MOLECULAR-DYNAMICS SIMULATION OF ELECTRON TRAPPING IN SAPPHIRE

Most phenomenological aspects of energy storage and release in dielect ric materials caused by the charge trapping mechanism have recently be en rationalized using the space charge model. We studied dynamical asp ects by performing molecular dynamics simulations. We show that an exc ess electron introduced into the sapphire lattice (alpha-Al2O3) can be trapped only at a limited number of sites. The energy gained by allow ing the electron to localize in these sites is of the order of 4-5 eV, agreeing well with the results of the space charge model. Displacemen ts of the neighboring ions due to the implanted charge are shown to be localized in a small region of about 5 Angstrom. Detrapping is observ ed at 250 K. The ionic displacements turn out to play an important rol e in modifying the potential landscape by dynamically lowering the bar riers that cause localization at low temperatures. (C) 1997 American I nstitute of Physics.