Precisely determined temperature window size for the growth of high quality c-axis oriented YBCO films by photo-assisted MOCVD

Abstract

It is well-known that there is a relatively small temperature window for the growth of epitaxial and c-axis oriented YBCO thin films by various methods. In this study, this window was more precisely examined for YBCO film growths by photo-assisted MOCVD. At specified total reactor pressure of 4.6 torr, and specified respective partial pressures for the oxidizing agents, O 2 and N 2O at 1.7 torr and 1.1 torr, the film growths were tested at several substrate temperature ( T s) points from 780 °C to 864 °C. The film growth time for each test was 3 min. As to compositional purity, purity in c-axis orientation, and crystal structural quality of these tested films by using photo-assisted MOCVD technique, it was found that for the growth of purely c-axis oriented YBCO thin films with high crystalline quality, the appropriate growth temperature range (or “ T s window”) was from about 800 °C to 830 °C, at relevant pressures as specified above. T c and J c of a typical YBCO film sample grown within this “ T s window”, i.e., 810 °C, were found as 90 K and 1.32 MA/cm 2 (77 K, 0 Oe) respectively by magnetization measurements. It is noticeable that this film, and other purely c-axis oriented YBCO films are all single-crystal like and dense, with no SEM visible grain boundary or void. The causes of precipitates found on top surface of these c-axis oriented YBCO films are also discussed.