氮化鋁鎵/氮化鎵高電子遷移率電晶體之電子遷移率與缺陷分析及結構優化

Abstract

本文主要分析AlGaN/GaN高電子遷移率電晶體的電子遷移率、缺陷對元件的影響、以及高頻特性優化。首先，在電子遷移率方面，我們分析了差排及界面粗糙度對電子遷移率的影響，發現高差排密度及粗糙的界面會顯著降低電子遷移率。而透過元件加不同偏壓，可以發現元件中電子濃度較高時，屏蔽效應較強，可以有效減少差排散射的影響。而當波函數靠近界面時，電子在界面處的分佈較集中，則會增強界面粗糙散射的效應，降低電子遷移率。此外，本文也討論了溫度對電子遷移率的影響，當溫度降低時，聲子散射率顯著下降，因此電子遷移率隨之上升。因此在低溫下，則是界面粗糙及差排散射對電子遷移率的影響變得更加顯著。 而在分析缺陷對元件的影響以及高頻特性優化前，我們首先擬合了實驗量測的數據。接著透過模擬分析實驗量測到的汲極遲滯的現象，發現不同厚度的背屏障層阻擋緩衝層碳摻雜引起的缺陷效果不同，因此較薄的背屏障層可能會有較高的汲極遲滯現象。而在結構優化方面，我們首先透過降低接觸電阻提升電流及通道轉導，從而提高元件的fT。接著，我們探討了閘極長度縮短對元件特性的影響，過短的閘極長度會引發短通道效應，使得通道轉導下降，影響fT的提升。 為了解決短通道效應，我們研究了減薄通道厚度及增加碳摻雜濃度的方法。減薄通道厚度可以提升閘極對通道的控制力，抑制短通道效應及漏電流。然而，過薄的通道厚度可能導致在背屏障層與緩衝層交界處形成第二通道，增加漏電路徑。此外，適當的碳摻雜可以有效減少漏電流，但過高的碳摻雜濃度會降低元件二維電子氣濃度，反而不利於元件特性的提升。本文通過實驗數的據擬合及模擬分析，探討了AlGaN/GaN高電子遷移率電晶體的結構優化及缺陷的影響。此外為追求更佳之高頻表現，也提供四元AlInGaN/GaN高電子遷移率電晶體結構，為元件設計及特性提升提供參考依據。

This thesis mainly analyzes the electron mobility in AlGaN/GaN HEMTs, the impact of traps on device performance, and the optimization of high-frequency characteristics. Firstly, we examine the influence of dislocations and interface roughness on electron mobility. High dislocation density and rough interfaces significantly reduce mobility. By applying different biases to the device, we find that higher electron density enhances screening effects, effectively reducing the impact of dislocation scattering. Conversely, when the wave function is closer to the interface, electron distribution near the interface increases, enhancing the effect of interface roughness scattering and reducing electron mobility. Additionally, the thesis discusses the effect of temperature on electron mobility, finding that as temperature decreases, phonon scattering rates significantly drop, thus increasing mobility. Therefore, at low temperatures, interface roughness and dislocation scattering become more pronounced. Before analyzing the impact of defects and optimizing high-frequency characteristics, experimental measurement data were fitted. Through simulation, we analyzed the observed drain lag phenomenon. Different back-barrier thicknesses have varying abilities to block buffer C-doped-induced traps. Thinner back barriers result in higher drain lag. For structural optimization, reducing contact resistance significantly improves current and transconductance, thereby increasing fT. We also explored the effects of reducing gate length, which, if too short, induces short channel effects that limit fT improvement. To suppress the short channel effects, we investigated reducing channel thickness and increasing C-doped concentration. Thinner channels enhance gate control over the channel, suppress short channel effects, and reduce leakage current. However, excessively thin channels may form a second channel at the back-barrier and buffer interface, increasing leakage paths. Additionally, appropriate C-doping effectively reduces leakage current, but excessively high C-doping concentrations decrease 2DEG concentration, adversely affecting device performance. This thesis, through experimental data fitting and simulation analysis, explores the structural optimization and the impact of defects in AlGaN/GaN HEMTs.To achieve better high-frequency performance, we also propose AlInGaN/GaN HEMTs structure, providing valuable insights for device design and performance enhancement.