Epitaxial growth of YBa2Cu3O7 films on GaAs with MgO buffer layers

Abstract
We have grown epitaxial YBa2Cu3O7 films on GaAs using MgO buffer layers similar to Fork, Nashimoto, and Geballe [Appl. Phys. Lett. 60, 1621 (1992)]. However, the YBa2Cu3O7 was deposited by thermal coevaporation at an even lower substrate temperature of 620 °C. We obtained substantially improved quality [Tc=86.8 K, jc(77 K)=1.2×106 A/cm2, ρ(100 K)≤100 μΩ cm] and smooth surfaces free of outgrowth. An important aspect is preventing As contamination from the gas phase. This was achieved by encapsulating the free sample surface.