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

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, O2 and N2O at 1.7 torr and 1.1 torr, the film growths were tested at several substrate temperature (Ts) 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 “Ts window”) was from about 800 °C to 830 °C, at relevant pressures as specified above. Tc and Jc of a typical YBCO film sample grown within this “Ts window”, i.e., 810 °C, were found as 90 K and 1.32 MA/cm2 (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.