Self-aligned SiGe-base heterojunction bipolar transistor by selective epitaxy emitter window (SEEW) technology

Abstract

In the device a SiGe epitaxial base is integrated in a structure which uses in situ doped epitaxial lateral overgrowth for the formation of the emitter window and the extrinsic base contact. Nearly ideal I-V characteristics have been achieved for a base width of 60 nm with an intrinsic base resistance of 4.6 k Omega / Square Operator and for emitter widths down to 0.4 mu m. A DC collector current enhancement factor of 3.1 was obtained relative to a Si homojunction transistor with a 1.25 times higher intrinsic base resistance. The breakdown voltage BV/sub CBO/ is identical for both Si and SiGe devices, even though the collector-base depletion region is partly overlapped with the reduced-bandgap SiGe strained layer. The lower BV/sub CEO/, measured for the SiGe-base transistor, is due to the higher current gain. Based on these results the fabrication of high-speed bipolar circuits that take advantage of SiGe-base bandgap engineering seems possible using selective epitaxy emitter window (SEEW) technology.