| 摘要: | 本研究探討圖案化的藍寶石基板表面形貌對LED的光型的影響。通過濕式蝕刻工藝製造了三個圖案化藍寶石基板。使用MOCVD在三個圖案化藍寶石基板上製造GaN-LED（NPSS I，NPSS II和NPSS III LED）。LED與YAG螢光粉一起封裝為白光LED。LED光型的測量顯示出藍寶石基板表面形貌對光型具有依賴性。NPSS I，NPSS II和NPSS III LED的發散角估計分別為42.5º，38º，32º。在NPSS I LED的白光封裝中，封裝了1.5 mm，1.7 mm，2.0 mm螢光粉半球的白光LED的平均色溫分別為6732 K，6283 K和6971K。同時其空間色偏分別為710 K，2131 K和4222K。螢光粉層中的光路徑長度和LED光形是影響白光LED空間色偏的關鍵。在二維分析中，建立了入射角變化模型以預測光從任何方向入射的入射角的變化，並預測將發生全內反射的入射角的範圍。同時還構建了光穿透圖案化藍寶石基板的特性模型，以描述入射到藍角區域的光的入射角變化，該藍色區域將光導回到GaN層並傳播到GaN/air界面。通過此模型當光線抵達GaN/air界面的入射角是可預測的，並且還表明，進入藍角區域的光既不能透射LED上表面，也不能透射進入藍寶石層。這導致側壁出光的減少。通過蒙地卡羅光追跡法，可以模擬光型。模擬結果表明，隨著圖案斜面角和圖案覆蓋率的增加，光型的高強度區域變得更加集中。另外，也模擬了LED在上表面發射和側壁發射中的輸出功率。側壁發射功率比隨著圖案斜面角和圖案覆蓋率的增加而減小。隨著側壁發射功率減小，光型變得更加集中並且使光形的發散角減小。三維模擬結果可與對應二維分析和實驗結果。;The morphological effect of the patterned sapphire substrate on the light radiation pattern of LED is investigated. Three patterned sapphire substrates are fabricated by the wet-etching process. The GaN-LEDs were processed on the three-patterned sapphire wafers (NPSS I, NPSS II, and NPSS III) by using MOCVD. The LED chips were packaged as white-light LEDs with YAG phosphors. The light radiation pattern of LEDs is measured and shows a dependence on patterned sapphire morphology. The divergence angle of the NPSS I, NPSS II, and NPSS III LED are estimated to be 42.5º, 38º, 32º, respectively. In the white-light package of NPSS I LED, the average CCT of white-light LED with 1.5 mm, 1.7 mm, 2.0 mm phosphor dome is 6732 K, 6283 K, and 6971 K, respectively. The ACCTD of white-light LED with 1.5 mm, 1.7 mm, 2.0 mm phosphor dome is 710 K, 2131 K, and 4222 K, respectively. The light path length in the phosphor layer and the light radiation pattern are the keys to affect the local CCT of the white-light LED.
In the 2-D analysis, an incident angle change model is built to predict the change of incident angle of light from any direction, and also the range of incident angle in which the total internal reflection will happen. The model of the characteristic of light transmitting the patterned sapphire is also built to describe the incident angle change of the light which travels into the blue angle region which guides the light back into the GaN layer and travels to the GaN/air interface. The incident angle to the GaN/air interface is predictable, and also shows that the light travel into the blue angle region can neither transmit the LED top surface nor transmit into the sapphire cavity. This results in a decrease of the sidewall emission.
By the Monte Carlo ray-tracing method, the light radiation pattern can be simulated. The simulation result shows that the high-intensity region of the light radiation pattern becomes more centralized as the dihedral angle and pattern coverage increases. The output power of the LED chip in top surface emission and sidewall emission are also simulated. The sidewall emission power ratio decreases as the pattern dihedral angle and the pattern coverage increases. As the sidewall emission power decreases, the light radiation pattern becomes more centralized and makes the divergence of the light radiation pattern decrease. The simulation result can correspond to the 2-D analysis and the experiment results. |
