ABSTRACT
Figure 19.1 Schematic drawings of (a) a magnetic semiconductor, (b) a nonmagnetic semiconductor, and (c) a DMS. Reproduced from J. Phys.: Condens. Mat., 17, pp. R657-R689 (2005). Copyright © 2005, IOP Publishing Ltd [1]. Compared with conventional semiconductors, spin becomes another information carrier together with charge, in DMSs, giving these types of new materials numerous advantages, especially in information technology. For example, current metal-based magnetic devices (such as hard drives) store information, whereas semiconductor-based devices (such as central processing units [CPUs]) process information. The exchange of information between these two separate units is both energy-and time-consuming [8]. With DMS-based spintronics, data manipulation and long-term storage can be realized in one computer chip, rather than separately
in a CPU and a hard drive, as is the current practice. Data manipulation would be much faster and require less power, and such a computer would be lighter and consume less energy [8]. 19.1.2 Ge1-xMnx-Diluted Magnetic Semiconductors
It has been well recognized that Ge and SiGe are key materials for advanced Si-based high-performance transistors [9]. Although tremendous progress toward spintronic devices has been made in the DMS system, such as III-V-and II-VI-based DMSs, the essential importance of Si in mainstream semiconductor technology makes the realization of Si-compatible, group IV-based DMSs highly desirable [10-16]. In addition, the fact that Ge has higher intrinsic hole mobility than either GaAs or Si makes Ge-based DMSs much more attractive for commercial devices [5]. Since the first successful growth of Ge:Mn DMSs was reported in the early 2000s [5], extensive attention has been paid in terms of their promising applications in spintronic devices. Many attempts have been devoted to obtaining room-temperature (RT) ferromagnetic Ge:Mn DMSs with high Mn concentrations [10, 11, 13-19]. However, the fact that the low solubility of Mn in Ge makes it a challenging task to secure a high-Tc DMS. In contrast, Mn-rich clusters or precipitates, such as Mn5Ge3 [11, 13, 20-23] and Mn11Ge8 [19, 24, 25], were commonly observed, which have a negative impact on the intrinsic magnetic properties of the Ge:Mn nanostructures. In this chapter, recent progresses on the growth and the of Ge:Mn DMS nanostructures are outlined with a focus on the growth and structural properties of Ge:Mn thin films and quantum dots (QDs). The magnetic properties and device fabrications were also briefly discussed.
