# What is the difference between emitter and collector for BJTs?

the (surely simplistic) model of a bipolar junction transistor one is taught in foundational physics course appears to be symmetric. - So, what is the difference between the collector and the emitter of a real BJT? If the transistor were symmetric one would not make this distinction...

Also:

• Do BJTs have a 0.6V voltage drop like diodes?
• Are BJTs conductive in both directions, i.e. E-C and C-E?

Many thanks.

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 – clabacchio♦ Jun 5 '12 at 13:47

The main differences between emitter and collector are doping concentration and size. The emitter is heavily doped, while the collector is lightly doped. You could try to swap them, but you'll get a very low $H_{FE}$, probably even less than 1.