EFFECT OF ION-IMPLANTED GERMANIUM PROFILE ON THE CHARACTERISTICS OF SI1-XGEX SI HETEROJUNCTION BIPOLAR-TRANSISTORS/

An optimum profile for Ge ion implantation in SiGe/Si heterojunction b ipolar transistors is determined by using a two-dimensional simulator code for advanced semiconductor devices. The simulation code is based on a two-dimensional drift-diffusion model for heterostructure degener ate semiconductors with nonparabolicity included in the energy band st ructure. The model allows accurate simulations of carrier transport in short base devices. The simulation results indicate that for high cur rent gain the Ge profile maximum must be close to the base-collector j unction, and that the unavoidable tail of the implanted germanium in t he collector region does not deteriorate the gain.