探討奈米面上銦氮化鎵與氮化鎵多重量子井包覆氮化鎵奈米柱之核殼結構的成長與發光性質

Abstract

近年來，一維奈米結構由於擁有以下特點，如降低缺陷密度、增加光取出效率和主動層面積，引起廣大的研究興趣。在此論文中，我們證明了核殼結構奈米柱，即奈米柱被有著多重奈米面的銦氮化鎵/氮化鎵多層量子井包覆，其有多重發光波長的特性，且在沒有螢光粉的情況下，仍能發出自然白光。製造方法如下：首先，利用奈米壓印的方式製造出氮化鎵奈米柱立於氮化鎵c平面上，這些奈米柱排列成十二重對稱的光子準晶體圖樣；接下來奈米柱樣品經歷重新成長，將多重量子井成長在奈米柱上且產生晶面。重長後的奈米柱，上部金字塔型頂端為半極性{"10" "1" ̅"1" }平面族，下部側壁為非極性{"10" "1" ̅"0" }平面族，兩種平面族圍住整個箭頭形狀的奈米柱。同時，c方向上既存的極化效應亦可被成長半極性以及非極性面抑止。我們近一步探討銦含量在多重量子井奈米面上分布的情形，主要有兩種模型描述奈米柱上不同銦含量分佈：(一)質量傳輸模型，包含不同平面有不同濃度含量的表面擴散過程，和同一平面上有漸變濃度分布的氣相擴散過程；(二)表面適性模型，包含晶面交界處化學位能降低，和產生新的平面族使應力釋放，進而使銦濃度提高，故核殼結構奈米柱上不同位置的銦含量有顯著的差異。降溫亦使銦含量有顯著的提升。歸納以上，核殼結構奈米柱因為銦含量在多重奈米面上有不同的分布，具多重發光波長的特性，且調變重長參數可調變其色溫。此外，核奈米柱排列成十二重光子準晶體結構，亦可發現隨機雷射現象。

Recently, one-dimensional structures are attracting much interest in the reduction of dislocations, the promotion of light extraction efficiency and the enlarged active area. In this thesis, we demonstrate the phosphor-free nanorods with core-shell structure have the polychromatic emission with color temperature about 6,000 K (a natural white light). A core-shell nanorod includes a shell of InGaN/GaN multi-quantum wells (MQWs) and a core of GaN nanorod. The fabrication procedure as follows: The nanorods arrays arrange in a 12-fold symmetric photonic quasicrystal (PQC) pattern on c-plane GaN template were fabricated by nano-imprint lithography, and followed by the regrowth of MQWs on the crystalline facets of nanorods. After regrowth, each core-shell nanorod with arrow shape is composed of nonpolar {"10" "1" ̅"0" } facets on sidewalls and semipolar {"10" "1" ̅"1" } facets on a pyramidal top. Accordingly, the polarization effects can also be suppressed by growing semipolar and nonpolar planes of nanorods. The core-shell nanorod with an inhomogeneous indium content distribution could be realized by two mechanisms: One is the mass transport model, including the different surface diffusion constants cause the different indium incorporation efficiency on semipolar and nonpolar planes. In the other hand, the gradient indium distribution on each facet is influenced by the gas phase diffusion. The other one is the surface modification model, including the lower chemical potential at the intersection of growth planes, and strain relaxed by the new-born facets. Therefore, whole core-shell nanorod has the obvious difference of indium incorporation efficiency distribute from the bottom to top portion of nanorods. In addition, a higher indium content of nanorods was also attained by lowering the regrowth temperature, whereas the degraded sidewalls of core-shell nanorods were caused by the lower species mobility. As a result, the polychromatic emission will be formed and the color temperature value can be tuned by the different regrowth parameters of MQWs nano-facets on nanorods. A phosphor-free white light emission is achieved by the core-shell nanorods technology. Worth a mention was that the random lasing action was achieved by nanorods arranged in a12-fold PQC pattern.