1. 半導體量測技術 Semiconductor Materials and Device Characterization Topic 6: charge pumping technique and HS experiment Instructor: Dr. Yi-Mu Lee Department of Electronic Engineering National United University

2. Topics: Ch. 6 in D. K. Schroder Charge pumping method (p. 379) Haynes-Shockley experiment (time of flight) Photoelectric effect (time of flight) Introduction to mobility Presentation: 12/29 = 3 students 01/05 = 5 students Final exam: (3:00pm~5:30pm)

3. Charge pumping (CP) method

4. Step-1

5. Step-2

6. Step-3

9. Good for small-size device:

10. Variable base mode:

13. The Haynes-Shockley Experiment (1/2)  1951, Bell Labs  independent measurement of minority carrier mobility (  ) and diffusion coefficient (D)  basic principles -  field applied to semiconductor bar -narrow pulse, high concentration of minority carriers generated -pulse drifts due to (time to drift a fixed distance  mobility

14. Haynes-Shockley Exp. (2/2) Minority Carrier: –generation by laser pulse –diffusion due to nonuniform concentration –drift by E-field –recombination to remove the excess carriers

16. - pulse spreads due to diffusion (  diffusion coefficient) In Fig. 4-18 (n-type material n 0 >> p 0 ) -pulse of holes generated at t=0 - - -pulse of holes drift in direction -pulse monitored at x = L; drift velocity V d is

17. H-S Pulse Spreading  consider diffusion without drift or recombination  Eq (13b) or (4-33b) (p. 418):

18. Note that  the amplitude decreases w/ time  the pulse width increased w/ time

20. pulse width = full width @ 1/e pts.  for a fixed peak height, the pulse width  x can be found where t d is the time corresponding to the pulse spread  x  (21) , or (22)(4-46) (21)(4-45)

21. Example 4-6n-type Ge is used in a Haynes-Schockley experiment. The length of the Ge bar is 1 cm, the probes are spaced 0.95 cm apart.  battery voltage is 2.0 V  td = 0.25 ms  pulse width  t (oscilloscope) = 117  s Find  p and D p (and check agreement w/ the Einstein relations

22. so

23. Homework 6 in D. K. Schroder: 6.4 6.5 6.6 Review: –P. 531~536(Fig. 8.16) –P. 540~551 (mobility) Interesting website: http://jas.eng.buffalo.edu/education/semicon/diffusion /diffusion.html