POWER BIPOLAR JUNCTION TRANSISTOR
Switching time and switching losses are primary concerns in high power
applications. These two factors can significantly influence the frequency of operation and
the efficiency of the circuit. Ideally, a high power switch should be able to turn-on and
turn-off controllably and with minimum switching loss. The Bipolar junction transistor is
an important power semiconductor device used as a switch in a wide variety of
applications. The switching speed of a BJT is often limited by the excess minority charge
storage in the base and collector regions of the transistor during the saturation state. The
conventional methods for improving the switching frequency by reducing the lifetime of
the lightly doped collector region through incorporation of impurities such as Au, Pt or
by introducing radiation-induced defects have been found unsuitable for high voltage
devices due to increased leakage, soft breakdown and high `ON' state voltage .
Among the techniques proposed to overcome these problems, use of universal contact
(UC) [2, 14] is particularly promising. The present work looks in detail at the various
aspects arising out of incorporation of UC in BJTs. The UC is incorporated in the
transistor by creating additional diffused regions in an otherwise conventional transistor.