本實驗中探討分子束磊晶系統再成長高濃度N型氮化鎵的四種方法，分別為直接成長法、遷移增強磊晶法、矽增強磊晶法和鎵金屬調整磊晶法，隨著不同方法的使用，濃度有逐漸提升的趨勢，其中鎵金屬調整法摻雜濃度可到1.04x1019 cm-3，此為上述方法可達到的最高濃度。在成長過程可透過III/IV比例去控制成長環境為二維或三維成長，這個比例為控制表面平坦度的關鍵。
使用分子束磊晶再成長高濃度N型氮化鎵於P GaN cap layer AlGaN/GaN上，並進一步實驗在元件上的可能性。由於高濃度摻雜的P型氮化鎵層和高濃度摻雜的再成長N型氮化鎵層，兩者接觸會形成穿隧接面，此接面有助於電流的傳導。量測再成長高濃度N型氮化鎵於P-GaN/AlGaN/GaN側向蕭特基二極體元件，大部份的元件On/Off ratio皆可以達到107~108，在10V時順向電流可達48 mA，且有0.79 A/mm的電流密度。再進一步進行崩潰電壓的量測，水平崩潰電壓可達405 V，垂直崩潰電壓則可達568 V。

In this study, the regrowth of high doping concentration N type GaN by molecular beam epitaxy was investigated. Four different growth conditions were used to improve the doping concentration including base line growth, migration enhanced epitaxy, Si enhanced epitaxy and Ga adjusted epitaxy. It is observed that the concentration is dramati-cally improved with different methods. Ga adjusted epitaxy can en-hance the concentration up to 1.04x1019 cm-3, which is the highest among these conditions. The III/V ratio was controlled to make the GaN film grown in 2-dimention or 3-dimention mode, which has a profound effect on the surface flatness.
The regrowth of a high doping concentration N type GaN was then applied on P type GaN cap layer on AlGaN/GaN to further explore it possibility on device performance. According to the high doping con-centrations of the P type GaN cap layer and the N type GaN regrowth layer, it is possible to form a tunnel junction in the device structure, which is beneficial for current conduction. From measurement results of fabricated regrowth N+ on P-GaN/AlGaN/GaN lateral SBDs, an on/off ratio greater than 107~108 order can be achieved. The best device shows 48 mA forward current at 10V, corresponding to a current density of 0.79 A/mm. The measured horizontal breakdown voltage and vertical breakdown voltage are 405 and 568V separately.

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