6H-SiC高场输运特性的多粒子蒙特卡罗研究

采用非抛物性能带模型,对6H-SiC高场电子输运特性进行了多粒子蒙特卡罗(Ensemble Monte Carlo)研究.研究表明：温度为296 K时,电子横向漂移速度在电场为2.0×104 V/cm处偏离线性区,5.0×105 V/cm处达到饱和.由EMC方法得到的电子横向饱和漂移速度为1.95×107 cm/s,纵向为6.0×106 cm/s,各向异性较为显著.当电场小于1.0×106 V/cm时,碰撞电离效应对高场电子漂移速度影响较小.另一方面,高场下电子平均能量的各向异性非常明显.电场大于2.0×105 V/cm时,极化光学声子散射对电子横向能量驰豫时间影响较大.当电场一定时,c轴方向的电子碰撞电离率随着温度的上升而增大.对非稳态高场输运特性的分析表明：阶跃电场强度为1.0×106 V/cm时,电子横向瞬态速度峰值接近3.0×107 cm/s,反应时间仅为百分之几皮秒量级.

An Ensemble Monte Carlo Study of High Field Electron Transport in 6H-SiC

Based on the new experiment result and an recent ab initio band structure calculation, the high-field electron transport properties in 6H-SiC have been analyzed by an Ensemble Monte Carlo technique with an nonparabolic band model. The result shows that the electron drift velocity deviates from the linear law at about 2.0×104 V/cm and saturates at 5.0×105 V/cm The impact ionization process has little effect on the high field electron drift velocities when the applied electric fields are lower than 1.0×106 V/cm. And the anisotropy of the electron saturation velocities is very pronounced in 6H-SiC. At 296 K, the peak saturation velocities given by the model are 6.0×106 cm/s and 1.95×107　cm/s for E‖c and E⊥c respectively. At high electric fields, the difference in electron mean energy for E⊥c and E‖c is also very pronounced. The polar optical phonons scattering is very important for electron energy relaxation times when the electron field is applied perpendicular to the c axis. Besides ,the electron impact ionization rates for E‖c increases with temperatures when the electric field is kept constant. The peak transient velocity for E⊥c at high step electric field such as 1.0×106 V/cm is 3.0×107 cm/s. The response time is only in deep subpicoseconds.