1.  P-N Junction Diodes  How do they work? (postponing the math) Chap. 5.2

2. p-n Junction Diode p-n Junction p-Type Materialn-Type Material

3. p-n Junction Diode  p-n Junction p-Type Material n-Type Material  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

4. p-Type Materialn-Type Material x N D - N A NDND NANA p-n Junction  p-n Junction p-n Junction Diode

5.  In regions far away from the “junction” the band diagram p-n Junction Diode p-Type Material n-Type Material ECEC EVEV EFEF EiEi ECEC EVEV EFEF EiEi

6.  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-n Junction Diode p-Type Material n-Type Material ECEC EVEV EFEF EiEi ECEC EVEV EFEF EiEi

7.  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 n-Type Material p-n Junction Diode ECEC EVEV EFEF EiEi ECEC EVEV EFEF EiEi

8.  Built-in-potential p-n Junction Diode ECEC EVEV EFEF EiEi ECEC EVEV EFEF EiEi - q  V BI p-Type Material n-Type Material x Electrostatic Potential Built-in-potential

9.  Built-in-potential p-n Junction Diode x Electrostatic Potential Built-in-potential x Electric Field  Electric Field

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

11. x Electric Field  Built-in-potential p-n Junction Diode  Charge Density x qN D qN A Charge Density - - - ++ +

12. p-n Junction Diode Energy Potential Electrical Field Charge Density

13. n no x x = 0 p no p po n po log(n), log(p) -eN a eN d M x E ( x ) B - h + p n M As + e – WpWp WnWn V o V(x) x PE(x) x –W p W n 0 eV o x –eV o Hole Potential Energy PE (x) o – E o E0E0  net M n i p-n Junction Principles Electron Potential Energy PE (x) Space charge region M -W p -W n Neutral n-regionNeutral p-region Metallurgical Junction