本論文的主旨在探討使用有機金屬化學氣相沉積法於傾斜7°(001)圖形化矽基板上選擇區域成長半極化(1-101)氮化鎵及氮化銦鎵/氮化鎵量子井材料並分析其材料與光學特性。由於氮化鎵材料與矽基板的晶格常數與熱膨脹係數差異甚大，為了避免氮化鎵材料裂縫的產生，我們於垂直V-形凹槽矽基板上覆蓋週期性條狀氧化層來降低氮化鎵與矽基板的接觸面積，此方法可有效降低以往氮化鎵材料成長在矽基板上產生的龐大舒張應力並成功成長無龜裂氮化鎵接合厚度達1 µm，面積約1x1 cm2。從穿遂式電子顯微鏡的分析結果顯示差排缺陷從成長區向[1-100]延伸並在靠近條狀氧化層邊緣開始轉往[11-20]方向，降低了差排向上竄升至表面的機會。此外，在光學特性上，我們也觀察到該氮化鎵及氮化銦鎵/氮化鎵量子井材料的室溫光激螢發光譜及陰極電子發光譜強度約高於無使用條狀氧化層成長時的1~2倍，顯示其較優越的品質。最後我們成功製作出(1-101)半極化發光二極體元件，其電性方面由於p-GaN活化較差導致開啟電壓略高(4 V)，而在逆偏-12 V下具有極低的漏電流。只要進一步改善p-GaN的摻雜濃度，此方法對於發展高效能氮化鎵光電元件如高速電子電晶體、蕭特基二極體、發光二極體、雷射等，將可被廣泛的應用進而創造出更大的產值。 最後，藉由模擬半極化(1-101) LEDs結構我們可以得知，在主動層中當量子井為3 nm和位障層為9 nm可以得到較佳的內部量子效率，並由於本身半極化的特性，其內建電場較小，使得載子有效輻射複合發光，並抑止電子的溢流現象，因此AlGaN (Electron Blocking Layer, EBL)電子阻擋層在此結構中並無發揮多大效能。此外，藉由調變主動區內位障層的摻雜濃度，相較於極化結構(c-plane)，可以發現半極化LED (Light Emitting Diode )的內部量子效率在低電流注入下，隨著摻雜濃度上升而有顯著提升，且在高電流下的效率下降(efficiency droop)也較為平緩。這是由於本身內部的半極化特性，量子井能帶較為平整，能容納較多來自於重摻雜的擴散電子，使之溢流至p型氮化鎵前就能有效的與電洞輻射複合發光，內部量子效率因此而改善。反之，極化結構中嚴重的量子侷限史塔克效應 (Quantum-Confined Stark Effect, QCSE)不但使得疊合的載子波函數下降，也使得電子一開始就產生溢流，並隨著摻雜濃度上升而增加，最後導致內部量子效率無法有效提升。 This dissertation describes an innovative method for selective epitaxial growth of semi-polar (1-101) GaN on V-grooved Si substrates. In addition to the SiO2 mask along the V grooves, SiO2 stripes perpendicular to the V grooves are introduced to overcome the issue of cracking caused by the large mismatch in the thermal expansion coefficients between GaN and Si. The structural and optical properties of the GaN films thus grown, particularly the reduction in dislocation density and the enhancement of their luminescence properties by the selective area epitaxial process, are investigated and elucidated. The growth of semi-polar (1-101) GaN films as thick as 1µm without cracks and InGaN/GaN multiple quantum wells (MQWs) on the resultant GaN have been successfully achieved on V-grooved (001) Si substrate in a dimension of 1x1 cm2. The transmission electron microscopy (TEM) measurements reveal that the dislocations bend toward the [1-100] and [11-20] directions as a consequence of the (1-101) and (11-22) facets that form during the initial stage of the lateral overgrowth upon the SiO2 stripes. This reduction in the dislocation density leads to an increase in the luminescence intensity as observed by photoluminescence (PL) and cathodoluminescence (CL) measurements at room temperature. Finally, the crack-free film was successfully fabricated to devices and showed low leakage current under the bias of -12 V while the turn-on voltage is about 4 V due to the inefficient ionization of Mg in p-GaN layer. Judging from the optical and electrical properties observed, the selective growth method holds promise for high quality free-standing semi-polar GaN substrates and III-nitride semiconductor devices once we further improve Magnesium (Mg) ionization in GaN layer. Secondly, the performance of semi-polar (1-101) light emitting diodes (LEDs) are simulated with variations in the thickness of the MQWs, the barrier doping concentration, and the Aluminum (Al) composition of the AlGaN Electron Blocking Layer (EBL). The highest efficiency is obtained when the thickness of the (1-101) semi-polar quantum wells (QWs) and quantum barriers (QBs) are 3 nm and 9 nm, respectively. It is also found that inserting an AlGaN EBL does not help much for blocking electrons possibly due to the inherently weak polarization, which suppresses the escape of the electrons out of the QW active region. Finally, an opposite IQE tendency was found when different doping concentrations in QBs were applied in (1-101) and (0001) LED structures. The lower polarization field in the semi-polar structure enables the QWs to accommodate more electrons and facilitates radiative recombination before spilling over to p-GaN region, thus light efficiency rises with increasing doping concentration to a specific degree; whereas the polarized (0001) LEDs exhibit an initial monotonic drop in efficiency due to the easy overflow of electrons from the MQWs. The higher the doping concentration in the barriers, the higher the spillover current is, suggesting that the Quantum Confined Stark Effect (QCSE) caused by the strong polarization field is the major factor in the observed efficiency degradation with barrier doping.
