IEEE Electron Device Letters

Graded-SiGe-Base, Poly-Emitter Heterojunction Bipolar Transistors

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Si/Si1-xGe, heterojunction bipolar transistors (HBT’s) have been successfully fabricated using a low-temperature epitaxial technique to form the SiGe graded-bandgap base layer. These devices were fabricated on patterned substrates and subjected to annealing cycles used in advanced bipolar processing. Excellent junction quality is demonstrated for these devices, which have base widths under 75 nm. Due to the small bandgap of SiGe, the collector current at low bias is ten times higher than that for Si-base devices that have the same pinched base resistance. This collector current ratio increases to more than 40 at LN2 temperature, resulting in current gains of 1600 for the SiGe-base transistors despite base sheet resistances as low as 7.5 kΩ/⊓. © 1989 IEEE