寬能隙的氮化鋁鎵/氮化鎵異質接面已廣泛的用於製作高電子遷移率電晶體做為高溫、高頻率與高功率的應用，對於高功率元件而言，歐姆接觸具有低接觸電阻、平坦的金屬表面與金屬側壁形態是相當重要的，這將影響到元件的特性、可靠度與再現性。 我們對於氮化鋁鎵/氮化鎵異質接面歐姆接觸的接觸電阻與金屬表面形態進行研究，包括鈦/鋁/鎳/金、鈦/鋁/鉬/金、鈦/鉻/鎳/金、鈦/鉻/鉬/金與 鈦/鋁/鉻/鉬/金 歐姆接觸金屬層。相較於傳統的鈦/鋁/鎳/金 歐姆接觸，利用鈦/鋁/鉻/鉬/金 歐姆接觸維持了接觸電阻達1.1×10-6 ohm-cm2，並達到了較為平坦的金屬表面。在氮氣環境中200 ℃高溫條件下進行熱穩定性分析，鈦/鋁/鉻/鉬/金 歐姆接觸依然維持低的接觸電阻，有以上之結果是由於利用鉻抑制了金與鋁金屬層間之擴散與合金的影響。 此外我們應用鈦/鋁/鉻/鉬/金 歐姆接觸於氮化鋁鎵/氮化鎵高電子遷移率電晶體(Lg= 2 μm, Lds= 6 μm)，獲得良好的高頻特性fT與fMAX分別為5.95 Gz與17.85 Gz，此結果說明了我們提出的鈦/鋁/鉻/鉬/金 歐姆接觸適合應用於高功率與高頻的氮化鋁鎵/氮化鎵高速電子遷移率電晶體。 Wide bandgap AlGaN/GaN heterostructures have been widely used in high electron mobility transistors (HEMTs) for high temperature, high frequency, and high power applications. For high power devices, ohmic contacts with low contact resistance, smooth surface and clear edge definition are essential as they are closely related to the performance, reliability and reproducibility of the devices. We carry out a comparative study on the specific contact resistivity and surface morphology of Ti/Al/Ni/Au, Ti/Al/Mo/Au, Ti/Cr/Ni/Au, Ti/Cr/Mo/Au, and Ti/Al/Cr/Mo/Au metal contact stacks on AlGaN/GaN heterostructure. Compared to the conventional Ti/Al/Ni/Au contact, the Ti/Al/Cr/Mo/Au contact has a much smoother surface and keeps its specific contact resistivity (ρc) as low as 1.1×10-6 ohm-cm2. This contact maintains its low contact resistivity after storing at 200 oC for 100 hours in nitrogen ambient. These results are attributed to the Cr interlayer, which suppresses inter-diffusion and reaction between the Au and Al layers in the contact stack. Moreover, we apply Ti/Al/Cr/Mo/Au ohmic contact to AlGaN/GaN HEMTs (Lg =2μm, Lds =6μm) and obtain fT and fMax of 5.95GHz and 17.85GHz respectively. These results suggest that the proposed Ti/Al/Cr/Mo/Au contact is a good ohmic electrode for high power and high frequency AlGaN/GaN HEMTs.
