藉由插入低溫氮化鋁鎵插入層與高壓氮化鎵孕核層在矽(111)基板上成長厚且具低差排密度的氮化鎵薄膜

Abstract

由於氮化鎵(GaN)材料具有寬能隙、高電子遷移率、高崩潰電場與極佳的熱傳導性，使得氮化鎵元件有優越的高崩潰電壓及高電流等特性。其中，隨著磊晶技術的成熟，氮化鎵與大尺寸矽基板的整合，更使得矽基氮化鎵成為次世代高功率元件的最佳選擇。然而，要運用於高功率電子元件，必須具備高崩潰電壓，而在磊晶成長上，則必須具備厚度厚且磊晶品質高的氮化鎵磊晶層。 在此研究中，為了成長較厚之氮化鎵薄膜，在氮化鋁鎵/氮化鎵高電子遷移率場效電晶體 (High Electron Mobility Transistor HEMT)插入一層低溫氮化鋁鎵插入層以增加氮化鎵磊晶層的厚度，使用不同溫度及生長時間的低溫氮化鋁鎵插入層，以獲得最佳化成長條件。其中使用950 °C成長200秒的氮化鋁鎵插入層，在此條件下，成功地成長出高品質無裂痕之2.8 μm磊晶薄膜。其中XRD (002)面 rocking curve半高寬為530 arcsec，XRD (102)面 rocking curve半高寬為872 arcsec。 最後，在此結構再插入高壓成長的氮化鎵孕核層，可進一步提升氮化鎵磊晶層的品質，進而提升氮化鋁鎵/氮化鎵高電子遷移率場效電晶體之效能。最終獲得的薄膜品質XRD (002)面 rocking curve半高寬為348 arcsec，XRD (102)面 rocking curve半高寬為506 arcsec。在元件量測下，於3 μm的電極間距下，其崩潰電壓為90 V，在5 μm的電極間距下，其崩潰電壓為170 V。而在36 μm的電極間距下，其崩潰電壓更是高達550 V。 由此結果證明藉由插入低溫氮化鋁鎵插入層可成長出較厚且磊晶品質好的磊晶層。最後再插入高壓成長的氮化鎵孕核層提升氮化鎵磊晶層的品質，進而獲得高的崩潰電壓。

GaN shows many superior physical properties such as wide bandgap, high carrier velocity, high breakdown field and good thermal conductivity. Therefore, normal AlGaN/GaN HEMTs show characteristics of high breakdown voltage and high current. Furthermore, normal 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. However, it is necessary to have high breakdown voltage for high power device applications. For epitaxial growth, you must have the thick and high quality gallium nitride epitaxial layer. In this study, in order to grow thicker GaN epitaxial layer, a LT-AlGaN interlayer was inserted. Use different growth temperature and growth time of LT-AlGaN to obtain the best parameter of LT-AlGaN interlayer. The 2.8 μm crack-free epilayer was grown with optimization of LT-AlGaN for 200 seconds at set temperature of 950°C. From rocking curve scan of XRD analysis, FWHM of GaN (002) was 530 arcsec and GaN (102) was 872 arsec. Finally, HP-GaN nucleation layer was inserted to this structure to further improve the quality of the gallium nitride epitaxial layer and enhance the performance of AlGaN/GaN HEMTs. At last, the result shows FWHM of GaN (002) and (102) were 348 arcsec and 506 arcsec, respectively. Breakdown voltage of the device obtains from the measurement for 3 and 5 µm spacing were 90 V and 170 V, respectively. At 36 μm spacing, the breakdown voltage was as high as 550 V. The results demonstrate that inserting LT-AlGaN interlayer can increase the thickness and improve the quality of film. Finally, HP-GaN nucleation layer was inserted to this structure to further improve the quality of the gallium nitride epitaxial layer and enhance breakdown voltage of AlGaN/GaN HEMTs.