High frequency Si/Si/sub 1-x/Ge/sub x/ heterojunction bipolar transistors

Abstract
Small-geometry, high-performance Si-Si/sub 1-x/Ge/sub x/ heterojunction bipolar transistors have been fabricated using chemical vapor deposition to form the epitaxial device layers and direct-write, electron-beam lithography. The measured value of f/sub T/ is approximately 29 GHz. Base-collector capacitance is one of the dominant limiting parasitic parameters in the mesa structure used to demonstrate high-speed performance. Advanced epitaxial techniques, such as selective deposition of Si/sub 1-x/Ge/sub x/, should reduce this parasitic element significantly, markedly increasing device speed. Selective deposition of Si/sub 1-x/Ge/sub x/ has been demonstrated.

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