1. Chapter 3. PN Junctions and Related Devices

2. Diffusion Currents
Electron
Vacancy

3. Dopant Impurity
Silicon at T = 0K containing a trace concentration of group V impurity atoms. There are no free charges so the crystal is still an insulator.
Silicon at T > 0K, with the group V impurities ionised and free electrons available for conduction

4. Interstitial Diffusion

5. Diffusion

6. Law of the Junction I. pn(xn) = pn0 exp(VA/VT) np(xp) = np0 exp(VA/VT)
Diffusion currents components
Jn = Dn dn/dx 
Jp = -Dp dp/dx
Drift currents components
Jn = q n mn E   and  Jp = q p mp E
Einstein relation

7. Law of the Junction II.
Mass Action Law
Shockley equation for the diode i-v characteristic

8. Summary

9. PN junction

10. Junction Capacitance I

11. Junction Capacitance II

12. Capacitance

13. Model

14. Junction Breakdown

15. Avalanche Breakdown
Avalanche breakdown occurs when a high reverse voltage is applied to a diode and large electric field is created across the depletion region. The effect is dependant on the doping levels in the region of the depletion layer. Minority carriers in the depletion region associated with small leakage currents are accelerated by the field to high enough energies so that they ionise silicon atoms when they collide with them. A new hole-electron pair are created which accelerate in opposite directions causing further collisions and ionisation and avalanche breakdown

16. Zener Breakdown
Zener breakdown occurs with heavily doped junction regions (ie. highly doped regions are better conductors). If a reverse voltage is applied and the depletion region is too narrow for avalanche breakdown (minority carriers cannot reach high enough energies over the distance travelled) the electric field will grow. However, electrons are pulled directly from the valence band on the P side to the conduction band on the N side. This type of breakdown is not destructive if the reverse current is limited

17. PIN Structure