高功率氮化鎵材料發光二極體之製作與光取出提升研究

Abstract

由於氮化鎵材料所研製的發光元件可被廣泛地應用於如指示燈、液晶面板的背光源以及各種樣式的照明設備、甚至醫療等領域，因此自 1960 年代以來氮化鎵相關材料的研究成為世界上各研發團體的重要發展課題之ㄧ，而內部或外部量子效率的提升也不斷地在國際研討會上被提出討論，在本研究論文中，我們的研究著重在高壓、高功率氮化鎵發光二極體(LED)製作方法於藍光波長或紫外光波長的光取出效率的提升，並研究分析各種高功率發光元件之主要特性。 第一部分，首先製作大面積發光 (1.15x1.15 mm2, 15串聯) 高壓藍光發光二極體於藍寶石基板上。高壓發光二極體的製作方式主要不同處是利用側壁保護層(Passivation Layer)與金屬跨接(Inter-connection)來達成，主要研究在探討正面出光(比較藍寶石底部有、無反射層的提升)與背面出光(高壓發光二極體以覆晶方式呈現)對光取出效率的影響。高壓發光二極體因具有使用較低的操作電流避免在高電流易造成電流擁擠效應(Current Crowding)以達到良好的電流擴散，並提供更均勻的發光分佈。而我們所提出的高壓覆晶發光二極體，同時具備高壓發光二極體的低操作電流、均勻電流擴散與覆晶發光二極體的低遮光效應的特性。實驗結果顯示(相同輸入電流20mA下，高壓發光二極體於藍寶石無添加反射層: 315mW; 高壓發光二極體於藍寶石添加反射層: 415mW; 高壓覆晶發光二極體: 432mW)，高壓覆晶發光二極體在發光強度的提升37.1%，而在相同1W消耗電功率下的效率的提升達到38.4%。 另外，我們也在高壓藍光發光二極體(1.15x1.15 mm2, 15串聯)的藍寶石基板底部透過幾何形狀的設計與蝕刻(8種幾何圖形設計)，再於刻蝕出的藍寶石基板底部表面上鍍上反射層，主要研究在探討具刻蝕出的藍寶石幾何圖形與平面搭配反射層對光取出效率的影響。實驗結果顯示(在相同1W消耗電功率下的效率，平面: 32.6%; 具刻蝕出的藍寶石幾何圖形(最佳設計): 37.1%)，所以，最佳的設計在效率上提升達到13.8%。針對這兩個研究方向所提及的發光強度的提升，也透過Trace Pro光學模擬方式加以佐證。 第二部分，製作大面積(1.15x1.15 mm2) 紫外光發光二極體於矽基板上。利用金屬接合(Wafer bonding)與雷射剝離(Laser Lift-off)製程，將成長於藍寶石基板上之紫外光發光二極體可以輕易地被轉移至矽基板上。主要研究在探討P-GaN上有、無使用非絕緣型電流阻擋層以及在發光面的粗化程度不同對紫外光發光二極體光取出效率的提升的影響。實驗結果顯示(相同輸入電流350mA下，使用非絕緣型電流阻擋層LOP : 433; 無使用非絕緣型電流阻擋層LOP: 138)，因為使用非絕緣型電流阻擋層使得電流擴散變得更好，進而對取光也有非常顯著的提升，藉由加入非絕緣型電流阻擋層使得發光強度被提升近214%，而效率也有近3.1倍的差異。再者，粗化程度的比較結果顯示(相同輸入電流350mA下，無粗化發光面LOP : 433, Rms: 17nm; 大角錐低密度LOP:698, Rms: 163nm; 小角錐高密度LOP:858, Rms: 377nm) ，粗化程度的差異直接影響散射程度的好壞與增加光逃脫出半導體的機率，進而對取光也有非常顯著的提升，根據發光面粗化程度的不同，使得發光強度分別地被提升61%與98%。當然，效率也有近1.8及2.1倍的差異。 另外，我們結合覆晶發光二極體可避免電極遮光特性與垂直發光二極體在高電流操作的優越散熱能力，探討與研究新型薄膜式垂直發光二極體與傳統垂直發光二極體在光電特性上的差異。新型薄膜式垂直發光二極體在金屬接合(Wafer bonding)前，經發光二極體結構的設計，將P電極與N電極引到同一側，再接續金屬接合(Wafer bonding)與雷射剝離(Laser Lift-off)製程，製作出大面積(1.15x1.15 mm2) 紫外光發光二極體於矽基板上，最後，再將P電極接引出來成為接觸電極。主要研究在探討新型薄膜式垂直發光二極體結構與傳統垂直發光二極體在電流擴散與遮光效應的差異，進而探討其對光取出效率的提升。 最後，我們提出晶圓級薄膜覆晶紫外光發光二極體的製作方法，除了簡化晶粒級的繁複工藝流程外，比起傳統垂直發光二極體及傳統覆晶發光二極體，有更優越的光電特性的表現。此晶圓級薄膜覆晶紫外光發光二極體架構於傳統覆晶發光二極體的製作方法，差異在於基板由金屬銅取代以及藍寶石透過雷射剝離來移除。

