Ca-doped Films Research Articles

Improved ferroelectricity and endurance in Ca doped Hf0.5Zr0.5O2 films

Doped Hf0.5Zr0.5O2 materials have drawn increasing attention due to the excellent ferroelectric properties, but the relevant research is just in the preliminary stage and the reported doped systems are rare. In this work, Ca doped Hf0.5Zr0.5O2 (Ca:HZO) ferroelectric films were successfully fabricated via chemical solution deposition and investigated for the first time. It is observed that Ca doping induces a phase transformation from monoclinic to orthorhombic/tetragonal and then to monoclinic/tetragonal. The highest orthorhombic phase fraction is achieved in 2.5 mol% Ca doped HZO film, contributing to the optimum ferroelectric property with the largest remnant polarization of 14.00 μC/cm2 after 105 cycles. Additionally, the leakage current density is observed to decrease with increasing Ca content, which is mainly associated with the changes of grain size and surface roughness. As a result, the endurance is significantly improved in the Ca doped films, and an excellent endurance of 1010 cycles is achieved in the 2.5 mol% Ca doped film. These results suggest that Ca doping can enhance the ferroelectric and endurance properties of HZO films by optimizing the phase and morphological structure.

Preparation of calcium-doped boron nitride by pulsed laser deposition

Calcium-doped BN thin films CaxBNy (x=0.05–0.1, y=0.7–0.9) were grown on α-Al2O3(001) substrates by pulsed laser deposition (PLD) using h-BN and Ca3N2 disks as the targets under nitrogen radical irradiation. Infrared ATR spectra demonstrated the formation of short range ordered structure of BN hexagonal sheets, while X-ray diffraction gave no peak indicating the absence of long-range order structure in the films. It was notable that Ca-doped film had 5.45–5.55eV of optical band gap, while the band gap of Ca-free films was 5.80–5.85eV. This change in the band gap is ascribed to interaction of Ca with the BN sheets; first principle calculations on h-BN structure indicated that variation of inter-plane distance between the BN layers did not affect the band gap. This study highlights that PLD could prepare BN having short-range structure of h-BN sheets and being doped with electropositive cation which varies the optical band gap of the films.

Co-doping Effect of Ca and N on the Structure and Properties of CuAlO2 Thin Film

Ca-doped films were prepared by the radio-frequency magnetron sputtering technique. As shown by X-ray diffraction measurements, single-phase hexagonal is formed for Ca concentrations up to 1.5 atom %. Hall measurements confirm the p-type conduction for all films. The introduction of Ca leads to a sharp improvement in electrical conductivity due to the increase in carrier concentration. With increasing doping concentrations, the bandgaps of thin films increase. We attribute this to Burstein–Moss shift from increased carrier concentrations. A nitrogen plasma treatment results in further enhancement of the electrical conductivity due to introducing N as an acceptor into thin film.

High corrosion stability of DyBa2Cu3Oz thin films relative to YBa2Cu3Oz films: A possible relation between corrosion and c-axis correlated extended defects

An enhanced stability towards corrosion was noted for DyBa2Cu3Oz relative to YBa2Cu3Oz. Between pure and Ca doped films, Ca doped films were found to be more corrosion resistant towards aqueous environment. The observed high corrosion stability in DyBa2Cu3Oz can be explained by the improved microstructure and the absence of c-axis correlated extended defects (EDs), while the remarkable increase in corrosion stability for the Ca doped films is presumed to be due to the notable improvement in the grain boundary region and the absence of ED. It is confirmed that the films with c-axis correlated ED are highly prone to corrosion by moisture.

Morphology and transport properties of Ca-doped superconducting epitaxial YBCOfilms

Oxygen doping enhancing the CuO plane density of statesnm iswell known to improve normal conducting and superconducting dc, ac and rf transport properties ofY Ba2Cu3O7−δ (YBCO) by orders of magnitude. By Ca dopingY1−xCaxBa2Cu3O7−δ,enhancing nm similarly, transport improvements by factors between two and ten havebeen found for bicrystal junctions and single crystals only. To study theeffect of Ca doping on epitaxial pulsed laser deposition (PLD) films onCeO2/Al2O3 we performed systematic transport studies for nominalx = 0, 0.1, 0.15 and 0.2 combined with energy dispersive x-ray (EDX) and Rutherfordback-scattering (RBS) analysis. The resulting superconducting rf properties,and therewith the mean values of the weak link critical current densityjcJ, degraded with Ca content, confirming trends found by dc measurements of PLD films onSrTiO3 (STO)and on LaAlO3 (LAO) and by rf measurements of Ca-doped films onCeO2 buffered Al2O3 (AO) and on LAO. The normal conducting weak link resistanceRbn decreased withx in line withnm enhancements butjcJRbn also decreased.Reasons for the jcJ and jcJRbn degradations and the morphology changes and for the differences between Ca-doped YBCObicrystal junctions and natural junctions in Ca-doped epitaxial YBCO films will be given.

