The formation of p-n junction is described below :
In actual practice , the characteristic properties of p-n junction will not be apparent if a p type block is just brought in contact with n type block. In fact , p-n junction is fabricated by special techniques .One common method of making p-n junction is called alloying. In this method, a small block of indium is placed on an n type germanium slab.
1 )This system is heated to a temperature of about 500 degree Celsius . The indium and some of the germanium melt to form a small puddle of molten germanium indium mixture.
2)The temperature is then lowered and puddle begins to solidify. Under proper conditions ,the atoms of indium impurity will be suitably adjusted in the germanium slab to form a single crystal. The addition of indium overcomes the excess of electrons in the n type germanium to such an extent that it creates a p type region.