I'm trying understand where electricians came to agreement that Ie = Ib + Ic. I know that the base of a NPN transistor is very thin, allowing electrons to flow through to the collector which explains why $I_{c} = \beta I_{b}$. Mathematically, I can also see that when we have $\alpha = \frac{I_{c}}{I_{e}} = \frac{\beta}{1+\beta}$ But I want to understand the actual physics behind this phenomenon, so that I could remember it for my E5 advancement exam.

  • $\begingroup$ $I_e=I_b+I_c$ is a statement of conservation of current. The net current that leaves the transistor must equal the net current that enters it. $\endgroup$ – garyp Apr 9 '17 at 19:38
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    $\begingroup$ @garyp That seems like an answer, not a comment. $\endgroup$ – rob Apr 9 '17 at 20:38

Charge conservation.

Emitter emits electrons and collector collect the electrons. When emitted electron goes into base region which is p type material (for npn transistor) this electron have a nonzero probability to recombine. However, after recombination charge neutral base becomes negative charged and pull hole from the base. This mechanism is one of the component of base current.

Think like you have 5 electron in emitter and you emit through them to collector. In the base this electrons have %20 recombination probability. You will lose one electron at the base and pull one hole to base to preserve charge neutrality. At the end you have 4 electron at collector side.

$$I_E = I_B+I_C$$

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