Abstract
本研究係利用改良型二溫區水平布式法成長砷化鎵單晶，並就此方法與傳統的二溫區水平布式法，水平溫度梯度凝固法及三溫區水平布式法在化學組成份控制，成長完晶體與石英船黏著的程度及矽雜質的污染等作一比較。晶體的成長條件，對於晶體品質有很大的影響。本研究針對成長界面形狀，溫度梯度，雜質的濃度及成長速率等成長變數作一詳細研究。結果發現成長界面是平面狀且向前傾斜時，不衹容易成長單晶，且差排密度較小，載子濃度在(100) 晶片的分佈也較均勻。溫度梯度的降低及雜質濃度的增加均有利於差排密度的降低。但溫度梯度太弓時容易導致小面生長的產生，嚴重時甚至導致雙晶的產生；而雜質濃度太高又會導玫微缺陷的產生。在最佳的成長條件下，N 型及P 型砷化錠單晶的差排密度可以控制在從頭至尾均小於600ｃｍ-2 ，且晶體內沒有任何微缺陷產生。本論文對於砷化錠晶體的缺陷如雙晶及小面生長亦作一詳細的探討，結果發現小面生長區域的載子濃度是其他地方的1.7 至2.0 倍。雙晶化以化學腐蝕法及高解析電子顯微鏡分析鑑定為 180°旋轉雙晶。至於在高載子濃度（大於４＊１０18ｃｍ-3）區域的缺陷，以穿透式電子顯微鏡分析，發現主要的缺陷是疊差，析出物及差排環。在解析電子顯微鏡晶格像裡，所有的差排環都有一額外的面，因此這些差排環可能是由砷間隙原子析出形成。///////An improved two temperature zone horizontal Bridgman method, which has noas zone but still can maintain an accurate contorl of the stoichiometry,was developed. With this method, the sticking between the quartz boat andGaAs crystal was thoroughly eliminated. In addition, the contaminationfrom the reaction of GaAs melt and quartz boat is less serious compared toother boat growth methods. GaAs single crystals with 2 or 2.5 inch indiameter and 30 cm in length can be routinely grown by this method. Theyield of single crystal is more than 95%. Keeping the solid╱meltinterface flat and eliminating the sticking between quartz boat and GaAscrystal were found to be critical for eliminating the lineage defects andobtaining low dislocation density GaAs crystals. Moderately Si-doped GaAscrystals grown by this technique have etch pit densities lower than 2000ｃｍ-2. For moderately Si-deped GaAs crystals, the best result shows thatEPDs are lower than 600ｃｍ-2 in the whole ingot. Nearly dislocation freeSi-doped GaAs crystals with high carrier concentration of１－４＊１０18ｃｍ-3 can also be grown by this technique. Zn-doped GaAscrystals with carrier concentration in the range of １－５＊１０19ｃｍ-3have EPDs lower than 3000 ｃｍ-2.The best Zn-doped GaAs crystals haveEPDs lower than 600 ｃｍ-2 in the whole ingot. The carrier concentrationand mobility of the undoped GaAs crystals are in the range of５＊１０15－１＊１０16ｃｍ-3 and 3600-5000 ｃｍ2╱Ｖ－ｓｅｃ respectively.The result indicates that high purity GaAs crystals with low Sicontamination can be grown by the M2T-HB technique.Facets in GaAs crystalswere found to form only on (111) planes. The reduction in temperaturegradient, and the increase in Si-doping concentration and the growth ratewere found to facilitate the facet formation. The carrier concentrationof the facet area, as measured by van der Pauw method, was 1.7-2.0 timeshigher than that of the non-facet area. The twins in GaAs crystals weregenerated from the (111) facet region, especially at the pisition wherethe size of the facet varied drastically, and there is no preferencefor the generation of twins from the (111) As or (111) Ga facets region.Whether or not facets directly cause twinning is still uncertain, but iscertain that the growth conditions that lead to generation of largeirregular facets also causes twinning. All the twins in GaAs crystalsgrown by HB technique were examined by chemical etching and HRTEM,and are identified to be 180°rotation twins. The microdefects observedin most of the heavily Si-doped GaAs crystals are stacking faults,precipitates and dislocation loops.Because all the dislocation loopsstudied by HRTEM have an extra plane and are of interstitial character,it was concluded that As interstitials are responsible for the dislocationloop formation.