xO Thin Films Research Articles

Effects of Mn doping on structural and dielectric properties of sol–gel-derived (Ba0.835Ca0.165)(Zr0.09Ti0.91)O3 thin films

We reported the effects of Mn doping on the structure and dielectric properties of (Ba0.835Ca0.165)(Zr0.09Ti0.91)O3 (BCZT) thin films prepared by sol–gel method. The (Ba0.835Ca0.165)Mnx(Zr0.09Ti0.91)1−xO3 (x=0, 0.002, 0.005, and 0.01) thin films exhibited a pure pseudo-cubic perovskite structure with random orientation. Scanning electron microscopy and atomic force microscopy observation showed that increasing Mn-doping amount caused a decrease in particle size and a cluster of the particles, while the film surface remained smooth and crack-free. Compared with the undoped film, Mn doped BCZT thin films exhibited smaller dielectric constant and lower dielectric loss. The figure of merit reached the maximum value of 16.7 with a tunability of 53.6% for the film with 0.5mol% Mn doping, when a bias electric field of 400kV/cm was applied at 100kHz. The results indicated that the Mn doped BCZT thin films are suitable for tunable microwave device applications.

Role of Mg doping on morphology and photoluminescence features of MgxZn1−xO films prepared by ultrasonic spray pyrolysis

The MgxZn1−xO thin films with thickness about several μm were fabricated for different Mg doping concentrations on p-type Si substrates by using an ultrasonic spray pyrolysis method. The morphologies, crystal structures and optical properties were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL), respectively. The SEM results indicated that the surface of MgxZn1−xO films with low Mg concentrations was flat and compact, and the roughness of films increased with Mg concentration. The XRD patterns demonstrated that the low Mg concentration MgxZn1−xO (x < 0.21) film had a wurtzite structure and the MgO phase was absent. The PL spectra revealed that UV emission has an obvious blue shift with the increase of Mg composition.

Optical parameters of Mg x Zn1−x O thin films prepared by using the sol-gel method

MgxZn1−xO thin films with different Mg contents were prepared by using the sol-gel spin-coating method. Optical parameters, such as the optical band gap, the absorption coefficient, the Urbach energy, the refractive index, the dispersion parameter, and the optical conductivity, were studied in order to investigate the effects of Mg content on the optical properties of MgxZn1−xO thin films. The optical band gap and the Urbach energy increased with increasing Mg content. The dispersion energy, the single-oscillator energy, the average oscillator wavelength, the average oscillator strength, and the refractive index at infinite wavelength of the MgxZn1−xO thin films were affected by the incorporation. Also, the optical conductivity of the MgxZn1−xO thin films increased with increasing photon energy.

Growth and characterization of ZnO and MgxZn1 − xO thin films by aerosol assisted chemical vapor deposition technique

Poly crystalline thin films of ZnO and MgxZn1−xO have been deposited on glass substrates with varying Mg-content under constant growth parameters. Aerosol assisted chemical vapor deposition technique has been adopted for the deposition of thin films in which we use the solution of zinc acetyl acetonate and magnesium acetate in isopropyl alcohol and O2 is used as the carrier gas. The depositions have been carried out at 480°C. The films were found to exhibit high transmittance (>90%), low absorbance and low reflectance in the visible regions. Absorption coefficient and thickness of the films have been determined from transmittance spectra in the ultraviolet–visible-near infrared regions by applying widely used envelope method. The energy band gap of the deposited samples increases from 3.25 to 3.75eV, with increasing Mg content in the films. The crystallographic structure of these films was analyzed by using x-ray diffraction method. The films were polycrystalline in nature with preferred (000¯1) orientation perpendicular to substrate surface. A systematic change in surface morphology is observed with increasing Mg content in the films.

