 P-N Junction Diodes  How do they work? (postponing the math)

 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 p-Type Material n-Type Material • p-n Junction p-Type Material n-Type Material p-n Junction • 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 p-Type Material n-Type Material • p-n Junction ND - NA ND x NA p-n Junction

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

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

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

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

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

p-n Junction Diode • Built-in-potential Electric Field x • Charge Density Charge Density qND + + + x - - - qNA

p-n Junction Diode Energy Potential Electrical Field Charge Density

p n + - As B + h – e M M Metallurgical Junction ( ) E x Neutral p-region E0 Neutral n-region -Wp -Wn 0 x – E o V ( x ) M V Space charge region o Wp Wn l o g ( n ) , l o g ( p ) p p o x n n o P E ( x ) n i e V o p Hole Potential Energy PE (x) o n o n p o x x = 0 r x n e t M Electron Potential Energy PE (x) e N d – W – e V p o x p-n Junction Principles W n - e N a

 P-N Junction Diodes  How do they work? (postponing the math)