JoSS: Joy of Sharing Science No: 3

Joy of Sharing Science
When there is no voltage difference applied across the base and emitter ends,
electrons from base and holes from the emitter attract each other. So, a chargeneutral
zone in between P and N is formed called EB. A similar process occurs
between the base and collector where electrons and holes attract each other to form
a second neutral zone called CB. In this state, it is not possible for a current to run
from emitter to collector through the transistor. However, when a voltage difference
(VEB) is applied across Emitter and Base, holes start to circulate. They are pushed
from Emitter to the neutral zone due to the voltage difference and then pulled from
the neutral zone to base. This way of applying a voltage difference across the
emitter and the base is called forward bias because it makes the EB neutral zone
thinner and forces holes to move forward. To complete the system and enable a
current from Emitter to Collector, another voltage difference needs to be applied.
This voltage difference is applied across the Collector and Base. The direction of the
voltage difference pulls holes away from the base and widens the CB neutral zone
while also starting another circulation of holes. This type of voltage difference is
called reverse bias.