Lecture 16 - pn junction non-idealities

Lecture 16 - pn junction non-idealities - pn Junction...

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1 pn Junction Diodes: Non-idealities Objective : Understand the physics and models of semiconductor devices including diodes . Questions to be answered : • What is breakdown and why does it happen? • What happens when we have recombination and generation in the depletion region? • What happens when we have high-level injection into the quas neutral regions? EE360 – Lecture 16 quasi-neutral regions? • What happens when we have series resistance in the quasi-neutral regions or the contacts? pn Junction I-V: Review I-V Relationship EE360 – Lecture 16 Reverse Bias Equilibrium Forward Bias
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2 Review: Ideal Diode The “ideal” diode: One-dimensional analysis Steady state conditions Non-degenerate, abrupt junction Low level injection in the quasi- neutral regions E 0 in the quas -neutral regions What happens if these are EE360 – Lecture 16 E 0 in the quasi neutral regions No R-G in the depletion region not true? Review: Ideal Diode Current () = kT qV e I I A 0 t tt i th i h 1 diode ideal the summarize To Exponential increase • Current increases exponentially with V A in forward bias. + = A i D i A N n L D N n L D qA I V I 2 N N 2 P P 0 0 and bias, applied the is current, saturation the is where From Pierret p 250 Constant at – I 0 EE360 – Lecture 16 • Current is small ( I = I 0 ) and approximately constant regardless of V A in reverse bias. I 0 depends on intrinsic carrier concentration, diffusion coefficient, carrier lifetime (though L ), doping, and area.
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3 Non-ideal pn Junction Overview IV Characteristics of a Typical Si Diode Forward bias: ideal diode: e I I kT qV A 0 kT qV I I A + 0 ln ln Reverse bias: Non-ideal behavior is clear when slope is not q/kT EE360 – Lecture 16 ideal diode: 0 I I Non-ideal behavior is clear when the current does not saturate at – I 0 From Pierret, p. 262 Reverse Bias Breakdown • A large reverse bias current begins to flow at some critical voltage IV Characteristics at some critical voltage, V A =- V BR . • Is completely reversible (not inherently destructive), but may excessively heat the EE360 – Lecture 16 excessively heat the device if the current is not limited.
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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 16 - pn junction non-idealities - pn Junction...

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