Superconducting properties of Ca-doped YBCO thick film by liquid phase epitaxy

Liquid phase epitaxial (LPE) Y 1− x Ca x Ba 2Cu 3O 7− δ (Ca–YBCO) was successfully grown in the fabrication of thick films with high T c values (over 90 K) even with a small thickness of 0.5 μm. ICP analyses reveal the Ca distribution coefficient (solid composition/liquid composition) is higher than unity, which may imply a Ca-poor grain boundary in Ca-doped LPE thick films. TEM-EDX analyses reveal Mg is non-detectable in a Ca-doped sample, while it is detected to be higher than 1 at.% in a non-doped YBCO thick film, suggesting that the interaction parameter between Ca and Mg ( e Ca Mg) is positively high and leads to suppressing the Mg contamination. J c decreases less in the Ca-doped film than in the non-doped film with increase of the applied magnetic field.

Bipolarity in electrical conduction of transparent oxide semiconductor CuInO2 with delafossite structure

A transparent oxide semiconductor with delafossite structure, CuInO2, was found to exhibit both p-type and n-type conduction by doping of an appropriate impurity and tuning of proper film-deposition conditions. Thin films of Ca-doped or Sn-doped CuInO2 (optical band gap=∼3.9 eV) were prepared on α-Al2O3(001) single crystal substrates by pulsed laser deposition method. The films were deposited at 723 K in O2 atmosphere of 1.0 Pa for the Ca-doped films or 1.5 Pa for the Sn-doped films. The positive sign of the Seebeck coefficient demonstrated p-type conduction in the Ca-doped films, while the Seebeck coefficient of the Sn-doped films was negative indicating n-type conductivity. The electrical conductivities of Ca-doped and Sn-doped CuInO2 thin films were 2.8×10−3 S cm−1 and 3.8×10−3 S cm−1, respectively, at 300 K.

Bipolar Electrical Conductive Transparent Oxide, CuInO2

ABSTRACTA transparent oxide semiconductor with delafossite structure, CuInO2, was found to exhibit both p-type and n-type conduction by doping of an appropriate impurity and tuning of proper film-deposition conditions. Thin films of Ca-doped or Sn-doped CuInO2 were prepared on -Al2O3 (001) single crystal substrates by pulsed laser deposition method. The films were deposited at 723 K in O2 atmosphere of 1.0 Pa for the Ca-doped films or 1.5 Pa for the Sn-doped films. The positive sign of the Seebeck coefficient demonstrated p-type conduction in the Ca-doped films, while the Seebeck coefficient of the Sn-doped films was negative indicating n-type conductivity. The electrical conductivities of Ca-doped and Sn-doped CuInO2 thin films were 2.8×10−3 S·cm−1 and 3.8×10−3 S·cm−1, respectively, at 300 K. The optical band gap of each film was estimated to be ∼3.9 eV. Since CuInO2 exhibited bipolarity in electrical conduction, transparent p-n homojunctions based on CuInO2 were fabricated on (111) surface of yttria-stabilized zirconia single-crystal substrates. The structure of the diode was In2O3:Sn / n-CuInO2:Sn / p-CuInO2:Ca / In2O3:Sn electrode on the substrate. The contact between the n-and p-type CuInO2 semiconducting oxides was found to be rectifying. The turn-on voltage was ∼1.8 V.

Growth and Magnetic Structure of La0.67Sr0.33MnO3 Films

ABSTRACTGrowth of LaMnO3 films that exhibit colossal magnetoresistance (CMR) has concentrated heavily on Ca doped materials. However, since the 33% Sr doped films are ferromagnetic at room temperature, they are ideal candidates for dual growth-magnetic structure studies using scanned probe techniques. In this study, interest was focused on the relations between growth/processing parameters, film morphology, and electronic/magnetic properties. In addition, films were grown on both LaA1O3 (LAO) and SrTiO3 (STO) to examine the results of stress induced by different substrate mismatches. La0.67Sr0.33MnO3 (LSMO) was grown using pulsed laser deposition (PLD) at temperatures between 500 °C and 800 °C. The film microstructure, crystallinity, and magnetic and electrical properties were characterized by room temperature scanning tunneling microscopy (STM), atomic force microscopy (AFM), magnetic force microscopy (MFM), x-ray diffraction, and temperature dependent transport and magnetization measurements. The growth trends follow those previously reported for Ca doped films. Grains increase in size with increasing temperature and coalesce into extended layers after annealing. Although topographic contributions complicate interpretation of some MFM data, local magnetic structure observed here is generally associated with film defects.

