Investigation of Surfactant Effects in Defects and Alloy Composition Controls of Semicon-ductors Thin Films

在半導體系統中，對表面性質的控制對於材料的生長以及器件的性能起著關鍵作用。在多種多樣的控制手段中，採用表面活性劑(surfactant)具有獨特的吸引力。在本文中，我們使用第一性原理密度泛函理論作為計算工具，研究在銦鎵氮(InGaN)和銅鋅錫硫(CZTS)系統中的表面活性劑效應。對表面活性劑效應的研究將結合反應熱力學和反應動力學兩個方向。 ; 在論文的第一部分，我們將研究銻(Sb)作為表面活性劑在銦鎵氮的表面上的作用。銦鎵氮是製備光電器件的理想系統，但是合金系統中銦的含量有限，影響了其作為綠色發光二極體(LED)的應用。通過分析表面結構，我們發現適量的銻可以產生表面應力效應並促進銦的摻入。我們的計算結果可以為生長高品質，高銦含量的銦鎵氮系統提供指導，最終説明製備基於銦鎵氮合金的綠色發光二極體。 ; 在論文的第二部分，我們將研究銅鋅錫硫表面的物理過程及可能的表面活性劑效應。銅鋅錫硫作為無毒且元素儲量豐富的薄膜太陽能材料吸引了很多關注，但是其光電轉化效率極大程度的受到了本征缺陷和次生相的限制。通過研究生長過程中的表面動力學過程，我們發現鋅銅反位缺陷在表面上的形成勢壘很低。這可能會導致高濃度的有害缺陷甚至大量的次生相。我們進一步發現鉀(K)在銅鋅錫硫表面具有表面活性劑效應。通過改變表面的熱力學和動力學過程，鋅銅反位以及相關的富鋅次生相會受到抑制。我們的計算證明了表面活性劑效應在控制表面過程和提升材料品質上具有一定的優越性。 ; For semiconductors, modifications of surface properties play an important role in both material growth and device performance. Among different control strategies, use of surfactants during growth is particularly appealing. In this thesis, we investigate surfactant effect on surfaces of InGaN and Cu2ZnSnS4 (CZTS), through first-principles calculations. Both thermodynamic and kinetic aspects of the surfactant effects are studied. ; In the first part of the thesis, we study the surfactant effect of antimony on InGaN surface. InGaN is an ideal alloy system of optoelectronic devices, yet indium concentration limits its use as green light-emitting-diodes (LEDs). Through analysis of surface structures, we show that suitable amount of antimony on the surface would induce stress effect and enhance indium incorporation. Our calculation is expected to provide some guidelines for growth of high-quality InGaN with high In concentration, enlightening the fabrication of InGaN-based green-light-emitting-diodes. ; In the second part of the thesis, we investigate surface processes and surfactant effect on Cu2ZnSnS4 surface. Cu2ZnSnS4 is a non-toxic and earth-abundant photovoltaic material, but its efficiency is largely limited by detrimental native defects and secondary phases. By analyzing the surface kinetics, we find a low reaction barrier of creating ZnCu defects near the surface, leading to high concentration of ...