Ti,N共掺杂4H-SiC复合增强缓冲层生长及其对PiN二极管正向性能稳定性的改善

Growth of 4H-SiC recombination-enhancing buffer layer with Ti and N co-doping and improvement of forward voltage stability of PiN diodes

"双极型退化"现象严重阻碍了4H-SiC双极型器件如PiN二极管等的产品化,其微观机理是电子-空穴复合条件下层错由基面位错处的扩展.为遏制"双极型退化"现象,不仅要消除漂移层中的基面位错,还需要通过生长复合增强缓冲层的方法阻止少子空穴到达含高密度基面位错片段的外延层/衬底界面.本文采用钛、氮共掺杂的方式进行缓冲层的生长,通过钛掺杂进一步降低缓冲层中的少子寿命.首先确定了钛掺杂浓度和钛源摩尔流量之间的定量关系,在此基础上制备了含钛、氮共掺杂缓冲层结构的4H-SiC PiN二极管,并在正向电流密度100 A/cm^2的条件下保持10 min,测量其正向压降随时间的变化.与无缓冲层结构、仅含高浓度氮掺杂缓冲层结构的4H-SiC PiN二极管相比,含钛、氮共掺杂缓冲层的二极管的正向压降稳定性得到了明显改善.

"Bipolar degradation"phenomenon has severely impeded the development of 4H-SiC bipolar devices.Their defect mechanism is the expansion of Shockley-type stacking faults from basal plane dislocations under the condition of electron-hole recombination.To suppress the"bipolar degradation"phenomenon,not only do the basal plane dislocations in the 4 H-SiC drift layer need eliminating,but also a recombination-enhancing buffer layer is required to prevent the minority carriers of holes from reaching the epilayer/substrate interface where high-density basal plane dislocation segments exist.In this paper,Ti and N co-doped 4H-SiC buffer layers are grown to further shorten the minority carrier lifetime.Firstly,the dependence of Ti doping concentration on TiCl4 flow rate in 4H-SiC epilayers is determined by using single-dilution gas line and double-dilution gas line.Then the p^+ layer and p^++ layer in PiN diode are obtained by aluminum ion implantation at room temperature and 500℃ followed by high temperature activation annealing.Finally,4H-SiC PiN diodes with a Ti,N codoped buffer layer are fabricated and tested with a forward current density of 100 A/cm^2 for 10 min.Comparing with the PiN diodes without a buffer layer and with a buffer layer only doped with high concentration of nitrogen,the forward voltage drop stability of those diodes with a 2μm-thick Ti,N co-doped buffer layer(Ti:3.70×10^15 cm^-3 and N:1.01×10^19 cm^-3)is greatly improved.