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UNIT-I_PN_junction.pptx
- 1. ANIL PRASAD DADI/ECE/ANITS ANIL NEERUKONDA INSTITUTE OF TECHNOLOGY & SCIENCES(A) Department of Electronics and Communication Engineering ECE 125 Basic Electronics Engineering Academic year : 2022-23 Class & Section : 1/4 ECE-A Name of the Faculty : Mr.D.Anil Prasad
- 2. UNIT-I(Semiconductor Diodes) • Fermi level in Intrinsic & Extrinsic semiconductors. Mass-Action law. Mobility and conductivity, Hall effect, Generation and recombination of charges, Drift and diffusion current, Band structure of open-circuit p-n junction, V-I characteristics, transition and diffusion capacitance, reverse recovery time, Avalanche and zener breakdown, zener diodes, Light Emitting Diodes. ANIL PRASAD DADI/ECE/ANITS
- 3. Energy bands and Fermi level ANIL PRASAD DADI/ECE/ANITS
- 4. Energy bands and Fermi level ANIL PRASAD DADI/ECE/ANITS Slope of CB ,VB or intrinsic fermi level represents electric field . Electric field is directed in positive slope direction of CB or VB or intrinsic fermi level.
- 5. PN junction • Most semiconductor devices contain at least one junction between p-type and n-type semiconductor regions. Semiconductor device characteristics and operation are connected to these PN junction • Applications of semiconductor devices – Rectification – Switching – Amplification ANIL PRASAD DADI/ECE/ANITS
- 6. PN junction in thermal equilibrium • Before PN junction is formed n-region has a large concentration of electron and few holes. P-region has a large concentration of holes and few electrons ANIL PRASAD DADI/ECE/ANITS
- 7. PN junction in thermal equilibrium • After joining the two regions diffusion of charge carriers takes place at the junction because of large concentration gradient. • Due to concentration gradient holes diffuse from p-side into n-side and electrons diffuse from n-side into p-side ANIL PRASAD DADI/ECE/ANITS • Holes leaving the p-region leave behind uncompensated acceptor ions in the p- region and Electrons diffusing from n- side to p-side leave behind uncompensated donar ions in the n- region as shown in fig.
- 8. PN junction in thermal equilibrium • Positive space charge near n-side of junction and negative space charge near p-side of junction is formed shown in fig. • The resulting diffusion current cannot build up indefinitely. Because of the development of space charge an internal Electric field is created at junction ANIL PRASAD DADI/ECE/ANITS • Positive space charge near n-side of junction and negative space charge near p-side of junction is formed shown in fig. • The resulting diffusion current cannot build up indefinitely. Because of the development of space charge an internal Electric field is created at junction
