有機金屬氣相磊晶法低溫成長砷化鎵及砷銻化鋁之熱力學分析

Abstract

本論文主要分兩部分.第一部分是以有機金屬氣相磊晶法成長AlAsSb化合 物半導體薄膜並以熱力學分析薄膜組成,相圖等磊晶結果.第二部分則是以 有機金屬氣相磊晶法在低溫成長GaAs化合物半導體薄膜,並以霍爾量測,深 能階暫態能譜,冷激光等方法對薄膜內的各種缺陷一一探討.在熱力學分析 AlAsSb的實驗中,我們使用規則溶液模型,DLP模型來預測AlAsSb的固相組 成及相圖.熱力學計算的結果和實驗結果相當符合.低溫成長砷化鎵的實驗 中,以TEGa,TBAs為反應分子源,在攝氏500度成長GaAs,霍爾量測結果顯示 薄膜電阻係數可高達8410歐姆公分.藉由 DLTS量測,我們發現在傳導帶下 約0.5ev到0.6ev有一和氧有關的缺陷,同時變溫霍爾量測亦顯示在傳導帶 下約0.5ev有一深能階缺陷.這個缺陷可能是造成薄膜高阻值之主因.將磊 晶溫度提升至攝氏600度,DLTS所量得和氧有關的缺陷消失,同時霍爾量測 得到低電阻質的結果,證明此深能階缺陷和低溫磊晶時薄膜之高電阻質有 關.除了和氧有關的缺陷外,DLTS亦量到在傳導帶下0.75ev到0.96ev有一和 EL2有關之深能階缺陷.由於EL2是砷佔據鎵之晶格基所造成的,高濃度之 EL2顯示磊晶介面缺乏高活動力之鎵原子.這在冷激光量測中亦得到證實. 冷激光的光譜顯示在傳導帶下1.36ev有鎵空缺和某種雜質作用形成之缺陷 能階,而在傳導帶下1.22ev處則有鎵空缺的存在.將磊晶溫度提升至攝 氏600度,鎵空缺消失而DLTS所量得EL2濃度較低溫磊晶時小100倍.因此,低 溫磊晶時鎵空缺的出現可能是造成DLTS量測中EL2濃度較高之主因. The thesis consists of two experiments . In the first exp- eriment , thermodynamic is used to analyze the new III-V compound AlAsSb grown by our MOCVD system . In the second experiment , we use MOCVD to grow GaAs at low substrate tem- perature called LT-GaAs . To fully understand the properties of the LT-GaAs , the sample were characterized by means of PL , DLTS , and Temperature Dependent Hall (TDH) method . In thermodynamic analysis , regular solution model , togeth- er with DLP model , were used to predict the solid composit- ion and phase diagram of AlAsSb thin film . It is found that the experimental data are in excellent agreement with the r- esults predicted by the thermodynamic calculation . The LT-GaAs sample were grown at 500C using TEGa and TBAs as precursors . Hall measurement data show that the Lt-GaAs is highly resistive . From the DLTS measurement , we find the phenimena may probably caused by the deep trap level , loca- ted at 0.5ev-0.6ev below the conduction band , which is bel- ieved to correlate with oxgyen in GaAs . It is interesting to note that the oxgyen trap is disappeared completely when we raise the growth temperature to 600C , and , according , the resistance of the sample reduce significantly . It can be concluded that the electrical property of LT-GaAs asmple is mainly controlled by the oxgyen related defect .