氧化鋅之矽基金氧半導體元件研究

Abstract

本論文以射頻磁控濺鍍在矽基板成長氧化鋅薄膜，再鍍上氧化層和電極，製成一個金氧半導體元件(金/二氧化矽/氧化鋅)。由於氧化鋅擁有較高的激子束縛能(60 meV)和高折射係數(2.45)，為一具有潛力發展LED的材料。輔以電流產生近能隙，波長為380nm 的UV發光元件。 在射頻磁控濺鍍的低溫製程下，氧化鋅具好的結晶特性，這有助於UV強度的增強。實驗發現以Al背電極和矽基板可形成歐姆接觸，另外，使用200W濺射功率在200oC下製成的氧化鋅薄膜具有較好晶體結構與較低元件的阻抗。利用電性分析來量測元件工作特性，發現在氮氣環境退火後，漏電流下降了100倍；電致發光實驗結果顯示，其啟動電壓約4~5V，電流約為25mA。且退火後整個元件有更佳的電性及UV光發射強度。成長不同厚度的氧化鋅薄膜發現，氧化鋅薄膜膜厚為555 nm之元件比200 nm厚氧化鋅薄膜，所產生的UV光具較高的強度。

Zinc oxide (ZnO) is a highly potential material for manufacturing UV LEDs due to its large exciton binding energy of 60 meV and inherent nature of high refractive index of ZnO (2.45). In this study, ZnO thin films were grown by RF magnetron sputtering epitaxy on the silicon (n-type 100) substrates accompanied with SiO2 films as gate dielectrics to form Au/SiO2/ZnO metal-insulator-semiconductor (MIS) structures. By applying external bias, it can emit near-band-edge ultraviolet (UV) emission of wavelength λ = 380 nm. Growing ZnO films using RF sputtering at low temperature shows better crystal quality that could enhance UV emission efficiency. An electric property study for the MIS device under N2 ambient annealing shows the reverse bias leakage currents decrease about 2 orders. Our results show the ZnO films grown under 200W RF sputtering power at 200oC have the best crystal quality and the lowest impedance. The leakage current of the devices decrease about 2 orders after post-annealing at 450 oC with the threshold voltage being 4-5V and the threshold current of ~ 25mA. The MIS devices reveal better I-V characteristic as well as the higher UV emission intensity. We also found that the MIS device with the thicker ZnO film with 550 nm has the higher emission efficiency than the 200 nm one.