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Lecture 7: Electrostatics and IV Characteristics of P-N DiodeECE5590: Nanoscale Devices and circuits
Mostafizur [email protected]
• R-G, Drift, Diffusion• Continuity Equation• P-N Junction
Recap
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Outline
• P-N Junctions• Drawing Band Diagram• Solution in Equilibrium• Non-Equilibrium Conditions (I-V)• Summary
ECE5590 Fall 2015 MR
ECE5590 Fall 2015 MR 8
Time < 0
P-type piece N-type piece
Time < 0: Pieces separated
At time = 0, slam the two pieces together
ECE 663
At time = 0, slam the two pieces together
Hole gradient
Jp, diffusion = -qDp dp/dx = current right, holes right
Electron gradient
Jn,diffusion = -qDn dn/dx = current right, electrons right
Gradients drive diffusion
left
ECE5590 Fall 2015 MR 17
Electric Field is Discontinuous for Heterojunction
How wide is the depletion region?
ECE 663
Depletion Approximation-step junction
x
ECE5590 Fall 2015 MR 29
Depletion Width
• Would current flow? Diffusion/Drift?
ECE 663
I-V Curve for Ideal Diode
qkT
V
eII VVA
0
/0 )1( 0
ECE 663
Ideal P-N Junction Diode
Assumptions:
• Steady-State conditions• Non-degenerate doping• One-dimensional• Low Level Injection• Only drift, diffusion,thermal R-G (no photons)
ECE5590 Fall 2015 MR 41
Summary
• P-N diodes are simplest semiconductor devices
• Operation lies in fundamental of physics• Useful for various applications