氧化鋅薄膜和單晶導電機制之研究

Abstract

氧化鋅的導電機制一直是令人相當好奇的課題，儘管從1930年代就已有相關的討論，讓人驚訝的是，直到現在都還沒有能讓大家滿意的物理圖像。本研究藉由量測單晶和薄膜氧化鋅電阻率隨溫度的變化，充分地探討在大範圍的溫區中氧化鋅所發生的各種導電過程，使我們對氧化鋅導電機制有深刻的了解。 本實驗以四點量測的方式得到單晶氧化鋅電阻率跟溫度的關係，由結果我們找到深層和淺層的雜質能階，兩者均以受熱激發的方式對導電帶提供導電電子，且分別在不同的溫區主導著導電機制。由真空高溫退火前後的數據確認了氧空缺為淺層雜質之一。 其次對一系列在氬氣、氧氣比例不同的環境中所濺鍍出來的薄膜樣品進行直流電阻的四點量測，並和單晶的結果作比較。我們發現溫度在498 K-100 K 時，薄膜的導電機制除了深層和淺層的雜質能階外，近程跳躍導電會在較低溫時主導著導電機制。 分析100 K 以下的實驗結果可以知道Mott 變程跳躍機制主導著電導率的行為趨勢，利用特徵溫度便可得知平均跳躍能量與距離，最後將受熱激發導電和近程跳躍機制的熱激發能與Mott 變程跳躍的平均跳躍能量作比較與分析。

The electrical conduction mechanisms of ZnO makes people curious for many years.Although there has been some researches since 1930’s,but the comprehension in electrical properties of ZnO nowadays is still not complete.In this thesis, we exhibit the conduction processes of ZnO between 498 K-10 K . We use four probes measurement to get ρ(T) of single crystal ZnO.The deep and shallow donor levels are verified in band structure,and each of them leading the conduction process in different temperature region upon 100 K.Both of them affect the total conductivity by thermally activation conduction.Comparing data with the results after vacuum annealing,we affirm oxygen vacancy to be one kind of shallow donors in ZnO. we found that thermally activation conductions caused by deep and shallow donor levels are the major conduction processes in higher temperature region between 498 K-100 K and nearest neighbor hopping (NNH) dominants the conductivity of films slight upon 100 K after performing four probes measurement on a serious of ZnO films deposited by rf sputtering in mixture of argon and oxygen atmosphere . Mott variable range hopping conduction (Mott VRH) occurs in films when temperature is below 100 K.By using characteristic temperature TM,we can calculatethe average hopping energy and distance.Finally we compare the activation energy of the two donor levels and NNH process with the average hopping energy of Mott VRH.