The luminous component developed by GaN materials can be widely used in such as indicators, traffic lights, LCD back-lighting source, and variety styles of lighting equipment, even in the medical domain. Since 1960 years, the relevant GaN materials to be an important research topic in the whole world. The internal or external quantum efficiency is at the same time constantly discussing and demonstrating in the international seminar. In this dissertation, we were focused on light extraction efficiency of GaN-based light emitting diode in high-voltage and high-power (LED) methods with blue or ultraviolet wavelength, and analyze the characteristics of these various high-power light emitting components. The first part, the first step was made high-voltage blue light emitting diodes with (1.15x1.15 mm2, 15 series-connection) on sapphire substrate. The achievement of high-voltage light emitting diode is adopting the side-wall protective layer (passivation layer) to protect the PN junction and using bridged metals to form a series circuit (Inter-connection). We were studied and investigated the differences in upper light output power (compared the differences at the bottom of the sapphire add reflective layer or not), downward light output power (presented by high-voltage light-emitting diode in flip-chip style) and effects on the light extraction efficiency. High-voltage light emitting diode with low operating current to avoid the high current is easy to cause the current crowding effect, achieve more uniform light distribution of good current spreading. We demonstrated the high-voltage flip-chip light emitting diode combine a good feature of the low light shielding effect in flip-chip style and the aforementioned advantages of high-voltage light emitting diode. Experimental results demonstrate that (under the same input current of 20mA. High-voltage light-emitting diode on sapphire without adding a reflective layer: 315mW; high-voltage light-emitting diode on sapphire add reflective layer: 415mW; high-voltage flip-chip light-emitting diode: 432mW), high-voltage flip-chip light-emitting diode enhance the 37.1% luminous intensity, and enhance the power efficiency reached 38.4% in the same 1 watt power consumption. We were also investigated in a high-voltage blue light-emitting diode (1.15x1.15 mm2, 15 series-connection), through geometry design and etching at the bottom of sapphire substrate (8 kinds of geometrical design), then etched the bottom of the sapphire substrate surface depositing on the reflective layer. The main research in discussion with etched sapphire geometry and planar reflective layer in the light extraction efficiency of collocation. The experimental results show that (the efficiency of the equivalent 1 watt power consumption, the plane: 32.6%; etching out of the sapphire geometry (the best design): 37.1%). The best design to enhance the efficiency of 13.8%. The improvement of these two studies can be referred by the TracePro optical simulation. In the second part, a large area (1.15x1.15 mm2) ultraviolet light emitting diode is fabricated on the silicon substrate. Through wafer bonding and laser lift-off (LLO) techniques to easily achieve the sapphire substrate be deleted and replaced by silicon substrates in UV light-emitting diode. The main research is to study the enhancement of light extraction efficiency of P-GaN with and without non-insulated current blocking layer and the degree of roughening in the ultraviolet light emitting surface. Experimental results show that (under the same input current of 350mA, using non-insulated type current blocking layer LOP: 433, without using non-insulated type current blocking layer LOP: 138), the difference is due to the non-insulated type current blocking layer makes the current spreading becomes more uniform, and takes the light has a very significant improvement. According to the result, the luminous intensity was promoted to 214%, and efficiency difference is nearly 3.1 times by adding non-insulated type current blocking layer. Furthermore, comparison results of different degree rough surface show (under the same input current of 350mA, flat-surface LOP: 433, Rms: 17nm; large pyramid & low density LOP: 698, Rms: 163nm; small pyramid & high density LOP: 858, Rms: 377nm), the differences in the extent of roughening directly influence scattering of quality and increase light escape probability, and brings very significant improvement on the light extraction. According to different degree of roughening surface that makes luminous intensity were improved 61% and 98%. The difference of efficiency was also improved nearly 1.8 and 2.1 times. Furthermore, we combine flip-chip light-emitting diode can avoid electrode shading effect and vertical light-emitting diode in high operating current with superior heat dissipation ability, explore and research the difference of optical and electrical properties in new thin-film type vertical light-emitting diode and the traditional vertical light-emitting diodes. In new thin-film type of vertical light emitting diodes, through the diode structure design leads P and N electrodes on the same side before the metal bonding. After that, continue complete the metal bonding and laser lift-off (LLO) process, making a large area (1.15x1.15 mm2) UV light emitting diode on the silicon substrate. Finally, p-electrode be induced outside and lead to a contact electrode. The main research is to discuss the differences of current spreading and the shading effect in both structures (the new thin-film type of vertical light-emitting diode and the traditional vertical light-emitting diode). And then discuss the improvement of the light extraction efficiency. Finally, we present the wafer-level thin-film flip-chip ultraviolet light-emitting diode and fabrication method, in addition to simplifying the chip-level of the complicated process, compared to traditional vertical light-emitting diode and the traditional flip-chip light emitting diode, it has superior performance of photoelectric characteristics. The wafer-level thin-film flip-chip ultraviolet light-emitting diode is fabricated by the traditional flip-chip method, and the difference is that the substrate is hereby replaced by the metal copper and the sapphire is removed by the laser.