Base transit time of a bipolar junction transistor considering majority-carrier current

In this paper an analytical expression for base transit time tau
_B
for an npn bipolar transistor considering majority-carrier current density is obtained. For finding tau
_B
, expressions for minority-carrier electron current density J
_n
, majority-carrier hole current density J
_p
and electron concentration, n(x) are analytically derived. In the model energy-bandgap-narrowing effects due to heavy doping, velocity saturation as well as doping and field dependent mobility are considered. It is found that, in the low-injection condition, tau
_B
depends on J
_p
and its value is found greater than the value if Jp is neglected. In finding tau
_B
, previous works neglected J
_p
. The closed-form analytical expressions offer a clear physical insight into device operations at various bias conditions.