The Science of Electricity

Semiconductors     Definition : The materials, whose electrical conductivity lies between those of conductors and insulators and have negative temperature coefficient of resistance, are known as semiconductors.   Semiconductor Materials : The few examples of semiconductor materials are as under : 1.Carbon (C) 2. Silicon (Si) 3.Germanium (Ge) 4. Selenium (Se) 5.Gallium Arsenide (GaAs) 6.Cadmium Sulphide (CdS). The commonly used semiconductor materials are Germanium and Silicon. These are tetravalent elements i.e. materials having  four valency.   Atomic Structures of Germanium and Silicon : (i) Atomic structure of Germanium and Silicon atoms :  Fig. 1.3 (b) shows the atomic structure of a Germanium atom  in which first, second, third and fourth orbits have 2, 8, 18 and  4 electrons respectively, with the result that the atomic  number for Germanium is 32. Fig. 1.3 (a) shows the atomic structure of a Silicon atom in  which first, second and th

1.1 Introduction: The property of solids that varies most from one solid to the other is the ability to conduct electric current. For example, the resistivity of copper is 1.7 ✕ 10   ^ -8 Ω-m whereas that of quartz is 7.5 ✕ 10 ^ 17 Ω-m. The electron energy bands present in the solids makes it possible to study such a wide variation in resistivity and conductivity. 1.2 Structure of an Atom Any substance, solid, liquid or gaseous is made up of molecules and molecules and molecules are made up of atoms. The atoms contains tiny particles called protons, neutrons and electrons which are called as fundamental particles. Protons have positive charge, electrons have negative charge and neutrons are electrically neutral. The protons, electrons and neutrons of various types of atoms ( atoms of different materials) are same as each other. That means there is no change in their physical properties though they are present in different materials. But the "arrangement" of prot