Properties of Solids
Some of the properties of solids which are useful in electronic and magnetic devices such as, transistor, computers, and telephones etc., are summarised below,
(1) Electrical properties: Solids are classified into following classes depending on the extent of conducting nature.
(i) Conductors: The solids which allow the electric current to pass through them are called conductors. These are further of two types; Metallic conductors and electrolytic conductors. The electrical conductivity of these solids is high in the range . Their conductance decrease with increase in temperature.
(ii) Insulators: The solids which do not allow the current to pass through them are called insulators. e.g., rubber, wood and plastic etc. the electrical conductivity of these solids is very low i.e., .
(iii) Semiconductors: The solids whose electrical conductivity lies between those of conductors and insulators are called semiconductors. The conductivity of these solid is due to the presence of impurities. e.g. Silicon and Germanium. Their conductance increase with increase in temperature. The electrical conductivity of these solids is increased by adding impurity. This is called Doping. When silicon is doped with P (or As, group 5th elements), we get n-type semiconductor. This is because P has five valence electrons. It forms 4 covalent bonds with silicon and the fifth electron remains free and is loosely bound. This give rise to n-type semiconductor because current is carried by electrons when silicon is doped with Ga (or in In/Al, group 3rd elements) we get p-type semiconductors.