12th-class solid state important topics part 2, Study notes of Chemistry

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Conduction bands: Crystal is formed by overlapping atomic orbitals. The wave functions are delocalized. The number of orbital increases with the number of atoms. Electrons are free to move. Conduction in metals. Valence bands: The highest energy band containing electrons at absolute zero temperature is called the valence band. Electrons in this band are not free to move. Bond between atoms. Valence electrons are bound to specific atoms and are not free. Energy band gap: The energy gap between the valence band and the conduction band. The energy required to excite an electron from the valence hand to the conduction Conductors have no energy gap (valence band and conduction band overlap). Semiconductors have a small energy gap. Insulators have a large energy gap. The energy gap determines the electrical conductivity of materials at room temperature. For example, diamond is an insulator with a large energy gap. Silicon and Germanium are semiconductors with smaller energy gaps. This property helps explain why materials like conductors, semiconductors, and insulators behave differently in terms of electrical conductivity. The size of the energy gap is crucial in determining if a material is a conductor, semiconductor, or insulator. Intrinsic Semiconductors: A pure semiconductor in which electrical conductivity is due to thermally excited electrons and holes is called an intrinsic semiconductor. Extrinsic Semiconductors: A doped semiconductor, meaning a semiconductor with impurity added to it to increase its conductivity, is called an extrinsic semiconductor. Doping: The process of adding impurity to a semiconductor to increase its electrical conductivity is called doping. The impurity added is called a dopant. Types of extrinsic semiconductor: There are two types of extrinsic semiconductors: n-type and p-type. n-type semiconductor n-type semiconductor contains increased number of electrons in the conduction band. n-type semiconductor is obtained by adding group 15 elements to intrinsic semiconductor which belongs to group 14. p-type semiconductor p-type semiconductor is produced by doping pure semiconductor material with an impurity of group 13. This type of semiconductor contains less no. of valence electrons than that of pure semiconductor. Feromagnetism The substance containing large number of unpaired electrons are attracted strongly by magnetic field. This substance is called Feromagnetic substances. This substances can be permanently magnetized. Ex. Fe, Co, Ni.