New growth approach of high-quality oxide thin films for future device applications: independent control of supersaturation and migration

摘要

In this paper we focus on supersaturation and migration of the atomic species involved in the growth of oxide films in order to search for new efficient methods for growth of flat, uniform and precipitate-free complex thin films with high quality.In this respect we have applied MOCVD to HTS thin films, 'interrupted growth' (consisting of on/off vapour deposition cycles, keeping the temperature and atmospheric conditions constant), similar to 'pulsed laser interval deposition' reported in the literature. We show that MOCVD can be easily and successfully applied to suppress island growth, contrary to the currently accepted idea that this approach is unique to PLD. This suggests that principles of supersaturation-migration-supersaturation cycles are universal for the films' growth. By this approach, high-quality Bi-2223 thin films with a uniform flat surface, having roughness less than half the c-axis unit cell, were grown by MOCVD.Using substrates with artificial steps of predefined width equal to 'twice the migration length' totally precipitate-free thin films were obtained: precipitates-segregates of impurity phases (Cu rich for HTS materials) are gathered at the step edges where the free energy is lowest.As-prepared films were used to fabricate intrinsic Bi-2223 and Bi-2212/Bi-2223 SIS-type Josephson junctions (IJJs).