低溫砷化鎵的冷激光光譜分析及砷銻化鋁的拉曼研究

Abstract

本論文主要是以冷激光來探討以TEGa,TBAs 為分子反應源,利用有機金屬 氣相磊晶法,在磊晶溫度為攝氏500度所成長的低溫砷化鎵薄膜的光學特性 。藉由改變磊晶溫度從500度到600度,我們發現較低的磊晶溫度會使薄膜 產生1.356eV及1.219eV的深層能階,其峰值位置恰與一般研究中所發現的 鎵晶格空缺及其相關缺陷的能階位置一致,所以這兩個深層能階的形成很 有可能和鎵晶格空缺有關。而在相同的磊晶條件下,以TEGa和Arsine所成 長的砷化鎵並無上述所觀察到的缺陷能階,故我們推測除了低磊晶溫度外, TBAs的使用也是造成深層能階的原因之一。在砷銻化鋁這種嶄新材料的實 驗中,我們使用拉曼光譜來研究具不同組成的砷銻化鋁薄膜的聲子振動光 學模。我們發現覆蓋層材料的選取,對砷銻化鋁的拉曼光譜量測有很大的 影響。因為砷銻化鋁薄膜品質極不穩定,我們尚未得到完整資料來判斷其 所屬光學模,但由實驗所得的部份資料顯示,砷銻化鋁薄膜似乎具有單模振 動行為。 We use Photoluminescence(PL) spectrum to investigate the low temperature gallium arsenide films (LT-GaAs), grown by the metalorganic chemical vapor deposition(MOCVD)method, using TEGa and TBAs as source precursor. For samples grown below 550C, we find there are two deep levels at 1.219eV and 1.356 eV below conduction band. It is confirmed that these traps are caused from the gallium vacancy and its releated defect. For comparison the sample using arsine doesn't show any relevant peaks. Therefore, we conclude that the origion of such defects may associate with the use of TBAs presursor, particularly at low growth temperature. In the second part of the thesis, Raman spectroscopy was emplyed to characterize the long-wavelength optical-mode behavior of AlAsSb alloys for a variety of Sb mole fract- ions. The cap layer play the important role in our Raman measurement. Because the AlAsSb films are not stable ,we can't get the enough information to judge their optical mode. From the limited data obtained from experiment, it seems likely that AlAsSb alloys belong to the single-mode behavior.