Chapter32_PN-IV

# Chapter32_PN-IV - 3.2 PN Junction I-V Characteristic 3.2.1...

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3.2 PN Junction: I-V Characteristic 3.2.1 Qualitative Derivation 3.2.2 Quantitative Derivation Minority Carrier Distribution Minority Carrier Currents I-V Characteristic Saturation Current 3.2.3 Junction Breakdown Avalanche Breakdown Zener Breakdown Pierret, Chapter 6.1, page 235-259 Slides courtesy of Prof. Oliver Brand

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2 3.2.1 Qualitative Derivation (a) Equilibrium Under equilibrium, the net current flow is zero , i.e. the electron/hole drift and diffusion currents balance each other Electron Currents: Majority carrier diffusion current from n- to p-side Minority carrier drift current from p- to n-side Hole Currents: Majority carrier diffusion current from p- to n-side Minority carrier drift current from n- to p-side J = J drift + J diff = 0 Pierret, Fig. 6.1
3 Qualitative Derivation (b) Forward Bias Forward bias (V A > 0) reduces the potential drop across the depletion region As a result, the majority carrier (electron and hole) diffusion over the potential hill increases exponentially, resulting in a net current flow across the junction The minority carrier drift currents remain constant Pierret, Fig. 6.1 Majority carrier density decreases exponentially with increasing energy E n(E) p(E)

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4 Qualitative Derivation (c) Reverse Bias Reverse bias (V A < 0) increases the potential drop across the depletion region As a result, the majority carrier (electron and hole) diffusion current over the potential hill is suppressed for –V A > few kT The minority carrier drift currents remain constant, thus resulting in a saturation current flowing in reverse direction Pierret, Fig. 6.1
5 3.2.2 Quantitative Derivation – Solution Strategy – 1. Calculate the minority carrier concentration in the quasineutral regions on the p- and n-side of the junction by solving the continuity equation 2. Calculate the minority carrier current densities at the edges of the depletion region x = x n and x = -x p 3. Calculate the total current density flowing through the diode by adding the hole and electron minority carrier density, assuming no generation/ recombination effects in the depletion region

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Chapter32_PN-IV - 3.2 PN Junction I-V Characteristic 3.2.1...

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