Why Do Bipolar Transistors Use N+PN Configuration for High Current Gain?

[nhrock3]

why we over dope one side of the transistor
why it lookes like
N+ P N

why not just
N P N
?

 

[cabraham]

To get high injection efficiency resulting in high beta value ("hfe" on data sheet). An "n-p-n" device would have a low beta, near 1, resulting in amplifiers with poor current gain. But an "n+-p-n" device has a large beta value, on the order of 50 to 500, resulting in amplifiers with high values of current gain.

Did that help?

Claude