Search

In order to improve the current gain via a reduction of the emitter base junction saturation current density, a perpendicular ordering of the grain boundaries (columnar grain boundaries) in the polysilicon emitter-region of a bipolar transistor is proposed. The complex polysilicon current component is obtained by a two-dimensional resolution of the current transport equation along the polysilicon region. The minority carrier current density component in the non-uniformly heavily doped single-crystal emitter is calculated by an average value approach. The influence of the two-dimensional structure of the polysilicon region on the current gain is analysed, and it is shown that the current gain decreases with increasing grain number. The evolution of the normalised current gain in terms of physical parameters is studied. The results show that the current gain improves with polysilicon thickness for a thin oxide layer, while it is insensitive for a thick oxide layer. In addition, the results show that the bulk recombination in a single-crystal emitter cannot be neglected in devices with a deliberately grown interfacial oxide. [ABSTRACT FROM AUTHOR]