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PVMD
Delft University of Technology
PVMD Miro Zeman Delft University of Technology Learning objectives - - PowerPoint PPT Presentation
PVMD Miro Zeman Delft University of Technology Learning objectives - - PowerPoint PPT Presentation
Band Diagram of a P-N Junction PVMD Miro Zeman Delft University of Technology Learning objectives What does the band diagram of P-N junction at thermal equilibrium look like ? How thick is the depletion region? Band diagram of isolated
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Band diagram of isolated Si materials
n = nn0 ≈ ND p = pn0 ≈ n2
i/ND
n-type EF EV EC
p = pp0 ≈ NA n = np0 ≈ n2
i/NA
p-type EF EC EV
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Forming the band diagram
EF EC EV EF EV EC n-type p-type
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Forming the band diagram
EF EC EV EF EV EC n-type p-type diffusion
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Forming the band diagram
EF EC EV EC EV EF diffusion drift n-type p-type
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Thermal equilibrium
Potential energy of water level ~ Fermi level
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Band diagram
diffusion drift
Quasi-neutral region Quasi-neutral region Depletion region
EC EV EC EV EF n-type p-type
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Built-in voltage
EF
qVbi
EG EFn EFp
EC EV n-type p-type Built-in voltage Vbi
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Charge density in the depletion region
qND
ρ
x qNA ln lp n-type p-type x=0 n-type: p-type:
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Electric field in the depletion region
Poisson’s equation:
ψ: electrostatic potential ξ: the electric field ϵr: relative permittivity ϵ0: the permittivity of free space
Electric field :
ξmax ξ ln lp x n-type p-type
x=0
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Potential across the depletion region
ψ
Vbi x n-type p-type ln lp x=0
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Thickness of the depletion region
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