藉改良鏡面結構與表面粗糙化處理提升發光二極體之亮度

Abstract

本論文主要的研究是藉著改變鏡面結構提高反射率及不同的表面粗糙化處理來提升磷化鋁鎵銦與氮化鎵發光二極體之元件特性。我們將探討氧化銦錫/銀(ITO/Ag)鏡面結構在晶圓接合過程中受到熱處理的影響，並提出新的鏡面結構以提升鏡面的反射率，進一步提高垂直型氮化鎵發光二極體(GaN-based LED)元件的亮度。在表面粗糙化的實驗中，我們則是利用了感應耦合電漿 (Inductively Coupled Plasma, ICP) 蝕刻與化學溼蝕刻法，將磷化鋁鎵銦發光二極體(AlGaInP-based LED)元件的單面(p-GaP) 與雙面(p-GaP, n-AlGaInP)進行粗化，並進一步探討粗糙化圖型與蝕刻深度對磷化鋁鎵銦發光二極體光電特性的影響。 氮化鎵發光二極體一般是在藍寶石基板上磊晶成長。而由於藍寶石基板的導熱係數較矽基板低，因此，會藉由晶圓接合的過程將LED轉移到矽基板上。而為了必免光吸收，一般都會在結構中加入一金屬層做為反射鏡面以提升光取出效率。在之前的研究中具高反射率的銀常被做為鏡面層，而ITO則是做為LED的甌姆接面與銀相接。在實驗中我們發現晶圓接合的熱處理會使得銀擴散至ITO導電層並產生聚集的現象，造成反射率的下降。鏡面經由添加2nm的鎳薄膜在ITO與銀的界面處理後，再經相同的熱處理；結果發現改良後的鏡面能有效提升反射率。最後在應用於氮化鎵發光二極體元件上的結果比較，新的鏡面結構在20mA的注入電流下能使元件的正向光強度提升87.3%。 於磷化鋁鎵銦發光二極體方面，也成功的利用晶圓接合技術將磷化鋁鎵銦磊晶層轉移至矽基板上。接著，運用化學溼蝕刻與ICP乾蝕刻的表面粗化技術製作具有單面(於p-GaP)及雙面粗化(於p-Gap和n-AlGaInP)的新結構磷化鋁鎵銦發光二極體。我們發現在20 mA 的注入電流下操作，其發光強度分別為傳統LED (p-GaP與n-AlGaInP均無粗化) 的2和2.56倍。同時在實驗中也將探討不同的粗糙化圖型與圖型的蝕刻深度對磷化鋁鎵銦發光二極體的光電特性的影響。

The primary objective of this dissertation is to improve the light output power of light-emitting diodes by mirror structure and surface roughening Process. Effect of thermal annealing of the reflectivity of ITO/Ag mirror during wafer bonding process has been investigated. We presented a new structure of mirror to improve the reflectivity and also the output power of the vertical GaN-based LEDs could be improved. In the experiments of surface roughening process, the p-GaP and n-AlGaInP surface of the AlGaInP-based LEDs would be roughened by inductively coupled plasma (ICP) dry etching and /or chemical wet etching. In addition, the effect of the etching pattern and etching depth on the characteristics of the LEDs would be discussed. In general, GaN epitaxial layers were grown on sapphire substrates. The LEDs epitaxial layer would then transferred to the Si substrate by wafer bonding, since the thermal conductivity of the sapphire is lower than Si. A metal layer usually added between the LEDs and transferred substrate as mirror to avoid the absorption of the generated photons by substrate. In previous studies, because of the high reflectivity, Ag usually was used to serve as mirror layer. And the ITO was used as ohmic contact layer on LEDs. In our experiment, the Ag atoms would diffuse into ITO layer and agglomerated after wafer bonding process. This would decrease the reflectivity of the ITO/Ag mirror. However, the new mirror structure with Ni thin film (2 nm) between interface of the ITO and Ag could improve the reflectivity after the same bonding process. Consequently, comparing with the ITO/Ag mirror, the new mirror structure could enhance the light intensity 87.3% under a 20-mA forward injection current. For the AlGaInP-based LED, vertical AlGaInP-based LED epitaxial films are successfully fabricated on a Si substrate using wafer bonding technology. Furthermore, the new structures of AlGaInP-based LEDs with single (p-GaP) and double roughened (p-GaP and n-AlGaInP) surfaces are fabricated by chemical wet etching and ICP dry etching technologies. It is found that the light output power of the single and double surface-roughened AlGaInP-based LED chips is 2 and 2.56 times higher than that of the conventional AlGaInP-based LEDs (flat p-GaP and n-AlGaInP layer) at an injection current of 20 mA, respectively. Finally, the effects of the different etching-patterns and the etching-depth on the optical and electrical characteristics of the surface-roughened AlGaInP-based LEDs will be investigated.