新型极化掺杂电流阻挡层GaN VHFET耐压理论与新结构

Gallium nitride (GaN) based power devices, which have high breakdown voltage and power conversion efficiency, are becoming the research focus of international research field in recent years. However, several scientific problems, including high leakage current and on-state resistance, are still remained to be solved. In this work, a novel GaN vertical heterojunction field effect transistor (GaN PD-VHFET) with graded Al content polarization-doped (PD) in AlGaN current blocking layer (CBL), which is based on the insight of breakdown mechanism and the root cause of leakage current, is proposed. The goal of GaN PD-VHFET is aim at realizing higher breakdown voltage and lower on-state resistance. This work will include the following three aspects: 1) Modeling of polarization-doped mechanism, 2) Key structure optimization of AlGaN current blocking layer, and 3) Heterojunction material epitaxial growth and device fabrication. First of all, the theoretical model of enhanced polarization-doped in AlGaN current blocking layer with graded Al content will be established, and followed by modeling of breakdown voltage of GaN PD-VHFET. Secondly, the key structure parameters of GaN PD-VHFET will be optimized, and the p-type dopant activation rate will be enhanced by the polarization electrical field in AlGaN current blocking layer, and the hole concentration in CBL will be much higher. This will lead to a obvious reduction of sub-threshold leakage current and a remarkable increase of breakdown voltage. Thirdly, some important technical technologies will be studied, including the heterojunction epitaxial growth of AlGaN layer with graded Al content and key fabrication processes of the device. The realization of the as-proposed GaN PD-VHFET will provide a novel solution and pave a new way of GaN HFET in next-generation power device applications.

具有更高耐压和电源转换效率的GaN功率电子器件正成为国际研究热点。针对目前横向与垂直结构GaN异质结器件存在的技术难点，经深入研究器件击穿机理和泄漏电流的产生根源，本项目创新提出具有极化掺杂电流阻挡层的GaN垂直异质结场效应晶体管（GaN PD-VHFET）来同时实现高击穿电压与低导通电阻。研究工作围绕极化掺杂增强理论建模、电流阻挡层结构优化以及材料器件实验验证三个方面展开。首先建立渐变Al组分AlGaN电流阻挡层极化掺杂增强理论模型和GaN PD-VHFET耐压优值物理模型；然后开展器件关键结构参数优化设计，利用AlGaN电流阻挡层产生的极化电场来提升p型杂质激活率以获得更高的空穴浓度，抑制亚阈值泄漏电流以实现器件击穿电压的提升；并探索新结构外延材料生长和器件实验验证等关键工艺技术。该新结构器件的实现将为拓展GaN HFET在新型功率电力电子器件领域的应用提供新的理论方案和技术途径。

在基金资助下，本项目针对当前GaN异质结器件实现高耐压存在的技术难点，全面深入研究了器件击穿机理和泄漏电流的产生根源，并创新提出了具有极化掺杂电流阻挡层的GaN垂直结构场效应晶体管（GaN PD-VHFET）来同时实现高击穿电压与低导通电阻。具体研究成果如下：（1）创新提出渐变Al组分AlGaN电流阻挡层的极化掺杂增强理论，建立了器件物理模型。经理论、仿真和实验的对比分析表明各数据结果基本吻合，验证了该模型的准确性。（2）完成了GaN PD-VHFET极化电流阻挡层（PD-CBL）关键结构参数优化，获得了器件功率优值；并进一步创新提出了三种新型垂直结构器件。（3）完成了工艺开发和器件试制，实现了GaN PD-VHFET外延材料生长和关键工艺技术突破，完成新结构器件的实验验证。研究表明，该新结构器件的功率优值更接近GaN材料的理论极限，证明了其在功率器件领域的明显优势。. 综上可知，申请人成功完成了各项研究任务，取得了丰硕的研究成果。共发表SCI期刊论文25篇，EI论文1篇，会议论文21篇，均标注了基金资助；申请美国发明专利一项，申请中国发明专利30项，已授权专利18项。. 国际合作方面，2014-2015年赴英国访问期间与国际著名的功率半导体器件专家谢菲尔德大学Shankar Ekkanath Madathil教授有深入合作交流，并合作发表了SCI期刊论文4篇（均标注了基金资助）；先后邀请了PHILIPS公司Dr. G.F. Zhou、西苏格兰大学Richard Yongqing Fu教授、MITSUBISHI ELECTRIC公司Dr. Rui Ma和台湾长庚大学Hsiang-Chun Wang博士后等专家学者来国内开展学术交流。在本基金项目支持下，培养了博士生3名，毕业博士1名，培养毕业了硕士生共11名。