Flat YBa2Cu3O7−x layers for planar tunnel-device technology

Abstract The conditions for achieving extremely flat YBa 2 Cu 3 O 7− x (YBCO) surfaces with large interstep distances as required for a reliable planar HTSC tunnel-device technology are analyzed. Considerations of thermodynamics, kinetics and transport of the growth species show that by liquid phase epitaxy (LPE) it is possible to achieve such flat YBCO surfaces, which is experimentally proven. Specifically, in LPE the growth from relatively concentrated solutions occurs at high temperatures near thermodynamic equilibrium. The small supersaturation (of a - and c -oriented YBCO films and explain the different degree of polygonization of the observed growth spirals. The concentrations of YBCO in physical vapour deposition (PVD) and in metal-organic chemical vapour deposition (MOCVD) are very small and the supersaturations at least 10 2 times higher than in LPE. This, together with the thermodynamic stability limit (temperature, oxygen partial pressure), sets an inherent limit to the interstep distance in PVD and MOCVD, thus limiting the achievable flatness of vapour-grown YBCO layers.