- The beauty of transistor structure lies in its different areas of each of the layers. Also, the base layer is kept between collector and emitter. We can say that the base acts just like a ‘door’ for the transfer of electrons from emitter to collector through it. When base voltage increases, this ‘door’ opens wider and more number of electrons are allowed to flow through it.
- The area of base layer is deliberately kept small because of two reasons. First, it creates strong repulsive forces among the crowded electrons in base layer. When electrons from emitter layer come into base layer, they get trapped, as they cannot go back, due to repulsive force of negative ions of base layer near B-E junction. In base layer they find very small number of holes to recombine. The base voltage is also small. So very small number of electrons are attracted towards positive terminal of Vbe battery.
- Eventually, all these electrons crowded in base layer have but one option, to surmount the ‘gap’ of C-B junction and enter into collector layer. But this junction is already reverse biased (note the polarity connections of Vcb battery). Now how they will jump over this ‘large gap’ of C-B junction? They will jump this gap because, the strong positive electric field of collector layer is ‘inviting’ them or attracting them. So with two forces: one is mutual repulsive force among them in base layer and one is the strong attractive force from collector layer, they succeed to surmount this large gap of C-B junction and enter into collector layer.
I am just a beginner in Semiconductors so I just had some doubts when I read the above statement, which include:
1) What the base voltage really is Vcb or Vbe and also base current?
2) Why does increasing base voltage increase the number of electrons?
3) What really happens in collector region? I am confused about how they explained above.
This is a common base configuration