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Low Temperature Bipolar Silicon Transistor

IP.com Disclosure Number: IPCOM000085344D
Original Publication Date: 1976-Mar-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Dumke, WP: AUTHOR [+2]

Abstract

Described is a low-temperature silicon bipolar transistor design and a method of fabricating it. "Low temperature" means temperatures at which a substantial fraction of the mobile charge carriers that are donated to the conduction or valence bands by donors or acceptors at 300 degrees K are trapped on the donors or acceptors. Conventionally designed silicon transistors will not operate properly at low temperatures, where the normally highly mobile charge carriers are immobilized by trapping by the normally electrically active impurities. [1] The new design described herein avoids the deleterious effects of trapping by donors and acceptors.

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Low Temperature Bipolar Silicon Transistor

Described is a low-temperature silicon bipolar transistor design and a method of fabricating it. "Low temperature" means temperatures at which a substantial fraction of the mobile charge carriers that are donated to the conduction or valence bands by donors or acceptors at 300 degrees K are trapped on the donors or acceptors. Conventionally designed silicon transistors will not operate properly at low temperatures, where the normally highly mobile charge carriers are immobilized by trapping by the normally electrically active impurities. [1] The new design described herein avoids the deleterious effects of trapping by donors and acceptors.

Trapping of electrons and holes is avoided in the present design by degenerate doping. It is known, for example, that electrons do not "freeze out"(become trapped) on donors in silicon with a donor concentration exceeding something like 5 X 10/18/cm/-3/. Instead, electrons remain in the conduction band to the lowest temperatures and the electrical conductivity of the silicon resembles that of a metal. Thus, a first aspect of this design is that the emitter, base, and collector regions are doped heavily enough to show degenerate or metallic conductivity.

A heavily doped base region generally requires that the emitter region be even more heavily doped to obtain high efficiency of emitter injection into the base. It is known, however, that extremely heavily doped emitters have low- injection efficiency because very heavy doping reduces the band gap of the silicon. The heavy base doping of this design requires emitters doped so heavily that the energy gap reduction is an important effect. Thus, the second feature of this design is the combination of degenerate doping with the use of a heterojunction emitter, in which high-emitter injection efficiency is preserved by fabricating the emitte...