- 9. PN junction in thermal equilibrium • Electric field creates drift component of current from n to p opposing diffusing current. • Since No net current can flow across the junction at equilibrium the current due to drift of carriers in the electric field must exactly cancel the diffusion current. ANIL PRASAD DADI/ECE/ANITS
- 10. PN junction in thermal equilibrium In an open circuited device the drift hole(electron) current must be equal and opposite to the diffusion hole (electron) current so that the net hole(electron) current is zero. ANIL PRASAD DADI/ECE/ANITS
- 11. Depletion width and charge density Under equilibrium • The amount of uncovered negative charge on the left hand side of the junction must be equal to the amount of positive charge on the right hand side of the metalurgical junction. Overall space-charge neutrality condition; • The higher doped side of the junction has the narrower depletion width A p D n N x N x 𝑊 = 𝑥𝑝 + 𝑥𝑛 ANIL PRASAD DADI/ECE/ANITS
- 12. Electric field and Built-in-potential ANIL PRASAD DADI/ECE/ANITS
- 13. Contd… • Electric field The built-in potential is given by area enclosed by the electric field curve i.e by Guass law 𝑉𝑏𝑖 = 1 2 𝐸𝑚(𝑥𝑝 + 𝑥𝑛) 𝑥𝑝 𝑥𝑛 = 𝑁𝑑 𝑁𝑎 𝐸𝑚 𝑥𝑛 = 𝑞𝑁𝑑 𝜀 𝑉𝑏𝑖 = 1 2 𝐸𝑚 𝑁𝑑 𝑁𝑎 + 1 𝑥𝑛 area = 𝑉𝑏𝑖 ANIL PRASAD DADI/ECE/ANITS
- 14. Contd… 𝑉𝑏𝑖 = 1 2 𝜀𝐸𝑚 2 𝑞𝑁𝑑 𝑁𝑑 𝑁𝑎 + 1 𝑉𝑏𝑖 = 1 2 𝐸𝑚 𝑁𝑑 𝑁𝑎 + 1 𝜀𝐸𝑚 𝑞𝑁𝑑 𝑉𝑏𝑖 = 1 2 𝜀𝐸𝑚 2 𝑞 1 𝑁𝑎 + 1 𝑁𝑑 𝐸𝑚 = 2𝑞𝑉𝑏𝑖 𝜀 1 𝑁𝑎 + 1 𝑁𝑑 ANIL PRASAD DADI/ECE/ANITS
- 15. Contd… • Width of depletion region(Wd) The built-in potential is given by area enclosed by the electric field curve i.e 𝑉𝑏𝑖 = 1 2 𝐸𝑚(𝑥𝑝 + 𝑥𝑛) 𝑉𝑏𝑖 = 1 2 𝐸𝑚𝑊𝑑 𝑊𝑑 = 2 𝑉𝑏𝑖 𝐸𝑚 𝑊𝑑 = 2𝜀𝑉𝑏𝑖 𝑞 1 𝑁𝑎 + 1 𝑁𝑑 𝑥𝑛 = 1 𝑁𝑑 2𝜀𝑉𝑏𝑖𝑁𝑎𝑁𝑑 𝑞(𝑁𝑎 + 𝑁𝑑) ANIL PRASAD DADI/ECE/ANITS
- 16. Energy level diagram for the Built-in voltage ANIL PRASAD DADI/ECE/ANITS
- 17. Built-in Potential(Vbi) 𝑉𝑏𝑖 = 𝑉 𝑝 + 𝑉 𝑛 𝑛0 = 𝑁𝑐 exp −(𝐸𝑐 − 𝐸𝐹) 𝐾𝑇 𝑛0 = 𝑛𝑖 exp (𝐸𝐹 − 𝐸𝑖) 𝐾𝑇 𝑞𝑉 𝑛 = 𝐸𝐹 − 𝐸𝑖 𝑛0 = 𝑛𝑖 exp (𝑞𝑉 𝑛) 𝐾𝑇 𝑉 𝑛 = 𝐾𝑇 𝑞 ln 𝑛0 𝑛𝑖 𝑉 𝑛 = 𝐾𝑇 𝑞 ln 𝑁𝐷 𝑛𝑖 𝑝0 = 𝑁𝑣 exp −(𝐸𝐹 − 𝐸𝑉) 𝐾𝑇 𝑝0 = 𝑛𝑖 exp (𝐸𝑖 − 𝐸𝐹) 𝐾𝑇 𝑞𝑉 𝑝 = 𝐸𝑖 − 𝐸𝐹 𝑝0 = 𝑛𝑖 exp (𝑞𝑉 𝑝) 𝐾𝑇 𝑉 𝑝 = 𝐾𝑇 𝑞 ln 𝑝0 𝑛𝑖 𝑉 𝑝 = 𝐾𝑇 𝑞 ln 𝑁𝐴 𝑛𝑖 ANIL PRASAD DADI/ECE/ANITS
- 18. Built-in Potential(Vbi) 𝑉𝑏𝑖 = 𝑉 𝑝 + 𝑉 𝑛 𝑉𝑏𝑖 = 𝐾𝑇 𝑞 ln 𝑁𝐴𝑁𝐷 𝑛𝑖 2 𝑉𝑏𝑖 = 𝐾𝑇 𝑞 ln 𝑁𝐴 𝑛𝑖 + 𝐾𝑇 𝑞 ln 𝑁𝐷 𝑛𝑖 ANIL PRASAD DADI/ECE/ANITS 𝑉𝑏𝑖 = 𝑉𝑇 ln 𝑁𝐴𝑁𝐷 𝑛𝑖 2
- 19. Forward bias(VD>0) ANIL PRASAD DADI/ECE/ANITS
- 20. Reverse bias(VD<0) ANIL PRASAD DADI/ECE/ANITS
- 21. Applying bias to pn junction ANIL PRASAD DADI/ECE/ANITS
- 22. Abrupt PN Junction heavily doped p-type ANIL PRASAD DADI/ECE/ANITS
- 23. The experimental I-V characteristic of a Si diode ANIL PRASAD DADI/ECE/ANITS 𝐼 = 𝐼0 𝑒𝑉/𝑉𝑇 − 1
- 24. References ANIL PRASAD DADI/ECE/ANITS • Robert L Boylestad, Electronic Devices And Circuit Theory, Prentice Hall, seventh edition,2021 • Jacob Millman and Christos Halkias, Electronics Devices and Circuits, Black edition, October,2017