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A Wide Bandgap Collector Transistor to Reduce Impact Ionization

IP.com Disclosure Number: IPCOM000121202D
Original Publication Date: 1991-Jul-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 1 page(s) / 33K

Publishing Venue

IBM

Related People

Crabbe, EF: AUTHOR [+3]

Abstract

Disclosed is a class of heterojunction bipolar transistors with improved breakdown voltages BVceo . A bipolar transistor with a base-collector region located in a wider bandgap material than silicon leads to a reduction of impact ionization allowing therefore higher collector doping levels to increase the high- frequency performance of the transistor.

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A Wide Bandgap Collector Transistor to Reduce Impact Ionization

      Disclosed is a class of heterojunction bipolar transistors with
improved breakdown voltages BVceo .  A bipolar transistor with a
base-collector region located in a wider bandgap material than
silicon leads to a reduction of impact ionization allowing therefore
higher collector doping levels to increase the high- frequency
performance of the transistor.

      Impact ionization occurs when some electrons gain energies of
the order of or above the silicon bandgap.  The use of a wider
bandgap material is disclosed here for the base-collector space-
charge region and the collector (Fig. 1).  As impact ionization is,
to first order, exponentially dependent on the bandgap, an increase
in bandgap should lead to a drastic reduction in electron-hole pair
generation by impact ionization.  This allows an increase of the
collector doping level resulting in a substantial improvement in
current drive capability.  Furthermore, the higher field and the
reduction in width of the base-collector space- charge region leads
to improved high-frequency performance of the device.

      Two candidates as wide-bandgap materials are silicon with a few
atomic percent of oxygen or nitrogen in the lattice.  Both materials
have already been fabricated by silicon molecular beam epitaxy.  They
can also be grown by a combination of indirect or remote plasma
enhanced chemical vapor deposition (RPECVD) with the Ultra Hig...