Quantum Transport in Diluted Magnetic Semiconductors

The chapter highlights selected electric charge transport phenomena studied recently in low dimensional structures of DMSs. The first part describes transport phenomena related to the quantum interference of scattered electron waves in diffusive transport regime at the boundary of metalinsulator transition. The second part is devoted to Landau quantization of electronic states, as quantum Hall effect and related phenomena. The focus is put on dramatic influence of exchange interaction between magnetic ions and charge carriers on transport. 1 Magnetically doped low dimensional semiconductor structures We start from a short preview of available low dimensional devices for transport studies in DMSs. There are two types of semiconductor devices containing two-dimensional electronic systems (2DES). In the field effect transistor (FET) also known as metal-insulator-semiconductor (MIS) structure, 2D conducting layer is formed at the interface between a semiconductor and an insulator, as shown in Fig. 1 (a). The insulator is equipped with electric gate. The electric field perpendicular to the interface attracts electrons from the semiconductor. As a result, a few nanometer wide potential dip is formed at the interface. Since its width is comparable with electronic wavelength λe, the motion perpendicular to the interface is quantized into discrete energy levels corresponding to the electronic standing waves. However, in such quantum well (QW) the carriers can move the plane parallel to the interface, forming a two-dimensional system of electrons (2DES). In particular, the most popular FET has Si for the semiconductor and SiO2 for the insulator. The earliest transport investigation of 2DES involving DMSs was carried out on metal-insulator-semiconductor structures fabricated on the surface of (Hg,Mn)Te [1]. It was followed by a study of 2DES formed at naturally grown inversion layers in the grain boundaries of the same material [2].