於矽(111)基板上成長應用在高電壓之氮化鋁鎵/氮化鎵/氮化鋁鎵雙異質接面場效電晶體元件之研究

Abstract

由於氮化鎵(GaN)材料有許多優越的物理性質，例如：寬能隙、高能障、強崩潰電場與高載子速度等，使得傳統式氮化鎵電晶體(AlGaN/GaN HEMTs)具有高電流、高崩潰電壓與高操作溫度等特性，且可成長於大尺寸矽基板上，大幅降低了製作成本，因此有潛力取代矽元件成為次一世代高功率電子元件的材料，若能更進一步提升氮化鎵的崩潰電壓，將有助在更高電壓應用上的推展。 在此研究中，藉由能障與崩潰電場更高的氮化鋁鎵(AlGaN)取代傳統式氮化鎵元件的氮化鎵緩衝層，成功地在矽(111)基板上成長1.4 μm無裂痕的氮化鋁鎵/氮化鎵/氮化鋁鎵雙異質接面場效電晶體(AlGaN/GaN/AlGaN Double Heterostructure Field Effect Transistors, AlGaN DH-FETs)之新式結構，其Al0.1Ga0.9N 的 XRD (002)面rocking curve半高寬為578.8 arcsec，顯示薄膜品質良好，霍爾量測得到電子遷移率為1125 cm2/V-s。 經過元件製作與電性量測後，其飽和電流295 mA/mm與轉導值128 mS/mm雖低於傳統式氮化鎵電晶體，但臨界電壓-2.3 V更靠近0 V，有利於增強型(E-mode)元件的製作；在漏電流測試中，於5 μm的電極間距，AlGaN DH-FET在200 V下，漏電流仍不超過1 mA/mm，於20 μm的電極間距，其漏電流僅9.2×10-5 mA/mm，較傳統式氮化鎵電晶體下降了兩個數量級；在元件量測中，其崩潰電壓能夠超過200 V。相較於傳統式氮化鎵電晶體，新式氮化鋁鎵雙異質電晶體具有較強的抗漏電與耐高壓能力，顯示在高電壓環境下，其特性更優於傳統式氮化鎵電晶體。

GaN shows many superior physical properties such as wide bandgap, high energy barrier, high breakdown field and high carrier velocity. Therefore, conventional AlGaN/GaN HEMTs show characteristics of high current, high breakdown voltage and high operation temperature. Furthermore, conventional AlGaN/GaN HEMTs can be grown on large-sized Si substrate, so the fabrication cost can be reduced significantly. Accordingly, GaN material is a candidate for replacing Si-based devices to become next-generation high-power electronics. If the breakdown voltage can be further enhanced, the applications will be promising in high-voltage field. In this study, we employed AlGaN-buffer layer to replace GaN buffer layer in conventional GaN HEMT due to its higher energy barrier and breakdown field. Then 1.4-μm thick and crack-free AlGaN/GaN/AlGaN double heterostructure field effect transistor (DH-FET) was successfully grown on Si substrate. The FWHM of (002) XRD peak of Al0.1Ga0.9N was 578.8 arcsec, indicating the good film quality. In addition, the average electron mobility was 1125 cm2/V-s as revealed by Hall measurement. The DC measurements indicatined the device possesses the saturation current density of 295 mA/mm and transconductance of 128 mS/mm, slightly lower than conventional GaN HEMT. But the threshold voltage (-2.3 V) was closer to 0 V. In buffer leakage current test of 5-μm ohmic gap, the leakage current of 1.4-μm AlGaN DH-FET was less than 1 mA/mm at 200 V; at 20-μm ohmic gap, the leakage current was reduced by two orders of magnitude, only 9.2×10-5 mA/mm. The device measurement indicated the breakdown voltage could be higher than 200 V. Compared to conventional GaN HEMTs, AlGaN DH-FETs possess higher with-stand voltage and ability to prevent leakage current. In conclusion, AlGaN DH-FETs show better performance than conventional GaN HEMTs in high voltage condition.