我們藉由極化工程提出了一個新穎的常關模式氮化鋁鎵/氮化鎵高電子遷移率場效電晶體。此研究最基本的概念是漸變阻擋層 ( barrier-layer ) 的鋁含量，由氮化鎵漸變至氮化鋁鎵，以減緩壓電極化對電子通道的影響，並使導電帶與費米能接重合部分減少，元件的閾值電壓移往正值，以利於常關模式的操作。此外，可以發現元件藉由操作氮化鋁鎵cap-layer的鋁含量，以及在氮化鎵緩衝層的頂部加入p型摻雜，可進一步調整直流電壓－電流特性。此項研究是基於元件的物理特性模擬，提供一個執行高效率常關模式氮化鎵高電子遷移率場效電晶體的方法。

We propose a novel normally-off AlGaN/GaN HEMT governed by the polarization engineering. The fundamental concept is to grade the Al-composition of barrier-layer from GaN to AlxGa1-xN, alleviating the impact of piezoelectric polarization on the 2-DEG and establishing the conduction-band profile well above the Fermi-energy. All of which leads to a positive shift for the threshold-voltage of the device, and benefits to the normally-off operation. Additionally, it is found that device’s DC transfer characteristics can be further modulated by simply adjusting the Al-composition of AlyGa1-yN cap-layer and the p-type doping concentration on the top of GaN buffer-layer. These findings based on the device’s physical simulation provide a guideline for the implementation of high-efficient normally-off AlGaN/GaN HEMTs.

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