It was recalled that B out-diffusion from the base and into the emitter and collector, caused by annealing of SiGe heterobipolar transistors, had a serious effect upon the transit frequency. One solution to the problem of B out-diffusion was the creation of intrinsic spacers between the base, emitter and collector layers to prevent diffusion of B across the hetero-interface. Several simulators were used for the optimisation of SiGe heterobipolar transistor properties. A quantitative analysis was presented for a SiGe heterobipolar transistor by using process simulators. Models for the simulation of a B-doped SiGe base of heterobipolar transistor were compared.Simulation of Boron Diffusion in Si and Strained SiGe Layers. R.Kinder, F.Schwierz, P.Beňo, J.Gessner: Microelectronics Journal, 2007, 38[4-5], 576-82