ECE615_Lecture_21

ECE615_Lecture_21 - Lecture 21 Semiconductor Nonlinearities...

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Semiconductors have allowed electronic energy states in broad bands. - The lower mostly filled valence bands. - Upper empty or mostly empty conduction bands. - Bandgap energy is difference between highest valence and lowest conduction bands. Lecture 21 Semiconductor Nonlinearities g E g c v E E E = - virtual transition 1 g h E ϖ g h E < Nonlinearities from Band-to-Band Transitions g h E ( 29 (0) c c c R N N dN I dt α τ - = - (1) absorption coefficient at incident frequency conduction band electron population in thermal equilibrium electron-hole recombination time. (0) c N R
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Steady state solution to (1): (2) - If pulse duration < , then increases monotonically during pulse. Change in electron concentration in (2) leads to change in optical properties: 1) Free electron response Electrons in conduction band respond freely to applied optical field. Drude formula : ) (0) R c c I N N α τ ϖ = + c N R τ 2 ( ) p ε ϖ ε = - (3) contribution to from bound charges the plasma frequency
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This note was uploaded on 01/10/2011 for the course ECE 615 taught by Professor Shalaev during the Fall '10 term at Purdue.

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ECE615_Lecture_21 - Lecture 21 Semiconductor Nonlinearities...

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