Si基GaN增强型功率开关器件阈值电压调控机理与新结构

GaN-on-Si Enhancement-mode (E-mode) power switching devices is a research hot topic in both academia and industries in recent years. Due to its superior properties of low cost and high device performance the GaN-on-Si E-mode power device is a promising candidate for next generation high efficiency and high speed power electronics. In purpose of fabricating high performance GaN-on-Si E-mode power devices with high threshold voltage (VTH) and high breakdown voltage, this project will carry out intensive study on the fundamental scientific theory of threshold voltage modulation and the corresponding key device fabrication technologies. 1) Based on the charge (e.g. polarization charge, interface states, fixed interface charge, doping charge) distribution of AlGaN/GaN heterojunction the Charge-control Threshold-Voltage Modulation (CTVM) model will be developed, which reveals the essential interaction of charges, energy band and VTH as well as the mechanism of threshold voltage modulation; 2) The origin of the interface charges will be investigated. Accordingly, the III-Nitride surface pre-treatment techniques and post gate dielectric thermal treatment technology for an effective suppression of the interface charges will be developed to achieve a large modulation range of the VTH (e.g. >10 V). 3) A novel E-mode device structure featuring a BUried-Fluorine Shallow-Trench gate is proposed, in which the dual modulation of VTH is achieved by using the shallow-trench gate and the buried F- layer. The fabricated E-mode GaN-on-Si power devices are expected to deliver a VTH higher than +6 V, a ΔVTH lower than 0.5 V, a breakdown voltage over 1000 V and a Ron lower than 5 mΩ•cm2.

Si基GaN增强型功率开关器件是近年来国际学术界和工业界的研究热点，凭借其低成本、高性能的优越特性有望成为下一代高效、高速电力电子的理想候选技术之一。本申请以研发高阈值电压（VTH ）Si基GaN增强型高压功率开关器件为目标，针对阈值电压调控基础科学理论和器件关键制备技术开展创新研究。1）基于AlGaN/GaN异质结电荷分布建立电荷控制阈值电压调控模型，阐明电荷、能带与阈值电压的本质关系，揭示其调控机理；2）研究界面电荷微观起源，开发有效抑制界面电荷的III-Nitride表面等离子体处理技术和栅介质热处理技术，实现VTH 的大范围调控（>10 V）；3）提出F-离子埋层半凹栅增强型器件新结构，利用半凹栅和F-离子埋层对VTH 的双重调控，研制出高性能Si基GaN增强型功率开关器件，实现VTH >6 V，ΔVTH<0.5 V，击穿电压超过1000 V，导通电阻小于5 mΩ•cm2。

GaN功率器件与传统Si基功率器件相比具有工作速度快、功率密度大、耐高温等优点，能够突破传统Si基功率器件的性能极限，目前已经在快充、无线充电、激光雷达、数据中心高效电源等方面获得应用，此外还在无人机、卫星等空间运载平台的高效、小型化电源具有巨大应用前景。然而，当前GaN功率器件的阈值电压普遍较低，器件高速工作中栅极驱动信号过冲所造成的器件误开启严重威胁GaN器件应用的安全可靠性。本项目开展之初，国际上GaN功率器件的阈值电压普遍低于3V，GaN功率器件阈值电压的大范围调控是本领域亟待突破的关键难题。. 针对上述问题，申请人围绕GaN功率器件阈值电压的大范围调控开展研究。课题提出基于F离子处理的半凹栅MISHEMT器件新结构，基于GaN异质结能带理论，从极化电荷和MIS栅极界面电荷工程出发，建立了“GaN异质结电荷控制阈值电压调控模型（CTVM）” ，从本质上建立了异质结极化电荷、MIS栅极界面电荷与器件阈值电压的内在关联。基于第一性原理揭示了(Al) GaN 材料表面O替位、N空位的施主态特征，阐明了MIS栅界面固定正电荷的微观起源，为GaN器件阈值电压的精确调控提供了理论基础。针对此，申请人开发了基于N等离子体界面修饰的界面电荷调控方法，降低了半凹栅刻蚀晶格损伤并有效抑制了MIS栅界面电荷，结合F离子处理突破了GaN功率器件阈值电压大范围调控的瓶颈。制备出阈值电压>7V，漏极电流>350 mA/mm，击穿电压>1 kV@ 1μA/mm的增强型GaN功率MOSFET，器件阈值电压达到目前国际报道最高水平。本课题的理论成果为GaN增强型功率器件阈值电压的大范围精确调控奠定了重要的理论依据；提出的半凹栅MOSFET器件新结构突破了高阈值电压与低导通电阻相互制约的瓶颈，为开发高性能增强型GaN功率器件探索出了一条可行的途径。. 基于上述研究工作，本课题发表SCI期刊论文18篇，其中在IEEE旗舰刊物IEEE Trans. on Ind. Elect.上实现了GaN功率器件0的突破；发表国际会议论文9篇，其中在功率半导体国际顶级会议ISPSD发表论文6篇，申请中国发明专利9项，其中授权5项。