Ultrathin Al-doped transparent conducting zinc oxide films fabricated by pulsed laser deposition

Al-doped transparent conducting zinc oxide (AZO) films, approximately 20-110 nm-thick, were deposited on glass substrates at substrate temperatures between 200 and 300 °C by pulsed laser deposition (PLD) using an ArF excimer laser (λ = 193 nm). When fabricated at a substrate temperature of 260 °C, a 40-nm-thick AZO film showed a low resistivity of 2.61 × 10^− 4 Ω·cm, carrier concentration of 8.64 × 10²⁰ cm^− 3, and Hall mobility of 27.7 cm²/V·s. Furthermore, for an ultrathin 20-nm-thick film, a resistivity of 3.91 × 10^− 4 Ω·cm, carrier concentration of 7.14 × 10²⁰ cm^− 3, and Hall mobility of 22.4 cm²/V·s were obtained. X-ray diffraction (XRD) spectra, obtained by the θ-2θ method, of the AZO films grown at a substrate temperature of 260 °C showed that the diffraction peak of the ZnO (0002) plane increased as the film thickness increased from 20 to 110 nm. The full-width-at-half-maximum (FWHM) values were 0.5500°, 0.3845°, and 0.2979° for film thicknesses of 20, 40, and 110 nm, respectively. For these films, the values of the average transmittance in visible light wavelengths (400-700 nm) were 95.1%, 94.2%, and 96.6%, respectively. Field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) observations showed that even the 20-nm-thick films did not show island structures. In addition, exfoliated areas or vacant and void spaces were not observed for any of the films.     

Copper doped nickel oxide transparent p-type conductive thin films deposited by pulsed plasma deposition

Transparent p-type conductive Ni_0.9Cu_0.1O thin films were prepared by pulsed plasma deposition (PPD) method. The effects of substrate temperature and oxygen pressure on the structural, electrical and optical properties of the films were investigated respectively. The film deposited at room temperature exhibits the highest conductivity of 5.17 S cm⁻¹, with an average transmittance of 60% in the visible region. A transparent p-Ni_0.9Cu_0.1O/n-In₂O₃:W (IWO) hetero-junction diode was fabricated exhibiting rectifying current-voltage characteristics.     

Thin films of In2O3 by atomic layer deposition using In(acac)3

Thin films of indium oxide have been deposited using the atomic layer deposition (ALD) technique using In(acac)₃ (acac = acetylacetonate, pentane-2,4-dione) and either H₂O or O₃ as precursors. Successful growth using In(acac)₃ is contradictory to what has been reported previously in the literature [J.W. Elam, A.B.F. Martinson, M.J. Pellin, J.T. Hupp, Chem. Mater. 18 (2006) 3571.]. Investigation of the dependence of temperature on the deposition shows windows where the growth rates are relatively unaffected by temperature in the ranges 165–200 °C for In(acac)₃ and H₂O, 165–225 °C for In(acac)₃ and O₃. The growth rates obtained are of the order 20 pm/cycle for In(acac)₃ and H₂O, 12 pm/cycle for In(acac)₃.     

When Pt meets BaTiO3: Interaction between metal nanoparticles and oxide thin films

With the help of a focused ion beam, we can control the location of BaTiO₃ (BTO) grains during pulsed laser deposition by the use of metal nanoparticles seeds as templates. The metal nanoparticles act as nucleation sites on which to grow the BTO grains. Combined with recent work where control of BTO grain orientation was successfully demonstrated [Thin Solid Films, 518, 5806 (2010)], we can widely use the method to deposit various oxide nanoparticles in particular locations with controlled size and orientation. Such an approach could be useful for nanotechnology and device fabrication.     

Physical properties of CuCrO2 films prepared by pulsed laser deposition

High-quality CuCrO₂ films were prepared by pulsed laser deposition (PLD). The film deposited with the pulse energy density (PED) of 2 mJ/cm² is highly c-axis oriented. The refractive index of the CuCrO₂ films is about 1.29 obtained by transmission spectra of the films, which implies that the CuCrO₂ film will be a potential antireflection coating in visible light. The films prepared with different PEDs show different conduction mechanism, which suggested the different band structure between these CuCrO₂ films.     

Growth and characterisation of CaCu2Ox thin films by pulsed injection MOCVD

Oxides with the structure MCu₂O₂ (M = Ca, Ba, Mg and Sr) are promising materials for the development of new p-type transparent conducting oxide thin films. This paper reports preliminary results on the growth and characterisation of CaCu₂O_x thin films by pulsed injection MOCVD. By using as precursors calcium and copper tetramethylheptanedionate dissolved in meta-xylene, mixed calcium-copper films have been grown in the temperature range from 450 °C to 550 °C. At these temperatures, deposited films exhibited a high mirror reflection effect, good adherence and were reasonably uniform with the cationic composition of the films being easily controlled by adjusting the copper-calcium ratio in the precursor solution. In CaCu₂O₂, copper is in the Cu¹⁺ oxidation state and depending on the oxygen partial pressure used, the films either contained CaCu₂O₃ or a mixture of CaO, CuO and Cu₂O. Optimisation of annealing conditions increased the presence of Cu¹⁺ in the film. Films had a maximum transmittance of 50% in the visible range and were highly resistive. Appropriate annealing conditions reduced the resistivity of the films.     

