Electron-Paramagnetic-Resonance Studies of the Fluorine Donor in Beryllum Oxide

A prominent point imperfection observed by electron paramagnetic resonance in x-irradiated single-crystalline BeO containing fluorine has been studied under varying conditions of temperature and uniaxial stress. This point imperfection in its neutral, paramagnetic charge state consists of one electron in excess of saturated bonds and closed shells, trapped near the fluorine impurity. The fluorine impurity substitutes for oxygen in the BeO lattice and, isolated from other defects, is a deep donor. The extra electron occupies an orbital localized primarily on two of the three basal beryllium ions nearest the fluorine. The observed temperature dependence of the ${\mathrm{Be}}^9$ hyperfine structure is analyzed by using a classical model of random hopping among the three two-beryllium states of the donor. The resulting slight dependence of the hopping rate on temperature is discussed in terms of a quantum-statistical picture. The three states are coupled through nonzero matrix elements of the vibrational energy but are partially decoupled as a result of large static random strains in the crystals.