In this chapter, you will learn about: Intrinsic semiconductors, doped – extrinsic materials, effective mass approximation, density of states, fermi-dirac distribution function, temperature dependence, generation-recombination,. | Dr. Nasim Zafar Electronics 1 EEE 231 – BS Electrical Engineering Fall Semester – 2012 COMSATS Institute of Information Technology Virtual campus Islamabad Electrons and Holes Lecture No: 2 Charge Carriers in Semiconductors Charge Carriers in Semiconductors: Electrons and Holes in Semiconductors: Intrinsic Semiconductors Doped – Extrinsic Materials Effective Mass Approximation Density of States Fermi-Dirac Distribution Function Temperature Dependence Generation-Recombination Revision: 1. Semiconductor Materials: • Elemental semiconductors • Intrinsic and Extrinsic Semiconductor • Compound semiconductors III – V Gap, GaAs II – V ZnS, CdTe • Mixed or Tertiary Compounds . GaAsP 2. Applications: Si diodes, rectifiers, transistors and integrated circuits etc GaAs, GaP emission and absorption of light ZnS fluorescent materials Intrinsic Semiconductors: Thermal ionization: Valence electron---each silicon atom has four valence electrons Covalent bond---two valence electrons from different two silicon atoms form the covalent bond Be intact at sufficiently low temperature Be broken at room temperature Free electron---produced by thermal ionization, move freely in the lattice structure. Hole---empty position in broken covalent bond, can be filled by free electron, positive charge Extrinsic-Doped Semiconductors: To produce reasonable levels of conduction, we have to dope the intrinsic material with appropriate dopants and concentration. silicon has about 5 x 1022 atoms/cm3 typical dopant levels are about 1015 atoms/cm3 In intrinsic silicon, the number of holes and number of free electrons is equal, and their product equals a constant actually, ni increases with increasing temperature ni2 This equation holds true for doped silicon as well, so increasing the number of free electrons decreases the number of holes In Thermal Equilibrium: n= number of free electrons p=number of holes ni=number of electrons in intrinsic silicon=10¹º/cm³ . | Dr. Nasim Zafar Electronics 1 EEE 231 – BS Electrical Engineering Fall Semester – 2012 COMSATS Institute of Information Technology Virtual campus Islamabad Electrons and Holes Lecture No: 2 Charge Carriers in Semiconductors Charge Carriers in Semiconductors: Electrons and Holes in Semiconductors: Intrinsic Semiconductors Doped – Extrinsic Materials Effective Mass Approximation Density of States Fermi-Dirac Distribution Function Temperature Dependence Generation-Recombination Revision: 1. Semiconductor Materials: • Elemental semiconductors • Intrinsic and Extrinsic Semiconductor • Compound semiconductors III – V Gap, GaAs II – V ZnS, CdTe • Mixed or Tertiary Compounds . GaAsP 2. Applications: Si diodes, rectifiers, transistors and integrated circuits etc GaAs, GaP emission and absorption of light ZnS fluorescent materials Intrinsic Semiconductors: Thermal ionization: Valence electron---each silicon atom has four valence electrons Covalent bond---two .
