SEMICONDUCTOR MATERIALS

group of materials that are neither good conductors nor good insulators.  At room temperature these materials have conductivities considerably lower than that of conductors but much higher than that of insulators  Examples - germanium, silicon  Semiconductors have a very important property that their conductivity can be changed to a very large extent by adding a very small amount of some specific materials (called impurities)  Consider a silicon atom as shown,

                       

nucleus contains 14 protons and 14 neutrons-  14 electrons revolving around the nucleus distributed in different orbits or shells  a shell can contain a maximum of 2n2 electrons, where n is the number of the shell  But there is an exception to this rule, That is, the outermost orbit cannot accommodate more than eight electrons ie., valence electrons  Applying this rule, the 14 electrons of.;the silicon atom are distributed as, 2 in first , 8  in  second orbit and the remaining 4 e in third . Similarly a germanium atom with atomic number 32 will have its 32 electrons distributed

as shown