Structural and surface property study of sputter deposited transparent conductive Nb-doped titanium oxide films

We have investigated structural and surface property of transparent conductive Nb-doped titanium oxides (TNO) thin film with high conductivity of 10⁻⁴ Ω cm order which were made by RF-magnetron sputtering at high deposition rates followed by an annealing in vacuum. The grain sizes of TNO evaluated by atomic force microscope were found to become larger by annealing at temperature higher than 500 °C. The measured work functions of the TNO films using ultra-violet light photoelectron spectroscopy were 5.02-5.47 eV, and depended on TNO grain size and on the amount of surface weakly bound oxygen that was estimated from peak area intensities of O(1 s) X-ray photoelectron spectra.     

Controlled growth and characteristics of single-phase Cu2O and CuO films by pulsed laser deposition

Copper oxide, Cu₂O and CuO, thin films have been synthesized on Si (100) substrates using pulsed laser deposition method. The influences of substrate temperature and oxygen pressure on the structural properties of copper oxide films were discussed. The X-ray diffraction results show that the structure of the films changes from Cu₂O to CuO phase with the increasing of the oxygen pressure. It is also found that the (200) and (111) preferred Cu₂O films can be modified by changing substrate temperature. The formation of Cu₂O and CuO films are further identified by Fourier transform infrared spectroscopy. For the Cu₂O films, X-ray photoelectron spectroscopic studies indicate the presence of CuO on the surface. In addition, the optical gaps of Cu₂O and CuO films have been determined by measuring the transmittance and reflectance spectra.     

Synthesis of SrSnO3 thin films by pulsed laser deposition: Influence of substrate and deposition temperature

SrSnO₃ thin films were prepared by pulsed laser deposition on amorphous silica and single crystal substrates of R-sapphire, (100)LaAlO₃ and (100)SrTiO₃. High quality epitaxial (100) oriented films were obtained on LaAlO₃ and SrTiO₃ while a texture was revealed for films on sapphire deposited at the same deposition temperature of 700 °C. Amorphous films were obtained on silica but a post annealing at 800 °C induced crystallization with a random orientation. The screening of deposition temperature showed epitaxial features on SrTiO₃ from 650 °C while no crystallization was observed at 600 °C. The influence of substrate and deposition temperature was confirmed by Scanning Electron Microscopy and Atomic Force Microscopy observations.     

Structural and optical analysis of nanocrystalline thin films of mixed rare earth oxides (Y1-xErx)2O3

Nanocrystalline thin films of mixed rare earth oxides (Y_1-xEr_x)₂O₃(0.1 ≤ x ≤ 1) were deposited by electron beam evaporation technique on polished fused silica glass at different substrate temperatures (200-500 °C). The effect of the substrate temperature as well as the mixing parameter (x) on the structural and optical properties of these films has been investigated by using X-ray diffraction (XRD), energy dispersive x-ray analysis and optical spectrophotometry. XRD investigation shows that mixed rare earth oxides film (Y_1-xEr_x)₂O₃ grown at lower substrate temperature (T_s ≤ 300 °C) are poorly crystalline, whereas films grown at higher substrate temperatures (T_s ≥ 400 °C) tend to have better crystallinity. Furthermore, the mixing parameter (x) was found to stabilize the cubic phase over the entire of 0.1 ≤ x ≤ 1. The crystallite size of the films was found to vary in the range from 25 to 39 nm. Optical band gap of the films was deterimined by analysis of the absoprtion coeffifcient. For films deposited at different substrate temperatures direct and indirect transitions occur with energies varied from 5.29 to 5.94 eV and from 4.23 to 4.51 eV, respectively. However, films of different composition x, give optical band gap varied from 6.14 to 5.86 eV for direct transition and from 5.23 to 4.22 eV for indirect transitions. Consequently, one may conclude that it is possible to tune the energy band gap by relative fraction of constituent oxides. It was found that optical constants increase with increasing the substrate temperature. Nevertheless, the values of n and k decrease with increasing the mixing parameter, x.     

