Lecture 2 - Announcements • HW1 will be posted later...

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EE105 Fall 2009 Lecture 2, Slide 1 Prof. Salahuddin, UC Berkeley Announcements HW1 will be posted later today, due Tuesday 9/8 No lab session on Monday 9/7 In the week of 10/5 Monday section will have a lab Other two sections will not have any labs
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EE105 Fall 2009 Lecture 2, Slide 2 Prof. Salahuddin, UC Berkeley Review of the last class 1. The band gap energy is the energy required to free an electron from a covalent bond. 1. E g for Si at 300K = 1.12eV 2. Substitutional dopants in Si: 1. Group-V elements (>4 valence electrons) can donate one electron/dopant( donors ) : intrinsic n type 2. Group-III elements (<4 valence electrons) can accept one hole/dopant ( acceptors ) : intrinsic p type 3. At thermal equilibrium : np=n i 2 hence if you know one, you know the other. 4. Dopants are fixed in lattice, but the electrons or holes that they generate can move and give current 5. Total charge density,   A D N N n p q
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EE105 Fall 2009 Lecture 2, Slide 3 Prof. Salahuddin, UC Berkeley Lecture 2 OUTLINE Semiconductor Basics (cont’d) Carrier drift and diffusion PN Junction Diodes Electrostatics Capacitance Reading: Chapter 2.1-2.2
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EE105 Fall 2009 Lecture 2, Slide 4 Prof. Salahuddin, UC Berkeley Carrier Drift The process in which charged particles move because of an electric field is called drift . Charged particles within a semiconductor move with an average velocity proportional to the electric field. The proportionality constant is the carrier mobility . E v E v n e p h Notation : p hole mobility (cm 2 /V·s) n electron mobility (cm 2 /V·s) Hole velocity Electron velocity
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EE105 Fall 2009 Lecture 2, Slide 5 Prof. Salahuddin, UC Berkeley Velocity Saturation In reality, carrier velocities saturate at an upper limit, called the saturation velocity ( v sat ) . E v E v b v bE sat sat 0 0 0 0 1 1
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EE105 Fall 2009 Lecture 2, Slide 6 Prof. Salahuddin, UC Berkeley Drift Current Drift current is proportional to the carrier velocity and carrier concentration : v h t A = volume from which all holes cross plane in time t p v h t A = # of holes crossing plane in time t q p v h t A = charge crossing plane in time t q p v h A = charge crossing plane per unit time = hole current Hole current per unit area ( i.e. current density) J p,drift = q p v h
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EE105 Fall 2009 Lecture 2, Slide 7 Prof. Salahuddin, UC Berkeley Conductivity and Resistivity In a semiconductor, both electrons and holes conduct current: The conductivity of a semiconductor is Unit: mho/cm The resistivity of a semiconductor is Unit: ohm-cm E E n p q J E qn E qp J J J E qn J E
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This note was uploaded on 10/05/2009 for the course EE 105 taught by Professor King-liu during the Fall '07 term at University of California, Berkeley.

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Lecture 2 - Announcements • HW1 will be posted later...

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