Characteristics of Ti0.97Co0.03O2:Sb0.01 dilute magnetic semiconducting thin films deposited at 500 °C by pulsed laser deposition

Epitaxial Ti_0.97Co_0.03O₂:Sb_0.01(TCO:Sb) films were deposited on R-Al₂O₃ (1 1 0 2) substrates at 500 °C in various deposition pressures by pulsed laser deposition. The solubility of cobalt within the films increases with decreasing deposition pressure at a deposition temperature of 500 °C. The TCO:Sb films deposited at 5×10⁻⁶ Torr exhibit a p-type anomalous Hall effect having a hole concentration of 6.1×10²²/cm³ at 300 K. On the other hand, films deposited at 4×10⁻⁴ Torr exhibits an n-type anomalous Hall effect having an electron concentration of about 1.1×10²¹/cm³. p- or n-type DMS characteristics depends on the change of the structure of TCO:Sb films and the solubility of Co is possible by controlling the deposition pressure.     

Influence of oxygen partial pressure on the properties of pulsed laser deposited nanocrystalline zirconia thin films

ZrO₂ thin films were deposited at various oxygen partial pressures (2.0 × 10⁻⁵-3.5 × 10⁻¹ mbar) at 973 K on (1 0 0) silicon and quartz substrates by pulsed laser deposition. The influence of oxygen partial pressure on structure, surface morphology and optical properties of the films were investigated. X-ray diffraction results indicated that the films are polycrystalline containing both monoclinic and tetragonal phases. The films prepared in the oxygen partial pressures range 2.0 × 10⁻⁵-3.5 × 10⁻¹ mbar contain nanocrystals of sizes in the range 54-31 nm for tetragonal phase. The peak intensity of the tetragonal phase decreases with the increase of oxygen partial pressures. Surface morphology of the films examined by AFM shows the formation of nanostructures. The RMS surface roughness of the film prepared at 2.0 × 10⁻⁵ mbar is 1.3 nm while it is 3.2 nm at 3.5 × 10⁻¹ mbar. The optical properties of the films were investigated using UV-visible spectroscopy technique in the wavelength range of 200-800 nm. The refractive index is found to decrease from 2.26 to 1.87 as the oxygen partial pressure increases from 2.0 × 10⁻⁵ to 3.5 × 10⁻¹ mbar. The optical studies show two different absorption edges corresponding to monoclinic and tetragonal phases.     

Transparent conducting Sn-doped Ga1.4In0.6O3 films prepared on α-Al2O3 (0 0 0 1) by MOCVD

Sn-doped Ga_1.4In_0.6O₃ films have been prepared on α-Al₂O₃ (0 0 0 1) substrates by the metalorganic chemical vapor deposition (MOCVD) method. The Sn-doping was varied from 0% to 7% (atomic ratio). Polycrystalline films with resistivity of 4.9 × 10⁻³Ω cm, carrier concentration of 5.9 × 10¹⁹ cm⁻³ and Hall mobility of 21.4 cm² v⁻¹ s⁻¹ was obtained at 5 at.% of Sn concentration. The average transmittance for the Sn-doped Ga_1.4In_0.6O₃ films in the visible range was over 90%. The bandgap of the films varies from 3.85 to 4.21 eV.     

A study of the optical properties of titanium oxide films prepared by dc reactive magnetron sputtering

TiO₂ thin films were deposited on the glass substrates by dc reactive magnetron sputtering technique at different sputtering pressures (2 × 10⁻³ to 2 × 10⁻² mbar). The films prepared at low pressures have an anatase phase, and the films prepared at high pressures have an amorphous phase. The optical properties were studied by measuring the transmittance and the ellipsometric spectra. The optical constants of the films in the visible range were obtained by fitting the transmittance combined with the ellipsometry measurements using the classical model with one oscillator. The refractive index of the films decreases from 2.5 until 2.1 as the sputtering pressure increases from 2 × 10⁻³ to 2 × 10⁻² mbar. The films prepared at the pressure higher than 6 × 10⁻³ mbar show a volume inhomogeneity. This volume inhomogeneity has been calculated by fitting the transmittance and the ellipsometric spectra. The volume inhomogeneity of the film prepared at the highest sputtering pressure is about 10%. Although the films prepared at high pressures show a large volume inhomogeneity, they have low extinction coefficients. It is suggested that the anatase phase results in more light scattering than amorphous phase does, and then a high extinction coefficient.     

