Chapter 5 Band Structure and Quantum Transport Phenomena in Narrow-Gap Diluted Magnetic Semiconductors

Abstract

Publisher Summary This chapter describes narrow-gap diluted magnetic semiconductors (DMS), known also as “semimagnetic semiconductors.” It focuses on their band structure in the presence of a strong, quantizing magnetic field. The small values of the effective masses, a characteristic of narrow-gap semiconductors, make them suitable for investigations in the quantum regime. The model that describes the diluted magnetic semiconductors with a narrow forbidden gap, based on the k·p approximation, assumes that two electronic subsystems can be distinguished. The first contains mobile delocalized electrons from the conduction and/or uppermost valence band. These electrons, which can be described in terms of the virtual crystal approximation, are mostly responsible for electrical and optical properties. The second subsystem consists of electrons from the 3d shells of, typically, Mn ions. It is assumed that these produce localized magnetic moments. The chapter also discusses the interaction between two electronic subsystems. It presents models of the band structure in a magnetic field for narrow gap DMS with the zinc blende lattice structure (e.g., Hg1–x,MnxTe). It also deals with experimental results for various DMS (including those with NaCl and tetragonal crystal structures) obtained in the course of investigations of quantum transport phenomena, mostly the Shubnikov de Haas effect. The chapter also discusses those features that are unique for the diluted magnetic semiconductors and that support the proposed model of the band structure. It also discusses the investigation of quasi two-dimensional electronic systems in diluted magnetic semiconductors.