Magnetic and magneto-optical properties of Ca-doped Bi-YIG sputtered films

Ca-doped Bi-YIG films were prepared by RF-sputtering, and their magnetic and magnetooptical properties in the visible wavelength region have been investigated. The films were deposited on vitreous SiO/sub 2/ and Corning 7059 glass substrates at 400 degrees C. The sputtering was conducted with an Ar pressure of 6.7 Pa, a deposition rate of 3.3 nm/min, and a RF-power density of 2.5 W/cm/sup 2/. The deposited films annealed in air at 500 approximately 700 degrees C were determined to be the garnet phase, and they showed large saturation magnetizations greater than 100 emu/cm/sup 3/. The magnetization of Ca doped films was constant in the range of Ca ratio x=0.0 approximately 1.0; however, the theta /sub F/ decreased with x in the same composition range. It was found that the theta /sub F/ of Bi/sub 2/YCaFe/sub y/O/sub 12/ films increased, while the M/sub s/ of the films decreased, in the composition range of y=3.5 approximately 5.0.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

HYDROGEN ANNEALING EFFECTS ON THE OPTICAL ABSORPTION OF Bi-SUBSTITUTED IRON GARNET FILMS

Reducing treatment effects on the optical absorption loss in the near-infrared region were studied for Ca-free and -doped Bi-substituted iron garnet films. (BiGd)3(FeAlGa)5O12 films were grown by the conventional LPE technique and annealed in hydrogen (H2) atmosphere at a step of 50°C between 150 and 400°C for 22 hours. The absorption loss at wavelength λ=0.8μm reached minimum values of 250 ∼ 300 dB/cm by annealing at 250°C for both Ca-free and -doped films. The decrease in the absorption loss at λ=0.8μm by this annealing is mainly ascribed to the reduction of Pb4+ to Pb2+ on the dodecahedral sites in garnets. The wavelength dependence of the difference of absorption loss between as-grown and 250°C-H2-annealed films has a peak around λ=0.56μm and the difference abruptly decreases in the longer wavelength side. This peak is thought to be due to a charge transfer transition from the crystal field split level of Fe3+ to Pb4+. Absorption loss at λ=1.15μm decreased for both Ca-free and -doped films by annealing at 250°C. The values reached ∑2 dB/cm for Ca-doped films and ∼9 dB/cm for Ca-free films. It is thought that the absorption loss of ∼9 dB/cm for the Ca-free films is due to Fe2+ which exists at the as-grown state. The increase in the absorption loss by annealing above 250°C may be due to Fe2+ ions created by the reduction of Fe3+→Fe2+.

Ｃａ添加Ｂｉ置換鉄ガーネット膜の光吸収損失に及ぼす還元効果

Reducing treatment effects on magneto-optical properties were studied for Ca-doped Bisubstituted iron garnet (BiGdCa)3(FeAlGa)5O12 films grown by the LPE technique. The films were reduced by using a hydrazine solution at 100∼110°C. Faraday rotation and absorption loss of as-grown and reduced films were measured at wavelength λ between 0.5 and 2.0 μm. By reducing treatment, the Faraday rotation remained unchanged, however, the absorption loss decreased for both Ca-free and Ca-doped films. The reduced Ca-doped films had lower absorption loss compared with that of the reduced Ca-free films. The minimum absorption loss reached 220 dB/cm at λ=0.79 μm and 1∼2 dB/cm at λ=1.15 μm. The saturation field was below 200 Oe for all the films.An optical isolator for the 0.8 μm region was constructed by using a reduced thick film. The forward loss of the isolator was 3 dB and the backward loss 27 dB at 0.79 μm.

Treatment effect of reducing environment on magneto-optical properties of Ca-doped Bi substituted Iron garnet films

Ca-doped Bi substituted iron garnet films (BiGdYb) 3-x Ca x Fe 5 O 12 ( 0\leqx\leq0.042 ) were grown by LPE technique and the effects of treatments in reducing environment on the absorption loss α at wavelength λ=0.8μm were studied by using a N 2 H 4 .H 2 O solution. It turned out that (1) the α of as-grown films increases with increase of Ca content, however, it decreases remarkably after reducing treatment, (2) the α of Ca-free films does not change by reduction, and (3) the α of Ca-doped and subsequently reduced films is lower than that of as-grown Ca-free films and has a almost constant value of 430 dB/cm in the Ca concentration region x>0.03. These results were explained by considering the coexistence of Fe2+and Fe4+in as-grown states and their content changes due to Ca-doping and subsequent reduction. Faraday rotation coefficients of the films remained unchanged by both Ca-doping and reducing treatment. The magneto-optical figure of merit of Ca-doped films reached 12 deg/dB at λ=0.8 μm which is 1.4 times higher than that of Ca-free films.