氮化鋁薄膜應用於氮化鎵發光二極體元件之特性研究

Abstract

本論文為將氮化鋁薄膜應用於氮化鎵發光二極體元件之特性研究，元件結構分別為電流阻擋層(CBL)及鈍化層(Passivation layer)，並且與傳統使用二氧化矽薄膜之元件相互比較其光電特性差異。 本實驗採用的是濺鍍(Sputtering)系統來成長薄膜。由穿透率量測可知，氮化鋁薄膜在可見光區域皆有90%以上穿透率，並可藉由顯影液對氮化鋁薄膜之蝕刻速率測試，得知氮化鋁薄膜在氮氣環境下熱處理一分鐘後，因晶格品質獲得改善，使薄膜抵抗顯影液蝕刻能力上升，以上實驗也證明了將氮化鋁薄膜應用於後續發光二極體元件實驗之可行性。 接著將氮化鋁薄膜做為發光二極體元件電流阻擋層，首先由電壓-電流(I-V)量測可知氮化鋁薄膜相較二氧化矽薄膜有較高的串聯電阻值，並且隨著薄膜厚度上升而增加，在氮化鋁厚度1800Å時，其20mA注入下所對應發光二極體光輸出功率較傳統結構增加了8%，光輸出功率增加的原因可歸因於電流阻擋層有效減少了電流流經p型電極下方區域的機率，使光被電極遮蔽的現象獲得改善。 本論文接著研究氮化鋁薄膜做為發光二極體元件側壁鈍化層，由熱處理實驗可知，熱處理製程雖然可以減少元件之漏電流，但同時也使發光二極體光輸出功率較傳統結構下降了約9%，光輸出功率下降的原因可歸因於側壁鈍化層區域薄膜穿透率下降所致。 最後本論文利用顯影液將經過熱處理之氮化鋁鈍化層去除，在20mA注入下，光輸出功率較傳統結構增加了約11%，光輸出功率增加的原因可歸因於位於發光二極體高台周圍之ITO薄膜電阻率上升，以及側壁阻值變化，使電流集中於未覆蓋氮化鋁薄膜之區域，產生類似電流阻擋層的效果，改善了發光二極體n型電極區域的電流散佈所致。

In this study, we examined the characteristics for the application of AIN thin films on GaN light-emitting diode (LED) devices. The devices structure contained a current blocking layer (CBL) and a passivation layer. We also compared the differences in optical and electrical properties between this devices structure and devices that traditionally employing silicon dioxide thin films. We used the sputtering system to grow thin films. Transmittance measurements indicated that the AIN thin film had a transmittance of above 90% in the visible light region. Additionally, a developer was used to test the etch rate of the AIN thin films. The results of this test indicated that after heat treatment in a nitrogen atmosphere for 1 min, the resistance of the AIN thin film to the developer etching increased because of improvements in lattice quality. The experiments also confirmed the feasibility of employing AIN thin films in follow-up experiments on LED devices. Next, we used the AIN thin film as the CBL in the LED. First, current-voltage (I-V) curve indicated that AIN thin films had higher series resistance values compared to that of the silicon dioxide thin films. These values increased with increases in the thin-film thickness. With an AIN thickness of 1800 Å, the corresponding LED light output power with 20 mA injection increased by 8% compared to the conventional LED. The light output power increased because the CBL effectively reduced the probability of the current flowing through the area under the p-type electrode. This improved the phenomenon of the electrode masking the light. Next, we investigated the use of AIN thin films as the sidewall passivation layer for LED devices. Heat treatment experiments indicated that although the heat treatment process can reduce the leakage current in the components, it also reduces the LED’s light output power by approximately 9% compared to the conventional LED. The decrease in light output power was caused by a decline in the thin-film transmittance in the sidewall passivation layer area. Finally, we used the developer to remove the heat-treated AIN passivation layer. The light output power with 20 mA injection increased by approximately 11% compared to that of the conventional LED. The light output power increased because the resistivity of the ITO thin film located in the area surrounding the LED mesa increased and the sidewall resistance value changed. This caused the current to concentrate in the area not covered by the AIN thin film, generating an effect similar to that of the CBL. This effect improved the current spreading in the LED n-type electrode area.