氮化鎵基板研製與應用

Abstract

在本論文中，我們利用有機金屬氣相磊晶法(MOCVD)以及氫化物氣相磊晶法(HVPE)成長及研究氮化鎵磊晶層材料特性，並利用MOCVD再成長完整發光二極體結構於上述氮化鎵磊晶層，以探討基板對於發光二極體的影響。首先，我們導入濺鍍氮化鋁緩衝層於平面藍寶石基板上，再經由黃光製程沉積二氧化矽圓盤於上述基板，接著透過MOCVD結合脈衝式成長法以及傳統側向磊晶成長技術(ELOG) 成功在二氧化矽圓盤上嵌入可控形狀之空氣洞隙，並開發出高品質之氮化鎵薄膜，此技術稱為不間斷式側向磊晶成長法 (Interruption-free ELOG)。從X-ray、AFM、TEM以及發散角量測分析，可知使用此磊晶技術可提升氮化鎵薄膜的品質以及光萃取率，主要歸功於嵌入之空氣洞隙。在20 mA電流注入下，提升61.9%的光輸出功率。 在提升量子效率以及元件散熱方面，我們使用HVPE機台開發出不間斷兩段式成長法，成功將10 μm 厚的氮化鎵厚膜成長於具有氮化鋁緩衝層之圖案化藍寶石基板。從X-ray、AFM、以及TEM量測分析，可知使用此磊晶技術可提升氮化鎵薄膜的品質。透過熱影像的觀測，可知使用此氮化鎵厚膜之發光二極體可大幅降低操作時的表面溫度，在350 mA電流注入下，可由254.1 OC降低至137.1 OC，主要歸功於氮化鎵相較於藍寶石機板具有較佳的熱傳導性。在20 mA電流注入下，可提升47.8%的光輸出功率。 在改善水平式發光二極體的電流擁擠效應方面，我們利用先前成功使用HVPE成長氮化鎵厚膜於具有氮化鋁緩衝層的圖案化藍寶石基板的經驗，使用HVPE成長矽摻雜之氮化鎵厚膜於具有氮化鋁緩衝層的高深寬比圖案化藍寶石基板。從X-ray、AFM、以及TEM量測分析可知，即使摻雜高濃度矽於磊晶層，亦可維持厚膜品質。透過二維影像的觀測，可知成長於矽摻雜氮化鎵厚膜之發光二極體發光區域較均勻，不會有電流擁擠的現象產生，進而增加光輸出功率，主要歸功於矽摻雜之氮化鎵厚膜降低元件中的串聯電阻，有效提升元件中的電流擴散長度。在20 mA電流注入下，可提升47.2%的光輸出功率。

This dissertation describes highly suitable GaN templates for light emitting diodes (LEDs). These templates were grown through metal organic chemical vapor deposition (MOCVD) or hydride vapor phase epitaxy (HVPE), and the full LED structure was then grown on the template by MOCVD. The construction of a GaN template grown through interruption-free epitaxial lateral overgrowth (IFELOG) technology was first demonstrated. X-ray diffraction (XRD) data indicate that the FWHM of GaN (0 0 2) and GaN (1 0 2) peaks can be decreased from 485 arcsec to 376 arcsec and from 600 arcsec to 322 arcsec, respectively. The IFELOG technology not only promotes a one-step GaN growth in MOCVD but also produces a void shape controlled by one template. Embedded air voids also play an important role in light extraction. On the basis of our results, we achieve a 61.9% enhancement compared with conventional LED. Therefore, the IFELOG technology is proposed as an effective method to improve the quality and light extraction efficiency of GaN-based LED devices. As for the internal quantum efficiency and heat dissipation, we successfully introduce the AlN/PSS template to HVPE via two-step growth method. This method simplifies the procedure, achieves an uninterrupted growth, and improves the crystal quality of films. According to the results, LED with a 10 μm thick uGaN template displays 47.8% higher output power than conventional LED. The saturation current and hot/cold factor were also enhanced because of its improved heat durability and crystal quality. The 10 μm thick nGaN layer is also successfully grown directly on the AlN/HARPSS template via HVPE. The schematic equivalent LED circuit of LEDs is proposed and discussed. The current spreading length of the LED device can be increased by using the template; as a result, heat dissipation ability and light output power can be further improved. In this study, LED with a 10 μm thick nGaN template yields 47.2% higher output power than conventional LED. Furthermore, the saturation current is greatly enhanced from 355 mA to 480 mA because the current crowding effect is reduced. In summary, several highly efficient GaN templates have been described. The crystal quality, light extraction efficiency, heat dissipation ability, and current crowding effect of LEDs have been successfully improved.