In a $p$-type semiconductor,

$A$ donor atom in a semiconductor has a loosely bound electron. The orbit of this electron is considerably affected by the semiconductor material but behaves in many ways like an electron orbiting a hydrogen nucleus. Given that the electron has an effective mass of $0.07 \, m_e$,where $m_e$ is the mass of the free electron,and the space in which it moves has a permittivity of $13 \, \varepsilon_0$,then the radius of the electron's lowermost energy orbit will be close to ................. $\mathring{A}$ (take the Bohr radius of the hydrogen atom as $0.53 \mathring{A}$).

The mobility of free electrons is greater than that of free holes because

$A$ semiconductor is placed in an electric field. Let the number density of charge carriers be $n$ and the average drift velocity be $v$. If the temperature is increased,then:

In $n$-type semiconductor,electrons are majority charge carriers,but it does not show any negative charge. The reason is:

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?