光電材料砷化鎵 (GaAs) 因其直接躍遷 (direct tranition)等 特性，一直以來即在發光元件的領域有著很好的應用。其電子遷移率 (mobility) 高達 8500(cm2/V-s)，將近是矽 (Si) 的 5 到 6 倍，更是 人們寄望能製成更高速更高頻的元件之材料。而以往在砷化鎵上成長 可靠的氧化層以製成 MOS 元件卻一直是技術上的一大瓶頸，近年來 此一部份技術卻有重大的突破，然而其氧化層介面的諸多性質仍是有 待探求的領域。
我們因此應用美國貝爾實驗室所提供的樣品試片，對其進行 XPS 的分析實驗。我們是在新竹的同步輻射中心以同步輻射所產生的 X 光光源來對試片進行量測。因其光源有極高的解析度。在一系列的實 驗中我們觀察到將 (Ga2O3-Gd2O3 )，Ga2O3或是 Gd2O3等化合物以電 子束蒸鍍方式在砷化鎵表面形成氧化層時，其中鎵會以不同的氧化型 式存在於氧化層中。這很可能是因為鎵 (Ga) 的電負度因為和釓 (Gd) 的電負度極為接近，因此在成長氧化層的過程中很容易因彼此和氧的 相結合競爭而形成某種混合化合物。再進一步的分析，我們發現例如 若原成長氧化層的材料是純質的 Ga2O3，則鎵會以此種氧化物型式形 成氧化層直至與砷化鎵的介面上，此時鎵的氧化態較高，所以所測得
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的 Ga(3d)價電子束縛能亦較高，約 21.5eV 左右。但若生成的材料是 (Ga2O3-Gd2O3 ) 或 Gd2O3 則 Ga(3d)價電子所表現的束縛能分別是 21.0eV 以及 20.3eV 左右。由此可推論氧化鎵化合物的鎵會以一價，
二價，三價的型式有條件的存在於這類氧化層中。我們觀察到這種差 異現象隨著用氬離子 (Ar+) 撞濺試片愈近這類氧化層與砷化鎵之介 面時，會愈明顯，很可能是在試片製程的過程中因為鎵 (Ga) 自試片 基板因熱擴散出所致。
本實驗所測試的樣品由於是近年來才以成功的製程技術長成，因 此仍有許多的領域有待瞭解，例如在後續的研究中我們也繼續嘗試以 能量反應的觀點 (dG = dH－TdS－SdT ) 來加以探討。或是製程條件 的控制否會因本文中所提到的性質而對載子於氧化介面傳輸有所影 響等等。最後希望我們所作的實驗成果能對於這些方面有所幫助。
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