Defect Engineering and Ferromagnetism in ZnO-Based Dilute Magnetic Semiconductors: A Review

Dilute Magnetic Semiconductors (DMSs) are the promising materials for spintronic, optoelectronic and photovoltaic technologies. This can be achieved by integrating the electron's spin with its intrinsic charge transport. Amongst oxide based host semiconductors, Zinc Oxide (ZnO) stands out due to its key features: wide direct energy bandgap (3.37 eV), large exciton binding energy (60 meV) and high thermal stability. Doping with transition metal (TM) or rare-earth (RE) elements into the ZnO crystal lattice induces spinpolarization and Room-Temperature Ferromagnetism (RTFM). This review highlights the crystal polymorphism, photoluminescence (PL) mechanisms, defect-mediated magnetic exchange interactions and related experimental advances in ZnO based DMSs. We also discuss the key technological applications ranging from spin field-effect transistors (Spin-FETs), spin light-emitting diodes (Spin- LEDs) and magnetoresistive random-access memory (MRAM) to transparent optoelectronics, photocatalysis and biological/gas sensing. Additinally, major challenges and prospective applications in spintronics, quantum computing, optoelectronics and catalysis are addressed.