Covalent effects and optical spectra of transition metal impurities in semiconductors

Abstract

Covalent interaction of the electrons from the unfilled d-shell of transition metal impurities in semiconductors with ligands results in swelling the d-electron wave functions. Several obvious results of this are a drastic increase of the absorption cross-section (antenna effect), lifting of bans for some dipole transitions due to mixing of the states with different parities. A less obvious consequence is a possibility of lines complementing the intracenter transitions to the forbidden energy gap. They appear due to multielectron structure of the d-shells and become observable in the luminescence due to an interference of the covalent effects and the electron phonon interaction. The same effects lead to a long living metastable electronically excited <SUP>2</SUP>E configuration of the d atom. As a result observation of the complementing lines in the absorption also becomes possible.