OFF-CENTER ATOMIC DISPLACEMENTS IN ZINCBLENDE SEMICONDUCTOR

We have studied theoretically the conditions for the occurrence of spontaneous off-center atomic displacements in pure zinc-blende semiconductors. A pseudo Jahn-Teller coupling of a chemically active valence d band with an s-like conduction band is predicted to lead to such a metastability. All-electron density functional calculations confirm that this is the case in CuCl. The unusual experimental manifestations of this metastability are outlined.