The molten region melts impure solid at its forward edge and leaves a wake of purer material solidified behind it as it moves through the ingot.

Zone refining was invented by John Desmond Bernal[1] and further developed by William G. Pfann[2] in Bell Labs as a method to prepare high-purity materials, mainly semiconductors, for manufacturing transistors.

Its first commercial use was in germanium, refined to one atom of impurity per ten billion,[3] but the process can be extended to virtually any solute–solvent system having an appreciable concentration difference between solid and liquid phases at equilibrium.

When high purity is required, such as in semiconductor industry, the impure end of the boule is cut off, and the refining is repeated.

[citation needed] In zone refining, solutes are segregated at one end of the ingot in order to purify the remainder, or to concentrate the impurities.

In zone leveling, the objective is to distribute solute evenly throughout the purified material, which may be sought in the form of a single crystal.

Another method is to pass an electric current directly through the ingot while it is in a magnetic field, with the resulting magnetomotive force carefully set to be just equal to the weight in order to hold the liquid suspended.

By melting a portion of such an ingot and slowly refreezing it, solutes in the molten region become distributed to form the desired n-p and p-n junctions.