Femtosecond magnetic spectroscopy of carrier localization in diluted magnetic semiconductor quantum structures

Abstract

A direct study of the optically induced magnetism in a semiconductor quantum-well system as a way to explore the connection between the electronic and magnetic properties of dilute magnetic semiconductor heterostructures is described. The magnetism is induced by optically generated carriers through a local spin-spin exchange interaction with the magnetic moments, so that the region of magnetization matches the extent of the carrier wave functions. The penetration of the excitonic wave function into the nearby barriers can be varied by changing the width of the potential well or by exciting carriers into higher quantum levels, where the carrier wave function penetration grows with increasing energy. These experiments employ Cd1-xMnx Te-Cd1-yMnyTe superlattice structures which are excited optically be subpicosecond pulses. Time-averaged magnetic spectroscopy measurements reveal a connection between the quantum confinement of the electrons and holes and the magnetic properties through the appearance of well-defined structure in the spectra. The time-resolved behavior of this magnetization is found to be critically dependent on the width of the quantum well and the energy of the confined carriers.