利用侷域表面電漿共振提升氮化鎵MSM光偵測器效能

Abstract

本論文利用具有良好光電特性的氮化鎵基板製成金屬-半導體-金屬紫外光偵測器，在基板表面製造次波長結構，利用電漿共振原理增進元件效率並探討其特性。 先在商業化的藍寶石晶版上沉積AlGaN緩衝層，再用HVPE快速長晶法，成長330um以上的GaN，再以雷射將氮化鎵與藍寶石分離以消除應力，並用CMP將表面磨平及完成氮化鎵基板的製作。接著沉積150nm左右的SiO2絕緣層，用BOE以濕蝕刻的方式蝕刻出主動區，經過標準清潔流程後以E-gun分別鍍上5nm的鎳與5nm的金，接這送氮氣與氧氣退火以形成次波長結構，觀察其表面，最後在用E-gun鍍上指叉狀的電極即完成金屬-半導體-金屬紫外光偵測器。 從電性研究來看，700℃ 氮氣退火時開始形成次波長結構，光響度提升，在800℃的氮氣退火條件下產生了400nm~500nm大小的金屬粒子，元件的響應度提升了一個數量級以上，900℃的氮氣退火時表面形成了200nm~300nm小於入射光波長的金屬粒子，光響應度提升2個數量級，效率增加最多。而氧氣退火900℃時產生了六角形的氧化鎳晶體，可使元件Barrier high提高，降低漏電流，並得到更佳的理想因子，同時表面未與氧氣反應的金也可使光響度增加1個數量級左右。

In this work, we studied how surface plasma influences the responsitivity of a GaN-based metal-semiconductor-metal photo detector. The device was fabricated on a freestanding GaN substrate. To manufacture the GaN substrate, an AlGaN buffer layer was deposited on a commercial sapphire substrate first. After epitaxial growth by Hydride Vapor Phase Epitaxy (HVPE), a 300-um thick GaN film was produced. The film was sequentially separated from sapphire by laser lift off (LLO), and hence the GaN substract was obtained. Chemical mechanical polishing (CMP) was used to treat the surface of the freestanding GaN substrate to achieve the requirement of an epi-ready substrate. To fabricate the device, a 150-nm SiO2 Insulating layer was deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) at 300℃. The active region with size of 500 um*260 um was formed by etch. 5-nm nickel and 5-nm gold were coated on the active region and annealed at various temperature in N2 or O2 ambient to form a sub-wavelength structure. Finally, electrodes were fabricated, and the metal-semiconductor-metal photo detector was obtained. Nanostructures were observed on the surfaces of the detectors. By electrical measurement, it is found that the responsitivity of the detector annealed at 800℃ in N2 ambient raised up about 2 order in comparison with a conventional one. However, the leakage current and the ideal factor also increased. On the other hand, the device annealed at 800℃ in O2 ambient has a lower leakage current and a more favorable ideal factor; which is owing to higher Schottky barrier height brought by the formation of nickel oxide. It had 1-order improvement of responsitivity which was not as large as the N2-anneal one; nevertheless, by taking account of the overall properties, its performance is superior.