Spontaneous Tunnel Transitions Induced by Redistribution of Trapped Electrons over Impurity Centers

A system of polyvalent impurity centers in a semiconductor (i.e. Au-centers in Si) is considered. The ground state of the impurity pair Au~(a) + Au° (b), where an extra electron is localized on the site a, may be turned into an excited state due to a change of the charge state of a third nearby impurity site. This happens because of different shifts of the Au~-level at sites a and b due to their different distances from the third center. As a result, the original pair is able to reach a new ground state Au° (a) + Au~ (b) through a slow spontaneous tunnel transition. The probability of this transition, when it is accompanied by an emission of a low energy photon, is calculated explicitly.