Characterization and ozone-induced coloration of ZnxNi1 − xO thin films prepared by sol–gel method

ZnxNi1−xO thin films were prepared by sol–gel spin coating method onto glass substrates in combination with annealing process. Effect of zinc content on the structural, optical and ozone-induced coloration properties of as-prepared films was investigated by X-ray diffraction, field emission-scanning electron microscope, atomic force microscopy and UV–VIS spectrophotometer, respectively. X-ray diffraction results reveal that the structures of all films are still cubic NiO structure. Average grain size of ZnxNi1−xO film increases with increasing annealing temperature and its crystallization is strongly affected by Zn content. Coloration of the films was obtained after UV/ozone exposure due to a presence of ozone-induced hydroxyl groups. Significant enhancement of coloration efficiency of the films is achieved as content of Zn increases.

Characterization of ternary MgxZn1−xO thin films deposited by electron beam evaporation

MgxZn1−xO (0≤x≤1) thin films were deposited on glass and quartz substrates by electron beam evaporation and effect of the Mg content of the film on its structural, optical and electrical properties were investigated. The structure, surface morphology, optical transmittance, band gap, refractive index and electrical resistivity were found to depend on the Mg content of the film. XRD data revealed that films were polycrystalline in nature. The structure of the films having Mg content in the range of 1–0.74 was cubic, mixed cubic-hexagonal phases for x=0.47 and hexagonal phase for x=0. The composition analysis showed that Mg content in MgxZn1−xO film is high as compared to the corresponding target alloy. It was observed that the optical band gap increases from 3.3 to 6.09eV, refractive index at 550nm decreases from 1.99 to 1.75, transmittance increases from about 70% to 90% and electrical resistivity increases from 0.5 to 1.48×106Ωcm with the increase of Mg concentration in the film from 0 to 1. The results reported in this work are useful for window layer of solar cells and other optoelectronic devices.

Microstructure evolution and photoluminescence in nanocrystallineMgxZn1 − xO thin films

The effects of Mg concentration and annealing temperature on the characteristics of nanocrystallineMgxZn1 − xO thin films(where x = 0–0.4) were studied using electron microscopy and photoluminescence. The films were preparedby a sol–gel method. The solid solubility limit of MgO in ZnO for the sol–gel-derivedMgxZn1 − xO films in the present study was determined to be ∼ 20 at.%. Microstructural characterization of the films showed that the wurtzite crystallitesdecrease in size with increase in Mg concentration up to the solubility limit. Increasing Mgconcentration beyond the solubility limit resulted in a decrease in crystallinityof the films. The bandgap energy was found to increase with Mg concentrationwhereas the linewidth first increased and then decreased when the Mg concentrationwas increased beyond the solubility limit. Photoluminescence properties havebeen correlated to the microstructure of the films. A growth mechanism forMgxZn1 − xO nanocrystalline films under the present processing conditions has also been proposed.

Electrical transport in strained MgxZn1−xO:P thin films grown by pulsed laser deposition on ZnO(000‐1)

AbstractPhosphorus‐doped MgxZn1−xO thin films with various Mg content (0.07 ≤ x ≤ 0.28) and up to 0.7 at% P were grown on ZnO(000‐1) single crystals by pulsed laser deposition (PLD). In dependence on the dopant concentrations, tensile or compressively strained, in‐plane lattice matched, i.e., pseudomorphic growth of the MgZnO:P films was confirmed by high‐resolution X‐ray diffraction (HR‐XRD). All investigated, high‐quality MgZnO:P films are n‐type, also after post‐growth annealing at 850 °C. From the Hall analysis the activation energy of the dominating donors was derived, yielding values of up to 345 meV for high oxygen partial pressure during growth, and shallow donors with an activation energy of about 30 meV for low oxygen pressure. The Hall‐mobility of the MgxZn1−xO:P films at a temperature of 65 K was as high as 740 cm2/Vs, and reached values up to 190 cm2/Vs at room temperature, close to the best values reported for bulk ZnO.

