SPIN TRANSPORT AND OPTICALLY-PROBED COHERENCE IN MAGNETIC SEMICONDUCTOR HETEROSTRUCTURES

Molecular beam epitaxy is used to ''spin engineer'' an environment whe rein quantum-confined electronic states in a wide band gap II-VI semic onductor quantum well (Zn1-xCdx Se) are strongly exchange-coupled to s ystematic 2D distributions of localized spins (Mn2+ ions). Magneto-opt ical spectroscopy of undoped structures demonstrates that such a schem e successfully produces well-confined excitonic states whose Zeeman sp litting in modest magnetic fields greatly exceeds the inhomogeneous li ne widths. In modulation-doped structures, a combination of magneto-tr ansport and magneto-optical measurements shows the formation of a ''ma gnetic'' two-dimensional electron gas characterized by spin gaps which are much larger than Landau level gaps. This results in a novel quant um Hall system which can be highly spin polarized even at large fillin g factors. Time-resolved Faraday/Kerr effect measurements in the Voigt geometry probe the electronic spin dynamics of the exciton/electron g as, revealing terahertz and gigahertz oscillations that originate from the coherent spin precession of electrons and local moments, respecti vely. (C) 1998 Elsevier Science B.V. All rights reserved.