What is the valency of donor impurity? Name these impurities.

If a small amount of antimony is added to germanium crystal,

Why are elemental dopants for Silicon or Germanium usually chosen from group $XIII$ or group $XV$?

In pure silicon,the electron-hole concentration at $T = 300 \ K$ is $7 \times 10^{15} \ m^{-3}$. Antimony is added as an impurity to silicon at a rate of $1$ atom per $10^7 \ Si$ atoms. Assume that half of the impurity atoms contribute their electrons to the conduction band. Calculate the factor by which the number of charge carriers increases. Given: the number density of silicon atoms is $5 \times 10^{28} \ m^{-3}$.

An intrinsic semiconductor is electrically neutral. What is the electrical state of an extrinsic semiconductor?

Let ${n_h}$ and ${n_e}$ be the number of holes and conduction electrons respectively in a semiconductor. Then