Wavelength selective metal-semiconductor-metal photodetectors based on (Mg,Zn)O-heterostructures

We report on the utilization of MgyZn1−yO/MgxZn1−xO heterostructures having two different Mg-contents (0 &amp;lt; y &amp;lt; x ≤ 0.5, wurtzite structure) for the construction of wavelength selective metal-semiconductor-metal ultraviolet photodetectors. The MgxZn1−xO thin film acts as an optical edge filter and the MgyZn1−yO layer is the active layer of the devices. A FWHM of only 7 nm was achieved for a photodetector operating around 3.4 eV and the center of band (370–325 nm) was shifted by different y:x-combinations. A maximum spectral photo response of about 1.8 A/W was achieved in visible-blind range. An internal gain mechanism in the device was observed and attributed to trapping of minority carriers at PdOz/(Mg,Zn)O-interface.

Tailoring the optical properties of Mg x Zn1−x O thin films by nitrogen doping

Thin films of MgxZn1−xO and MgxZn1−xO doped with nitrogen were deposited by Radio Frequency plasma beam assisted Pulsed Laser Deposition (RF-PLD) in oxygen or oxygen-nitrogen discharge with different nitrogen/oxygen ratios. A Nd:YAG laser working at a wavelength of 266 nm, having a 10 Hz repetition rate was used for the depositions. The energy density of the incident beam was 3 J/cm2 and the RF power was set to 100 W for all the samples. X-ray Diffraction (XRD) and Spectroscopic Ellipsometry (SE) were employed to investigate the samples. The degree of crystallinity is fount to decrease with increasing the Mg concentration, while the solubility of Mg in ZnO increases by 30% in the N-doped MgxZn1−xO thin films grown by RF-PLD. Segregation of MgO phase at a Mg concentration of 30% for MgxZn1−xO thin film is detected both by XRD and SE. The band gap of the samples increases from 3.37 up to 3.57 eV with increasing the Mg concentration and the nitrogen/oxygen ratio for each Mg concentration. A dependence of the dielectric function (refractive index) on both stoichiometry and degree of crystalinity is also found, the refractive index having values between 1.7 and 2 in visible spectral range.

Fabrication and properties of p-type K doped Zn 1− xMg xO thin film

A series of K doped Zn 1− x Mg x O thin films have been prepared by pulsed laser deposition (PLD). Hall-effect measurements indicate that the films exhibit stable p-type behavior with duration of at least six months. The band gap of the K doped Zn 1− x Mg x O films undergoes a blueshift due to the Mg incorporation. However, photoluminescence (PL) results reveal that the crystallinity decreased with the increasing of Mg content. The fabricated K doped p-type Zn 0.95Mg 0.05O thin film exhibits good electrical properties, with resistivity of 15.21 Ω cm and hole concentration of 5.54 × 10 18 cm −3. Furthermore, a simple ZnO-based p–n heterojunction was prepared by deposition of a K-doped p-type Zn 0.95Mg 0.05O layer on Ga-doped n-type ZnO thin film with low resistivity. The p–n diode heterostructure exhibits typical rectification behavior of p–n junctions.

Hydrogen Production via Chemical Looping Redox Cycles Using Atomic Layer Deposition-Synthesized Iron Oxide and Cobalt Ferrites

Iron oxide (γ-Fe2O3) and cobalt ferrite (CoxFe3−xO4) thin films were synthesized via atomic layer deposition (ALD) on high surface-area (50 m2 g−1) m-ZrO2 supports. The oxide films were grown by sequentially depositing iron oxide and cobalt oxide, adjusting the number of iron oxide to cobalt oxide cycles to achieve a desired stoichiometry. High resolution transmission electron microscopy and X-ray diffraction indicate that the films are crystalline and have a thickness of ∼2.5 nm. Raman spectroscopy was used to confirm the predominance of the spinel phase in the case of cobalt ferrite. Films were chemically reduced at 600 °C using mixtures of H2, CO, and CO2. The evolution of oxide phases as a function of time during this reduction was observed using in situ X-ray diffraction, showing that γ-Fe2O3 are reduced only to FeO, while CoxFe3−xO4 are reduced all the way to a Co/Fe alloy. Subsequent water splitting measurements in a stagnation flow reactor yielded peak H2 rates exceeding virtually all of those rep...

