Schottky defects : When cations and anions both are missing from regular sites, the defect is called Schottky Defect. In Schottky Defects, the number of missing cations is equal to the number of missing anions in order to maintain the electrical neutrality of the ionic compound.

Schottky Defect is type of simple vacancy defect and shown by ionic solids having cations and anions; almost similar in size, such as NaCl, KCl, CsCl, etc. AgBr shows both types of defects, i.e. Schottky and Frenkel Defects.

Since, Schottky Defects arises because of mission of constituent particles, thus it decreases the density of ionic compound.

It is a type of vacancy defect. In ionic compounds, some of the ions (usually smaller in size) get dislocated from their original site and create defect. This defect is known as Frenkel Defects. Since this defect arises because of dislocation of ions, thus it is also known as Dislocation Defects. As there are a number of cations and anions (which remain equal even because of defect); the density of the substance does not increase or decrease.

Ionic compounds; having large difference in the size between their cations and anions; show Frenkel Defects, such as ZnS, AgCl, AgBr, AgI, etc. These compounds have smaller size of cations compared to anions.

Semiconductor: In instrinsic semiconductors, the energy gap, Eg, is relatively small (≈ = 1 eV). At absolute zero, conduction band is empty and valence band is full. Therefore, the solid behaves as an insulator at very low temperatures. However, at room temperature, some electrons from the top of valence band acquires enough thermal energy to jump into the conduction band. They leave behind a number of holes. Both electrons and holes movement contribute to conduction.
In extrinsic semi-conductor of n-type, the donor energy level is close to the bottom of conduction band.
In p-type the acceptor energy level is close to the top of valence band.