應用光致電化學法製作高效率氮化鎵基發光二極體

Abstract

本論文主要研究主題為探討光致電化學氧化和蝕刻法應用在氮化鎵微米孔洞陣列發光二極體和薄膜垂直式發光二極體(VTF-LED)上對於發光強度和電性的影響。 和傳統發光二極體相比，氮化鎵微米孔洞陣列發光二極體裸露出的氮化鎵和主動層表面積大為增加，因此搭配上光致電化學氧化蝕刻法，會使得氧化或蝕刻的表面積增加，對於外部出光效率的增強，會比在傳統的broad-area發光二極體使用光電化學氧化法來的更有效果。 在光致電化學氧化法應用於氮化鎵微米孔洞陣列發光二極體發光強度影響的探討中，我們利用光致電化學氧化方法進行微米孔洞陣列發光二極體發光區域的表面和微米孔洞陣列中側壁氧化處理，並討論LED元件製作流程及光致電化學氧化對元件特性的影響，再將製作完成的LED元件進行I-V和L-I以及AFM和SEM以及beam view分析，以確定在表面微孔洞陣列LED結構上使用光致電化學氧化可以增加LED的外部發光強度。實驗結果，我們得到最佳的參數是在偏壓5V下經過20分鐘的光致電化學氧化處理後的表面微孔洞陣列LED元件，在20mA的操作電流下，未經氧化處理表面微孔洞陣列的元件以及經氧化處理的微孔洞陣列元件和原本的broad-area的發光二極體元件相比，發光強度分別增加了38%和82%。 在氮化鎵微米孔洞陣列發光二極體的光致電化學蝕刻探討中，我們利用不同濃度的氫氧化鉀濃度和不同的蝕刻時間，搭配上表面微米孔洞陣列發光二極體結構，使得微米孔洞陣列中側壁產生糙化表面，再進行I-V和L-I以及AFM，SEM，beam view分析，實驗結果，在不同KOH濃度下，我們得到最佳參數為在低濃度0.015M的氫氧化鉀溶液中，2.5V外加偏壓下經過5分鐘後的蝕刻處理後，和原本的broad-area發光二極體相比，發光強度增加了34%。在高濃度0.03M的氫氧化鉀溶液中，以同樣的外加偏壓經過5分鐘蝕刻後，發光強度增加了51%。 我們成功利用光致電化學氧化法於氮化鎵薄膜垂直式發光二極體(vertical thin film LED)在n型氮化鎵表面成長出100nm左右厚度的GaOx氧化層，經過L-I-V量測，和原本的VLED相較，在100mA電流注入時可增加36%外部出光效率。

The enhancement of light extraction efficiency of InGaN-based light emitting diodes has fabricated and studied by photoelectrochemical wet etching/oxidation in the thesis. The fabricated InGaN-based LED structures are treated through micro-hole array process and photoelectrochemical (PEC) wet oxidation and etching process using Hg lamp illumination and DI water or KOH solution. We study the influence of photoelectrochemical (PEC) oxidation and etching methods on micro-hole array LED structures. In this study, two ways were used to increase the light extraction efficiency. Firstly, micro-hole array patterning structure was fabricated on the broad area LED structures. It can increase light extraction efficiency from the sidewall area of multiple quantum wells (MQWs). Secondly, photoelectrochemical (PEC) oxidation and etching methods were applied to the micro-hole LED structures. PEC process on GaN/ LED can decrease total reflection angle between GaN and air and also has surface roughness effect on GaN material. Compared with the conventional broad-area LED structure, micro-hole array LED structure has larger GaN and InGaN surface area. It increases PEC oxidation and etching area on LED structures. Theoretically, The more oxidation or etching area, the higher light extraction efficiency increases. We combined micro-hole array structure and photoelectrochemical methods performed on the conventional broad-area structure to increase light extraction efficiency. PEC oxidation is used to form oxidation layer and increase surface roughness on the micro-holes array sidewall surface. After PEC oxidation process, the micro-hole array LEDs were performed L-I-V, SEM , AFM, and beam-view image measurement. Comparing with the conventional broad-area LEDs, the experiment results show that the light output power of micro-hole array LEDs and 10min PEC-oxidized micro-a array LEDs have increase of 1.38 and 1.82 times at bias current of 20mA, respectively. PEC KOH roughening is only used to increase surface roughness on the micro-holes array sidewall surface. After PEC oxidation process, the micro-hole array LEDs were performed L-I-V, SEM , AFM, and beam-view image measurement. Compared with conventional broad-area LEDs, micro-hole array LEDs with 5min PEC KOH roughening has a increase of 1.51 times at a bias current of 20mA GaN thin-film vertical LED is fabricated by photoelectrochemical oxidation method. GaOx film about 100nm thickness is successively deposited on n-GaN surface. Compared with thin-film vertical LED without GaOx film, 36% light output power increases at 100mA.