Influence of Deposition Temperature on Properties of Multilayered Gallium Doped Zinc Oxide Films Prepared by DC Magnetron Sputtering Technique

Multilayered transparent conducting films based on ZnO: Ga were deposited onto glass substrateby DC magnetron sputtering technique. The films were prepared from alloy (Zn: Ga) and ceramic(ZnO: Ga) targets with gallium composition of 3 at% and 4 at%, respectively. Crystal structure andphase analysis were measured using X-ray diffractometer (XRD). The XRD structural analysisresults indicated that all multilayered films were polycrystalline with (002) orientation slightlyshifted of diffracting angles due to gallium dopant concentrations as increase in the depositiontemperatures. The films were hexagonal wurtzite structure, having preferred growth orientation inc-axis perpendicular to the substrate surface. The cross section micrographs imaging and elementalcomposition of multi-layered ZnO: Ga films were studied by Scanning Electron Microscopy (SEM)and Energy Dispersive X-ray spectroscopy (EDX), respectively. The films' surface morphologyand grain size approximations were studied by Atomic Force Microscopy (AFM) operated in thetapping mode. Grain size approximations observed in atomic force microscopy scans wereconfirmed by Debye Scherrer's formula. Optical transmittance and electrical properties of multilayeredfilms were studied using the UV-VIS spectrophotometer and Ecopia HMS-3000 HallEffect measurement equipment. Film deposited at substrate temperature of 270 °C showed the bestdesired results of structural, optical and electrical properties. The film has optical transmittance ofover 91% and the lowest resistivity of 1.8 10–4 Ω-cm corresponding to the highest carrierconcentration of 4.8 1021 cm-3 and Hall mobility of 7.5 cm2 /Vs were obtained. The film’s bandgaps of 3.6 eV and extinction coefficient of 0.43 were computed empirically, while refractiveindex of 1.75 was calculated by Swanepoel’s envelope method from the transmittance spectra. Theincrease of the films optical band gap arises from among other factors Ga doping concentrationand increase of deposition temperatures. Keywords: ZnO: Ga; DC Magnetron Sputtering; Swanepoel’s Envelope Method; Thin Film

Magnesium Diboride (MgB2) and Ca-doped YBa2Cu3O7-? : Thin Films and Devices. Fabrication and Characterization

Magnesium diboride (MgB2) is a superconductor with an exceptionally high transition temperature, Tc, of 39 K. This work describes deposition of high quality and superconducting films of MgB2 for electronic applications. Experiments on Ca-doped YBa2Cu3O7-? films and fabrication of bicrystal Josephson junctions are also described. Pulsed laser deposition (PLD) was used to prepare in-situ superconducting MgB2 films on SrTiO3(100) substrates with an onset to superconductivity at 30 K and a transition to the superconducting state at 20 K. ?-2? x-ray diffraction spectra showed no film peaks indicating that the films consisted of small grain sizes. A small value of the root-mean-square (RMS) roughness and a maximum peak-to-valley distance of 3 nm were indicative to the films smooth surface morphology. A two-step method was used to grow superconducting thin films of MgB2 on SrTiO3(001) and Al2O3(1-102) substrates by first preparing precursors of Mg-B bilayers at room temperature. The precursor films were subsequently annealed in Mg vapour to obtain the superconducting MgB2 phase, with Tc ranging from 22 K to 30 K. The films grown on SrTiO3(001) substrates showed a growth in the (101) direction while those on Al2O3(1-102) were c-axis oriented. The films exhibited a fairly smooth surface with an RMS roughness of about 8.5 nm and a peak-to-valley distance between 20 and 27 nm. As-grown MgB2 films with Tc in the range of 32 K to 34 K were deposited by co-evaporation technique on Al2O3(0001), MgO(111) and SiC(0001) substrates. The films were highly oriented in the c-axis and exhibited a smooth surface morphology. Through optimization of the growth parameters, films with Tc ~35 K and an RMS roughness of 2 nm were obtained. The films were used to fabricate microbridges, weak link junctions and proximity effect Josephson junctions by using conventional photolithography, Ar-ion beam and focused ion beam (FIB) milling. The current-voltage (I-V) characteristics of the weak links and proximity effect Josephson junctions showed the dc and ac Josephson effect. MgB2 films grown by a customer-designed molecular-beam epitaxy (MBE) system (at NTT-Basic Research Laboratories, Japan) were used to fabricate nanobridges. Electron beam lithography and Ar-ion beam milling by utilizing amorphous carbon as etching mask were used to realize the nanobridges. The nanobridges showed the dc Josephson effect. Tri-layer devices (MgB2/Pd/Nb and MgB2/Al-AlOx/Nb) and multilayers involving normal metals and superconductors (MgB2/Au/Nb/Al-AlOx/Nb and MgB2/Pd/Fe/Nb) were also fabricated. The films of palladium (Pd) and gold (Au) for the metal interlayers and aluminium (Al) forming the oxide barriers after oxidation as well as the superconducting niobium (Nb) were deposited by RF sputtering. The Pd/Fe bilayer in the MgB2/Pd/Fe/Nb devices was deposited by ebeam evaporation. These devices exhibited both the ac and dc Josephson effect and I-V characteristics close to the resistively shunted junction (RSJ) type. Ca-doped YBa2Cu3O7-δ films were deposited by pulsed laser deposition on asymmetric 30\ub0, 40\ub0 and 45\ub0 bicrystal SrTiO3(001) substrates. The films were patterned into bicrystal grain boundary Josephson junctions by conventional photolithography and Ar-ion beam milling. An increase in Jc and IcRN product was observed in the 30\ub0 and 40\ub0 bicrystal junctions when compared with similar junctions of normal YBa2Cu3O7-?

