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

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Bipolar transistors use an N+PN configuration to achieve high current gain due to over-doping one side, which enhances injection efficiency. This design results in a significantly higher beta value, typically ranging from 50 to 500, compared to the low beta near 1 found in standard NPN configurations. The increased beta allows for more effective amplification in circuits. Consequently, N+PN transistors are preferred for applications requiring superior current gain. This configuration is essential for optimizing amplifier performance.
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why we over dope one side of the transistor
why it lookes like
N+ P N

why not just
N P N
?
 
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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.

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