PN Junction Diodes How do they work postponing

P-N Junction Diodes How do they work? (postponing the math) Chap. 5. 2

p-n Junction Diode p-Type Material n-Type Material p-n Junction

p-n Junction Diode q p-n Junction p-Type Material n-Type Material Ø A p-n junction diode is made by forming a p-type region of material directly next to a n-type region.

p-n Junction Diode q p-n Junction p-Type Material n-Type Material ND - NA ND x NA p-n Junction

p-n Junction Diode q In regions far away from the “junction” the band diagram EC EC EF Ei Ei EF EV EV p-Type Material n-Type Material

p-n Junction Diode q But when the device has no external applied forces, no current can flow. Thus, the Fermi-level must be flat! q We can then fill in the junction region of the band diagram as: EC EC EF Ei Ei EF EV EV p-Type Material n-Type Material

p-n Junction Diode q But when the device has no external applied forces, no current can flow. Thus, the Fermi-level must be flat! q We can then fill in the junction region of the band diagram as: EC EC Ei EF EF Ei EV EV p-Type Material n-Type Material

p-n Junction Diode q Built-in-potential p-Type Material n-Type Material EC - q VBI Ei EF EC EF Ei EV EV Electrostatic Potential Built-in-potential x

p-n Junction Diode q Built-in-potential Electrostatic Potential Built-in-potential q Electric Field x

p-n Junction Diode q Poisson’s Equation Charge Density Electric Field (NOT Resistivity) in 1 -dimension Relative Permittivity of Semiconductor ( r) Permittivity of free space

p-n Junction Diode q Built-in-potential Electric Field x q Charge Density q. ND + - q. NA + x

p-n Junction Diode Energy Potential Electrical Field Charge Density

p n As + Bh+ e– M Metallurgical Junction E 0 Neutral p-region M E (x) Neutral n-region -Wp 0 -Wn x –Eo V (x) M Wp lo g (n ), lo g (p ) Vo Space charge region Wn p po x n no P E (x) ni e. Vo p no npo x x = 0 r ne t Hole o Potential Energy PE (x) x M e. N d Electron Potential Energy PE (x) – Wp x Wn -e N a –e. Vo p-n Junction Principles