he word doping is used for impurity incorporation up to certain concentrations till the band gap of the host material does not change. Normally, this is at ppm level. When impurity is added at large concentration, a new alloy is formed which will have different band gap. In case of composite also, if the concentration of second phase is very small then only the properties of host material will be observed whether we measure band gap or do structural analysis.

Composite material consists of 2 or more constitute materials with significantly different physical and chemical properties and which remains separate and distinct on a macroscopic level within the finished structure whereas alloy is a partial or complete solid solution of one or more element in a metallic matrix.

Doping is addition of a secondary material while retaining the phase of the first such that macroscopically the presence and identity of the second phase is not revealed. The incoming atom may take a lattice position when it is called substitutional or take an interstitial position. It is simply the case of solution formation, when sugar is dissolved in water, which is why by analogy the doped materials are also called Solid Solution. By analogy, the material in small amount is called the solute and the major one is the solvent. Alloying by definition, is a solid solution where one of the two components is a metal. If the doping is more, that is if the amount of solute exceeds the solubility limit, then the solute tends to precipitate out either in the native form or as a reaction product.