Beryllium sites in MBE-grown BeZnO alloy films

We report the possible sites that beryllium atoms can occupy in BeZnO alloy films by a comparative study. The epitaxial BexZn1-O-x (x = 0, 0.06, 0.1, 1) films were prepared by a molecular beam epitaxy technique, and their structural properties were characterized with x-ray diffraction, Raman spectroscopy and x-ray photoelectron spectroscopy, while the Be composition, x, was measured with time of flight elastic recoil detection analysis. When x is 6%, substitutional and interstitial Be atoms are revealed to be co-existing in BexZn1-xO films. Furthermore, phase segregation of BeO is observed when x increases to 10% due to the huge difference of the bond length between Be-O and Zn-O. In this case, most of the Be atoms are found to form BeO particles, rather than a BeZnO alloy, so as to reduce the formation energy. The incorporation of Be atoms in the ZnO lattice consequently decreases in Be0.1Zn0.9O, resulting in a smaller bandgap than that of Be0.06Zn0.94O.