Materials and electrical characterization of physical vapor deposited LaxLu1−xO3 thin films on 300 mm silicon

La x Lu 1 − x O 3 thin films were deposited on 300 mm silicon wafers by physical vapor deposition and fabricated into field-effect transistors using a gate-first process flow. The films were characterized using transmission electron microscopy, Rutherford backscattering spectrometry, and synchrotron x-ray diffraction. The results show the films remain amorphous even at temperatures of 1000 °C. The dielectric properties of LaxLu1−xO3 (0.125≤x≤0.875) thin films were evaluated as a function of film composition. The amorphous LaxLu1−xO3 thin films have a dielectric constant (K) of 23 across the composition range. The inversion thickness (Tinv) of the LaxLu1−xO3 thin films was scaled to &amp;lt;1.0 nm.

Effects of Mg on the electrical characteristics and thermal stability of MgxZn1−xO thin film transistors

The effects of the Mg composition (x=0, 0.06, and 0.10) on the electrical characteristics and thermal stability of MgxZn1−xO thin film transistors (TFTs) are investigated. The Mg0.06Zn0.94O TFT shows the smallest subthreshold slope and highest field effect mobility. The O1s spectra of x-ray photoelectron spectroscopy measurements indicate that the oxygen vacancies are reduced in Mg0.06Zn0.94O relative to a pure ZnO channel device. Mg0.06Zn0.94O TFTs also show higher thermal stability compared to the pure ZnO TFTs, which is mainly attributed to the suppression of oxygen vacancies in the channel.

Effects of oxygen partial pressure and substrate temperature on the structure and optical properties of Mg xZn 1− xO thin films prepared by magnetron sputtering

Deposited with different oxygen partial pressures and substrate temperatures, Mg x Zn 1− x O thin films were prepared using a Mg 0.6Zn 0.4O ceramic target by magnetron sputtering. The structural and optical properties of the prepared thin films were investigated. The X-ray diffraction spectra reveal that all the films on quartz substrate are grown along (2 0 0) orientation with cubic structure. The lattice constant decreases and the crystallite size increases with the increase of substrate temperature. Both energy dispersive X-ray spectroscopy and calculated results suggest the ratio of Mg/Zn increases with increasing substrate temperature. The thin film deposited with T s = 500 °C has a minimal rms roughness of 7.37 nm. The transmittance of all the films is higher than 85% in the visual region. The optical band gap is not sensitive to the oxygen partial pressure, while it increases from 5.63 eV for T s = 100 °C to 5.95 eV for T s = 700 °C. In addition, the refractive indices calculated from transmission spectra are sensitive to the substrate temperature. The photoluminescence spectra of Mg x Zn 1− x O thin films excited by 330 nm ultraviolet light indicate that the peak intensity of the spectra is influenced by the oxygen partial pressure and substrate temperature.

Synthesis and characterization of nanocrystalline Zn 1− xM xO (M = Ni, Cr) thin films for efficient photoelectrochemical splitting of water under UV irradiation

Nanocrystalline thin films of Zn 1− x M x O (M = Ni, Cr) were deposited on glass substrate by sol–gel method. To a solution of zinc acetate 2-hydrate in dimethyl formamide, calculated quantities of nickel nitrate or chromium acetate were added. The clear solution, obtained after 2 h of continuous stirring, was coated on conducting glass (ITO plates). After preannealing at 250 °C to remove organic impurities, films were sintered at 400, 500 and 600 °C. XRD analysis reveals dominant evolution of hexagonal ZnO with a possible simultaneous growth of meta-stable cubic ZnO. AFM analysis indicated preferential growth of nanocrystallites along c-axis, while SEM analysis confirmed films having uniform morphology. Optical characterization led to two band gap values; one matching with the band gap of bulk ZnO and the second slightly higher, which suggest quantum confinement effect in nanocrystallites. Ni and Cr incorporation influenced the two band gap energies differently. Photoelectrochemical (PEC) splitting of water was attempted, using prepared thin films as working electrode, in conjunction with Pt counter electrode and saturated calomel reference electrode along with 150 W Xenon Arc light source and aqueous solution of NaOH (0.01 M). Results indicate Ni:ZnO films yielding improved photoresponse compared to Cr:ZnO films. Ni:ZnO (5 % at.) films sintered at 600 °C resulted in significantly enhanced photocurrent due to improved optical absorption and decrease in resistivity.

