Question

why is emitter region kept moderate in size?

Answer 1

The three distinct layers of the transistor are the emitter, base and collector.The emitter: this region is on one extremity of the transistor. It has large conductivity. It is always forward biased with respect to the base of the transistor. The emitter, thus supplies a large number of majority carriers. This region is heavily doped. While the collector region is on the other extremity of the transistor. It collects charged carriers emitted by the emitter.It has low conductivity and is moderately doped. The collector region is made physically larger than the emitter region in most transistors since it is required to dissipate more heat.