Progress in the growth of YBa2Cu3O7−x thin films by MOCVD and prospects for large area, low temperature deposition AIP Conf.

The distribution of defects in Si ͑100͒, ͑110͒, and ͑111͒ after boron implantation and annealing processes was measured by means of different methods. Boron implantation was carried out at 300 K with three energies ͑50, 150, and 300 keV or 30, 90, and 180 keV͒ in multiple mode to obtain a homogeneously damaged layer. Ion fluences ranged from 10 14 to 10 16 B ϩ cm Ϫ2 . The profile of vacancy-type defects was detected by variableenergy positron annihilation spectroscopy ͑VEPAS͒. The defect concentration increases proportionally to ͱ⌽, where ⌽ is the ion fluence. It was found that the line-shape parameter S of the positron-electron annihilation peak in the implanted layer increases with ⌽. The divacancy (2v) concentration observed by infrared absorption spectroscopy ͑IRAS͒ was nearly constant in all samples ͑about 1.8ϫ10 19 cm Ϫ3 ͒. It can be concluded that divacancies are not the main vacancy-type defect and the increasing S parameter must be attributed to additional defects of larger open volume. A value S defect /S bulk ϭ1.048 was fitted for the dominating defect, where S 2v /S bulk ϭ1.04. Rutherford backscattering ͑RBS͒ measurements were carried out to detect the distribution of displaced lattice atoms. The defect-production rate was proportional to ͱ⌽ again. The concentration profiles of implanted ions were measured with sputtered neutral mass spectrometry ͑SNMS͒. In addition, Monte Carlo calculations were done with the TRIM code. The nearly homogenous defect distributions up to a depth of 1 m found by VEPAS, TRIM, and RBS are in very good accordance. The samples were annealed up to 1150 K. It was found that the annealing behavior of vacancylike defects depends on the implantation dose and on the sample material under investigation. The divacancies are annealed at 470 K as measured by IRAS. An annealing stage of vacancy clusters at 725 K was observed in all samples by VEPAS. In Czochralski material, a decrease of the S parameter below the value of defect-free Si was observed after annealing at about 750 K. This can only be explained by the appearance of a different defect type, most likely an oxygen-vacancy complex. At high ion fluences (10 16 B ϩ cm Ϫ2 ), an increase of the S parameter above the defect value at room temperature was observed after annealing at 700 K in a region 100 nm below the surface. This high S parameter is caused by the creation of larger vacancy clusters. These defects remain stable after annealing at 850 K. Correlated RBS and SNMS measurements were done at identically implanted samples for all annealing stages.

An arrangement for large area PLD on 3-inch wafers is proposed. In order to get a homogeneous stoichiometry and thickness distribution and small variations of superconducting properties on the 3-inch diameter, the substrate is foreseen to be rotated and additionally laterally moved up to 45 mm during deposition whereas the laser plume remains fixed.YSZ buffer layers showed thickness homogeneity of 1% within 10 mm, of 4% within 2 inch and of 8% within 3 inch diameter, respectively. For in-situ deposited YBCO thin films on r-plane sapphire with YSZ buffer layer we inductively measured within 3 inch diameter values of the critical temperature Tc(90%) from 85.9 K to 86.7 K and values of the critical current density jc(77 K) from 1 × 106 to 2 × 106 A/cm2. However, up to now the degree of epitaxy of the YBCO thin films on r-plane sapphire with YSZ buffer layer is lower compared to YBCO on MgO(100) as determined by Raman spectroscopy. Nevertheless, large area PLD seems to be a very promising technique for homogeneous coating of 3-inch wafers by epitaxial oxide thin films.

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