"Any departure from perfectly ordered arrangement of atoms/ions in crystal is called imperfection or crystal defect".
These imperfections modify the properties of the crystal and also sometimes impart new properties to the solids.There are two types of imperfections:
- Electronic imperfections
- Atomic or point imperfection
Electronic Imperfections
At zero K (absolute zero) electrons in covalent or ionic crystals (e.g., Si or NaCl) occupy the lowest energy level.
Above zero K in pure silicon or germanium electrons are released thermally from the covalent bonds. This leads to the presence of free electrons and electron deficient bonds called holes, which are responsible for intrinsic conduction.These free electrons and the holes in solid give rise to electronic imperfections.