PLD of Fe3O4 thin films: Influence of background gas on surface morphology and magnetic properties

Ablation of Fe₃O₄ targets has been performed using a pulsed UV laser (KrF, λ = 248 nm, 30 ns pulse duration) onto Si(100) substrates, in reactive atmospheres of O₂ and/or Ar, with different oxygen partial pressures. The as-deposited films were characterised by atomic force microscopy (AFM), X-ray diffraction (XRD), conversion electron Mössbauer spectroscopy (CEMS) and extraction magnetometry, in order to optimise the deposition conditions in the low temperature range. The results show that a background mixture of oxygen and argon improves the Fe:O ratio in the films as long as the oxygen partial pressure is maintained in the 10⁻² Pa range. Thin films of almost stoichiometric single phase polycrystalline magnetite, Fe_2.99O₄, have been obtained at 483 K and working pressure of 7.8 × 10⁻² Pa, with a high-field magnetization of ∼490 emu/cm³ and Verwey transition temperature of 112 K, close to the values reported in the literature for bulk magnetite.     

Characterization of single-crystalline In2O3 films deposited on Y-stabilized ZrO2 (1 0 0) substrates by MOCVD

Epitaxial In₂O₃ films have been deposited on Y-stabilized ZrO₂ (YSZ) (1 0 0) substrates by metalorganic chemical vapor deposition (MOCVD). The films were deposited at different substrate temperatures (450-750 °C). The film deposited at 650 °C has the best crystalline quality, and observation of the interface area shows a clear cube-on-cube epitaxial relationship of In₂O₃(1 0 0)||YSZ(1 0 0) with In₂O₃[0 0 1]||YSZ[0 0 1]. The Hall mobility of the single-crystalline In₂O₃ film deposited at 650 °C is as high as 66.5 cm² V⁻¹ s⁻¹ with carrier concentration of 1.5 × 10¹⁹ cm⁻³ and resistivity of 6.3 × 10⁻³ Ω cm. The absolute average transmittance of the obtained films in the visible range exceeds 95%.     

Mössbauer study of the pulsed laser deposition of polycrystalline magnetic films

Polycrystalline magnetite films were grown by pulsed laser deposition from an α-Fe₂O₃ target at 450 °C. X-ray diffraction analysis showed the presence of a single-phase spinel film with preferred orientation when the deposition was performed at low oxygen pressure. Mössbauer spectroscopy at both room temperature and 120 K was used to identify the hyperfine parameters of the magnetite film deposited on glass at 450 °C and at an oxygen partial pressure of 10⁻⁴ Torr.     

Electrical properties of La2O3 thin films grown on TiN/Si substrates via atomic layer deposition

The electrical as well as the structural properties of La₂O₃ thin films on TiN substrates were investigated. Amorphous stoichiometric La₂O₃ thin films were grown at 300 °C via atomic layer deposition technique by using lanthanum 2,2,6,6-tetramethyl-3,5-heptanedione [La(TMHD)₃] and H₂O as precursors. Post-annealing of the grown film induced dramatic changes in structural and the electrical properties. Crystalline phases of the La₂O₃ film emerged with the increase of the post-annealing temperature. Metal-insulator-metal (MIM) capacitor was fabricated to measure the electrical properties of the grown film. The dielectric constant of the La₂O₃ thin films increased with annealing temperature to reach the value of 17.3 at 500 °C. The leakage current density of the film post-annealed at 400 °C was estimated to be 2.78 × 10⁻¹⁰ and 2.1 × 10⁻⁸ A/cm² at ±1 V, respectively.     

