PH101 ENGINEERING PHYSICS DR. Chetan Barde Department of Electronics and Communication Engineering, Indian Institute of Information Technology Bhagalpur 1-Feb-22 Email:- cbarde.ece@iiitbh.ac.in 1 Prevention Is Better Then Cure 1-Feb-22 2 Module IV Introduction • Thermal Voltage • Electron Volt • Energy Gap • Electric Field Intensity • Mobility of Charge Carrier • Leakage Current • Resistivity • Conductivity • Current Density • Intrinsic Concentration 2/1/2022 Indian Institute of Information Technology Bhagalpur 3 Module IV Cont.… Introduction • Mass Action Law • Current Drift Diffusion • Hall Effect • Classification of Semiconductors • Law of Electrical Neutrality 2/1/2022 Indian Institute of Information Technology Bhagalpur 4 Module IV Cont.… Thermal Voltage (VT) or (Vt) 2/1/2022 Indian Institute of Information Technology Bhagalpur 5 Module IV Cont.… Thermal Voltage (VT) or (Vt) 2/1/2022 Indian Institute of Information Technology Bhagalpur 6 Module IV Cont.… Electron Volt (eV) or (ev) 2/1/2022 Indian Institute of Information Technology Bhagalpur 7 Module IV Cont.… Electron Volt (eV) or (ev) Vacuum electrons 1 Volt 2/1/2022 Indian Institute of Information Technology Bhagalpur 8 Module IV Cont.… Electron Volt (eV) or (ev) 2/1/2022 Indian Institute of Information Technology Bhagalpur 9 Module IV Cont.… Energy Gap (EG) or (Eg) • Larger the orbit, greater is the energy associated with it. • Each orbit in a single isolated atom represent energy level. L M Energy Level K Nucleu s M L K • As the distance from the orbit are increasing the electrons present in the respective orbit their energy also increase.. • Higher levels have less bonding with respect to the nucleus. 2/1/2022 Indian Institute of Information Technology Bhagalpur 10 Module IV Cont.… Energy Gap (EG) or (Eg) • Range of energy possessed by an electrons in a solid is known as energy band. Energy Band Conduction Band Energy Gap Valence Band • Valence Band:- The range of energy possessed by the valence electrons. • Electron in the outermost orbit of an atom are known as valence electron. • Conduction Band:- The range of energy possessed by the conduction electrons. • Free electron are called conduction electron. • Energy Gap:- Gap between the conduction band and valence band is called band gap or forbidden energy gap or energy gap. 2/1/2022 Indian Institute of Information Technology Bhagalpur 11 Module IV Cont.… Energy Gap (EG) or (Eg) Metal/Conductor Conduction Band Conduction Band Valence Band Valence Band At 0 Kelvin (Eg=0) At 300 Kelvin • As temperature increases gap between valence band and conduction band reduces and both the band start overlapping each other, and more electron are now available in the conduction band and hence current flow increases. • Overlapping of valence band and conduction increases with temperature. • In metal electron concentration increases with temperature. 2/1/2022 Indian Institute of Information Technology Bhagalpur 12 Module IV Cont.… Energy Gap (EG) or (Eg) Insulator Conduction Band Empty Conduction Band Partially Filled Valence Band At 300 Kelvin Partially Filled Energy Gap = 1 ev Valence Band At 0 Kelvin Filled • At 0 Kelvin conduction band is empty i.e., no charge carrier is present hence conductivity is 0. • No electrons of a solid can stay in forbidden energy gap as there is no allowed energy state in this region. • At 300 Kelvin or room temperature charge carrier is available in conduction band and therefore there will be small flow of current through semiconductor. 2/1/2022 Indian Institute of Information Technology Bhagalpur 13 Module IV Cont.… Energy Gap (EG) or (Eg) Insulator Conduction Band Empty Conduction Band Empty Conduction Band Filled Valence Band Filled Energy Gap = 5 to 15ev Valence Band At 0 Kelvin Filled Valence Band At 300 Kelvin Partially Filled At high temperature • At 0 Kelvin conduction band is empty i.e., no charge carrier is present hence conductivity is 0. • At 300 Kelvin also conduction band is empty i.e., no charge carrier is present hence conductivity is 0. • If very high temperature is applied, then large amount of current flow and then insulator get destroyed or burn out. 2/1/2022 Indian Institute of Information Technology Bhagalpur 14 Module IV Cont.… Energy Gap (EG) or (Eg) Germanium (Ge) Silicon (Si) Gallium Arsenide (GaAs) Eg (0 kelvin) 0.785 eV 1.21 eV **** Eg (300 kelvin) 0.72 eV 1.1 eV 1.47 eV 2/1/2022 Indian Institute of Information Technology Bhagalpur 15 Module IV Cont.… 2/1/2022 Indian Institute of Information Technology Bhagalpur 16 Module IV Cont.… Linearly Increases 2/1/2022 Indian Institute of Information Technology Bhagalpur 17 Module IV Cont.… • For larger field intensity is applied in the semiconductor, the mobility of charge carrier will be very small, and mobility of charge carrier will be remain almost constant. • For smaller field intensity is applied in the semiconductor, the mobility of charge carrier will linearly increase. Germanium (Ge) Silicon (Si) Gallium Arsenide (GaAs) 2.1:1 2/1/2022 2.6:1 Indian Institute of Information Technology Bhagalpur 14.5:1 18 Module IV Cont.… Germanium (Ge) Silicon (Si) Micro Ampere Nano Ampere Advantage of Small Leakage Current I. Suitable for higher temperature applications. II. Material or service having good thermal stability. 2/1/2022 Indian Institute of Information Technology Bhagalpur 19 1-Feb-22 20
