ECE 875: Electronic Devices

1. ECE 875:Electronic Devices Prof. Virginia Ayres Electrical & Computer Engineering Michigan State University ayresv@msu.edu

2. Lecture 22, 28 Feb 14 • Chp. 02: pn junction and Chp 03: metal-semiconductor junction • About HW06 problems VM Ayres, ECE875, S14

3. Pr. 2.04: Assume: Si at 300 K

4. Remember this sequence in real research: find: • Charge Q and charge density r • Electric field E • Potential y • Energy barrier q y from y • Depletion region WD or equivalent local region from y • C-V to find concentration and ybi • I-V to find concentration and energy barrier MODEL MODEL EXPERIMENT

5. Pr. 2.04: • Charge Q and charge density r • Electric field E • Potential y • Energy barrier q y from y • Depletion region WD or equivalent local region from y • C-V to find concentration and ybi • I-V to find concentration and energy barrier MODEL

6. : r01 = qND01 = a constant (C/cm3) : r02 = qND02 = another constant (C/cm3) VM Ayres, ECE875, S14

7. VM Ayres, ECE875, S14

8. What are the two places that you know any E info for? Answer:E02 (x = WDn) = 0E 01 (x = 0.2 mm) = Em-02 VM Ayres, ECE875, S14

9. Solve for Emax-02 VM Ayres, ECE875, S14

10. Solve for Emax-01 Emax-01 is in terms of WDn because Emax-02 is in terms of WDn . So need to find WDm (= Wm). VM Ayres, ECE875, S14

11. Pr. 2.04: • Charge Q and charge density r • Electric field E • Potential y • Energy barrier q y from y • Depletion region WD or equivalent local region from y • C-V to find concentration and ybi • I-V to find concentration and energy barrier MODEL

12. Find ybi (= potential V). Easiest way is graphically: VM Ayres, ECE875, S14

13. Find ybi (= potential V). Easiest way is graphically: VM Ayres, ECE875, S14

14. Find ybi (= potential V). Easiest way is graphically: Now have an expression for ybi in terms of WDn. If you had a value for ybi on the LHS, you could use the expression to solve for WDn. VM Ayres, ECE875, S14

15. Find value of ybi: VM Ayres, ECE875, S14

16. Find value of ybi: qy1-2: + = VM Ayres, ECE875, S14

17. Find value of ybi: qy2-3: = VM Ayres, ECE875, S14

18. Find value of ybi: qy1-2 - qy2-3 = qybi = VM Ayres, ECE875, S14

19. Put in value for ybi and solve for WDn: Now have an expression for ybi in terms of WDn. If you had a value for ybi on the LHS, you could use the expression to solve for WDn. VM Ayres, ECE875, S14

20. Put in value for WDn and solve for Emax-01 Solve for Emax-01 Emax-01 is in terms of WDn because Emax-02 is in terms of WDn . So need to find WDm (= Wm). VM Ayres, ECE875, S14

21. Pr. 3.01: Draw band-diagrams with the following values marked on it: Barrier height on metal side: qfBn0 = 0.8 eV = given Barrier height on semiconductor side: qybi Barrier width W: primarily on n-side: WDn

24. Pr. 3.08:

28. W-Si example:

30. = 2.76 x 1019 cm-3 Too high

32. Too low

33. Pr. 3.08: Use: X 1/1010