IIRC one side is more heavily doped than the other, but I cannot recall anything beyond that... Update: The lack of symmetry [with respect to electrical rather

IIRC one side is more heavily doped than the other, but I cannot recall anything beyond that... Update: The lack of symmetry [with respect to electrical rather than structural properties] is primarily due to the doping ratios of the emitter and the collector. The emitter is heavily doped, while the collector is lightly doped, allowing a large reverse bias voltage to be applied before the collector–base junction breaks down. The collector–base junction is reverse biased in normal operation. The reason the emitter is heavily doped is to increase the emitter injection efficiency: the ratio of carriers injected by the emitter to those injected by the base. For high current gain, most of the carriers injected into the emitter–base junction must come from the emitter. https://en.wikipedia.org/wiki/Bipolar_junction_transistor#Structure https://en.wikipedia.org/wiki/Bipolar_junction_transistor#St...