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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

• 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)

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

• Minority Carrier:

• generation by laser pulse

• diffusion due to nonuniform concentration

• drift by E-field

• recombination to remove the excess carriers

-pulse spreads due to diffusion ( diffusion coefficient)

In Fig. 4-18 (n-type material n0 >> p0)

-pulse of holes generated at t=0

-

-

-pulse of holes drift indirection

-pulse monitored at x = L; drift velocity Vd is

consider diffusion without drift or recombination

 Eq (13b) or (4-33b) (p. 418):

 the amplitude decreases w/ time

 the pulse width increased w/ time

 for a fixed peak height

, the pulse width x can be found

(21)(4-45)

where td is the time corresponding to the pulse spread x

 (21) 

, or

(22)(4-46)

Example 4-6 n-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 Dp (and check agreement w/ the Einstein relations

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