Semiconductors

* PHYSICS PROJECT[2013-14]

PROJECT ON: Semi-Conductors
REPRESENTED BY-                     NAME: Sohan Biswas
CLASS: 12[Science]                   INDEX N0: 21
INTRODUCTION
There are three basic types of materials that we are concerned with in electronics. Thus solids can be placed in one of the two classes:
  i. Metals: Those through which electric charges can easily flow.
  ii. Insulators: Those through electric charges is difficult to flow.
Materials that have very low electrical resistivity are called conductors (Examples of conductors: Copper, Aluminum, Silver, Gold etc.). Materials that have very high electrical resistivity are called insulators (Examples of insulators: Rubber PVC Paper Mica Examples of Semiconductors: Silicon, Germanium etc.). Semiconductors are materials that have resistivity values in between those of conductors and insulators, they are neither good conductors nor good insulators. This distinction between the metals (conductors) and the insulators can be explained on the basis of the number of free electrons in them.   Likely; a semiconductor is a material which has electrical conductivity between that of a conductor such as copper and an insulator such as glass. Metals have a large number of free electrons which act as charge carriers, while insulators have practically no free electrons. There are however, certain solids whose electrical conductivity is intermediate between metals and insulators. They are called ‘Semiconductors’. [Carbon, silicon and germanium are such examples of semi-conductors]. In semi-conductors, the outermost electrons are not so rigidly bound with the atom as in an insulator, nor so loosely bound as in metal.
                                                                                                                            Semiconductor materials are nominally small band gap insulators. The defining property of a semiconductor material is that it can be doped with impurities...