1µ P-N Junction Diodes ¸How do they work?(postponing the math)Chap. 5.2Diode: Why we need to understand diode?• The base emitter junction of the BJT behaves asa forward bias diode in amplifying applications.• The behavior of the diode when reverse bias is the key to the fabrication of the integrated circuits.• The diode is used in many important nonamplifer applications.Chapter-2: Diode circuitsCreating a Diodep-n Junction Diodep-n Junctionp-Type Material n-Type Material2p-n Junction Diode p-n Junctionp-Type Materialp-Type Material n-Type Materialn-Type Material¾ A p-n junction diode is made by forming a p-type region of material directly next to a n-type region.p-n Junction3p-Type Material n-Type MaterialxND -NANDNAp-n Junction p-n Junctionp-n Junction Diode In regions far away from the “junction” the band diagramp-n Junction Diodep-Type Material n-Type MaterialECEVEFEiECEVEFEi But when the device has no external applied forces, no currentcan flow. Thus, the Fermi-level must be flat! We can then fill in the junction region of the band diagram as:p-n Junction Diodep-Type Material n-Type MaterialECEVEFEiECEVEFEi But when the device has no external applied forces, no currentcan flow. Thus, the Fermi-level must be flat! We can then fill in the junction region of the band diagram as:p-Type Materialn-Type Materialp-n Junction DiodeECEVEFEiECEVEFEi4 Built-in-potentialp-n Junction DiodeECEVEFEiECEVEFEi-qxVBIp-Type Materialn-Type MaterialxElectrostatic Potential)(1refCEEqV −=Built-in-potentialBIV Built-in-potentialp-n Junction DiodexElectrostatic Potential)(1refCEEqV −=Built-in-potentialBIVxElectric FielddxdVE −= Electric FieldCharge Density (NOT Resistivity) Poisson’s Equationp-n Junction Diode0ερ⋅−=⋅∇SKE0ερ⋅−=SKdxdEin 1-dimensionElectric FieldPermittivity of free spaceRelative Permittivity of Semiconductor(εr))(ADNNnpq−+−=ρxElectric FielddxdVE −= Built-in-potentialp-n Junction Diode Charge DensityxdxdEKS 0ερ⋅=qNDqNACharge Density---+ ++5p-n Junction DiodeEnergyPotentialElectrical FieldCharge DensitydxdEKS 0ε⋅dxdV−q1−nnoxx =0pnopponpolo g (n ), log(p )-eNaeNdMxE(x)B-h+pnMAs+e–WpWnVoV ( x )xPE(x )x–WpWn0eVox– eVoHole Potential Energy PE (x)o–EoE0ρnetMnip-n Junction PrinciplesElectron Potential Energy PE (x)Space charge regionM-Wp-WnNeutral n-regionNeutral p-regionMetallurgical