AlGaInP發光二極體特性之提升

Abstract

本研究為改善四元發光二極體與金屬反射層之特性，使用晶圓接合技術將LED磊晶層轉移至鑽石基板並配合金屬反射層增加光的取出與降低焦耳熱之問題。可分為鑽石基板與表面粗化兩部份。由於鑽石的熱傳導係數比起砷化鎵來得高，焦耳熱效應的問題可以獲得解決，使得鑽石基板LED有更高的飽和電流。在電流=350mA時，鑽石基板LED的發光強度為1849 mcd。 另一部份，發光二極體元件可藉由表面粗化和金屬反射層以增加光取出效率。當光由多重量子井發出經過發光二極體和空氣的介面時，粗糙的表面可以減少光線全反射的機率，而增加光取出效率。 經由化學溼式蝕刻的方式，我們製作了p-side粗化之砷化鎵基板AlGaInP LED，蝕刻一分鐘的LED元件在20mA時，發光強度提昇了57.4%。 經由化學溼式蝕刻、鏡面系統和晶圓接合的方式，我們製作了p-side粗化之矽基板AlGaInP LED。 P-side蝕刻3µm圖形的LED元件在20mA時，發光強度提昇了53.5%，另外由於接觸阻抗的降低使得驅動電壓略為下降。 經由化學溼式蝕刻、鏡面系統、晶圓接合與ICP乾蝕刻的方式，我們製作了雙面粗化之矽基板AlGaInP LED，但是關於發光強度的下降目前原因還不明瞭，而驅動電壓增加則因為電流分散效應的降低與磊晶層的損傷所造成。

In this thesis, the AlGaInP epi layer was successfully transferred from GaAs to diamond substrate by wafer bonding technology at first. Then the light-extraction efficiency was also increased by metal mirror reflector. The results of the experiments showed that the saturation current of diamond-light emitting diodes (LEDs) was increased. Therefore, the issue of joule-heat effect was solved by using diamond substrates because of the better heat conduction diamond substrates have. This allows the diamond-substrate LED with mirror system to operate a current up to 350 mA and a peak luminous intensity of 1849 mcd. The improvement of the light-extraction efficiency was due to the surface roughening and metal reflector. As the light driven by multi-quantum well passed through the boundary of air and LED, the rougher surface can decreased the probability of the total reflection. Therefore, the light-extraction efficiency was improved. A structure with p-roughed AlGaInP LED on GaAs substrate was fabricated by wet etching. The luminous intensity of LED was enhanced 57.4% at an injection current of 20 mA after wet etching 1 minute. A structure with p-roughed AlGaInP LED on silicon substrate was fabricated by wet etching, mirror system and wafer-bonding. The luminous intensity of LED with 3µm wet etching pattern was enhanced 53.5% at an injection current of 20 mA. Moreover, the forward voltage was decreased slightly because the augmentation of contact area. A structure with double-roughed AlGaInP LED on silicon substrate was fabricated by wet etching, mirror system, wafer-bonding and ICP dry etching. The luminous intensity was decreased after ICP dry etching. We do not know the reason exactly right now. Moreover, the forward voltage was increased because the debasement of current spreading and damage to the epi layer.