Fermi Level Effects on Mn Incorporation in III-Mn-V Ferromagnetic Semiconductors

The chapter deals with III_1-xMn_xV alloys. The III–V-based ferromagnetics taken together have already opened a number of fundamental issues in magnetism and magnetotransport, as well as in the interrelationship between the two. The development of these materials holds promise of integrating ferromagnetic and nonmagnetic semiconductors, with an eye on developing new devices that depend on electron charge as well as on its spin. Hole-mediated ferromagnetism in III_1-xMn_xV alloys is described. Calculations based on the Zener model predicted that TC in Ga_1-x Mn_x As could be improved by increasing the Mn content and/or the free hole concentration in the alloy. In the Zener model description of the ferromagnetism in Ga_1-xMn_xAs, only the substitutional Mn²⁺ ions are considered (Mn_Ga). To incorporate the higher Mn concentrations into the III–V lattice that are required for achieving ferromagnetism, it is necessary to resort to low-temperature molecular beam epitaxy (LT-MBE), in which strong nonequilibrium growth conditions are realized. The chapter explains the determination of the location of Mn in the GaMnAs lattice by ion channeling. Magnetoresistance, Hall measurements, and superconducting quantum interference device (SQUID) magnetometry are most commonly used for electrical and magnetic characterization of III_1-xMn_xV ferromagnetics, including the determination of their Curie temperature (T_C). The effects of Mn location on the electronic and magnetic properties are discussed along with T_C enhancement by elimination of Mn_I.