Characterization of Y2O3 gate dielectric on n-GaAs substrates

Physical and electrical properties of sputtered deposited Y₂O₃ films on NH₄OH treated n-GaAs substrate are investigated. The as-deposited films and interfacial layer formation have been analyzed by using X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). It is found that directly deposited Y₂O₃ on n-GaAs exhibits excellent electrical properties with low frequency dispersion (<5%), hysteresis voltage (0.24 V), and interface trap density (3 × 10¹² eV⁻¹ cm⁻²). The results show that the deposition of Y₂O₃ on n-GaAs can be an effective way to improve the interface quality by the suppression on native oxides formation, especially arsenic oxide which causes Fermi level pinning at high-k/GaAs interface. The Al/Y₂O₃/n-GaAs stack with an equivalent oxide thickness (EOT) of 2.1 nm shows a leakage current density of 3.6 × 10⁻⁶ A cm⁻² at a V_FB of 1 V. While the low-field leakage current conduction mechanism has been found to be dominated by the Schottky emission, Poole-Frenkel emission takes over at high electric fields. The energy band alignment of Y₂O₃ films on n-GaAs substrate is extracted from detailed XPS measurements. The valence and conduction band offsets at Y₂O₃/n-GaAs interfaces are found to be 2.14 and 2.21 eV, respectively.     

Studies on the effect of nozzle-to-substrate distance on the structural, electrical and optical properties of spray deposited CdIn2O4 thin films

The physical, chemical, electrical and optical properties of as-deposited and annealed CdIn₂O₄ thin films deposited using spray pyrolysis technique at different nozzle-to-substrate distances are reported. These films are characterized by X-ray diffraction, XPS, SEM, PL, Hall effect measurement techniques and optical absorption studies. The average film thickness lies within 600-800 nm range. The X-ray diffraction study shows that films exhibit cubic structure with orientation along (3 1 1) plane. The XPS study reveals that CdIn₂O₄ films are oxygen deficient. Room temperature PL indicates the presence of green shift with oxygen vacancies. The typical films show very smooth morphology. The best films deposited with optimum nozzle-to-substrate distance (NSD) of 30 cm, has minimum resistivity of 1.3 × 10⁻³ Ω cm and 2.6 × 10⁻⁴ Ω⁻¹ figure of merit. The band gap energy varies from 3.04 to 3.2 eV with change in NSD for annealed films. The effect of NSD as well as the annealing treatment resulted into the improvement of the structural, electrical and optical properties of the studied CdIn₂O₄ thin films.     

Growth of Ga-doped ZnO films with ZnO buffer layer by sputtering at room temperature

Gallium-doped zinc oxide films have been grown on glass substrates with and without ZnO buffer layers by r.f. magnetron sputtering at room temperature. In this approach, the grey relational Taguchi method analysis is adopted to solve the coating process with multiple deposition qualities. Optimal coating parameters can then be determined by using the gray relational grade as a performance index. The GZO coating parameters (r.f. power, sputtering pressure, O₂/(Ar+O₂) flow-rate ratios, and deposition time) are optimized, by taking into account the multiple performance characteristics (structural, morphological, deposition rate, electrical resistivity, and optical transmittance). The results indicate that with the grey relational Taguchi method, the electrical resistivity of GZO films is reduced from 9.23×10⁻³ to 5.77×10⁻³ Ω cm and optical transmittance increases from 79.42% to 82.95%, respectively. The ZnO buffer layer can reduce the electrical resistivity of GZO films from 5.77×10⁻³ to 2.38×10⁻³ Ω cm. It can be anticipated that room temperature deposition enables film deposition onto polymeric substrates for flexible optoelectronic devices.     

Investigation of chemical bath deposition of CdO thin films using three different complexing agents

Chemical bath deposition of CdO thin films using three different complexing agents, namely ammonia, ethanolamine, and methylamine is investigated. CdSO₄ is used as Cd precursor, while H₂O₂ is used as an oxidation agent. As-grown films are mainly cubic CdO₂, with some Cd(OH)₂ as well as CdO phases being detected. Annealing at 400 °C in air for 1 h transforms films into cubic CdO. The calculated optical band gap of as-grown films is in the range of 3.37-4.64 eV. Annealed films have a band gap of about 2.53 eV. Rutherford backscattering spectroscopy of as-grown films reveals cadmium to oxygen ratio of 1.00:1.74 ± 0.01 while much better stoichiometry is obtained after annealing, in accordance with the X-ray diffraction results. A carrier density as high as 1.89 × 10²⁰ cm⁻³ and a resistivity as low as 1.04 × 10⁻² Ω-cm are obtained.     

