It was noted that, in heterojunction bipolar transistors, out-diffusion of the base dopant from the SiGe region and into emitter or collector markedly degraded device performance. An extremely sensitive method was described for the quantitative determination of the extent of this diffusion. The method was used to investigate the reduction in B diffusion, by C-doping, as a function of the C concentration and position within the base. It was found that C was effective only when it was placed within the doped base region.

The Reduction of Base Dopant Out-Diffusion in SiGe Heterojunction Bipolar Transistors by Carbon Doping A.Gruhle, H.Kibbel, U.König: Applied Physics Letters, 1999, 75[9], 1311-3