Low-pressure Metalorganic Chemical Vapor Deposition and Characterization of YBa₂Cu₃O_7−x Thin Films

Abstract

Low-pressure metalorganic chemical vapor deposition (LP-MOCVD) is a technique which has been used with great success for the growth of compound semiconductors. In this study, we have successfully applied this technique to the deposition of yttrium barium cuprate (YBCO) superconducting thin films grown on a variety of substrate materials. These superconducting films have been deposited in a commercial-scale MOCVD reactor with a capacity of over 100 cm² per growth run. The EMCORE System 5000 reactor is based on a high-speed rotating disk susceptor (0–2000 rpm) design.

Thin films of the binary oxides were initially deposited in order to determine the respective growth rates. This data was then used to calculate trial values of reactant flows for YBCO growth. YBCO layers were grown at 76 Torr on substrates held at 500–550 °C. The ß-diketonates of Y, Ba and Cu, heated to 130, 240 and 120 °C, respectively, were used as sources. A 4.5 slpm flow of pure oxygen, representing a partial pressure of 38 Torr, was introduced uniformly at the top of the reaction chamber.

Post-growth annealing was performed in pure oxygen for 30–60 minutes at 900–950 °C. After annealing, initial YBCO layers grown on (100) YSZ substrates exhibited semiconducting behavior above the 90 K onset of the superconducting transition. The zero resistance temperature, T_c(R=0), was 40 K. Under slightly different growth conditions, YBCO deposited on (100) SrTiO₃ exhibited a metallic characteristic, with onset and T_c(R=0) values of 95 and 85 K, respectively. These layers also showed a rather smooth morphology compared to previously reported results using LP-MOCVD. Results of characterization by x-ray diffraction, SEM, EDAX and XPS are reviewed. Evidence of low carbon/carbonate contamination was observed, however a significant substrate/layer interaction was detected in the case of YSZ.