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Measuring the Mobility Ionization Bandgap Factor in a Bipolar Transistor Base using DC and Capacitance Data

IP.com Disclosure Number: IPCOM000108376D
Original Publication Date: 1992-May-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 71K

Publishing Venue

IBM

Related People

Fischer, SE: AUTHOR [+3]

Abstract

The factor mnx(NA/N-A)e^Eg/kT can be measured as a function of depth in the neutral base of a bipolar transistor using only DC and capacitance vs. voltage data.

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Measuring the Mobility Ionization Bandgap Factor in a Bipolar Transistor Base using DC and Capacitance Data

       The factor mnx(NA/N-A)e^Eg/kT can be measured as a
function of depth in the neutral base of a bipolar transistor using
only DC and capacitance vs. voltage data.

      The technique as it will be described applies to any NPN
(heterojunction or homojunction) bipolar transistor with a much more
heavily doped emitter than base.  This ensures that a reverse bias on
the emitter-base junction depletes the base, rather than the emitter.
A large-area device (emitter perimeter/area<.5) is preferred, since
data from such a device can be used in the equations directly.  If
such a device is not available, area components of current and
capacitance must be extracted from data on various sizes of smaller
devices.  These area components can then be used to derive the
profile, assuming the profile is independent of device size.

      The same technique applies to PNP devices, except that hole
mobility and donor densities replace electron mobility and acceptor
densities in the equations.  Also, for both NPNs and PNPs, if the
collector is doped more heavily than the base, the technique applies
as long as the device is operated in forward, rather than inverse,
mode during the measurement.  The technique cannot be used on devices
which have bases heavily doped with respect to both emitter and
collector.

      The NPN bipolar transistor to be profiled should be biased in
inverse...