Effect of ion implanted germanium profile on the characteristics of Si_1−xGe_x/Si heterojunction bipolar transistors

An optimum profile for Ge ion implantation in SiGe/Si heterojunction bipolar transistors is determined by using a twodimensional simulator code for advanced semiconductor devices. The simulation code is based on a two-dimensional drift-diffusion model for heterostructure degenerate semiconductors with nonparabolicity included in the energy band structure. The model allows accurate simulations of carrier transport in short base devices. The simulation results indicate that for high current gain the Ge profile maximum must be close to the base-collector junction, and that the unavoidable tail of the implanted germanium in the collector region does not deteriorate the gain.