增強型p型氮化鎵/氮化鋁鎵/氮化鎵高電子遷移率電晶體之研製

Fabrication and Characterization of Enhancement-mode p-GaN/AlGaN/GaN HEMTs

蕭琮介(Tsung-Chieh Hsiao)

指導教授 ： 黃智方

國立清華大學/電機資訊學院/電子工程研究所/碩士(2013年)

https://doi.org/10.6843/NTHU.2013.00059

摘要

本篇論文中，我們選用矽基板上磊晶p型氮化鎵/氮化鋁鎵/氮化鎵試片製作增強型高電子遷移率電晶體，主要於閘極區域利用高濃度的p型氮化鎵與底層氮化鋁鎵/氮化鎵形成PN接面的特性，空乏二維電子氣通道使通道關閉，藉此實現增強型元件。當元件通道長度2µm，閘極至源極長度5µm，閘極至汲極長度7µm時，量得臨界電壓值(Vth)為0.3V，轉移電導值為45mS/mm，導通阻抗值為3.43mΩ‧cm^2，以及不錯的電流開關比(Ion/off ≈10^8)。
在元件關閉崩潰特性方面，利用磊晶較厚的緩衝層(4.2µm)， 減少基板漏電路徑，同時提升垂直方向承受電壓能力。在基板為浮動電位並且浸泡在冷卻液的條件下，量測結果顯示，閘極至汲極長度為60µm元件，獲得最高崩潰電壓值為2760V。而閘極至汲極長度為20µm元件，則有最佳評比效能BFOM值604MW/cm^2，表示崩潰電壓與導通電阻達到最佳的平衡。最後，我們觀察到汲極電流呈現不穩定的現象，有別於表面與內部缺陷所導致的電流衰減，故嘗試分析並加以解釋可能成因。

關鍵字

氮化鎵 ； 氮化鋁鎵/氮化鎵 ； P型氮化鎵 ； 增強型

並列摘要

In this thesis, enhancement-mode p-GaN/AlGaN/GaN HEMTs on a silicon substrate were fabricated. The p-type doped GaN and AlGaN/GaN barrier junction can be considered as a PN junction, so using p-type GaN as gate is able to deplete the 2DEG channel at a Vg=0V, thus yielding a normally-off device.
For the on-state characteristics, the threshold voltage (Vth) and the maximum transconductance (Gm,max) for the device with 2μm Lch, 5μm Lgs and 7μm Lgd is 0.3V and 45mS/mm. And the on-resistance and on/off current ratio is 3.43mΩ‧cm^2 and 10^8 for the same device.
For the reverse breakdown characteristics, we use a thick buffer layer to reduce substrate leakage current and raise the capability of vertical breakdown voltage. The highest breakdown voltage for the device with Lgd=60μm is 2760V, and the best BFOM is 604 MW/cm^2 for the device with Lgd=20μm. A drain current instability that is different from the current collapse due to surface and bulk traps is observed and explained.

並列關鍵字

GaN ； AlGaN/GaN ； p-GaN ； enhancement-mode

參考文獻

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