A SiGe spacer layer 151, a graded SiGe base layer 152 including boron, and
an Si-cap layer 153 are sequentially grown through epitaxial growth over a
collector layer 102 on an Si substrate. A second deposited oxide film 112
having a base opening portion 118 and a P+ polysilicon layer 115 that will
be made into an emitter connecting electrode filling the base opening
portion are formed on the Si-cap layer 153, and an emitter diffusion layer
153a is formed by diffusing phosphorus into the Si-cap layer 153. When the
Si-cap layer 153 is grown, by allowing the Si-cap layer 153 to include
boron only at the upper part thereof by in-situ doping, the width of a
depletion layer 154 is narrowed and a recombination current is reduced,
thereby making it possible to improve the linearity of the current
characteristics.
