摘要:
本文提出了一种带栅漏间表面p型外延层的新型MESFET结构并整合了能精确描述4H-SiC MESFET工作机理的数值模型,模型综合考虑了高场载流子饱和、雪崩碰撞离化以及电场调制等效应.利用所建模型分析了表面外延层对器件沟道表面电场分布的改善作用,并采用突变结近似法对p型外延层参数与器件输出电流（I_（ds））和击穿电压（V_B）的关系进行了研究.结果表明,通过在常规MESFET漏端处引入新的电场峰来降低栅极边缘的强电场峰并在栅漏之间的沟道表面引入p-n结内建电场进一步降低电场峰值,改善了表面电场沿电流方向的分布.通过与常规结构以及场板结构SiC MESFET的特性对比表明,本文提出的结构可以明显改善SiC MESFET的功率特性.此外,针对文中给定的器件结构,获得了优化的设计方案,选择p型外延层厚度为0.12μm,掺杂浓度为5×10_（15）cm-3,可使器件的V_B提高33%而保持I_（ds）基本不变.
Abstract:
A novel SiC MESFET structure with a p-type surface epi-layer is proposed and 4H-SiC MESFET models are presented which precisely describe the working mechanism of the device.Considering carrier velocity saturation,impact ionization and electric field modulation,the effect on distribution of electric field is analyzed.Also,the output current（I_（ds）） and breakdown voltage（V_b） dependences on the dimensions of the p-type epi-layer are studied based on abrupt junction approximation.The high electric field peak at the gate edge is suppressed by introducing a new electric field peak at the drain side,and the built-in field of p-n junction formed along channel surface further weakens the electric field peaks,leading to smoother distribution of electric field.By comparison with the conventional and the fieldplated MESFETs,it is shown that the proposed structure greatly improves the characteristic of SiC MESFET.In addition,the optimized dimensions are obtained and the results show that V_b is greatly increased by 33%with I_（ds） unchanged（less than 3%） when the thickness and the doping concentration of the surface epi-layer are chosen as 0.12μm and 5×10~（15） cm~（-3）,respectively.
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