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

In extrinsic $P$ and $N$-type semiconductor materials,the ratio of the impurity atoms to the pure semiconductor atoms is about

If the ratio of the number density of electrons to the number density of holes in a semiconductor is $7/5$ and the ratio of their currents is $7/4$,what is the ratio of their drift velocities?

The charge carriers in a $p$-type semiconductor are

Pure $Si$ at $500\,K$ has equal number of electron $(n_e)$ and hole $(n_h)$ concentrations of $1.5 \times 10^{16}\,m^{-3}$. Doping by indium increases $n_h$ to $4.5 \times 10^{22}\,m^{-3}$. The doped semiconductor is of

$A$ crystal of intrinsic silicon at room temperature has a carrier concentration of $1.6 \times 10^{16} / m^3$. If the donor concentration level is $4.8 \times 10^{20} / m^3$, then the concentration of holes in the semiconductor is