摘要：本計畫中，我們提出兩種方法來實現高效率長波長（綠、黃、紅色光）氮化銦鎵/氮化鎵量子井發光二極體，此種長波長發光二極體在顯示及照明應用上具有極大的市場價值。第一種方法係利用生長氮化物奈米柱時側向應變鬆弛之特性。在沿c-軸延伸之氮化鎵奈米柱上生長量子井時，不管是頂端c-平面量子井、斜平面{1-101}-面量子井或側壁m-平面量子井，其氮化銦鎵量子井層內之壓縮性應變都可沿測向部分釋放，如此即可增大生長氮化銦鎵時之銦結合（亦即增大銦成份）。這個現象主要歸因於氮化銦鎵比氮化鎵之結晶格子大。若銦結合之效率可以增大，表示在一個特定之發光波長或必要之銦成分條件下，我們可以提高長晶溫度以提升晶體品質而增加發光二極體之效率。奈米柱的生長除了側向應力釋放以提高銦結合效率外，在發光二極體應用上，尚有較高晶體品質、較大發光區體積及較高取光效率之優點。基於本團隊對於生長規則排列、均勻大小之c-軸氮化鎵奈米柱的豐富經驗，我們已成功的於奈米柱上生長頂端c-平面量子井、側壁m-平面量子井及量子井發光二極體結構。本計畫中，我們將一方面研究生長氮化銦鎵時，氮化鎵奈米柱上應變分佈與銦結合效率之關係，另一方面製作藍、綠、黃、紅光規則排列奈米柱發光二極體陣列。本計畫中第二個方法係利用在矽基板上生長氮化物時所產生較弱的壓縮性應變（比起在藍寶石基板上生長情況）來提高銦結合效率。我們將探討在矽基板上生長氮化物發光二極體結構時內部應力分佈與銦結合效率之間的關係，同時我們也將製作基於矽基板生長之長波長垂直型發光二極體，這當中，我們將使用圖案化生長技術來避免表面龜裂現象並改善晶體品質。利用矽基板生長氮化物發光二極體結構，除了提高銦結合效率優點外，尚有低成本、大晶元尺寸及易移除矽基板以製作垂直型發光二極體之好處。本計畫中，我們結合臺灣大學三位不同但互補專長之教授及三位工研院工程師，共同為提出計畫目標努力。
Abstract: In this project, two approaches are proposed for implementing high-efficiency long-wavelength (green, yellow, and red colors) InGaN/GaN quantum well (QW) light-emitting diodes (LEDs), which have a great market value for the applications of display and lighting. The first approach is to use the lateral strain relaxation property in growing a nitride nanorod (NR). In growing QWs on a c-axis GaN NR, the built compressive strains in either the top-face c-plane QWs, slant-facet {1-101}-plane QWs, or sidewall m-plane QWs can be partially relaxed in the lateral directions for increasing indium incorporation in growing InGaN (InGaN has a larger lattice size than GaN). With increased indium incorporation, for a given emission wavelength or indium content, the growth temperature of the InGaN QW layer can be elevated for achieving higher crystal quality. Besides the advantage of lateral strain relaxation for increasing indium incorporation, NR growth can also achieve higher crystal quality, larger emission volume, and stronger light extraction in fabricating an LED. Based on our experiences in growing regularly patterned c-axis GaN NRs of uniform geometry on sapphire substrate, we have accomplished the growths of c-plane top-face QWs and m-plane (non-polar) sidewall QWs on NRs, and NR QW LED structures. In this project, we will study the relationship between the indium incorporation efficiency and strain condition on a GaN NR. Also, regularly patterned NR LED arrays with blue, green, yellow, and red colors will be fabricated. The second approach is to use the weaker compressive stress in a nitride epitaxial layer on Si substrate, when compared with that on sapphire substrate, for increasing indium incorporation. The relationship between the epitaxial stress condition and indium incorporation efficiency will be investigated. The patterned growth technique on Si substrate will be used for avoiding surface cracking and improving crystal quality. Long-wavelength vertical LEDs will be fabricated based on Si substrate growth. Besides indium incorporation enhancement, the growth of LED structures on Si substrate has the advantages of low cost, large wafer size, and easy removal of the absorbing Si substrate for fabricating a vertical LED. Three faculty members of National Taiwan University of different expertise, including crystal growth, LED process, and simulation/design, work together with three engineers from Industrial Technology Research Institute for achieving the research goals.
