傳統氮化鋁鎵/氮化鎵高電子遷移率電晶體(AlGaN/GaN HEMT)之歐姆接觸多採用 Ti/Al/Ni/Au金屬堆疊，並經高溫快速熱退火形成低阻接觸。本研究於歐姆金屬與 AlGaN/GaN異質結構之間導入不同厚度之碳(C)與碳化鈦(TiC)插入層，並進一步結合孔洞式凹槽蝕刻結構，以探討其對歐姆接觸特性及元件電性的影響。 首先，比較傳統型歐姆接觸結構、2 nm與5 nm碳插入層，以及1.5 nm與3 nm碳化鈦插入層之歐姆接觸特性。傳輸線模型(TLM)量測結果顯示，導入2 nm碳插入層可獲得最佳歐姆接觸特性，其接觸電阻與特徵接觸電阻率分別降低至Rc = 0.119 Ω·mm 與 ρc = 2.28 × 10-7 Ω·cm2，顯著優於傳統型歐姆接觸結構。元件直流特性分析亦顯示，2 nm碳插入層元件具有較低導通電阻、較低關閉漏電流及較高開關電流比。崩潰電壓量測結果顯示，導入碳或碳化鈦插入層後元件之耐壓特性未出現明顯劣化。於動態特性分析中，3 nm碳化鈦插入層元件於Gate-lag與Drain-lag條件下展現較低之電流崩塌率及較小之動態/靜態導通電阻比值，而2 nm碳插入層元件之動態特性亦優於傳統型歐姆接觸元件。此外，長時間熱儲存測試結果顯示，2 nm碳插入層元件具有較佳之熱穩定性。值得注意的是，雖然直接導入碳化鈦插入層亦可改善歐姆接觸特性，但其接觸電阻仍高於2 nm碳插入層元件，顯示碳插入層於退火過程中所誘發之界面反應及TiC界面相形成，對歐姆接觸改善具有更顯著之貢獻。 為探討歐姆接觸改善機制，本研究進一步利用FIB與TEM進行材料分析。結果顯示，2 nm碳插入層可調控歐姆金屬與 AlGaN/GaN異質結構之間界面反應，促進TiC與TiN混合反應層形成，改變界面結構並降低有效蕭特基能障，進而改善歐姆接觸特性；3 nm碳化鈦插入層則促進TiN與TiCxN1-x混合反應層形成，顯示不同插入層在高溫快速熱退火後會有不同界面反應相組成，也導致不同的歐姆接觸特性。 本研究亦探討孔洞式凹槽蝕刻結構搭配碳或碳化鈦插入層之影響。結果顯示，不同孔洞尺寸會影響歐姆接觸與元件電性，其中3 µm孔洞尺寸搭配2 nm碳插入層具有最佳表現。然而，相較於未導入凹槽蝕刻之2 nm碳插入層元件，孔洞式凹槽蝕刻結構並未進一步降低歐姆接觸電阻，顯示其改善效果有限。 最後，透過熱離子場發射(TFE)與場發射(FE)模型擬合溫度相依特徵接觸電阻率，結果顯示導入2 nm碳插入層後可有效降低界面等效能障高度，兩者綜合顯示碳層誘發之界面反應可能與載子穿隧傳輸改善及接觸電阻降低有關。整體而言，本研究結果顯示，碳插入層可有效降低AlGaN/GaN HEMT之歐姆接觸電阻並改善元件導通特性；相較之下，孔洞式凹槽蝕刻結構雖可維持良好的元件電性，但並未進一步降低歐姆接觸電阻，其改善效果有限。;Conventional ohmic contacts for AlGaN/GaN HEMTs are commonly formed using a Ti/Al/Ni/Au metal stack followed by high-temperature annealing. In this study， carbon (C) and titanium carbide (TiC) insertion layers with various thicknesses were introduced between the ohmic metal stack and the AlGaN/GaN heterostructure. In addition， hole-type recessed structures were incorporated to investigate their effects on ohmic contact characteristics and device electrical performance. First， the ohmic contact characteristics of conventional contacts， 2 nm and 5 nm C insertion layers， and 1.5 nm and 3 nm TiC insertion layers were compared. TLM measurements showed that the 2 nm C insertion layer exhibited the best ohmic contact performance， with the contact resistance and specific contact resistivity reduced to Rc = 0.119 Ω·mm and ρc = 2.28 × 10-7 Ω·cm2， respectively， which were significantly lower than those of the conventional ohmic contact structure. DC characteristics also demonstrated that the device with the 2 nm C insertion layer exhibited a lower on-resistance， lower off-state leakage current， and higher on/off current ratio. Breakdown voltage measurements indicated that the introduction of C or TiC insertion layers did not cause significant degradation in the breakdown characteristics. Under dynamic operating conditions， the device with the 3 nm TiC insertion layer exhibited lower current collapse and smaller dynamic-to-static on-resistance ratios under both gate-lag and drain-lag conditions， while the dynamic performance of the device with the 2 nm C insertion layer was also superior to that of the conventional ohmic contact device. In addition， long-term thermal storage measurements showed that the device with the 2 nm C insertion layer exhibited better thermal stability. Notably， although direct insertion of a TiC layer also improved the ohmic contact characteristics， its contact resistance remained higher than that of the device with the 2 nm C insertion layer. This result suggests that the interfacial reactions induced by the C insertion layer during annealing and the resulting formation of an interfacial TiC phase make a more significant contribution to the improvement of ohmic contact characteristics. To investigate the mechanism underlying the improvement in Ohmic contact characteristics， FIB and TEM analyses were further performed. The results show that the 2 nm carbon insertion layer can modulate the interfacial reactions between the Ohmic metal stack and the AlGaN/GaN heterostructure， promoting the formation of a mixed TiC/TiN reaction layer. This modification of the interfacial structure reduces the effective Schottky barrier height， thereby improving the Ohmic contact characteristics. In contrast， the 3 nm TiC insertion layer promotes the formation of a mixed TiN/TiCxN1-x reaction layer. These results indicate that different insertion layers lead to distinct interfacial reaction phases after high-temperature RTA， resulting in different Ohmic contact characteristics. The effects of combining hole-type recessed structures with C or TiC insertion layers were also investigated. The results showed that different hole dimensions affected both the ohmic contact characteristics and device electrical performance， with the combination of 3 µm holes and a 2 nm C insertion layer exhibiting the best overall performance among the recessed structures. However， compared with the non-recessed device using the 2 nm C insertion layer， the hole-type recessed structure did not further reduce the ohmic contact resistance， indicating that its improvement in contact characteristics was limited. Finally， the temperature-dependent specific contact resistivity was analyzed using thermionic-field-emission (TFE) and field-emission (FE) models. The fitting results showed that the introduction of the 2 nm C insertion layer effectively reduced the effective interfacial barrier height. Combined with the material analysis results， these findings suggest that the interfacial reactions induced by the C insertion layer are associated with enhanced carrier tunneling transport and reduced contact resistance. Overall， the results demonstrate that the C insertion layer can effectively reduce the ohmic contact resistance of AlGaN/GaN HEMTs and improve their conduction characteristics. In contrast， although the hole-type recessed structure maintained favorable device electrical performance， it did not further reduce the ohmic contact resistance， and its improvement in ohmic contact characteristics was therefore limited.