High mobility, transparent, conducting Gd-doped In2O3 thin films by pulsed laser deposition

Highly transparent and conducting thin films of gadolinium doped indium oxide, which have high electron mobility, were deposited on quartz substrate to study the effect of growth temperature and oxygen pressure on their structural, optical, and electrical properties. X-ray diffraction study reveals that these films are randomly oriented on the quartz surface. The average particle size of the films grown at 600 °C was calculated to be ∼ 23 nm. The optical transparency of the films increases with an increase in the growth temperature. The film transparency is also found to increase with increased oxygen pressure during deposition. The electrical properties of these films strongly depend on both the growth temperature and the oxygen pressure. Analysis of the electrical data shows that the mobility of the films increases with increase in the growth temperature.     

Improved dielectric and ferroelectric properties in Ti-doped BiFeO3-PbTiO3 thin films prepared by pulsed laser deposition

Ti-modified thin films of multiferroic 0.72Bi(Fe_1 − xTi_x)O₃-0.28PbTiO₃ (BFPT, x = 0 and 0.02) solid solution were prepared by pulsed laser deposition. The BFPT (x = 0 and 0.02) films possess a tetragonal structure with highly preferential (001) orientation. The effects of the ionic substitution on the properties of BFPT (x = 0 and 0.02) films have been investigated. The leakage current of the BFPT (x = 0.02) thin film is significantly reduced, and the dielectric and ferroelectric properties greatly improved by the aliovalent ionic substitution of Ti⁴⁺ for Fe³⁺. The BFPT (x = 0.02) thin film exhibits a reasonably high remnant polarization P_r with 2P_r up to 90 μC/cm² at 312 kV/cm and a switchable polarization up to 92 μC/cm² at 417 kV/cm.     

Optical properties of the c-axis oriented LiNbO3 thin film

C-axis oriented Lithium Niobate (LiNbO₃) thin films have been deposited onto epitaxially matched (001) sapphire substrate using pulsed laser deposition technique. Structural and optical properties of the thin films have been studied using the X-ray diffraction (XRD) and UV-Visible spectroscopy respectively. Raman spectroscopy has been used to study the optical phonon modes and defects in the c-axis oriented LiNbO₃ thin films. XRD analysis indicates the presence of stress in the as-grown LiNbO₃ thin films and is attributed to the small lattice mismatch between LiNbO₃ and sapphire. Refractive index (n = 2.13 at 640 nm) of the (006) LiNbO₃ thin films was found to be slightly lower from the corresponding bulk value (n = 2.28). Various factors responsible for the deviation in the refractive index of (006) LiNbO₃ thin films from the corresponding bulk value are discussed and the deviation is mainly attributed to the lattice contraction due to the presence of stress in deposited film.     

Development of thickness measurement program for transparent conducting oxide thin films

The gallium doped zinc oxide has been one of the candidates for the transparent conducting oxide thin film electrode. It is not suitable to use a conventional light interference method to measure the thickness of the gallium doped zinc oxide thin film because the refractive index and extinction coefficient of the thin film is unknown during the optimization of the deposition conditions. In this paper, we report on the details of the film thickness program which uses the measured optical and electric properties and relationship between the plasma frequency and the optical constant of the film. The obtained film thickness of the prepared gallium doped zinc oxide thin film using the program was comparable with thicknesses measured by a cross-sectional analysis of the atomic force microscopy and the surface profiler. Moreover, the optical constant of refractive index and extinction coefficient of the film could also be estimated.     

Large nonlinear optical response of a Bi1.5Zn1.0Nb1.5O7 thin film fabricated by pulsed laser deposition

The Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin film has been fabricated on MgO (001) substrate by pulsed laser deposition. The nonlinear optical properties of the BZN film were investigated using Z-scan technique at a wavelength of 532 nm with 25 ps pulse duration. The two-photon absorption coefficient and the nonlinear refractive index of the BZN film were obtained to be 4.2 × 10^− 6 cm/W and 1.6 × 10^− 10 cm²/W respectively, which are comparable with those of some representative nonlinear optical materials. The large and fast response optical nonlinearities indicated that the BZN film is a promising candidate for future photonics devices.     

Dielectric and structural characterization of KNbO3 ferroelectric thin films epitaxially grown by pulsed laser deposition on Nb doped SrTiO3

KNbO₃ thin films were deposited on SrTiO₃ substrates by pulsed laser deposition. The X-ray diffraction patterns highlight an epitaxial growth according to the (011) orientation. This epitaxial growth was then confirmed by Electron Channeling Pattern. In agreement with the structural characteristics the dense microstructure consists in regular and ordered grains. Dielectric measurements were performed in the 20 Hz to 1 MHz frequency range on a KNbO₃ thin film grown on 2 at.% Nb doped (100)SrTiO₃ substrate in a large range of temperature in order to investigate the paraelectric-ferroelectric transition. Measurements at room temperature revealed a dielectric constant of 450 at 10 kHz and a minimum value of the loss tangent of 0.075 at 100 kHz. Dielectric study in the 20-600 °C temperature range showed a maximum of permittivity at the Curie temperature T_c = 410 °C and evidenced a “progressive” first-order phase transition, different from the classical “diffuse” transition.     

