# why some elements of same group cannot be used for doping semiconductors?

15th group elements like As, Sb, P can be used for doping whereas N and Bi cannot be used for doping even though they too belong belong to 15th group. Why ?

Bismuth certainly has a donor level not much lower than As, satisfying (2). However, the solid solubility of Bi is roughly 3 orders of magnitude less than As, peaking at below $10^{18}/cm^3$. This limits the utility of Bi in current device technology - you just can't get enough in.