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Leakage Current Mechanisms in SiGe HBTs Fabricated Using Selective and Nonselective Epitaxy

Leakage Current Mechanisms in SiGe HBTs Fabricated Using Selective and Nonselective Epitaxy
Leakage Current Mechanisms in SiGe HBTs Fabricated Using Selective and Nonselective Epitaxy
SiGe heterojunction bipolar transistors (HTBs) have been fabricated using selective epitaxy for the Si collector, followed in the same growth step by nonselective epitaxy for the p+ SiGe base and n-Si emitter cap. DC electrical characteristics are compared with cross-section TEM images to identify the mechanisms and origins of leakage currents associated with the epitaxy in two different types of transistor . In the first type, the polysilicon emitter is smaller than the collector active area, so that the extrinsic base implant penetrates into the single-crystal Si and SiGe around the perimeter of the emitter and the polycrystalline Si and SiGe exrtrinsic base. In these transistors, the Bummel plots are near-ideal and there is no evidence of emitter/collector leakage. In the second type, the collector active area is smaller than the polysilicon emitter, so the extrinsic base implant only penetrates into the polysilicon extrinsic base. In these transistors, the leakage currents observed depend on the base doping level. In transistors with a low doped base, emitter/collector and emitter/base leakage is observed, whereas in transistors with a high doped base only emitter/base leakage is observed. The emitter/collector leakage is explained by punch through o fhte base caused by thinning of the SiGe base at the emitter perimeter. The emitter/base leakeage is shown to be due to Poole-Frenkel mechanism and is explained by penetration of the emitter/base depletion region into the p+ polysilicon extrinsic base at the emitter periphery. Variable collector/base reverse leakage currents are observed and a variety of mechanisms are observed, including Shockley-Read-Hall recombination, trap assisted tunneling, Poole Frenkel and band to band tunneling. These result s are explained by the presence of polysilicon grains on the sidewalls of the field oxide at the collector perimeter.
2492-2499
Schiz, J.F.W.
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Lamb, Andrew C.
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Cristiano, Fuccio
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Bonar, J.M.
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Ashburn, Peter
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Hall, Stephen
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Hemment, Peter L. F.
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Schiz, J.F.W.
9b756d29-6669-42a2-b23a-6f125b945fc9
Lamb, Andrew C.
3e9f8898-4f83-4231-8b2e-242e2b15baf8
Cristiano, Fuccio
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Bonar, J.M.
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Ashburn, Peter
68cef6b7-205b-47aa-9efb-f1f09f5c1038
Hall, Stephen
c2e5d7c3-2591-4c7a-83a3-976156ee35ba
Hemment, Peter L. F.
d1f86fcf-91f4-4423-8389-77f8fe4bc4ac

Schiz, J.F.W., Lamb, Andrew C., Cristiano, Fuccio, Bonar, J.M., Ashburn, Peter, Hall, Stephen and Hemment, Peter L. F. (2001) Leakage Current Mechanisms in SiGe HBTs Fabricated Using Selective and Nonselective Epitaxy. IEEE Transactions on Electron Devices, 48 (11), 2492-2499.

Record type: Article

Abstract

SiGe heterojunction bipolar transistors (HTBs) have been fabricated using selective epitaxy for the Si collector, followed in the same growth step by nonselective epitaxy for the p+ SiGe base and n-Si emitter cap. DC electrical characteristics are compared with cross-section TEM images to identify the mechanisms and origins of leakage currents associated with the epitaxy in two different types of transistor . In the first type, the polysilicon emitter is smaller than the collector active area, so that the extrinsic base implant penetrates into the single-crystal Si and SiGe around the perimeter of the emitter and the polycrystalline Si and SiGe exrtrinsic base. In these transistors, the Bummel plots are near-ideal and there is no evidence of emitter/collector leakage. In the second type, the collector active area is smaller than the polysilicon emitter, so the extrinsic base implant only penetrates into the polysilicon extrinsic base. In these transistors, the leakage currents observed depend on the base doping level. In transistors with a low doped base, emitter/collector and emitter/base leakage is observed, whereas in transistors with a high doped base only emitter/base leakage is observed. The emitter/collector leakage is explained by punch through o fhte base caused by thinning of the SiGe base at the emitter perimeter. The emitter/base leakeage is shown to be due to Poole-Frenkel mechanism and is explained by penetration of the emitter/base depletion region into the p+ polysilicon extrinsic base at the emitter periphery. Variable collector/base reverse leakage currents are observed and a variety of mechanisms are observed, including Shockley-Read-Hall recombination, trap assisted tunneling, Poole Frenkel and band to band tunneling. These result s are explained by the presence of polysilicon grains on the sidewalls of the field oxide at the collector perimeter.

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Published date: November 2001
Organisations: Nanoelectronics and Nanotechnology

Identifiers

Local EPrints ID: 256154
URI: http://eprints.soton.ac.uk/id/eprint/256154
PURE UUID: c54e4d0f-542c-4f9e-874e-61c661798f04

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Date deposited: 05 Jan 2004
Last modified: 14 Mar 2024 05:38

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Contributors

Author: J.F.W. Schiz
Author: Andrew C. Lamb
Author: Fuccio Cristiano
Author: J.M. Bonar
Author: Peter Ashburn
Author: Stephen Hall
Author: Peter L. F. Hemment

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