Simulating Boron Diffusion in Silicon Germanium

Introduction

The silicon germanium heterojunction bipolar transistor (SiGe HBT) is a promising technology for combining the operating speed of compound material devices with the production capability of bulk silicon. The presence of a narrower-bandgap material in the base region where most of the bandgap offset occurs in the valence band, creates an energy well for holes. With the lower energy barrier, a lower hole current density can be obtained for a given electron current density increasing the transistor’s gain [1]. Thus the base can then be highly doped, greatly increasing high frequency performance whilst still retaining a reasonable gain. For this reason, the diffusion of boron in SiGe is of great interest.