Simulation of band-to-band tunneling in Si/Ge and Si/Si1−xGex heterojunctions by using Monte Carlo method

In this paper, we investigate the band-to-band tunneling (BTBT) in Si/Ge and Si/Si_1-xGe_x heterojunctions by employing a two-dimensional (2D) full band Monte Carlo (FBMC) heterojunction simulator. The FBMC simulator is used to get the electrostatic potential and field in a heterojunction, based on which we can calculate the BTBT rate and current by Hurkx´s tunneling model. The model parameters have been carefully calibrated to reproduce the experimental reverse current in a Si p-n junction. With this framework, it is shown that the BTBT current in the Si/Ge or Si/Si_1-xGe_x heterojunction is largely enhanced when compared with conventional Si homojunctions. We ascribe this to the smaller bandgap of Ge and the SiGe alloy than that of Si. It is further found that whether the smaller bandgap material is used as the relative lower or higher doping side of the heterojunction is much different. The former can produce a BTBT current significantly larger than that of the latter.