本篇論文主要為研製水平式閘極氮化鎵金氧半場效電晶體於藍寶石基板上並採用不同表面處理方式，分別為：(a) RCA Clean(b) ICP乾式蝕刻(c)在350°C環境下進行4次的Digital etch等方式互相搭配，期望透過不同表面處理的方式，降低表面粗糙度，並進一步提升各項電性，讓元件有更好的運作。

由量測結果可得，以RCA進行表面處理之試片擁有最佳的電性，其閾值電壓為8.75 V，最大汲極電流密度為1.915 mA/mm，計算後得到其場效遷移率為0.801 cm2/V-s。

而經過乾蝕刻的電性表現普遍低於未經乾蝕刻的sample，而經由比較也可發現，Digital etch處理過的表面普遍較乾蝕刻處理來得平滑。

In this study, GaN planar gate MOSFETs were fabricated on sapphire substrates. In order to recover the surface quality, several methods of surface treatment were carried out and compared, namely: (a) RCA clean (b) ICP dry-etching (c) 4 cycles of digital etch at 350 °C.
From the measurement, it was found that the best device performance was achieved with RCA clean. With a threshold voltage of 8.75 V and a maximum drain current density of 1.915 mA/mm, the calculated field-effect mobility is 0.801 cm2/V-s.
The electrical performance of the dry etched surface is generally worse than that of the sample without dry etching. However, it is observed by comparison with digital etched sample that the roughness of the surface is slightly higher than that of the dry etched ones.

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