To reduce the ripples in rectifier circuit with capacitor filter
The breakdown in a reverse biased $p-n$ junction is more likely to occur due to
Why are elemental dopants for Silicon or Germanium usually chosen from group XIII or group XV?
The size of the dopant atom should be such that their presence in the pure semiconductor does not distort the semiconductor but easily contribute the charge carriers on forming covalent bonds with Si or Ge atoms, which are provided by group XIII or group XV elements.
$\mathrm{Sn}, \mathrm{C}$ and $\mathrm{Si}, \mathrm{Ge}$ are all group XIV elements. Yet, Sn is a conductor, C is an insulator while Si and Ge are semiconductors. Why?
A material is a conductor if in its energy band diagram, there is no energy gap between conduction band and valence band. For insulator, the energy gap is large and for semiconductor the energy gap is moderate.
The energy gap for Sn is 0 eV, for C is 5.4 eV , for Si is 1.1 eV and for Ge is 0.7 eV , related to their atomic size. Therefore Sn is a conductor, C is an insulator and Ge and Si are semiconductors.
Can the potential barrier across a $p-n$ junction be measured by simply connecting a voltmeter across the junction?
We cannot measure the potential barrier across a $p-n$ junction by a voltmeter because the resistance of voltmeter is very high as compared to the junction resistance.