(a) What is doping in a semi conductor? (b) Draw the symbol for OR gate.

Answer Details

(a) Doping in a semiconductor

Doping is the deliberate addition of a small, controlled amount of impurity (a dopant) to a pure (intrinsic) semiconductor such as silicon or germanium in order to increase its electrical conductivity. The impurity increases the number of mobile charge carriers (free electrons or holes) available for conduction.

• Adding a pentavalent impurity (e.g. phosphorus or arsenic) donates extra free electrons, producing an n-type semiconductor.
• Adding a trivalent impurity (e.g. boron or aluminium) creates extra holes, producing a p-type semiconductor.

(b) Symbol for the OR gate

The OR gate has two (or more) inputs and one output. Its output is HIGH (logic 1) when at least one of its inputs is HIGH, and LOW (logic 0) only when all inputs are LOW. It is drawn with the standard curved-back distinctive shape:

The logic operation is written as \( Q = A + B \), giving the truth table: