透過原子結構的分析我們發現,無論是 Sapphire 或是 Silicon 基板,
藉由通入製成環境氣體 O2及 N2,分別形成 monoclinic 結構的 CuO 與 cubic 結構的 Cu2O。而在電子結構的分析,以下我們依基板的選擇分成兩個部 分說明:
1. Sapphire-based:
(1) CuO:主要以 Cu 3d/4sp 軌域的電荷 charge transfer 到 O 2p 軌域為主,
而在 CuO 250℃-sa 時有 O 2p-Cu 4sp 的 hybridization 出現,隨溫度上 升後出現 sp-d 的 rehybridization。
(2) Cu2O:主要以 O 2p-Cu 3dhybridization 及 Cu 3d 電子 charge transfer 到 O 2p 軌域並伴隨 O 2p-dangling bond 生成為主。隨溫度的上升,
由 Cu2+貢獻轉變為 Cu1+主導。
2. Silicon-based:
(1) CuO:在 CuO 250℃- si 時,Cu 3d 電子 charge transfer 到 O 2p 軌域並 伴隨 O 2p-dangling bond 生成,此時發現電子容易累積在 VB。隨溫 度上升時則以 O 2p-Cu 3d/4sp 的 hybridization 為主。
(2) Cu2O:主要以 Cu1+ 3d 和 Cu2+4sp 電子 charge transfer 到 O 2p 軌域並 伴隨 O 2p-dangling bond 生成為主, 其中還有 O 2p-Cu2+3d 的 hybridization。當溫度上升後,電子會累積在 Cu 4sp 的未佔據帶。
成長於 Sapphire-based 時,由於 Cu2O 樣品無論製程溫度,都有 O 2p-dangling bond 的生成,所以較 CuO 樣品有較好的導電性。此結果正好 說明了先前光穿透率的量測,亦即對 CuO 而言,Cu2O 有較小的 band gap,
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使得電子容易躍遷,因而有較好的導電性。而成長於 Silicon-based 的樣品,
由於 CuO250℃- si 的電子多累積於 VB,且 conduction band 提供較多的未 佔據態態密度,因此電性上的表現較 CuO500℃- si 佳。
成長在 Silicon-based 時,CuO 樣品以及 Cu2O250℃- si 屬於雙極切換。
主要是因為此時的樣品內擁有許多 O 2p-dangling bond,且由 MIS 結構以 及我們的能譜上並未見金屬 Cu 的訊號,可以認為是由氧空缺提供陰離子 傳導,形成絲路進行低阻態的切換,屬於價電子轉換效應。而 Cu2O500℃
- si 屬於單極切換,起因於電子累積在 Cu 4sp 的導帶,於低阻態時可作為 自由電子進行歐姆傳導,而在施予偏壓後,電子即填入樣品中的缺陷,使 樣品形成空間電荷限制傳導漏電流機制。此時熱化學效應影響加劇,致使 絲路斷裂,也使缺陷造成 trap-empty state 的現象,進而切換回穩定的高阻 態。
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