| 摘要: | 氮化鋁鎵/氮化鎵高電子遷移率電晶體的歐姆接觸多半是藉由Ti/Al/Ni/Au在高溫熱退火下，來形成良好的歐姆接觸。例如此論文中的850 ℃退火，其金屬與半導體之特徵歐姆接觸電阻(Specific contact resistivity, ρc)為3.26 × 10-5 Ω·cm2，接觸電阻(Contact resistance, RC)為1.39 Ω·mm。若在歐姆接觸區域內利用乾轉印方式，將石墨烯轉印至AlGaN/GaN試片上，可以有效降低特徵歐姆接觸電阻至1.30 × 10-5 Ω·cm2。此外進一步結合歐姆接觸區挖槽，2 μm水平線條凹槽式圖案蝕刻結構結合單層石墨烯，可獲得最低的特徵歐姆接觸電阻(ρc = 1.98 × 10-8 Ω∙cm2)。
此論文研究包含石墨烯轉印流程，以拉曼光譜分析快速熱退火(氮氣環境中進行850 °C、30秒)對石墨烯所造成的影響，最後利用I-V電性量測分析使用石墨烯的歐姆接觸變化。由於石墨烯所帶來與傳統歐姆接觸不同的傳導機制，除了進行高溫熱退火的過程中，可促進Ti/Al/Ni/Au金屬的合金形成(如氮化鈦)，並與2DEG通道接觸，石墨烯可在氮化鈦合金的邊界處形成碳化鈦，使其形成等效高參雜濃度，進一步讓歐姆接觸電阻降低。
此外，在歐姆接觸區以不同的凹槽式圖案進行圖案蝕刻結合單層或雙層石墨烯，製作氮化鋁鎵/氮化鎵高電子遷移率電晶體，並比較其特性。結果顯示歐姆接觸區網格凹槽式圖案蝕刻結合雙層石墨烯之元件，呈現最低的導通電阻。此外二種不同凹槽式蝕刻深度(深度在2DEG通道上方或下方)結合雙層石墨烯製作之元件，其直流電性比較結果呈現凹槽式圖案蝕刻深度在2DEG通道上方之元件在導通電阻上較小，其中在歐姆接觸區洞陣列凹槽式元件具有最低的導通電阻。;In traditional AlGaN/GaN HEMTs, ohmic contacts are typically formed using Ti/Al/Ni/Au through high-temperature annealing. For example, in this study, annealing at 850 °C was used to achieve good ohmic contacts, resulting in a specific contact resistivity (ρc) of 3.26 × 10-5 Ω·cm2 and a contact resistance (RC) of 1.39 Ω·mm. By dry transferring graphene onto the AlGaN/GaN sample in the ohmic contact area, the specific contact resistivity was effectively reduced to 1.30 × 10-5 Ω·cm2. Furthermore, by combining the 2 μm horizontal line recessed pattern structure with monolayer graphene in the ohmic contact area, the lowest specific contact resistivity (ρc = 1.98 × 10-8 Ω·cm2) was achieved.
The study includes the graphene transfer process, Raman spectroscopy analysis after rapid thermal annealing at 850 °C for 30 seconds in a nitrogen environment, and basic I-V electrical measurements to analyze the changes in ohmic contact resistance with the use of graphene. The presence of graphene introduces a different conduction mechanism compared to traditional ohmic contacts. During high-temperature annealing, the formation of Ti/Al/Ni/Au alloys (such as titanium nitride) may be promoted, forming a good ohmic contact with the 2DEG channel. Graphene can form titanium carbide at the boundaries of these titanium nitride alloys, resulting in an equivalent high doping concentration, further reducing the ohmic contact resistance.
Additionally, various recessed patterns were etched into the ohmic contact area, combined with either monolayer or bilayer graphene, to fabricate AlGaN/GaN HEMTs, and their characteristics were compared. The comparison of devices with different recessed patterns in the ohmic contact area showed that those with a grid recessed pattern combined with bilayer graphene exhibited the lowest on-resistance. Finally, a DC electrical comparison of devices with two different recessed depths (above or below the 2DEG channel) combined with bilayer graphene showed that the devices with recessed depths above the 2DEG channel had lower on-resistance. Among these, the hole array recessed pattern devices with bilayer graphene demonstrated the lowest on-resistance. |
