圖案化基板與粗化表面在氮化鎵LEDs之光電特性研究

Abstract

本論文中，我們利用有機金屬化學氣相沉積法(metalorganic chemical vapor phase deposition,MOCVD)之技術與噴霧裂解法(spray pyrolysis)技術 ，製作出氮化銦鎵/氮化鎵材料之藍光結構的粗化表面發光二極體，來達到改善光萃取效率之目的。在此研究中，同時我們也展示了以反應氣體處理製程方法在氮化鎵系列材料發光二極體之氮化鎵與圖案化藍寶石基板間之界面進行抑制表面缺陷的技術。 開始先利用有機金屬化學氣相沉積將氮化鎵(gallium nitride,GaN)薄膜成長在一個平台金字塔圖案化藍寶石基板，利用溼式蝕刻定義出圖案化藍寶石基板後並利電感式偶合電漿（inductively coupled plasma,ICP）的反應性氯氣製程進行在圖案化基板表面處理。透過表面處理，晶體生長可以受到控制，因此，在圖案化基板的側面會形成以相同的纖鋅礦氮化鎵結構成長，並在後續LED的成長，結果顯示可以抑制表面缺陷。 利用ICP氯氣處理過後的基板表面，再基板表面成長LED結構，電性分析在20mA下的光輸出功率為11.8mW，比較與利用ICP的氬離子氣體處理與未任何氣體處理後的輸出功率分別提高3.5%以上。 在樣品經氬離子氣體處理與未任何氣體處理過後，經電性測試的抗靜電放電模擬，兩者樣品在超過-1000V測試後，耐受程度皆快速下降，最後測試在-2000V時合格率則變為零。然而，在經氯氣處理的樣品，直到反向測試電壓-4500V時還有50％的合格率，顯示有較高的磊晶品質。 之後我們為了達到改善光取出效率之目的，我們利用有機金屬化學氣相沉積成長技術在氮化鎵LED形成自然粗糙表面。而以此技術自我組成的表面構造有倒六角形孔洞形態，並且尺寸與密度可藉由調變磊晶成長條件之環境溫度以得到良好的控制，在p-GaN成長溫度條件800℃時的元件光電特性，由實驗結果顯示，以磊晶技術自我組成的表面構造，所製成之氮化鎵系列材料發光二極體比一般表面平滑構造之發光二極體，其亮度的輸出功率有效的提昇至少35%。 最後，以噴霧裂解法沉積摻硼氧化鋅(boron-doped zinc oxide, BZO)在玻璃基板上，並探討硼摻雜對於BZO薄膜的性質、電性及光性。 在摻雜比例為[B]/[Zn]=1at%時，可以得到載子濃度約為1019cm-3以上，並經大氣環境溫度600℃進行熱處理之後，當摻雜比例超過0.75at%，薄膜的導電機制則由B-Zn的摻雜形式所主導。 接著，以氯化鋅當作前驅物(precursors)溶液製備奈米柱結構(nanorods, NRs)的氧化鋅，分別沉積在玻璃基板與氮化鎵(gallium nitride, GaN)的發光二極體(light emitting diode,LED)晶粒上，改變沉積時間並觀察其奈米柱的表面形貌與電光性質，明顯在適當沉積時間的LED粗糙化表面，可使發光強度增加，並在晶粒垂直方向的發光強度有9%的提升。

In this thesis, In order to improve the light extraction efficiency (LEE)，we demonstrated the surface roughening techniques in InGaN/GaN-based LEDs by metalorganic chemical vapor phase deposition technique and spray pyrolysis. We also demonstrated a suppressing the surface defects technique at the GaN/patterned sapphire substrate interface in GaN-based LEDs using reactive gas-treatment process. The GaN film was grown on a flat top pyramid patterned sapphire substrate by using metal organic chemical vapor deposition; the sapphire substrate was patterned by wet etching followed by an Inductively Coupled Plasma process to surface treatment with reactive Cl2 gas. The wurtzite GaN structure was found on the sidewall surface of PSS; hence crystal growth was controlled to form the same wurtzite GaN structure result in suppressing the surface defects after the LED epitaxy process. The output power of a light-emitting diode grown on the FTPPSS by ICP process with Cl2 gas reactive was increased by 11.8mW at a forward current of 20 mA, presenting an improvement of 3.5% over that of an LED that were grown on FTPPSS with Ar+ ion ICP process and normal FTPPSS, separately. The ESD pass yield of the FTPPSS with Ar+ ion gas reactive and normal FTPPSS dropped over -1000V and finally the yield became 0% at -2000V. However, the FTPPSS with Cl2 gas reactive showed much higher pass yield, and 50% chip endured -4500V reverse voltage, it should be noted that epitaxal high-quality was achieved. In second parts, In order to improve the light extraction efficiency (LEE), naturally texturing surface on GaN-LEDs was demonstrated by Metal Organic Chemical Vapor Deposition. The self-assembled surface textures morphology including inverted hexagonal cones; the size and density could well controlled by changing growth conditions such as growth temperature. The growth temperature of p-GaN layer at 800 ℃, the electroluminescence measurement was performed to characterize the LEDs diode, the experimental results indicated that the surface textures on GaN-based LEDs could effectively enhance light output power by at least 35 % compared to smooth surface LEDs. Finally, the boron-doped zinc oxide thin film was deposited on glass substrates by spray pyrolysis. The boron doping on the structural, electrical and optical properties in BZO films were investigated. In the as-deposited films, the carrier concentration of ~1019cm-3 was achieved in [B]/[Zn]=1at%. With followed heat treatment under air ambient and temperature is 600℃, the conductive mechanism of the film dominated by B-Zn type as the doping ratio exceeds 0.75at%. Then zinc chloride as a precursor solution preparation of zinc oxide nanorods, were deposited on glass substrate and GaN_LED chips, changing the deposition time to observe the surface morphology and electro-optical properties of nanorods. At appropriate deposition time, the luminous intensity in perpendicular to the chip direction can be enhanced about 9% by surface roughening.