氧化鋅奈米線應用於LED與其特性改良

Abstract

發光二極體是一種極具潛力成為下一世代主要光源的固態照明技術。在發光二極體的發展過程中，歷來技術上之突破大幅改善其光電特性，但現階段發光效率仍不足，故發光二極體發光效率的提升，是目前技術發展的重點之一。過去的研究指出，相較於傳統薄膜型發光二極體，具奈米線結構之發光二極體在相同注入電流下，會因量子侷限效應而提升其發光強度。本論文採用水熱法製備N型氧化鋅奈米線，選擇氮化鎵薄膜作為P型材料則，製作成異質接面發光二極體結構，並進行其特性之研究。另一方面，氮化鎵發光二極體因菲涅爾損失(Fresnel loss)及全反射現象而降低其光萃取效率，同樣可藉由氧化鋅奈米線之應用而有所改善，故本論文於氮化鎵垂直型發光二極體之出光面，成長氧化鋅奈米線，以提升其光萃取效率。 在P型氮化鎵薄膜/N型氧化鋅奈米線異質結構的製備上，本論文致力於元件串聯電阻的降低，以及改善漏電流現象。在降低元件串聯電阻的部份，經快速熱處理製程後，氧化鋅鋁成核層及氧化鋅鋁電流擴散層之最佳電阻率分別為7.165×10-3、2.141×10-3 Ω-cm。鋁摻雜之氧化鋅奈米線，分別使用硝酸鋁、氯化鋁及醋酸鋁做為鋁摻雜來源，由歐傑電子能譜及X光光電子能譜儀可檢測出氧化鋅奈米線有鋁的成分。在改善漏電流現象的部份，採用液態二氧化矽之溶液，旋塗在奈米線之間，並烤乾以形成薄膜，實驗結果顯示旋塗3次可以得到最佳之旋塗效果，並以RIE通CF4氣體蝕刻絕緣材料至露出奈米線表面，完成奈米線間之絕緣填充。 在N型氮化鎵出光表面製備氧化鋅成核層/氧化鋅奈米線，以改善光萃取效率的部分，本論文於未粗化與已粗化出光表面製備氧化鋅成核層/氧化鋅奈米線。實驗結果顯示，在未粗化之N型氮化鎵表面製備氧化鋅成核層/氧化鋅奈米線，可提升氮化鎵發光二極體之光輸出功率，當氧化鋅成核層之厚度為100 nm，水熱法溶液之濃度為35 mM，在350 mA之注入電流下，氮化鎵發光二極體之光輸出功率可提升151.47 %，為最佳結果。將氧化鋅成核層/氧化鋅奈米線製備於已粗化之N型氮化鎵表面，則會略微降低其光輸出功率。此外，製備氧化鋅成核層/氧化鋅奈米線於氮化鎵發光二極體之出光表面，可改善其二極體特性，IR良率亦略微提升，顯示成長氧化鋅奈米線可以減少漏電流現象。Light emitting diode (LED) is considered as the major next-generation luminescence technology, but nowadays insufficient light efficiency of high power LED limits its application for illumination lighting. Some research group have developed nanowrie-inserted LED structure, and the EL intensity shows that the novel LED structure can improve light efficiency effectively. In this study, hetero-junction diode is made by N-type ZnO nanowires fabricated by hydrothermal method and P-type GaN film. Finally, the characteristics of N-type ZnO nanowires/P-type GaN structure LED will be studied. Fabricating ZnO nanowires on GaN LED can reduce the Fresnel loss and the total reflection of light, improving the light extraction efficiency of GaN LED, and it is the other research topics in this study. For p-GaN/n-ZnO nanowires heterostructure LED, reducing the series resistance and leakage current yield of device is the research focus in this study. After RTA process, the resistivity of AZO seedlayer and current spreading layer are 7.165×10-3 and 2.141×10-3 Ω-cm, respectively. To prepare the Al-doped ZnO nanowires, Al(NO3)3, AlCl3 and AlOH(CH3COO)2 powders were added. AES and XPS examination can confirm that the Al were successfully doped in the ZnO nanowires. In the part of reducing the leakage current yield, liquid type SiO2 (SOG, spin-on-glass) can be filled into the spare space among each ZnO nanowires, and the sequent baking process is necessary to form a solid-type isolation layer. The result of this experiment shows that the triple coating SOG is optimum for successive process. CF4 RIE process can be used to selectively etch SiO2 but remain ZnO nanowires, so that the current spreading layer (AZO) of LED could be directly deposited on the top of ZnO nanowires. In this study, ZnO seedlayer/ZnO nanowires was fabricated on non-texturing and texturing GaN surface. Fabricating ZnO seedlayer/ZnO nanowires on non-texturing GaN surface can significantly improve the light output power of GaN LED. When ZnO seedlayer was 1000 Å, and the mol-concentration of reaction solution was 35 mM, light output power increased by 151.47 % at an injection current of 350 mA. Fabricating ZnO seedlayer/ZnO nanowires on texturing GaN surface will Slightly decrease the light output power of GaN LED. Besides, the ZnO seedlayer/ZnO nanowires formed on texturing and non-texturing LED surface can improve IV characteristic and IR yield of LED dies. Keywords：light-emitting diode, ZnO nanowrie, hydrothermal method, light extraction efficiency, Al-doped ZnO nanowires