利用分子束磊晶(molecular beam epitaxy)在低溫的基版上成長砷化鎵磊晶薄膜稱為低溫成長砷化鎵(Low- temperature- grown GaAs, LT-GaAs)。低溫成長的砷化鎵因受應力影響會產生過量的缺陷，經退火處理後可降低缺陷的密度、改變缺陷的分佈，但許多光電特性與高溫成長的GaAs不同，例如106 Ω-cm的高電阻值，超短光激發載子生命期(carrier lifetime)約為幾百飛秒(femtosecond)，這些特性可以增加在光導方面的應用。在本論文中，第一部份我們利用光調制光譜探討不同低溫成長的砷化鎵的光電特性。利用實驗數據和理論公式之最小平方擬合所得的參數，討論在不同成長溫度的樣品，其表面態密度、表面勢壘、能隙等變化，我們發現其缺陷密度及表面態密度隨成長溫度的降低而增加。第二部份我們量測低溫成長砷化鎵之拉曼光譜及雙晶X-光繞射光譜，藉由譜線的不同討論其成長溫度對於晶格振動模式及晶體結構的影響，我們發現其晶體結構隨成長溫度的降低而趨於多晶格結構。同時比較兩系列不同來源的樣品的拉曼及X-ray光譜，發現成長LT-GaAs時III-V族元素的流量對所成長樣品的品質有極大的影響。

　　Crystalline film of GaAs grown by molecular beam epitaxy on low temperature substrate is called low temperature grown GaAs(LT-GaAs). Excess defects exist in the LT–GaAs layer due to strain effect. After annealing, LT-GaAs has unique electro-optic property, such as resistivity of mega order, ultrashort carrier lifetime (about hundreds of femtosecond). LT-GaAs is commonly used in photoconductive application. In the first part of this study, we discuss the electro-optic property of LT-GaAs layer grown at various temperatures using modulation spectroscopy of photoreflectance(PR). We measured the intensity of photoreflectance as function of pump beam power. By least squares fitting the experimental results to the theoretical relation, the density of surface state, surface barrier height, and band gap of LT-GaAs grown at various temperatures can be obtained from the fitting parameters. It is found that the density of defects and surface states increase as the growth temperature decreases. In the second part of this study, we investigate the vibrational mode and crystal structures of the LT-GaAs samples from Raman spectra and double crystal X-ray diffraction. Results from Raman spectra and X-ray diffraction spectra are consistent, which indicate that the quality of the LT-GaAs is degraded as the growth temperature decreases and the film structure becomes more and more polycrystalline .

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