In a transistor

1. Emitter is heavily doped while the collector is moderately doped
2. Collector bgase junction is forward biased
3. Emitter made wider than collector
4. The input resistance is much larger than output resistance

In a transistor emitter is very highly doped. Base is very lightly doped and collector is moderately doped, i.e. Doping profile: E > C > B.