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Semiconductor Band DiagramAtomic organization
Silicon atom
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Covalent linkageEK LevelsL LevelsM Levels(Valence)Conduction levels
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EK BandL BandM Band (Valence)Conduction Band
Band Gap
Band diagram
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Crystalline structure (Crystal cell)Polycrystalline structureAmorphous Silicon
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Free Charge Carriers
EValence BandConduction BandSi
Band Gap (1.12 eV)Energy (E> Band Gap)
Charge carrier generation
electronhole Electron is a free charge carrier Electron has a negative charge
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EValence BandConduction BandSi
Band Gap (1.12 eV)
Holes as charge carriers
electronhole
Electron movementHole movement Hole is a free charge carrier Hole has a positive charge
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EValence BandConduction BandSi
Band Gap (1.12 eV)
Charge carrier recombination
electronhole
Energy
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SummaryBoth electrons (negative charge) and holes (positive charge) are free charge carriers
There is an equilibrium between electrons-hole pairs generated (G) and recombined (R).
This equilibrium between R and G depens on the energy applied to the system (mainly due to temperature)
So, electron concentration (n) = hole concentration (p) = ni (T)
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Free Charge Carriers Movement: Currents
Free charge carriers (Electrons or holes)
Diffusion currentElectrical charge movement => Electric currentCharge carriers movementIf charge carriers are electronsDiffusion currentIf charge carriers are holesDiffusion current
Drift current
ElectronsHoles Electric Field Drift currentDrift current
n = 1350 cm2/V sp = 480 cm2/V sq = 1.6 10-19 Cni = 1.5 1010 cm-3
s = 4.39 10-6 S/cm= 4.39 10-4 S/m
Materials (S/m)
Silver6,30 107Gold5,96 107Copper4,10 107Aluminium3,50 107PET10-21TEFLON10-25 - 10-23
Summary
Since both charge carriers have an electrical charge, they can move when applying an electric field, causing a Drift Current (Ia)
If the concentration of a charge carrier type is high in a determined semiconductor region, the repulsing forces between equal charges produces the diffusion of the charge carriers, causing a Diffusion Current (Id)
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Doping Semiconductors
Doping semiconductors
Si
Intrinsic semiconductorWe have as many holes as electronsn=pnp=ni 2
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Doping semiconductors
Si
P
N- Type semiconductorWe are generating free electrons without generating holes (n>p)+
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Doping semiconductors
Si
Si
BP- Type semiconductorWe are generating holes without generating electrons (n
Resistivity of n-type (red curve) and p-type (blue curve) silicon versus doping density
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