Absorption Band Edge of Magnetic Semiconductors

Abstract

The shift of the absorption band edge with temperature and that due to an external magnetic field in magnetic semiconductors are investigated theoretically by studying a system in which a single conduction electron is interacting with localized spins on magnetic ions and a hole fixed on a magnetic ion.
A general formula for the optical absorption band shape in the system is derived by using the Green’s function method. The result shows that the bend edge shift arises through the temperature and magnetic field dependence of the spatial correlation function between the localized spins. The electron-hole interaction also affects the band shape.
The band shape functions near the absorption edge are numerically calculated for EuO and EuS at various temperatures and for several magnetic field strengths in classical spin approximation. The calculated results explain reasonably well the behaviour of the band edge shift with temperature and magnetic field.