熱退火處理之鈷摻雜氧化鋅稀磁性半導體薄膜其電性、磁性與結構變化

Transformation of structural, electrical and magnetic properties of thermally annealed Co:ZnO film

我們利用不同溫度的退火研究以離子束濺鍍成長之氧化鋅摻雜鈷稀磁性半導體薄膜之電性、磁性與結構變化。利用同步輻射X光吸收光譜技術可觀察到伴隨著不同溫度退火而產生的磁性轉變主要與微結構的變化有關。當退火溫度超過500℃時，原本取代鋅位置的鈷會稀出形成金屬團簇。而當750℃退火時，鈷金屬團簇會聚集為較大的顆粒而顯現出低自發磁化的行為。此外，這些顆粒亦會發生表面氧化的行為而可能造成光譜判讀上的混淆。我們的實驗結果說明了在釐清氧化鋅摻雜鈷稀磁性半導體的磁性來源時，除了檢測鈷的價數外，鈷周遭的局域結構的探討亦是扮演重要的角色。We report the annealing effect on electrical, magnetic and structural properties of ZnO:Co multilayers by ion beam sputtering. The observed change on magnetic properties could be related to the variations of the microstructure measuring by x-ray absorption(XAS). Our results suggest that the local structure around Co changes from Zn substitution in ZnO to that of Co clusters-like phase while annealing above 500℃. For annealing at 750℃, Co clusters aggregate to larger size and reveal low spontaneous magnetization beahvior. In addition, formation of Co oxide was taken place on the surface of Co clusters. The oxidization in the Co clusters surface could smear out the XANES result. We demonstrate that not only the charge states of Co but also the local structure surrounding Co atoms are important to clarify the origin of RT ferromagnetism.