To a germanium sample,traces of gallium are added as an impurity. The resultant sample would behave like

When a small amount of impurity atoms are added to a semiconductor,then generally its resistivity:

The impurity atom added to germanium to make it $N-$type semiconductor is

$A$ silicon sample is made into a $p$-type semiconductor by doping. Indium atoms are added at a rate of one atom per $5 \times 10^7$ silicon atoms. If the number density of silicon is $5 \times 10^{28} \text{ atoms/m}^3$,calculate the number density of acceptor atoms per $\text{cm}^3$.

$A$ 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 $0.53 \mathring{A}$).

In an intrinsic semiconductor,the energy gap $E_{g}$ is $1.2 \; eV$. Its hole mobility is much smaller than electron mobility and independent of temperature. What is the ratio between conductivity at $600 \; K$ and that at $300 \; K$? Assume that the temperature dependence of intrinsic carrier concentration $n_{i}$ is given by $n_{i} = n_{0} \exp \left(-\frac{E_{g}}{2 k_{B} T}\right)$,where $n_{0}$ is a constant.