A p-n junction may be produced by one of the following methods:-

Firstly the semiconductor material is obtained in an extremely pure form. The acceptable impurity level is less than one part of impurity in one billion parts of the semiconductor material. Then raw materials are subjected to a series of chemical reactions and then to a zone refining process which employs induction heating to reduce the impurity level. Then floating zone technique is used to form single crystals of Ge or Si which are further used in the manufacture of diodes. The crystals are then cut into wafers as thin as 0.025 mm.

Such junctions are produced by employing the Czochralski or floating zone technique.

A single crystal seed of the desired impurity level is immersed in the molten semiconductor material contained in a crucible. It is then withdrawn keeping the shaft holding the seed turning. When the crystal is being pulled out, impurities of p and n-type are alternately added to produce a p-n junction. The large crystal is then cut into a large number of smaller area diodes.

After placing a tiny dot of indium or any other p-type impurity on the surface of an n-type silicon wafer and the two are heated well above the melting point of indium (i.e., to about 1500C) when the Indium melts and dissolves some of the silicon. The temperature is then lowered and silicon resolidifies to form a p-n junction.

This process involves either solid or gaseous diffusion.

(b)Gaseous Diffusion: In this process an n-type material is heated in a chamber containing a high concentration of an acceptor impurity in vapour form. The diffusion technique enables simultaneous fabrication of many hundreds of diodes in a one small disc of a semiconductor material. This is the most frequently used technique not only for diodes but also for the production of transistors, ICs etc.

Epitaxial Junction: Such junctions are grown on top of an n-type wafer in a high temperature chamber. The growth proceeds atom by atom and the resulting growth is exactly similar to the crystal lattice of the wafer on which it is grown.

Point Contact Junction: It consists of an n-type germanium or silicon wafer of about 1.25mm square by 0.5mm thick one face of which is soldered to a metal base by radio frequency heating.

The other face has a phosphor bronze (or tungsten) spring pressed against it. The junction is formed by passing a large current for a second or two through the wire and keeping the crystal with the wire point positive.