ABSTRACT
In the last couple of years, dilute magnetic semiconductors (DMSs) have drawn signicant interest in the scientic community. Primarily, this is due to its potential for application in spintronic devices. Conventional semiconductor (such as Si, Ge, and GaAs) devices and integrated circuits are based on the manipulation of the charge of electrons. They do not contain magnetic ions and are nonmagnetic semiconductors. However, in recent years, people are trying to incorporate spin degree of freedom simultaneously with the charge of the carriers (electrons and holes) in a single semiconductor device to achieve integration of functions like reading or writing information, data storage, etc., that is, try to achieve spin-or magnetism-based semiconductor devices. This emerging branch of next generation devices is known as spin electronics or spintronics. Spintronic devices such as spin-valve transistors, spin light-emitting diodes, nonvolatile memory, logic devices, optical isolators, ultrafast optical switches, and magnetic sensors are some of the areas of interest for
6.1 Introduction .......................................................................................................................... 113 6.2 Results and Discussion ......................................................................................................... 116
6.2.1 Ion Beam Irradiation-Induced Modication of Materials ....................................... 116 6.2.2 Irradiation-Induced Modication in ZnO ................................................................. 118 6.2.3 Irradiation-Induced Modication in TM-Doped ZnO.............................................. 121
6.2.3.1 Ion Implantation Effect .............................................................................. 121 6.2.3.2 Ion Irradiation Effect ................................................................................. 127
6.3 Conclusion ............................................................................................................................ 143 Acknowledgments .......................................................................................................................... 144 References ...................................................................................................................................... 144
introducing the ferromagnetic properties at room temperature in a semiconductor (Pearton et al. 2004). Study of magnetic semiconductors started in the late 1960s. Europium chalcogenides (e.g., EuS, EuO, and EuSe) and semiconducting spinels (e.g., CdCr2Se4 and CdCr2S4) that have a periodic array of magnetic elements were studied comprehensively, but they were not found suitable for practical applications because of lower Curie temperature (Tc). A different way to achieve ferromagnetism in a semiconductor is to insert a transition metal (TM) ion like Mn, Co, Fe, Cr, and Ni in a nonmagnetic semiconductor matrix (zinc oxide [ZnO], GaN, …). This new class of materials is commonly known as dilute magnetic semiconductors (DMSs). DMSs are the solid solution of nonmagnetic semiconductor doped with magnetic elements (Mn, Fe, Co, and Ni) with a few to several atomic percent. A true DMS is one in which the host semiconductor is randomly doped with a small amount of magnetic impurities such as TMs or rare earths. In this way, both localized spins of the magnetic ions and itinerant free carriers (electrons or holes) coexist in the semiconductors. In the presence of free carriers, the localized spins of the magnetic impurities interact with each other and develop magnetic characteristics of the host material. At a suitable concentration of free carriers and magnetic impurities, the exchange interaction between localized spins may be ferromagnetic, and in this case, the DMS would exhibit ferromagnetic behavior (Özgür et al. 2005). However, for practical applications, ferromagnetic DMS is required to operate at room temperature. The nature of exchange interaction between the free carriers and magnetic ions, that is, carrier-induced ferromagnetism, in DMS depends upon their respective concentration; a precise control over carrier doping and magnetic alloying is essential to achieve room temperature ferromagnetic semiconductors.
