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

The electron mobility in $N$-type germanium is $3900 \ cm^2/V \cdot s$ and its conductivity is $6.24 \ mho/cm$. If the effect of holes is negligible,what is the impurity concentration?

In a $P$-type semiconductor,there is

In an $N$-type $Ge$ semiconductor,the mobility of electrons is $5000 \ cm^2/V \cdot s$ and the conductivity is $5 \ mho/cm$. If the effect of holes is negligible,what is the concentration of impurity atoms?

The width of the forbidden gap in a silicon crystal is $1.1 \, eV$. When the crystal is converted into an $N$-type semiconductor,the distance of the Fermi level from the conduction band is:

In a $p$-type semiconductor,the acceptor level is at $50 \text{ meV}$ above the valence band. To produce one hole,the maximum wavelength of the light photon required is (Planck's constant,$h = 6.6 \times 10^{-34} \text{ Js}$ and speed of light in vacuum,$c = 3 \times 10^8 \text{ m/s}$) (in $\mu \text{m}$)