Dynamic displacement anisotropy of atoms, streamer discharges and phonon focusing in BeO and CdSe crystals and I-VII compounds

Abstract

Streamer discharges at 77 K and crytallographically oriented surface spark breakdown at 295 K have been obtained in BeO crystals. An inverted temperature dependence has been found for the breakdown anisotropy compared with that in CdSe crystals. It is shown that the temperature dependences of the excitation thresholds of the incomplete electric breakdown at different crystallographic orientations in dielectrics as well as those of the streamer discharges in hexagonal semiconductors are controlled by the anisotroply of ionic dynamic displacements. The directions of maximum phonon focusing have been calculated in the localoisation planes of the incomplete breakdown in NaCl, KBr and LiF crystals at room temperature in accordance with well-known breakdown model along phonon streams. It is shown that the alkali halide breakdown data do not agree with this model. An anisotropy is predicted of the dynamic displacement of atoms in alkali halide crystals as well as in the basis plane and mirrorsymmetric directions of planes containing the crystallographic c-axis in hexagonal II–VI compounds, which allows us to explain the observable particularities of the discharge anisotropy in both cubic and hexagonal crystals.