| Abstract: | 本論文針對石墨烯對於歐姆接觸電阻研究，並應用於氮化鋁鎵/氮化鎵高電子遷移率電晶體進行電性探討與研究。研究包含磊晶片材料分析、石墨烯轉印的流程和特性分析、元件的設計與製作、直流電性與動態特性分析以及Silvaco TCAD的模擬。
在氮化鋁鎵/氮化鎵之高電子遷移率電晶體，使用高溫退火來形成歐姆接觸是常用的方式，然而傳統的氮化鋁鎵/氮化鎵高電子遷移率電晶體，金屬-半導體特徵接觸電阻(specific contact resistivity, ρc)約在1.7 × 10-5 Ω∙cm2，接觸電阻(RC)為1.07 Ω∙mm。而石墨烯使用兩種不同轉印方式(乾式轉印和濕式轉印)，轉印石墨烯於氮化鋁鎵表面，其特徵接觸電阻(ρc = 2.32 × 10-8 Ω∙cm2；4.69 × 10-7 Ω∙cm2)，歐姆接觸電阻(RC = 0.29 Ω∙mm；0.69 Ω∙mm)。使用轉印石墨烯的方式，因為只需要在磊晶片表面轉印單層的石墨烯，所以不需要額外的製程流程。在不影響製程流程下，改善金屬與半導體接面達到降低接觸電阻效果，對於引入商業的製程流程是一大利處。以此條件下來製作石墨烯改善氮化鎵高電子遷移率電晶體歐姆接觸，並比較氮化鎵高電子遷移率電晶體以兩種石墨烯轉印方式的元件特性。在直流偏壓下，具有石墨烯層的元件最佳增益轉導值(transconductance, gm = 141.3 mS/mm)，比較導通電阻(RON)的改善，有石墨烯層的元件導通電阻為9.5 Ω∙mm 相較於傳統元件導通電阻有35%的下降，顯示歐姆接觸電阻的降低可以有效改善元件端的特性。
在動態特性的分析，乾式轉印石墨烯元件有較嚴重的電流崩塌和動態導通電阻的變化，顯示元件在閘極與汲極之間有較多的缺陷使電子被捕捉，而導致元件會有較多的缺陷與石墨烯轉印的製程有關。所以本篇論文會介紹石墨烯材料的特性與這次實驗所使用的兩種轉印方式：「乾式轉印和濕式轉印」，並分析兩種轉印方式的石墨烯對於電晶體特性的影響。
;This paper discusses and studies the research on the ohmic contact resistance with graphene and its application in the AlGaN/GaN high electron mobility transistor (HEMT). The research includes epiwafer material analysis, graphene transfer process and characteristic analysis, component design and fabrication, DC electrical and dynamic characteristics analysis, and Silvaco TCAD simulation.
In AlGaN/GaN high electron mobility transistors, high-temperature annealing to form ohmic contacts is a common method. However, for conventional AlGaN/GaN high electron mobility transistors, the metal-semiconductor specific contact resistance (ρc) is about 1.7 × 10-5 Ω∙cm2, and the contact resistance (RC) is 1.07 Ω∙mm. The specific contact resistance of the devices with a graphene layer is 2.32 × 10-8 Ω∙cm2 (dry transfer graphene layer), 4.69 × 10-7 Ω∙cm2 (wet transfer graphene layer), and ohmic contact resistance is 0.29 Ω∙mm (dry transfer graphene layer), 0.69 Ω∙mm (wet transfer graphene layer). It can be observed that graphene improves the metal-semiconductor junction. Under this condition, a graphene-improved ohmic contact AlGaN/GaN HEMT is fabricated and compared using two transfer methods. Under DC bias, the best transconductance gm is 141.3 mS/mm in the device with the graphene layer. Compared with the on-resistance (RON) of the traditional AlGaN/GaN HEMT, there is a 35% reduction, indicating that the decrease in contact resistance can effectively improve the I-V characteristics of the device.
In the analysis of dynamic characteristics, the devices with the dry transfer graphene have severe current collapse and changes in dynamic on-resistance. The reason is that the device has more defects between the gate and drain, so electrons are captured, resulting in performance degradation, which is related to the graphene transfer process. |
