Inverted level ordering for a double acceptor or acceptor-bound exciton

Abstract

The J=0,2 levels of two equivalent P8 holes bound at a tetrahedral site should exhibit the normal ordering given by Hund's rule, with J=0 above J=2, despite departures from effective-mass theory caused by central-cell corrections, Stark effects, and strain, if the holes interact only through their Coulomb repulsion. A dynamic Jahn-Teller effect, arising from coupling the individual holes to E and/or T 2 vibrational modes, tends to invert this ordering, splitting J=2 into its Λ 3 and Λ 5 components and shifting J=0 below both components of J=2 if the Jahn-Teller coupling is strong enough to offset the holes' Coulomb repulsion. We suggest that it is the dynamic Jahn-Teller effect that explains the inverted ordering observed for such centers as the double acceptor Zn in Ge and the exciton bound at the acceptors Al, Ga, and In in Si.