course230B2

course230B2 - P-N Junctions/Diodes p n I V log I I slope =...

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P-N Junctions/Diodes p n I V g log I lope = 60 mV/decade I slope = 60 mV/decade V V
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Static Properties (a) c E E i E f c E E i E f E v n-type p-type E v c E (b) q ψ bi E v E i E f c E E v E i E f 0 = + = dx dn q kT n q J n n E μ o net current dx d = i E dE dx f = 0 No net current flow at thermal equilibrium: nn e n e i E E kT i q fi i f = = ( )/ ( )/ ψψ
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Built-in Potential • Fermi level E f is spatially constant (flat), causing a built-in potential difference across the diode. Built-in potential: p = = = 0 0 2 ln ln ln n p d a bi n kT p kT N N kT q ψ p p = (majority) hole density on p-side N a 0 0 p n i n p n p n = (minority) hole density on n-side n n = (majority) electron density on n-side N d n = (minority) electron density on p-side p
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Forward Bias c E E n-type p-type c E E f (a) E v i E f E v E i (b) q ψ bi c E E v E i E f c E E E f 0.08 E v i c E c E 0.06 nt (mA) (c) E v E f E v E f qV app 0.02 0.04 Diode curre n V app -0.5 0 0.5 1 0 Applied voltage (V)
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Abrupt Junctions: Depletion Approx. Quasi-neutral p-region n-region Depletion region x x - x ρ ( x ) qN d −= d dx qN id si 2 2 ψ ε dq N ia 2 for 0 x x n r - 0 n p a -qN E i d n ap d qN x qN x = = = − dx si 2 for x p x 0 x E ( x ) -E - x p x n 0 m x si si dx = 0 ) ( d m p n m m W x x E E = + = m p ψ ( x ) - (- x ) i i W NN qN N d si a d m a d = + 2 εψ () 2 2 x m x n - x p 0 m bi app V = ±
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One-Sided n + -p Diode Quasi-neutral n-region p-region Depletion region ρ ( x ) qN d -x x p 0 x n a -qN Charge neutrality: N d x n = N a x p , if N d >> N a x p >> x n , e depletion layer and v ltage drop primarily appear i.e., depletion layer and voltage drop primarily appear on the lightly doped side.
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One-Sided n + -p Diode Built-in potential: .05 + i a g bi n N kT E q ln 2 ψ 0.95 1.00 1.05 (V) 0.85 0.90 in potential 0.75 0.80 Built- i 1E+14 1E+15 1E+16 1E+17 1E+18 0.70 Doping concentration (cm 3 ) Built-in potential a weak function of doping conc.
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One-Sided n + -p Diode Depletion-layer width: p p n a app bi si d x x x qN V W + = ± = ) ( 2 ψ ε Depletion-layer capacitance: C d dQ d / dV app = si / W d 10 /μm2) 11 citance (fF / width (μm ) C d 0.1 -layer capa c etion-layer 1E+14 1E+15 1E+16 1E+17 1E+18 0.01 Depletion - Depl e W d Doping concentration (cm ) -3
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Quasi-Fermi Potentials φ n and p c E E f (a) -q n c E E f qV >0 app φψ ni kT n ≡− ln E v p E v x n -x p c E i q n pi i q p n ≡+ <0 (b) n p c E E f E v E f Nonequilibrium near the nction n 2 n-type p-type E v x n p [ ] pn n q ip n =− 2 exp ( ) / φφ junction, pn n i . Jq n d dx qn dn d nn i n n μ ψ p d qp dp d pp i p p +
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Spatial Variations of φ n and p c E E f (a) -q n - c E E E f qV >0 app V app = p − φ n at junction boundaries.
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This note was uploaded on 10/09/2010 for the course ECE 230 at UCSD.

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course230B2 - P-N Junctions/Diodes p n I V log I I slope =...

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