Preparation of transparent conductive TiO2:Nb thin films by pulsed laser deposition

This study investigated the optical and electrical properties of Nb-doped TiO₂ thin films prepared by pulsed laser deposition (PLD). The PLD conditions were optimized to fabricate Nb-doped TiO₂ thin films with an improved electrical conductivity and crystalline structure. XRD analyses revealed that the deposition at room temperature in 0.92 Pa O₂ was suitable to produce anatase-type TiO₂. A Nb-doped TiO₂ thin film attained a resistivity as low as 6.7 × 10⁻⁴ Ω cm after annealing at 350 °C in vacuum (<10⁻⁵ Pa), thereby maintaining the transmittance as high as 60% in the UV-vis region.     

Chemical spray pyrolysis deposition and characterization of p-type CuCr1−xMgxO2 transparent oxide semiconductor thin films

A chemical spray pyrolysis technique for deposition of p-type Mg-doped CuCrO₂ transparent oxide semiconductor thin films using metaloorganic precursors is described. As-deposited films contain mixed spinel CuCr₂O₄ and delafossite CuCrO₂ structural phases. Reduction in spinel CuCr₂O₄ fraction and formation of highly crystalline films with single phase delafossite CuCrO₂ structure is realized by annealing at temperatures ?700 °C in argon. A mechanism of synthesis of CuCrO₂ films involving precursor decomposition, oxidation and reaction between constituent oxides in the spray deposition process is presented. Post-annealed CuCr_0.93Mg_0.07O₂ thin films show high (?80%) visible transmittance and sharp absorption at band gap energy with direct and indirect optical band gaps 3.11 and 2.58 eV, respectively. Lower (∼450 °C) substrate temperature formed films are amorphous and yield lower direct (2.96 eV) and indirect (2.23 eV) band gaps after crystallization. Electrical conductivity of CuCr_0.93 Mg_0.07O₂ thin films ranged 0.6-1 S cm⁻¹ and hole concentration ∼2×10¹⁹ cm⁻³ determined from Seebeck analysis. Temperature dependence of conductivity exhibit activation energies ∼0.11 eV in 300-470 K and ∼0.23 eV in ?470 K region ascribed to activated conduction and grain boundary trap assisted conduction, respectively. Heterojunction diodes of the structure Au/n-(ZnO)/p-(CuCr_0.93Mg_0.07O₂)/SnO₂ (TCO) were fabricated which show potential for transparent wide band gap junction device.     

Influence of substrate temperature and post-treatment on the properties of ZnO:Al thin films prepared by pulsed laser deposition

Highly transparent conductive Al₂O₃ doped zinc oxide (AZO) thin films have been deposited on the glass substrate by pulsed laser deposition technique. The effects of substrate temperature and post-deposition annealing treatment on structural, electrical and optical properties of AZO thin films were investigated. The experimental results show that the electrical resistivity of films deposited at 240 °C is 6.1 × 10⁻⁴ Ω cm, which can be further reduced to as low as 4.7 × 10⁻⁴ Ω cm by post-deposition annealing at 400 °C for 2 h in argon. The average transmission of AZO films in the visible range is 90%. The optical direct band gap of films was dependent on the substrate temperature and the annealing treatment in argon. The optical direct band gap value of AZO films increased with increasing annealing temperature.     

Fabrication of p-type Li-doped ZnO films by pulsed laser deposition

p-Type ZnO thin films have been realized via doping Li as acceptor by using pulsed laser deposition. In our experiment, Li₂CO₃ was used as Li precursor, and the growth temperature was varied from 400 to 600 °C in pure O₂ ambient. The Li-doped ZnO film prepared at 450 °C possessed the lowest resistivity of 34 Ω cm with a Hall mobility of 0.134 cm² V⁻¹ s⁻¹ and hole concentration of 1.37 × 10¹⁸ cm⁻³. X-ray diffraction (XRD) measurements showed that the Li-doped ZnO films grown at different substrate temperatures were of completely (0 0 2)-preferred orientation.     

