A STUDY OF THE CUO PHASE-FORMATION DURING THIN-FILM DEPOSITION BY MOLECULAR-BEAM EPITAXY

The kinetics of CuO growth under molecular beam epitaxial (MBE) condit ions has been investigated. The evaporation of Cu and its deposition o nto Si(111) substrate maintained at 823 K was carried out using an ele ctron beam heated source. For the oxidation of Cu, sources of both mol ecular and atomic oxygen species were employed. The films were charact erized by electron spectroscopy for chemical analysis (ESCA), X-ray di ffraction (XRD), infrared (IR) transmission and scanning electron micr oscopy (SEM). The application of a fairly high flux of molecular oxyge n (3.4 x 10(20) molecules/(m(2) s)) and O-2 to Cu flux ratio of simila r to 250 during the deposition was found to be insufficient to convert a detectable amount of Cu into Cu+/Cu2+ state. On the other hand, Cu2 O films could be grown with relative ease by maintaining atomic oxygen flux of 1.6 times the stoichiometric value. In contrast, the kinetics of CuO formation has been found to be quite slow. For atomic oxygen t o copper flux ratio of similar to 80, only similar to 95% of the coppe r was found to be in fully oxidized state. (C) 1998 Elsevier Science S .A. All rights reserved.