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ECE216-Lecture-12-PN-Junction-Diodes

ECE216-Lecture-12-PN-Junction-Diodes - ECE 216 DEVICE...

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ECE 216 DEVICE PHYSICS FOR INTEGRATED CIRCUITS Lecture 12 PN-JUNCTION DIODES Professor Hisham Z. Massoud Department of Electrical and Computer Engineering Fitzpatrick Building, Room 3521 Duke University, Durham, NC 27708–0291 [email protected] https://courses.duke.edu/webapps/portal/frameset.jsp ECE 216 Chapter 08 – PN-Junction Diodes Lecture 12.1
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LECTURE 12 - TOPICS 8. Reverse-Bias Static Current-Voltage Characteristics 9. Reverse-Bias Breakdown in a PN-Junction Diode 10. Small-Signal Capacitance-Voltage Characteristics 10.1. Small-Signal Capacitance Measurement 10.2. Definitions 10.3. The Bias-Voltage Dependence of the Depletion and Diffusion Charge Densities 10.4. The Bias-Voltage Dependence of the Depletion and Diffusion Capacitances 10.5. The Bias-Voltage Dependence of the PN-Junction Capaci- tance ECE 216 Chapter 08 – PN-Junction Diodes Lecture 12.2
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8. REVERSE-BIAS STATIC I D ( V PN ) CHARACTERISTICS When the applied bias voltage V PN is negative, the PN-junction diode is reverse-biased. Under such conditions The width the depletion region increases, The electric-field magnitude in the depletion region increases, The voltage drop across the junction ( V bi - V PN ) increases (because V PN is negative), The hole concentration at the n -side depletion-region edge is smaller than p N because V PN < 0 and exp( q V PN /k B T ) is smaller than 1, Holes in the n -side quasi-neutral region diffuse towards the junction, The electron concentration at the p -side depletion-region edge is smaller than n P because V PN < 0 and exp( q V PN /k B T ) is smaller than 1, Electrons in the p -side quasi-neutral region diffuse towards the junc- tion, ECE 216 Chapter 08 – PN-Junction Diodes Lecture 12.3
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8. REVERSE-BIAS STATIC I D ( V PN ) CHARACTERISTICS The n ( x, V PN ) · p ( x, V PN ) product in the depletion region is smaller than n 2 i , again because exp( qV PN /k B T ) is smaller than 1. In that case, according to the SRH theory, the net recombination rate in the depletion region is negative, i.e., there is a net generation rate of electron-hole pairs in the depletion region, Holes generated in the n -side quasi-neutral region diffuse towards the depletion region where they join holes generated there. These holes are swept by the electric field in the depletion region towards the p -side depletion-region edge. More holes are generated in the p -side quasi-neutral region, and all holes are transported there by drift and diffusion towards the metal contact at x = - W P , and Electrons generated in the p -side quasi-neutral region diffuse towards the depletion region where they join electrons generated there. These electrons are swept by the electric field in the depletion region towards the n -side depletion-region edge. More electrons are generated in the n -side quasi-neutral region, and all electrons are transported there by drift and diffusion towards the metal contact at x = W N .
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