For an intrinsic semiconductor,where $n_{h}$ and $n_{e}$ are the number of holes per unit volume and the number of electrons per unit volume respectively,which of the following relations holds true?

If $n_e$ and $n_h$ are electron and hole concentrations in an extrinsic semiconductor and $n_i$ is the intrinsic carrier concentration,then:

What is the number density of donor atoms which must be added to a pure germanium semiconductor to make an $n$-type semiconductor of conductivity $6.4 \ \Omega^{-1} \ cm^{-1}$? The mobility of electrons in $n$-type germanium is $4 \times 10^3 \ cm^2 \ V^{-1} \ s^{-1}$. Neglect the contribution of holes to conductivity.

Explain $n$-type and $p$-type semiconductors based on energy band theory.

In the energy band diagram of a material shown below,the open circles and filled circles denote holes and electrons respectively. The material is

The number of silicon atoms per $m^3$ is $5 \times 10^{28}$. This is doped with $4.5 \times 10^{21}$ atoms $/ m^3$ of Arsenic. The ratio of the number of electrons to the number of holes after doping is (Take $n_i = 1.5 \times 10^{16} / m^3$)