In an $n$-type semiconductor,the free electrons donated by the impurity atoms occupy energy levels in:

When germanium is doped with phosphorus,the doped material has

An $N-$type and $P-$type silicon can be obtained by doping pure silicon with

At a temperature of $500 \ K$,the intrinsic electron number density $(n_e)$ and hole number density $(n_h)$ in a pure semiconductor are equal to $1.5 \times 10^{16} \ m^{-3}$. Now,by adding indium impurity,the hole density $(n_h)$ increases to $4.5 \times 10^{22} \ m^{-3}$. This doped semiconductor is:

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

$A$ 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 $\text{cm}^3$.