ratio of 0.5. According to the Hall measurement results the carrier concentration and mobility of the film decrease and thus the resistivity increases as the O₂/Ar flow ratio increases. The transmittance of the ZnO:Al film deposited on the glass substrate is characteristic of standing wave. The transmittance increases as the O₂/Ar flow ratio in-RF magnetron sputtering increases up to 0.5. Considering the effects of the the O₂/Ar flow ratio on the electrical resistivity and transmittance of the ZnO:Al film the optimum O₂/Ar flow ratio is 0.5 in the RF magnetron sputter deposition of the ZnO:Al film.