Optical properties of BiCrxFe1−xO3 films grown by sol-gel method

The BiCrxFe1−xO3 thin films were fabricated on Si substrate by sol-gel method with x range from 0 to 0.05. X-ray diffraction analysis shows that both pure BiFeO3 thin film and Cr-doped BiFeO3 thin films have rhombohedral structure with space group R3c. Moreover, the influence of different values of x on the extinction coefficient and refractive index were investigated in order to exploit their possible application in optoelectronic devices. The optical constants of the Cr-doped BiFeO3 thin films in the wavelength range 500–1100 nm were obtained by spectroscopic ellipsometry, and the band-gap energy of BiCr0.03Fe0.97O3 was found to be 2.40 ±0.02 eV, and that of BiCr0.05Fe0.95O3 was 2.30 ±0.02 eV.

Ultraviolet photodetector fabricated from metal-organic chemical vapor deposited MgZnO

Wurtzite MgxZn1−xO thin films were grown on sapphire substrates by low-pressure metal-organic chemical vapor deposition. The as-grown films show clear exciton absorption at room temperature until the composition x=0.25. A representative metal–semiconductor–metal structured photodetectors were fabricated from Mg0.06Zn0.94O film showed a peak responsivity of about 14.62 A/W at 340nm, and the ultraviolet-visible rejection ratio (R340 nm/R400 nm) was more than two orders of magnitude at 3V bias. The photodetector showed fast photoresponse with a rise time of 20ns and a fall time of 400ns.

Characterization of MgxZn1 − xO thin films grown on sapphire substrates by metalorganic chemical vapor deposition

Wurtzite-structure MgxZn1−xO materials with five different compositions of x from 0 to 0.14 were grown on sapphire substrates by metalorganic chemical vapor deposition. It was found that increasing Mg content in the MgxZn1−xO not only increased the band gap energy of the film but was also beneficial to the epitaxial growth of p-type MgxZn1−xO without using any doping sources. In addition, the combined ultraviolet photoluminescence (PL) and Raman scattering spectra were measured with PL–Raman signals obtained together, showing a blue-shift of PL band and variation of resonant Raman multi-order longitudinal optical phonon modes with an increase of Mg content.

Effect of Li doping in NiO thin films on its transparent and conducting properties and its application in heteroepitaxial p-n junctions

Li doped NiO (LixNi1−xO) thin films were epitaxially grown along [111] orientation on c-sapphire by pulsed laser deposition. The structural, electrical, and optical properties of the films were investigated using x-ray diffraction, four probe technique, and UV-visible spectra, respectively. The epitaxial growth of [111] Li doped NiO on [0001] sapphire was determined by using high resolution x-ray Φ scan. Effects of the deposition condition and Li doping concentration variations on the electrical and optical properties of Li doped NiO films were also investigated. The analysis of the resistivity data show that doped Li ions occupy the substitutional sites in the films, enhancing the p-type conductivity. The minimum resistivity of 0.15 Ω cm was obtained for Li0.07Ni0.93O film. The activation energy of Li doped NiO films were estimated to be in the range of 0.11–0.14 eV. Based upon these values, a possible electrical transport mechanism is discussed. A p-n heterojunction has also been fabricated for the optimized p-Li doped NiO with n-ZnO. The insertion of i-MgZnO between the p and n layer led to improved current-voltage characteristics due to reduced leakage current. In the diode architecture, a heteroepitaxial relationship of [111]NiO‖[0001]MgZnO‖[0001]ZnO‖[0001]GZO‖[0001]Al2O3 among the layers was obtained. The p-i-n heterojunction showed good rectification behavior with turn on voltage of 2.8 V and breakdown voltage of 8.0 V.