Cobalt-doped zinc oxide dilute magnetic semiconductors for spintronics devices
Date of Issue2009
School of Materials Science and Engineering
In recent years, Dilute Magnetic Semiconductors (DMS) with ZnO as host materials have attracted enormous attention. Structural and magnetic properties of Zno.95Coo.05O thin films grown on rc-type (001) silicon by pulsed laser deposition method were characterized. Contributions by metallic cobalt nanoclusters, oxygen partial pressure and substrate deposition temperature to ferromagnetism were investigated. Experiments have shown that the observed ferromagnetism in Co-doped ZnO thin films was not due to the metallic cobalt nanoclusters. Bound magnetic polaron (BMP) model and Ruderman- Kittel-Kasuya-Yosida (RICKY) interaction are the two mechanisms that most likely explain the origins of Zno.95Coo.05O ferromagnetism. The amount of oxygen vacancies, which could be adjusted by varying the oxygen partial pressure during DMS thin film deposition, affects the polaron density in the BMP model that leads to formation of long range order of magnetic cations. It was also demonstrated that there is an optimal substrate temperature range for maximum saturation magnetization as a balance between the carrier concentration and carrier mean free path have to be achieved. Metal-insulatorsemiconductor structures were fabricated by pulsed laser deposition method to investigate the injection of carriers by an external electric field into the DMS layer. Under different applied electric field, the carrier concentration in the Co-doped ZnO layer was adjusted. This led to a change in the ferromagnetic properties of the DMS layer that could be explained by the RKKY mechanism.
DRNTU::Engineering::Materials::Microelectronics and semiconductor materials
Nanyang Technological University