17III–V‐Based Magnetic Semiconductors and Spintronics Devices
Hiro Munekata
Tokyo Institute of Technology, Kanagawa, 226‐8503, Japan
17.1 Introduction
Ferromagnetism in semiconductors was studied systematically in the 1980s in a heavily p‐type, narrow‐gap IV–VI diluted magnetic semiconductor, (Pd,Sn,Mn)Te. In samples with Mn content of 0.005–0.09 [1,2], it was found that ferromagnetic order develops when holes start to occupy the heavy hole band at hole concentration p beyond 3 × 1020 cm−3, whereas ferromagnetic interaction is weakened for p values higher than 8 × 1020 cm−3. The entire behavior was explained successfully in terms of the Rudelman–Kittel–Kasuya–Yoshida (RKKY) interaction, originally derived to explain the behavior of magnetic impurities interacting with each other by polarizing conduction electrons in metals [3]. The work in ferromagnetic p‐(Pd,Sn,Mn)Te has given a strong motivation to pursue ferromagnetism in technologically important semiconductors based on group IV elements and III–V compounds.
In this chapter, we are concerned with ferromagnetism in III–V‐based diluted magnetic semiconductors (III–V‐DMS), especially those having narrow and middle band gaps. This class of semiconductor materials, as first demonstrated successfully by (In,Mn)As [4,5], contain a large amount of magnetic ions (1020–1021 cm−3) in the host crystals, despite its low equilibrium solubility limit. The work carried out for more than two decades has revealed that various transition‐metal elements ...