梯度掺杂纳米晶碳化硅/晶体碳化硅双缓变结的反向软恢复特性

The fast recovery diode (FRD) with a semiconductor abrupt junction would easily yield surge currents in the reverse recovery operating, which will be limited to apply in the communication equipments, high frequency power electronic systems, and so on..In this project, a kind of double graded junction (DGJ) with progressive doped nano-crystalline silicon carbide (nc-SiC) multi-layers deposited on two sides of a crystalline silicon carbide (SiC) wafer, is proposed to construct a (p+p ML)nc-SiC/(n-)c-SiC/(nn+ ML)nc-SiC FRD of DGJ. According to the controll principles of emitter efficiency and lifetime of minority carrers, via numerical calculating the parameters such as reverse recovery currents and time, etc, the relation between inverse recovery properties and SiC material parameters, electronic characteristics of DGJ, concentrations and locations of defect recombination centers,etc will be clarified. Further, using the plasma enhanced chemical vapor deposition (PECVD) technique, the p type and n type multi-layers of progressive increase doped nc-SiC films will be deposited respectively on both sides of c-SiC implanted by ions to form the (p+p ML)nc-SiC/(n-)c-SiC/(nn+ ML)nc-SiC DGJ. Subsequently, with the same method,the p+ type and n+ type nano-crystalline Si (nc-Si) films will be separately grown on the same type doped nc-SiC films on the wafer to yield ohmic hetero-junctions and to contact the alloy electrodes. The backward recovery properties will be illustrated through structural and component characterization and performance analysis on the DGJ. The ultra-fast reverse soft recovery behavior of the DGJ could be realized while its synthetic performance would be optimized via adjusting the design parameters and improving the techniques of ion implantation and PECVD..This scheme should be useful to design and fabricate the power devices with electromagnetic compatibility.

半导体突变结快速恢复二极管(FRD)，反向恢复时因结区电荷难以控制而产生浪涌电流，影响了它在通信、高频电力电子设备中的应用。本项目拟在晶体碳化硅(c-SiC)二侧沉积梯度掺杂纳米晶碳化硅(nc-SiC)多层膜(ML)，构建(p+p-ML)nc-SiC/(n-)c-SiC/(nn+ -ML)nc-SiC双缓变结FRD。根据阳极发射率及少子寿命控制原理，模拟计算反向恢复时间、电流等参数，探究它们与不同结构及原子面SiC材料性质、双缓变结电学特性、低寿命少子控制区的位置及宽带、复合中心浓度及能级的关系。用PECVD在离子注入c-SiC两侧生长掺杂浓度递增的nc-SiC多层膜，形成双缓变结；再制备nc-SiC/nc-Si异质欧姆结与电极连接。表征双缓变结的结构、成份，分析电学性质，查明反向恢复特征，揭示导电机理。改进设计及工艺，实现超快反向软恢复，优化综合性能，为制造功率型电磁兼容器件提供思路。

按照电极发射效率控制和基区局域少子寿命控制的思路，制备了系列纳米晶SiC/晶体SiC结及其反向恢复二极管，改善器件的反向软恢复性能，项目开展了如下工作：.(1)模拟计算并优化了晶体SiC材料p-i-n型二极管的反、正向恢复性能。(2) 采用PECVD技术，研制了梯度掺杂纳米晶SiC/晶体SiC双缓变结、多层纳米晶SiC/外延SiC结反向快恢复二极管样品，以及纳米晶Si/晶体Si马赛克电极的p+-n--n+ 型、阴极结嵌入p+型纳米晶SiC的纳米晶Si/晶体Si/纳米晶Si型反向快恢复二极管样品。表征了材料的结构，分析了二极管样品的电学性质，特别是反向恢复性能。(3)设计了反向恢复时间测试仪、数字式二极管反向动态参数测试仪、二极管正向恢复参数测试仪、功率器件瞬态热阻测试仪等设备。.研究发现，利用纳米晶SiC制备的二极管样品，可通过调节纳米晶SiC电极的有效掺杂、基区纳米晶SiC的缺陷来实现发射效率控制和少子寿命控制，改善反向恢复性能，为研制高性能器件提供新的思路。设计的反向恢复时间等瞬态参数测量设备已经用于科研、教学实验，可进一步开发推广到器件生产线上。已在Applied Physics A、IET Power Electronics、Journal of Semiconductors等期刊上发表论文8篇，在Surface and Coatings Technology、Measurement、Materials Research Express期刊上各投稿论文1篇；已授权发明专利8项，实用新型专利2项；培养青年教师3名，毕业研究生3名、本科生6名。