| 摘要: | 本論文使用高阻值碳化矽基板成長氮化鋁銦鎵/氮化鎵異質結構，針對氮化鋁鎵緩衝層中不同鋁組成進行設計與比較，以改善短閘極元件常見之電流崩塌與汲極引發位障下降效應的問題，並藉由直流特性、暫態輸出特性、小訊號以及大訊號評估緩衝層的鋁組成對元件性能的影響。
在本研究中製作的高電子遷移率電晶體，具5 %、3 % 鋁組成的氮化鋁鎵緩衝層的元件於閘極長度為140 奈米的DIBL值為分別為62.8、95.8 mV/V，顯示較高鋁組成的氮化鋁鎵緩衝層可更有效抑制短通道效應，並使開關電流比由9×103 提升至2×104。然而，5 % 鋁組成的氮化鋁鎵緩衝層有著較嚴重的缺陷效應，藉由暫態輸出量測， 5 % 鋁組成的氮化鋁鎵緩衝層的Gate Lag電流降低幅度為2 %，Drain Lag電流降低幅度為13 %；3 % 鋁組成的氮化鋁鎵緩衝層的Gate Lag電流降低幅度為3%，Drain Lag電流降低幅度為9 %，顯示較高鋁組成的氮化鋁鎵緩衝層仍會因材料本身缺陷以及與氮化鎵的晶格不匹配所產生缺陷造成更為嚴重的缺陷效應。在28 GHz Class AB大訊號操作下，5 %、3 % 鋁組成的氮化鋁鎵緩衝層元件的輸出功率19.28 / 20.05 dBm、功率增益12.09 / 11.35 dB、功率附加效率32.08 / 40.24 % 與功率密度2.12 / 2.64 W/mm。研究結果顯示，降低氮化鋁鎵緩衝層之鋁組成，降低材料缺陷，將有助於同時兼顧高頻增益、效率與大訊號線性，進而改善元件於短閘極結構下之整體性能。
;In this study, high-resistivity silicon carbide (SiC) substrates were used to grow AlInGaN/GaN heterostructures. AlGaN buffer layers with varying aluminum compositions were designed and compared to mitigate common issues in short-gate devices, such as current collapse and drain-induced barrier lowering (DIBL). The influence of aluminum composition in the buffer layer on device performance was evaluated through DC characteristics, transient output response, small-signal, and large-signal measurements.
High electron mobility transistors (HEMTs) fabricated in this work with 5% and 3% aluminum composition in the AlGaN buffer layer exhibited DIBL values of 62.8 and 95.8 mV/V, respectively, for gate lengths of 0.14 µm. This indicates that higher aluminum content in the buffer layer more effectively suppresses short-channel effects, increasing the on/off current ratio from 9×10³ to 2×10⁴. However, the 5% Al composition buffer exhibited more severe defect-related effects. From transient output measurements, the current reduction due to gate lag and drain lag was 2% and 13%, respectively, for the Al0.05GaN buffer layer, compared to 3% and 9% for the Al0.03GaN buffer layer. These results suggest that a higher aluminum content leads to more pronounced defect effects, likely due to intrinsic material defects and lattice mismatch with GaN.
Under 28 GHz Class AB large-signal operation, devices with 5% and 3% Al content exhibited output powers of 19.28/20.05 dBm, power gains of 12.09/11.35 dB, power-added efficiencies (PAE) of 32.08/40.24%, and power densities of 2.12/2.64 W/mm, respectively. These findings demonstrate that reducing the aluminum composition in the AlGaN buffer layer helps suppress material defects, thereby improving high-frequency gain, efficiency, and large-signal linearity, and ultimately enhancing overall device performance in short-gate structures. |
