Introduction:-

                        Solids in which Atoms are arranged reqularly are called crystals.according to band theory  of solids.Solids Divied in Three Classes 1-Conductor 2-Semiconductor 3-Insulators. Semiconductor are further Divied in  Two Classes 1- intrinsic Semiconductor 2-Extrinsic Semiconductor

Extrinsic Semiconductor Are divided In  Two Types 1- N-Type Semiconductor  2- P-Type Semiconductor

N-type And P-type Combine the both material and get New junction Is called PN Junction.PN junction is working as a diode.current the conducts  in Forward biased and do not conduct the current in reveres biased.PN junction is used in solar cell the solar cell convert the  solar energy in electrical energy

Types of Solid in the flow of current

Conductor:-

                                In conductor valence and conduction bands are partially filled  very small gap between the valence and conduction band.very small  amount energy is need to take an electron form the valnce band to conduction band when conducts the electron are become free. A large number of electron are free and the current flow through is due to the motion of free electrons

Insulators:-

                        In insulators the valence electron are tightly with nucleus.the valance band and the conduction band is almost is empty. electron  cannot easily go form the valance band to the conduction band how ever at very large temperature some electron may be jump to conduction band. Insulators resistance is very high

Semiconductor:-

                                A material  than is neither a good conductor or nor an insulator is called semiconductor.they have partially filled with valance band and conduction band. When  the electron goes form valance band to conduction band its leave a hole in the valance band semiconductor temperature is increased.its Conductivity increases and its resistance is decreased due to the breakinf of covalent band