Lecture9-P-N+Junction+2

Lecture9-P-N+Junction+2 - ECE 3040 Dr Ying Zhang Georgia...

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Unformatted text preview: ECE 3040 - Dr. Ying Zhang Georgia Tech ECE 3040: Microelectronic Circuits Lecture 9 Reading: Pierret 5.6, 6.1 ECE 3040 - Dr. Ying Zhang Georgia Tech Recapture pn Junction Under Equilibrium ECE 3040 - Dr. Ying Zhang Georgia Tech Recapture Built-In Potential ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ − = ) ( ) ( ln p n bi x n x n q kT V ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ = 2 ln i D A bi n N N q kT V non-degenerate case n(x n )=N D n(-x p )=n i 2 /N A ECE 3040 - Dr. Ying Zhang Georgia Tech Recapture ( ) ( ) ⎪ ⎪ ⎪ ⎩ ⎪ ⎪ ⎪ ⎨ ⎧ ≥ − ≤ ≤ ≤ − − ≤ ≤ − + − = ⎪ ⎩ ⎪ ⎨ ⎧ ≥ − ≤ ≤ ≤ ≤ ≤ − − = n p n n o S D p p o S A n p n D p A x x and x x for x x for x x K qN x x for x x K qN E x x and x x for x x for qN x x for qN ε ε ρ Quantitative electrostatic relationship with the depletion approximation: Since E (x=0- )= E (x=0 + ) N A x p =N D x n ECE 3040 - Dr. Ying Zhang Georgia Tech Recapture Quantitative electrostatic relationship with the depletion approximation: ( ) ( ) ⎪ ⎪ ⎪ ⎩ ⎪ ⎪ ⎪ ⎨ ⎧ ≥ − ≤ ≤ ≤ − − ≤ ≤ − + = n p n n o S D bi p p o S A x x and x x for x x for x x K qN V x x for x x K qN x V 2 2 ) ( 2 2 ε ε ( ) ( ) ( ) bi D A D A o S n p bi D A A D o S p bi D A D A o S n V N N N N q K x x W V N N N N q K x and V N N N N q K x + = + = + = + = ε ε ε 2 2 2 ECE 3040 - Dr. Ying Zhang Georgia Tech ¡ pn Junction with Applied Voltage ¡ pn Junction I-V Characterstics Agenda ECE 3040 - Dr. Ying Zhang Georgia Tech Depletion Region Approximation: Step Junction Solution V bi V bi |V A | V bi |V A | V bi V A =0 : No Bias V A <0 : Reverse Bias V A >0 : Forward Bias ECE 3040 - Dr. Ying Zhang Georgia Tech Depletion Region Approximation: Step Junction Solution ( ) ( ) ( ) ( ) ( ) ( ) A bi D A D A o S n p A bi D A A D o S p A bi D A D A o S n V V N N N N q K x x W V V N N N N q K x and V V N N N N q K x − + = + = − + = − + = ε ε ε 2 2 2 Thus, only the boundary conditions change resulting in direct replacement of V bi with (V bi -V A ) ECE 3040 - Dr. Ying Zhang Georgia Tech Step Junction Solution: What does it mean? Consider a p + -n junction (heavily doped p-side, normal or lightly doped n side). ECE 3040 - Dr. Ying Zhang Georgia Tech Step Junction Solution: What does it mean? E fp -E fn =-qV A Fermi-level only applies to equilibrium (no current flowing) Majority carrier Quasi-fermi levels ECE 3040 - Dr. Ying Zhang Georgia Tech P-n Junction I-V Characteristics Electron Diffusion Current Electron Drift Current Hole Diffusion Current Hole Drift Current In Equilibrium, the Total current balances due to the sum of the individual components ECE 3040 - Dr. Ying ZhangECE 3040 - Dr....
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This note was uploaded on 09/05/2009 for the course ECE 3040 taught by Professor Hamblen during the Spring '07 term at Georgia Tech.

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Lecture9-P-N+Junction+2 - ECE 3040 Dr Ying Zhang Georgia...

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