Magnesium Diboride (MgB₂) and Ca-doped YBa₂Cu₃O_7-? : Thin Films and Devices. Fabrication and Characterization

Magnesium diboride (MgB₂) is a superconductor with an exceptionally high transition temperature, <i>T_c</i>, of 39 K. This work describes deposition of high quality and superconducting films of MgB₂ for electronic applications. Experiments on Ca-doped YBa₂Cu₃O_7-_? films and fabrication of bicrystal Josephson junctions are also described. <p>Pulsed laser deposition (PLD) was used to prepare <i>in-situ </i>superconducting MgB₂ films on SrTiO₃(100) substrates with an onset to superconductivity at 30 K and a transition to the superconducting state at 20 K. <i>?</i><i>-2? </i>x-ray diffraction spectra showed no film peaks indicating that the films consisted of small grain sizes. A small value of the root-mean-square (RMS) roughness and a maximum peak-to-valley distance of 3 nm were indicative to the films smooth surface morphology. <p>A two-step method was used to grow superconducting thin films of MgB₂ on SrTiO₃(001) and Al₂O₃(1-102) substrates by first preparing precursors of Mg-B bilayers at room temperature. The precursor films were subsequently annealed in Mg vapour to obtain the superconducting MgB₂ phase, with <i>T_c </i>ranging from 22 K to 30 K. The films grown on SrTiO₃(001) substrates showed a growth in the (101) direction while those on Al₂O₃(1-102) were <i>c</i>-axis oriented. The films exhibited a fairly smooth surface with an RMS roughness of about 8.5 nm and a peak-to-valley distance between 20 and 27 nm. <p>As-grown MgB₂ films with <i>T_c </i>in the range of 32 K to 34 K were deposited by co-evaporation technique on Al₂O₃(0001), MgO(111) and SiC(0001) substrates. The films were highly oriented in the <i>c</i>-axis and exhibited a smooth surface morphology. Through optimization of the growth parameters, films with <i>T_c </i>~35 K and an RMS roughness of 2 nm were obtained. <p>The films were used to fabricate microbridges, weak link junctions and proximity effect Josephson junctions by using conventional photolithography, Ar-ion beam and focused ion beam (FIB) milling. The current-voltage (<i>I-V) </i>characteristics of the weak links and proximity effect Josephson junctions showed the <i>dc </i>and <i>ac </i>Josephson effect. <p>MgB₂ films grown by a customer-designed molecular-beam epitaxy (MBE) system (at NTT-Basic Research Laboratories, Japan) were used to fabricate nanobridges. Electron beam lithography and Ar-ion beam milling by utilizing amorphous carbon as etching mask were used to realize the nanobridges. The nanobridges showed the <i>dc</i> Josephson effect. Tri-layer devices (MgB₂/Pd/Nb and MgB₂/Al-AlO<i>_x</i>/Nb) and multilayers involving normal metals and superconductors (MgB₂/Au/Nb/Al-AlO<i>_x</i>_/Nb and MgB₂/Pd/Fe/Nb) were also fabricated. The films of palladium (Pd) and gold (Au) for the metal interlayers and aluminium (Al) forming the oxide barriers after oxidation as well as the superconducting niobium (Nb) were deposited by RF sputtering. The Pd/Fe bilayer in the MgB₂/Pd/Fe/Nb devices was deposited by e–beam evaporation. These devices exhibited both the <i>ac </i>and <i>dc </i>Josephson effect and <i>I-V</i> characteristics close to the resistively shunted junction (RSJ) type. <p>Ca-doped YBa₂Cu₃O_{7-<i>&#948;</i>}<i> </i>films were deposited by pulsed laser deposition on asymmetric 30°, 40° and 45°<i> </i>bicrystal SrTiO₃(001) substrates. The films were patterned into bicrystal grain boundary Josephson junctions by conventional photolithography and Ar-ion beam milling. An increase in <i>J_c </i>and <i>I_cR_N</i> product was observed in the 30°<i> </i>and 40°<i> </i>bicrystal junctions when compared with similar junctions of normal YBa₂Cu₃O_7-_?