Lecture 13 - pn Junction Electrostatics

# Lecture 13 - pn Junction Electrostatics - pn Junction...

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1 pn Junction Electrostatics Objective: Understand the physics and models of semiconductor devices including diodes. Questions to be answered: • When p-type and n-type materials are brought in contact, what happens to the carriers? • How do we describe the electric field that is present in a pn junction? • What is the built in potential and how do we calculate it? EE360 – Lecture 13 • What is the depletion region and how do we determine its width? • What happens (electrostatically) when we apply a bias to a pn junction? pn Junction Real pn junction (p-type region formed by diffusion of dopants) 1-D Idealized step (or abrupt) pn junction From S.M. Sze, Physics of Semiconductor Devices From Pierret, p. 209. pn x EE360 – Lecture 13 From Pierret, p.209. 1-D pn junction diode with contacts and applied bias

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2 Band Diagram of a pn Junction Given: impurity concentration ( N D - N A ) as a function of position: No current in equilibrium, so the Fermi level is constant : Equilibrium band diagrams if n- and p- type materials were separated: When we bring the materials together we observe band bending near the junction: EE360 – Lecture 13 Diagrams from Pierret, p. 199. Band Diagram of a pn Junction • When we bring p - and n -type materials together electrons diffuse toward the p-side and holes diffuse toward the n-side and holes diffuse toward the n side p-side n-side EE360 – Lecture 13 From Pierret. p side
3 pn Junction Electrostatics: Overview • Recall: , and •o r • Also recall (from electromagnetics) Poisson’s equation: o ρ = E D - 1 in d = E EE360 – Lecture 13 or where K S is the semiconductor dielectric constant, and ε 0 is the permittivity of free space Pierret p. 90

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## This note was uploaded on 04/20/2008 for the course EE 360 taught by Professor Hastings during the Spring '08 term at Kentucky.

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Lecture 13 - pn Junction Electrostatics - pn Junction...

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