電子阻擋層於氮化鎵發光二極體之研究與應用

Abstract

本論文中主要研究應用p型氮化鋁鎵電子阻擋層與u型氮化鋁鎵電子阻擋層各自成長於氮化鎵發光二極體，探討不同設計之電子阻擋層對於發光二極體磊晶層品質與表面形貌的影響，並應用電流-電壓量測、積分球量測、二維強度影像分佈量測等，進行分析p型與u型氮化鋁鎵電子阻擋層對於氮化鎵發光二極體元件光電特性的表現與比較。 首先將樣品進行X-ray繞射儀與原子力顯微鏡分析，藉由觀察其LED-1、LED-2、LED-3、LED-4、LED-5的(102)面半高寬量測值分別為277arc sec、297arc sec、287arc sec、282arc sec、296arc sec，與RMS值分別為0.49nm、0.41nm、0.48nm、0.31nm、0.49nm；由以上實驗結果顯示，以p型或u型氮化鋁鎵電子阻擋層應用於氮化鎵發光二極體之實驗材料特性量測結果，可得知皆未影響其磊晶層品質與表面形貌。 接續進行為氮化鎵發光二極體元件光電特性的量測與比較，由量測數據顯示可知優化摻雜之p型氮化鋁鎵電子阻擋層鋁含量條件下可有效抑制順向偏壓的升高與逆向電流的產生，亦可得知其能直接提升能帶高度以侷限電子溢流達到發光效率較佳與擁有較好的熱/冷因子於高溫操作時發光效率；觀察u型氮化鋁鎵電子阻擋層可確認除了有相同的對比於未加入電子阻擋層傳統結構之光電特性優勢之外，由光電特性量測結果顯示， u型氮化鋁鎵電子阻擋層相較於傳統的p型氮化鋁鎵電子阻擋層應用於氮化鎵發光二極體之光電特性表現，其主要優勢在於可以減少受到價電帶上因晶格不匹配造成能帶彎曲所衍生出的位能障凹陷(Notch)與位能障釘狀突起(Spike)等問題所影響，進而提升發光區之導電帶與價電帶上的電子、電洞出現機率，得到u型氮化鋁鎵電子阻擋層的發光層之電子電洞輻射複合效率較高的結果。 觀察模擬能帶示意圖(1D-DDCC) 於施加3V偏壓設定條件下的ΔEc LED-2為1eV，LED-4為0.9 eV，可知其導電帶上的電子侷限能力雖然略高於u型氮化鋁鎵電子阻擋層LED-4的ΔEc為0.9eV，但LED-2其價電帶上的電洞阻擋能力ΔEv為0.7eV則明顯高於u型氮化鋁鎵電子阻擋層ΔEv的0.55eV；此一現象可直接說明造成LED-2電洞傳輸效率與發光效率降低的原因。 加入優化摻雜之u型氮化鋁鎵電子阻擋層的氮化鎵發光二極體元件其光輸出功率、外部量子效率、功率轉換效率等量測值與換算值皆為呈現高於優化摻雜p型氮化鋁鎵電子阻擋層約2~3%，可證明u型氮化鋁鎵電子阻擋層用以取代傳統之p型氮化鋁鎵電子阻擋層應用於氮化鎵發光二極體可獲得較佳的發光區電子侷限功能與較高的發光效率。

In this dissertation, we focus on p-type AlGaN Electron Blocking Layer (EBL) and un-doped AlGaN EBL, which growth on the GaN based Light Emitting Diodes(LED) separately, to investigate the influence of crystal quality and surface morphology about epitaxial layer of LED with different type of EBL. Furthermore by the use of the several methods for electrical and optical measurements such as I-V, Integrate Sphere, 2D images and Hot/Cold Factor to compare and analyze the performance of GaN based LED with p-type and un-doped EBL. At first, through the study of measurement with X-ray diffractameter and atomic force microscope included (002)crystal quality, (102)FWHM, (006)composition, 3D surface top view and values of RMS. By the result of experiments, we can easily confirmed that there are no obviously difference on crystal quality and surface morphology about epitaxial layer of GaN based LED with neither p-AlGaN nor u-AlGaN EBL by the result of experiments. To follow with the measurement and comparison about optical and electrical characteristics of GaN based LED, owing to the measured data, we confirm that not only the effectiveness of forward voltage(Vf) and reverse current(Ir) can be suppressed successfully, but also the height of energy band can be improved in order to confine the electron overflow and resulted in better recombination efficiency even under high temperature operated environment that is so called Hot/Cold factor. Subsequently by observation of the measured data it was realized that u-AlGaN EBL had not merely better performance which relate to p-AlGaN EBL but most important of all, there is advantage for u-AlGaN EBL on reduction of Notch and Spike influence, which caused by lattice mismatch and band bending, under comparing to the optical and electrical data with p-AlGaN EBL, This creates an increase in the probability of Electron-Hole pair that is located in conduction and valance band of the active region, and obtain the result that indicate, u-AlGaN EBL have better radiative recombination rate. By observation with simulation band diagrams of LED-2 and LED-4,we can noticed that the ΔEc is 1eV and 0.9 eV along with the ΔEv is 0.7eV and 0.55eV. It can be easily determined which LED-2 had more seriously problem on blocking of hole transportation. Lastly, with suitable Al composition, the chip of GaN based LED with u-AlGaN EBL showed better performance on light output power, external quantum efficiency and wall plug efficiency by about 2~3% improvement compared to the conventional p-AlGaN EBL. It showed the proof that by replacing p-AlGaN with u-AlGaN EBL, it will exhibit more LED’s superiority with lower energy consumption and longer lasting life.