Growth and characterization of nitrogen-doped TiO2 thin films prepared by reactive pulsed laser deposition

Nitrogen-doped titanium dioxide (TiO₂) thin films were grown on (001) SiO₂ substrates by reactive pulsed laser deposition. A KrF* excimer laser source (λ = 248 nm, τ_FWHM ≅ 10 ns, ν = 10 Hz) was used for the irradiations of pressed powder targets composed by both anatase and rutile phase TiO₂. The experiments were performed in a controlled reactive atmosphere consisting of oxygen or mixtures of oxygen and nitrogen gases. The obtained thin film crystal structure was investigated by X-ray diffraction, while their chemical composition as well as chemical bonding states between the elements were studied by X-ray photoelectron spectroscopy. An interrelation was found between nitrogen concentration, crystalline structure, bonding states between the elements, and the formation of titanium oxinitride compounds. Moreover, as a result of the nitrogen incorporation in the films a continuous red-shift of the optical absorption edge accompanied by absorption in the visible spectral range between 400 and 500 nm wavelength was observed.     

Characterization of ZnO-In2O3 transparent conducting films by pulsed laser deposition

Transparent conducting oxide (TCO) films in the ZnO-In₂O₃ system were prepared by a pulsed laser deposition method. A target that consists of the mixture of ZnO and In₂O₃ powders was used. Influences of the target composition x (x = [Zn]/([Zn] + [In])) and heater temperature on structural, electrical and optical properties of the TCO films were examined. Introduction of oxygen gas into the chamber during the deposition was necessary for improvement in the transparency of the deposited films. The amorphous phase was observed for a wide range of x = 0.20-0.60 at 110 °C. Minimum resistivity was 2.65 × 10⁻⁴ Ω cm at x = 0.20. The films that showed the minimum resistivity had an amorphous structure and the composition shifted toward larger x, as the substrate temperature increased. The films were enriched in indium compared to the target composition and the cationic In/Zn ratio increased as the substrate temperature was increased.     

Characterization and optoelectronic properties of sol-gel-derived CuFeO2 thin films

In this study, CuFeO₂ thin films were deposited onto quartz substrates using a sol-gel and a two-step annealing process. The sol-gel-derived films were annealed at 500 °C for 1 h in air and then annealed at 600 to 800 °C for 2 h in N₂. X-ray diffraction patterns showed that the annealed sol-gel-derived films were CuO and CuFe₂O₄ phases in air annealing. When the films were annealed at 600 °C in N₂, an additional CuFeO₂ phase was detected. As the annealing temperature increased above 650 °C in N₂, a single CuFeO₂ phase was obtained. The binding energies of Cu-2p_3/2, Fe-2p_3/2, and O-1s were 932.5 ± 0.1 eV, 710.3 ± 0.2 eV and 530.0 ± 0.1 eV for CuFeO₂ thin films. The chemical composition of CuFeO₂ thin films was close to its stoichiometry, which was determined by X-ray photoelectron spectroscopy. Thermodynamic calculations can explain the formation of the CuFeO₂ phase in this study. The optical bandgap of the CuFeO₂ thin films was 3.05 eV, which is invariant with the annealing temperature in N₂. The p-type characteristics of CuFeO₂ thin films were confirmed by positive Hall coefficients and Seebeck coefficients. The electrical conductivities of CuFeO₂ thin films were 0.28 S cm^− 1 and 0.36 S cm^− 1 during annealing at 650 °C and 700 °C, respectively, in N₂. The corresponding carrier concentrations were 1.2 × 10¹⁸ cm^− 3 (650 °C) and 5.3 × 10¹⁸ cm^− 3 (700 °C). The activation energies for hole conduction were 140 meV (650 °C) and 110 meV (700 °C). These results demonstrate that sol-gel processing is a feasible preparation method for delafossite CuFeO₂ thin films.     

Pulsed laser deposition of La0.67Ca0.33MnO3 thin films on LiNbO3 and surface acoustic wave studies

Surface Acoustic Waves on piezoelectric substrates can be used to investigate the dynamic conductivity of thin films in a non-contact and very sensitive way, especially at low conductivities. Here, we report on such surface acoustic wave studies to characterize thin manganite film like La_0.67Ca_0.33MnO₃, exhibiting a Jan Teller effect with a strong electron phonon interaction and a metal insulator transition at high temperatures.

We report on the deposition of La_0.67Ca_0.33MnO₃ on piezoelectric substrates (LiNbO₃ in different crystal cuts, employing a pulsed laser deposition technique. The structural quality of the thin films are examined by X-Ray Diffraction, Scanning Electron Microscope and Energy Dispersive X-ray spectroscopy. For the electrical characterization, we employ the surface acoustic wave technique, accompanied by conventional direct current resistance measurements for comparison.