why does p side and n side of p-n junction are heavily doped in zener diode? why zener diode connected in reverse bias not forward biased?? what is the function of load resistance in zener diode?

Zener diode is used in reverse biasing because in breakdown region the current changes many folds with a negligble change in voltage.sO That it could be used as a voltage regulator and we can take output voltage through load resistance .