Carriers effects on the room temperature ferromagnetism in nitrogen doped TiO2 thin films

• Main Authors: Hu, Yen-Ming, 胡彥銘
• Other Authors: Juang, Jenh-Yih
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/08749841351754902635

碩士 === 國立交通大學 === 電子物理系所 === 103 === Obtaining room-temperature ferromagnetism (RTFM) in semiconductors has been considered as one of the key ingredients in realizing much anticipated spintronics. Recently, there is an increasing interest in searching for RTFM in several wide bandgap semiconductors by doping with non-magnetic elements. In this study, we have made a series of TiN_(2-x) O_x thin films, which is believed to play an important role in inducing carrier doping necessary for obtaining RTFM with various oxygen annealing treatments. It is expected that, after proper annealing, the process may lead to different degrees of N-doping in the TiN_(2-x) O_x matrix, and hence RTFM. Preliminary x-ray diffraction results have evidently indicated that the primary diffraction peak of oxygen annealed TiN_(2-x) O_x appears to shift more drastically toward the Anatase TiO_2 (004). Furthermore, by utilizing photoluminescence (PL) and X-ray photoelectron spectroscopy, N impurity and oxygen vacancy were proved to decrease with prolong oxygen annealing. However, from our study, the density of states near Fermi energy was found to remain exactly the same regardless the duration of annealing treatment. This result implies that the p-p coupling interaction between N and O are not affected by oxygen annealing, and hence, the features of Stoner splitting that gives rise o local magnetic moments. The annealing-induced weakening of RTFM thus is probably caused by the reduction of itinerant carriers associated with N-doping and oxygen vacancies. Our results are in line with the general features predicted by the bound magnetic polaron (BMP) model for the occurrence of RTFM in this system.