次世代高效率氮化鎵發光二極體之奈米製程與元件特性之研究

Abstract

近年來，三五族半導體尤其是氮化鎵材料系列由於發光波長涵蓋了短波長的紫外光波段和大部分的可見光，其相關的光電元件如發光二極體、雷射和光偵測器等元件被大量的研究，同時這些光電元件被大量的應用在新一代光儲存、平面顯示、生物檢測和照明等光電產品中，也由於新的應用產品刺激下，氮化鎵材料的研究越來越受到大家的重視。 本論文主要在於開發製作氮化鎵奈米結構並應用奈米結構於氮化鎵發光二極體元件上，同時研究奈米發光元件及結構之製作、材料特性、及光電特性。主要分為四個部分，第一部份為開發一個新穎性的奈米結構製作技術，用以製作氮化鎵奈米柱結構。利用調變製程參數得到不同形狀的奈米結構，針對不同深度、不同直徑大小的奈米助陣列探討其發光特性、抗反射特性，同時利用valence force field (VFF)模型瞭解氮化鎵材料在應用釋放過程中對材料特性的影響為何。第二部分為應用奈米結構在氮化鎵發光二極體上，利用表面蝕刻技術，製作高深寬比的氮化鎵奈米結構提升元件出光效率。在考量到蝕刻對元件可能的電性影響後，我們嘗試了化學合成的方式，在元件表面上化學合成氧化鋅奈米柱結構降低表面全反射以提升元件萃取效率。最後我們結合了再磊晶的技術，在SiO2奈米柱結構上進行再磊晶同時改善元件內部量子效率和光萃取效率。 在本論文的後半部，我們針對氮化鎵發光二極體的內部量子效率進行研究，採用了圖案化基板的方式提升元件的內部量子效率。在第三部分，我們改善了傳統光學方法量測內部量子效率的方法，首先調變激發雷射的光波長，接著利用一連串的變溫和變功率光學方法定義並量測元件內部量子效率，同時分析了在光學量測過程中內部載子發光機制等特性。在本論文的最後一部分，延續內部量子效率的研究議題，我們建立了一套可控制環境溫度的電注入量測設備，這將幫助我們進行一系列不同溫度和電流注入下的效率量測，不僅可幫助我們更瞭解內部量子效率的變化情形，更可對高電流注入下效率急降的有更深入的瞭解。同時，利用APSYS模擬軟體模擬低溫下元件的行為，對次世代高效率元件的設計和製作有絕對的幫助。

Recently, Nitride (III) light-emitting diodes (LEDs) with emission wavelength ranging from ultraviolet to the short-wavelength part of the visible spectrum have been intensely developed in the past 10 years. Due to the rapid developing in efficiency improvement, applying the opto-electronic device such as LED, laser and photo-detectors into our life becomes possible. Besides, because of the next generation application in optical storage, flat display, bio-detection and general lighting, the research about GaN lighting devices attracted more and more attentions. In this study, we mainly focus on developing GaN nano structures and applying these nano structures on GaN LED. The device fabrication process, efficiency improvement, material and opto-electronic characteristics of the nano-structured GaN-based LEDs will be also discussed. The entire dissertation could be divided into four parts. The first is developing a novel GaN nano structure fabrication process. By well control the metal depositing thickness, annealing temperature, etching conditions, we could achieve different length and diameter GaN nanorod arrays. The emission and anti0refelction characteristics of the fabricated nanorod structures will be discussed. Besides, we applied the valence force field model to help us to realize the influence of strain relaxation within GaN multiple quantum wells (MQWs). The second part of this dissertation is applying these nano structures on the surface of GaN-based LEDs to improve the lighting efficiency. We first utilizing etching method assisted by spinning nano spheres on device surface serving as masks to form high-aspect-ratio GaN nanorods. However, considered the possible deterioration of reduced current spreading paths, we then adopted a bottom-up method to synthesize ZnO nanorod on the surface to suppress the total internal reflection and improve the light extraction efficiency. The third method we used to improve the device performance is combing the overgrowth technique on nano-patterned sapphire substrate to improve the internal quantum efficiency (IQE) and light extraction efficiency simultaneously. At the later half of this dissertation, we focused on the studying of the IQE performance of GaN-based LEDs. We grow our LED structure on the patterned sapphire substrate (PSS) and an increment in IQE is expected. In the third part of this study, we modified the traditional method for IQE measurement. We firstly modify the excitation laser wavelength and a serious of power and temperature dependent study was performed to define the IQE of LED device. The internal carrier lighting mechanism was also studied. The last part of this dissertation is based on the third part but a electrical injection setup was established. This instrument enabled us doing a serious of temperature and injection current dependent measurement. It not only helped us understand more about the IQE, but also well for discovering the origins of efficiency droop phenomenon. Besides, simulation software of APSYS was also performed to simulate the device performance under different temperature. The output of this dissertation provided a great help on realizing the solid state lighting in next generation.