Hybrid liquid phase epitaxy processes forYBa2Cu3O7 film growth

Abstract

A number of liquid phase epitaxy (LPE) related growth methods have been investigated.These hybrid-LPE processes enable high rate ‘liquid assisted’ growth of epitaxialYBa2Cu3O7 films without the many disadvantages of classical LPE. Growth occurs by diffusive transport ofY through a thin liquid flux layer. This layer may be pre-deposited onto the substrate byvarious means including vacuum and non-vacuum techniques, or deposited at the growthtemperature. The composition of the liquid layer is maintained during film growth by feedingYBa2Cu3O7, or the separate components, either from the vapour or by a powder route. Growth rates up to10 nm s−1 have been demonstrated.Deposition of c-axisoriented epitaxial YBa2Cu3O7 is reported on both seeded and non-seeded substrates; the process is tolerant of a high substrate mismatch.Films 1–2 µm thick with K and a critical current densityJc>2 MA cm−2 have been grown on a range of single crystal substrates as well as on buffered texturedmetallic tapes. The mechanism of nucleation and growth from a thin liquid layer isdescribed within the general theoretical framework of crystal growth. Particular features ofthe growth are the short time constant for equilibration of transients in the depositionconditions, the wide range of relative supersaturation spanned by the process, anddominance of interface kinetic effects compared to volume diffusion in the liquid flux.