Investigation of the performance of strained-SiGe vertical IMOS-transistors

A vertical impact ionization MOSFET (IMOS) with a thin layer of biaxially strained SiGe in the impact ionization (II) region near the drain and in the channel is thoroughly investigated by Full-Band Monte Carlo (FB-MC) and Hydrodynamic simulations. An anisotropic II model based on the constant matrix element approximation is integrated into the FB-MC to simulate II in relaxed-Si- and strained-SiGe-Vertical-IMOSs. The II generation currents obtained by FB-MC are, in turn, used to calibrate the II model of the Hydrodynamic simulator. The final results show that the reduction of the energy barrier caused by the strained SiGe layer in the channel improves the IMOS characteristic by lowering the threshold voltage. However, when the strained SiGe layer is placed in the region with the highest II near the drain, an improvement of the vertical IMOS by a higher II rate of the strained layer is not observed.