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Potential diagram of Schottky barrier (n-type material). Metal. Semiconductor. b. CBM. Fermi-level. VBM. Electrostatics of p++ / n junction or n-Schottky barrier. + + + + + + +. r. d 2 V/dx 2 = - r / e = - q N d /e. E. x=0. E = dV/dx = - r / e dx = - q N d x /e. - PowerPoint PPT Presentation
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N. Newman, MSE494/598 Handout #8 page 1
N. Newman, MSE494/598 Handout #8 page 2
N. Newman, MSE494/598 Handout #8 page 3
N. Newman, MSE494/598 Handout #8 page 4
Potential diagram of Schottky barrier (n-type material)
Metal Semiconductor
CBM
VBM
b
Fermi-level
N. Newman, MSE494/598 Handout #8 page 5
N. Newman, MSE494/598 Handout #8 page 6
N. Newman, MSE494/598 Handout #8 page 7
N. Newman, MSE494/598 Handout #8 page 8
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N. Newman, MSE494/598 Handout #8 page 16
Electrostatics of p++ / n junction or n-Schottky barrier
d2V/dx2 = - /q Nd+ + + + + + +
E = dV/dx = - / dx = - q Nd x
V = - q Nd x dx = - q Nd x2 / 2
x=0
-qNdxd/
Ex=xd
-V
N. Newman, MSE494/598 Handout #8 page 17
Transition Capacitance of p++ / n junction
or n-Schottky barrier
Vd - Vapplied = - q Nd xd2 / 2
i.e. xd = (Vapplied-Vd) 2 / q Nd
PARALLEL PLATE CAPACITOR C = A / xd
CT = A [q Nd / 2 (Vapplied - Vd)]1/2
N. Newman, MSE494/598 Handout #8 page 18
1/CT2 = 2 (Vapplied - Vd) / (q Nd A2)
1/CT2
Vapplied
Slope o 1/Ndc
Vd
N. Newman, MSE494/598 Handout #8 page 19
Nd 1 Nd 2
Vapplied
1/CT2
Slope o 1/Nd 1c
Vd
Slope o 1/Nd 2c
Nd 2 >> Nd 1
Can tailor C(V) by the control of the doping profile, for example for a hyperabrupt junction C is proportional to V-2
facilitating = (LC)-1/2 being proportional to a control voltage
1/CT2 = 2 (Vapplied - Vd) / (q Nd A2)
N. Newman, MSE494/598 Handout #8 page 20
Diffusion Capacitance of p++ / n junction
In forward bias, holes are injected into the n-type region.
QD = A q pno Lp (evD/VT - 1) = (Lp
2/Dp) I = I
CD = dQ/dV = dI / dV = I / (n Vt)
N. Newman, MSE494/598 Handout #8 page 21
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NPN Bipolar Junction Transistor (BJT)
N. Newman, MSE494/598 Handout #8 page 30