以射頻磁控濺鍍法成長氧化鋅摻鈷稀磁性半導體薄膜

Co-Doped ZnO Diluted Magnetic Semiconductor Thin Films Fabricated by RF Magnetron Sputtering

鄭賀名(Ho-Ming Cheng)

指導教授 ： 王耀德

國立臺北科技大學/電資學院/光電工程系研究所/碩士(2010年)

摘要

稀磁性半導體薄膜能夠被應用在自旋電子學的領域，讓我們在很低的功率下有較快的操作速率。由於氧化鋅的寬能隙特性和鈷在氧化鋅中能展現良好磁矩等原因，氧化鋅摻雜鈷的材料很適合用來製作稀磁性的半導體。
本實驗所製備的薄膜有很大的電阻，因此薄膜的磁性應當是由氧空缺和束縛電子所形成的束縛磁極化子來產生的。實驗所製備的樣品要儘可能避免在薄膜中出現磁性離子的團簇與二次相位析出，因為當這些磁性析出物產生後會產生蕭基位障，而形成傳導電子散射中心，所以要對薄膜作XRD的晶格結構分析，希望薄膜能以C軸為優先成長的方向，再來是用電子顯微鏡觀察薄膜的表面形貌，希望能夠看到微小晶粒的出現，以期望薄膜中有較多的氧空缺來形成束縛磁極化子。最後再透過超導量子干涉儀進行磁滯曲線的測量，希望能展現室溫的鐵磁性。
本實驗觀察到薄膜的表面若是有較微小的晶粒，可以有比較明顯的磁滯現象，而透過在45 mtorr的500℃低壓退火製程30分鐘後，晶格結構會從原本的C軸改為以(103)為主要的成長方向。從文獻上的結果推論以此方向生長有助於介電常數的增加，且因為有縮短的晶格面距離故應有較大機會讓束縛磁極化子半徑重疊，進而提升了對齊磁離子磁矩的可能。增大膜厚，則是減少雜訊干擾的辦法。

關鍵字

氧化鋅摻鈷稀磁性半導體薄膜 ； 束縛磁極化子模型 ； 居禮溫度

並列摘要

Diluted magnetic semiconductors can utilize charge and spin degrees of freedom of a single device and could be applied to the spintronics. By virtue of the wide-bandgap characteristic of ZnO and the large magnetic moment of Co in ZnO, Co-doped ZnO material is ideal for fabricating the diluted magnetic semiconductor.
By using the instruments like XRD, SEM, and SQUID, we can examine the crystal structure, the surface morphology, and the magnetic behaviors of the deposited thin film respectively. We observed that as the grain size decreases, the measured hysteresis loop has more obvious remanance and coercivity. The phenomenon may be due to the richer oxygen vacancies of the sample with smaller grain size and can be illustrated by the bound magnetic polaron model.
If we annealed the as-deposited ZnCoO thin film under the pressure of 45 mtorr, the resulted sample would display higher remanence and larger saturated magnetization. We infer that the improvement is due to the higher dielectric constant and lower d-spacing of the (103) crystal plane when compared with the (002) one.

並列關鍵字

Curie temperature ； DMS ； Co-doped ZnO thin film ； ferromagnetism

參考文獻

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