面向太赫兹应用的(In)AlN/GaN高频HFETs器件基础研究

For the GaN based Heterostructure Filed-Effect Transistors (HFETs), the frequency characteristics have been limited by the size of the devices, and new theories and methods are needed to improve the frequency characteristics. Based on the epitaxial (In)AlN/GaN heterostructures with high crystal quality, in this project, we further develop and optimize the key and new device technology, such as, nano T-shaped gate, regrown n+GaN Ohmic contacts, high quality passivation by Atomic Layer Deposition (ALD). Then, we are mainly going to investigate the influence of the key and new device technology on the strain distribution of barrier layer and the electron mobility, especially after device scaling. Moreover, we study the effect of the key and new device technology on the transport mechanism which scattering the electron after device scaling, especially on the polarization Coulomb field (PCF) scattering. Through establishing the theory model and function expression of the PCF scattering, it’s going to investigate the influence of the PCF scattering on the electronic transport properties in the access region, and further on the parasitic resistance (such as RS and RD), exploring the relationship between the PCF scattering and frequency characteristics. Besides, it’s going to compare the transport mechanisms in the InAlN/GaN and AlN/GaN HFETs, especially studying the different effects of PCF scattering on the transport and frequency characteristics in the two kind devices. As a result, we explore the methods to weaken the effect of relevant scattering mechanisms, improving the frequency characteristics. Based on the explored theories and methods, optimization of materials and device structures is carried out to achieve the high-frequency (In)AlN/GaN HFETs for Terahertz application.

GaN基异质结场效应晶体管(HFETs)频率特性已受到器件尺寸的限制，亟需新理论和方法改善频率特性。本项目基于高质量(In)AlN/GaN异质结材料外延工作基础，优化纳米T型栅、再生长n+GaN欧姆接触和原子层沉积（ALD）介质等新型工艺，分析器件尺寸等比例缩小后，新型工艺对势垒层应变分布和沟道电子迁移率的影响，系统研究对与电子迁移率相关的散射机理，尤其是极化梯度库仑场散射的影响。建立相关器件中极化梯度库仑场散射的理论模型和表达式，研究极化梯度库仑场散射对栅源和栅漏区域沟道电子输运机理以及寄生电阻（如RS和RD等）的影响，探索与器件频率特性的关联。对比研究InAlN/GaN和AlN/GaN HFETs器件纳米尺度下输运机理的差异，分析相关差异对器件频率特性的影响。寻求消弱相关散射机理影响的有效方法，指导材料和器件结构优化设计，实现面向太赫兹应用的(In)AlN/GaN高频HFETs器件。

新型(In)AlN/GaN异质结材料具有超薄势垒和强极化的特点，是实现GaN器件向更高频、更大功率应用的最具潜力候选者。本项目基于高质量(In)AlN/GaN异质结材料外延工作基础，优化了纳米T型栅、再生长n+GaN非合金欧姆接触以及原子层沉积（ALD）等新型工艺，分析了器件尺寸等比例缩小后，新型工艺对势垒层应变分布和沟道电子迁移率的影响，系统研究了对与电子迁移率相关的散射机理，建立了相关器件中极化梯度库仑场散射的理论模型和表达式，研究了极化梯度库仑场散射对栅源和栅漏区域沟道电子输运机理以及寄生电阻的影响，并建立了与器件频率特性的关联，用以指导材料与器件结构优化设计。.通过优化帽层结构，结合栅区域预处理技术，解决了InAlN/GaN HFET器件可靠性难题，器件平均失效时间（MTTF）从10^3小时提升至10^6小时量级，为国际首次报道，为工程化应用奠定了有力基础；基于结构优化设计，采用再生长n+GaN非合金欧姆接触工艺将有效源漏间距缩小至600 nm，结合40 nm T型栅，研制出最大振荡频率（fmax）为405 GHz的InAlN/GaN HFET，该值为InAlN/GaN HFET国际已报道最高值；结合34 nm直栅工艺，研制出电流截止频率（fT）为350 GHz的InAlN/GaN HFET，该值为GaN HFET国内已报道最高值。本项目研制的高频器件为GaN HFET向更高频段功率放大器和更高速开关电路的应用奠定了良好基础。.本项目完成了项目既定的研究内容和研究目标，超额完成项目既定指标，发表相关SCI收录论文18篇，授权美国发明专利1件，授权国家发明专利4件。研制的GaN 高频HFET器件已在90 GHz以上频段功率放大器中进行了良好验证，90-96 GHz频段内输出功率大于2 W，并应用于国家重大装备，相关成果荣获中国电子科技集团公司科技进步二等奖。

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