Influence of [S2O3]/[Sm] on Sm2S3 thin films deposited by liquid phase deposition method on self-assembled monolayers

Sm₂S₃ thin films were prepared on Si (1 0 0) substrates using SmCl₃ and Na₂S₂O₃ as precursors by liquid phase deposition method on self-assembled monolayers. The influence of the molar concentration ratio of [S₂O₃²⁻]/[Sm³⁺] on the phase compositions, surface morphologies and optical properties of the as-deposited films were investigated. The as-deposited Sm₂S₃ thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), ultraviolet-visible (UV-vis) and photoluminescence spectrum (PL). Results show that it is important to control the [S₂O₃²⁻]/[Sm³⁺] during the deposition process and monophase Sm₂S₃ thin films with orientation growth along (0 1 1) direction can be achieved when [S₂O₃²⁻]/[Sm³⁺] = 2.0, pH 3.0, with citric acid as a template agent. The as-deposited thin films exhibit a dense and crystalline surface morphology. Good transmittance in the visible spectrum and excellent absorbency of ultraviolet light of the thin films are observed, and the band gap of the thin films first decrease and then increase with the increase of the [S₂O₃²⁻]/[Sm³⁺]. The as-deposited thin films also exhibit red photoluminescence properties under visible light excitation. With the increase of the [S₂O₃²⁻]/[Sm³⁺] in the deposition solution, the PL properties of Sm₂S₃ thin films are obviously improved.     

Microstructural, optical and spectroscopic studies of laser ablated nanostructured tantalum oxide thin films

Thin films of tantalum oxide (Ta₂O₅) have been prepared by pulsed laser deposition technique at different substrate temperatures (300-973 K) under vacuum and under oxygen background (pO₂ = 2 × 10⁻³ mbar) conditions. The films are annealed at a temperature of 1173 K. The as-deposited films are amorphous irrespective of the substrate temperature. XRD patterns show that on annealing, the films get crystallized in orthorhombic phase of tantalum pentoxide (β-Ta₂O₅). The annealed films deposited at substrate temperatures 300 K and 673 K have a preferred orientation along (0 0 1) plane, whereas the films deposited at substrate temperatures above 673 K show a preferred orientation along (2 0 0) crystal plane. The deposited films are characterized using techniques such as grazing incidence X-ray diffraction (GIXRD), atomic force microscopy (AFM), micro-Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy and UV-visible spectroscopy. FTIR and micro-Raman measurements confirm the presence of Ta-O, Ta-O-Ta and O-Ta-O bands in the films. Grain size calculations from X-ray diffraction and AFM show a decrease with increase in substrate temperature. The variation of transmittance and band gap with film growth parameters are also discussed.     

Structure and optoelectronic properties of multi-element oxide thin film

This paper focuses on analyzing structural and optoelectronic properties of (ZnSnCuTiNb)_1 − xO_x films. The results of XRD and HRTEM indicate that the (ZnSnCuTiNb)_1 − xO_x films are all of amorphous without any multi-phase structure. XPS analysis confirms that the increase of the oxygen content makes the cations electron binding energy higher, suggesting the removal of valence electrons or the extent of oxidation can change the optoelectronic properties of the films. The (ZnSnCuTiNb)_1 − xO_x films possess the characteristics of optoelectronic semiconductor whose oxygen content are 51.6 and 56 atom%. These films have carrier concentrations of 2.62 × 10²⁰ and 1.37 × 10¹⁷ cm⁻³, and conductivities (σ) of 57.2 and 9.45 × 10⁻³ (Ω cm)⁻¹, and indirect band gaps of 1.69 and 2.26 eV, respectively. They are n-type oxide semiconductors.     

Structure and properties of transparent conductive doped ZnO films by pulsed laser deposition

High quality transparent conductive ZnO thin films were deposited on quartz glass substrates using pulsed laser deposition (PLD). We varied the growth conditions such as the substrate temperature and oxygen pressure. X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS), and atomic force microscopy (AFM) measurements were done on the samples. All films show n-type conduction, the best transparent conductive oxide (TCO) performance (Al-doped ZnO = 1.33 × 10⁻⁴ Ω cm, Ga-doped ZnO = 8.12 × 10⁻⁵ Ω cm) was obtained on the ZnO film prepared at pO₂ = 5 mTorr and T_s = 300 °C.