三維的半極性{10-11}與非極性{10-10}平面核殼狀多重晶面量子井氮化銦鎵/氮化鎵光電元件之製作與特性研究

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。此論文中，我們提出了核殼結構奈米柱光電元件，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，傳統(0001) c平面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，在核奈米柱排列成十二重光子準晶體結構研究中，亦可發現光激發雷射現象，特別是我們發現多重波峰雷射行為以及隨機雷射的特性。經過FDTD模擬的理論計算成功解釋不規則的共振訊號來自十二重光子準晶體結構排列。進一步，實驗結果觀察到激發臨界能量和面積尺寸大小成反比，這證明屬於隨機雷射的特性。

Recently, one-dimensional structures are attracting much interest in the reduction of dislocations, the promotion of light extraction efficiency and the enlarged active area. Further, high-efficiency full-color light sources with high brightness and low power consumption are required for mobile device displays. For full-color display applications, inorganic compound semiconductors have many advantages over organic materials, including high carrier mobility and radiative recombination rate, as well as long-term stability and reliability. However, conventional inorganic thin-film LEDs emit only a single color that is determined by the quantum well layer thickness and composition. Achieving multiple color generation from inorganic LEDs on a substrate is a major obstacle to using inorganic semiconductors in full color displays. To overcome this obstacle, we used multifaceted gallium nitride (GaN) nanorod arrays with InxGa1-xN/GaN MQWs anisotropically formed on the nanorod tips and sidewalls. In this thesis, phosphor-free Core-shell semipolar (10-11) and nonpolar (10-10) InGaN/GaN core-shell nano-LEDs have been successfully demonstrated. A core-shell nanorod includes a shell of InGaN/GaN multi-quantum wells (MQWs) and a core of GaN nanorod. One thing worth noticing is that polychromatic emission with color temperature about 6,000 K (a natural white light) was observed. 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 have been 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. We have observed a lasing action in an optically pumped 12-fold symmetric quasicrystal nanorod arrays. Under optical pumping, multiple lasing peaks emerged from broad emission background. The irregular multiple lasing wavelengths and the inverse dependence of threshold pump intensity on pump spot area resembles the characteristics of random lasing. The irregularity of resonant peaks is qualitatively explained by a simplified FDTD simulation.