Semiconductor Physics (Part I), Lecture notes of Electrical and Electronics Engineering

Download Semiconductor Physics (Part I) and more Lecture notes Electrical and Electronics Engineering in PDF only on Docsity! 1 ELE 241 Electronics I Department of Electrical Engineering College of Engineering American University of Sharjah 2 Lecture 3. Semiconductor Physics (Part I) ELE 241 Electronics I 5 Learning Outcomes 1. Calculate the electron and hole concentrations in intrinsic and doped semiconductor materials. 2. Calculate the built-in potential, depletion region width and junction capacitance of a PN junction. 3. Analyze diode circuits. 4. Describe the BJT structure, operation, and I-V characteristics. 5. Design BJT DC biasing circuits. 6. Describe the MOSFET structure, operation, and I-V characteristics. 7. Analyze MOSFET DC biasing circuits, amplifiers, and CMOS logic gate circuits. 8. Design MOSFET amplifiers and CMOS logic gate circuits. 9. Analyze CMOS inverter circuits. ELE 241 Electronics I | L3 | Learning Objectives 6 Semiconductor § Conductor has LOW resistivity § Insulator/Dielectric has HIGH resistivity § Semiconductor has INTERMEDIATE resistivity § Conductivity between conductor and insulator § Typically crystalline solid § Non-crystalline solid for example polycrystalline has become commercially available and very important material in photovoltaic panels (solar cells) production. Image: Eddy Brinkman/Betase BV ELE 241 Electronics I | L3 | Semiconductor 7 Solid-State Materials § Solid-state electronic materials fall into three categories of resistivity: § Insulators 𝜌 > 105 𝛀-cm § Semiconductors 10-3 < 𝜌 < 105 𝛀-cm § Conductors 𝜌 < 10-3 𝛀-cm § Silicon and Germanium (group IV) are the most commonly used semiconductor materials. § Boron (group III) and Arsenic (group V) are used to form compound semiconductors. ELE 241 Electronics I | L3 | Solid-State Materials 10 Intrinsic Silicon Crystal § A two-dimensional representation of Si crystal lattice. § Each atom is connected to its four nearest neighboring atoms by two bonding electrons. § Each line represents a covalent bonding electron. § Each double line represents a covalent bond of two electrons. ELE 241 Electronics I | L3 | Intrinsic Silicon Crystal 11 Intrinsic Silicon Crystal § Intrinsic (pure) Si has a relatively high electrical resistivity at room temperature. § 2 types of charged carriers in Si: § Electrons – negatively charged § Holes – positively charged § The carrier concentration of electrons and holes in a semiconductor can be varied to control the conductivity by: § Adding other elements (doping) § Applying electric field (voltage) § Changing the temperature § Irradiation with electromagnetic energy ELE 241 Electronics I | L3 | Intrinsic Silicon Crystal 12 Electron-Hole Pair Generation § At room temperature, some of the covalent bonds are broken by thermal generation. § Each broken bond gives rise to a free electron and a hole, which become available for current conduction. ELE 241 Electronics I | L3 | Electron-Hole Pair Generation 15 Hole Conduction in Intrinsic Si § The electrons arrangement (a) before and (b) after the previous sequence of bonding electron jump. § The net change, from (a) to (b), may be described as either the motion of one bonding electron two atomic distance to the left, § Or the motion of one free hole two atomic distance to the right. ELE 241 Electronics I | L3 | Hole Conduction in Intrinsic Si Hole C nduction in Intrinsic Si • The electronic arrangement (a) before and (b) after the previous sequence of bonding electron jumps • The net change, from (a) to (b), may be described as either the motion of one bonding electron two atomic distance to the left, or the motion of one free hole two atomic distance to the right 16 Energy Band Theory § Bands are allowed states for carriers. § Bandgaps are forbidden states for carriers. § Valence band filled with electrons, § Conduction band partially filled with electrons. ELE 241 Electronics I | L3 | Energy Band Theory Dr Lutfi Albasha ELE241 Electronics I Energy Band Diagram Ev – Maximum energy of a valence electron or hole Ec – Minimum energy of a free electron Eg – Energy required to break the covalent bond 17 Energy Band Theory § Ev = Maximum energy of a valence electron or hole § Ec = Minim energy of a free electron § Eg = Energy required to break the covalent bond ELE 241 Electronics I | L3 | Energy Band Theory Dr Lutfi Albasha ELE241 Electronics I Energy Band Diagram Ev – Maximum energy of a valence electron or hole Ec – Minimum energy of a free electron Eg – Energy required to break the covalent bond 20 n-Type Si Semiconductor § If impurities have more valence electrons than the host semiconductor, they are said to be donors, and the semiconductor becomes n-type semiconductor. § N-doping materials (Group V): § P: Phosphorus § As: Arsenic § Sb: Antimony ELE 241 Electronics I | L3 | n-Type Si Semiconductor 9 EEET 2018 Autumn - Lect 1 University of South Australia Alex Hariz 17 Doped semiconductors - extrinsic • N-doping: addition of pentavalent atoms such as Sb, As, or Phosphorus. • Energy required to bring a donor electron to conduction state is 0.05 eV for Si; that is, almost free. At room temperature it is free. • P-doping: this process involves the addition of trivalent atoms such as In, Ga, Al, or Boron. • An impurity concentration of about 1014 cm-3 would drop the resistivity to 23 Ω-cm. Yet in a host crystal of 5 × 1022 cm-3, this doping level results in only two impurity atoms per one billion atoms of silicon. EEET 2018 Autumn - Lect 1 University of South Australia Alex Hariz 18 Energy bands in extrinsic SCs Donation of electrons from a donor level to the conduction band Acceptance of valence band electrons by an acceptor level, resulting in creation of holes 21 p-Type Si Semiconductor § If impurities have less valence electrons than the host semiconductor, they are said to be acceptors, and the semiconductor becomes p-type semiconductor. § P-doping materials (Group III): § B: Boron § Al: Aluminium § Ga: Gallium ELE 241 Electronics I | L3 | p-Type Si Semiconductor 9 EEET 2018 Autumn - Lect 1 University of South Australia Alex Hariz 17 Doped semiconductors - extrinsic • N-doping: addition of pentavalent atoms such as Sb, As, or Phosphorus. • Energy required to bring a donor electron to conduction state is 0.05 eV for Si; that is, almost free. At room temperature it is free. • P-doping: this process involves the addition of trivalent atoms such as In, Ga, Al, or Boron. • An impurity concentration of about 1014 cm-3 would drop the resistivity to 23 Ω-cm. Yet in a host crystal of 5 × 1022 cm-3, this doping level results in only two impurity atoms per one billion atoms of silicon. EEET 2018 Autumn - Lect 1 University of South Australia Alex Hariz 18 Energy bands in extrinsic SCs Donation of electrons from a donor level to the conduction band Acceptance of valence band electrons by an acceptor level, resulting in creation of holes 22 End of Lecture 3. Semiconductor Physics (I) Some materials/figures in this presentation are adapted/taken from (with permission): Microelectronic Circuits 8th International Edition. By Adel Sedra and Kenneth Smith, Lecture notes from Dr. Oualid Hammi, Dr. Lufti Albasha, and Dr. Alex Hariz, and Other online resources. ELE 241 Electronics I