1. LIFETIMES AND DIFFUSION LENGTHS A STUDY IN SEMICONDUCTOR PHYSICS Ashley Finger and Dr. Tim Gfroerer Davidson College

2. INTRODUCTION PROPERTIES AND BEHAVIOR OF SEMICONDUCTORS.

3. WHAT ARE SEMICONDUCTORS? University of Colorado at Boulder. “Semiconductor Fundamentals.” Accessed 4 Dec. 2013. ecee.colorado.edu. Streetman, Ben G. Solid State Electronic Devices. 6 th ed. Englewood Cliffs, N.J.: Prentice Hall, 2006. Online Resources. Image 3.4.

4. WHY ARE THEY USEFUL? n-typep-type Voltage Current Dark Illuminated

5. THEORY BASIS FOR OUR EXPERIMENT

6. ELECTRON-HOLE PAIRS AND RECOMBINATION

7. DEFECTS IN SOLAR CELLS

8. DIFFUSION

9. OUR EXPERIMENT SET-UP AND PROCEDURE

10. EXPERIMENT 1: SET-UP

11. EXPERIMENT 1: ANALYSIS

12. EXPERIMENT 2: SET-UP Pulsed Laser

13. EXPERIMENT 2: ANALYSIS

14. RESULTS SUMMARY OF OUR FINDINGS

15. DATA COMPILATION ~10 15 Exponential BehaviorReciprocal Behavior ~10 16

16. RATE EQUATIONS WITH TRAPPING Orton, J.W. and P. Blood. The Electrical Characterization of Semiconductors: Measurement of Minority Carrier Properties. San Diego: Academic Press, 1990. p.20. Steady State (Exp.1) After Pulse (Exp. 2) G≠0G≠0G=0

17. MODEL RESULTS Time (10 -8 s) 1x10 16 1x10 14 1x10 15 Carrier Density (cm -3 ) Experimental fit Theoretical response 2 468 10 21 2x10 13 1.5x10 15 10 22 2x10 14 1.5x10 15 10 23 7x10 15 1.5x10 16 10 24 8x10 16 2x10 16 10 25 3x10 17 2x10 16 Steady State After Pulse 10 23 7x10 15 1.5x10 16 10 24 8x10 16 2x10 16 10 25 3x10 17 2x10 16 traps available traps filled

18. CONCLUSIONS REFLECTIONS AND DIRECTION OF FUTURE WORK

19. CONCLUSIONS At moderate and high carrier densities, the lifetimes and diffusion lengths behave as expected. At low densities, the behavior is unexpected. The difference in the threshold density is due to the nature of the experiment. WHAT NEXT? Quantitative model of trapping. Modelling the low density behavior of carriers (screening?)