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Exploring Lifetimes and Diffusion Lengths in Semiconductors: A Study by Ashley Finger and Dr. Tim Gfroerer

This study by Ashley Finger and Dr. Tim Gfroerer from Davidson College investigates the effective lifetimes and diffusion lengths of carriers in semiconductors. The research focuses on the behaviors of n-type and p-type semiconductors and explores the impact of carrier density on recombination processes. Our experiments, including pulsed laser tests, reveal unexpected behaviors at low densities but align with theoretical models at moderate to high densities. Future work will concentrate on quantitative trapping models and low-density carrier behavior.

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Exploring Lifetimes and Diffusion Lengths in Semiconductors: A Study by Ashley Finger and Dr. Tim Gfroerer

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  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. 6th ed. Englewood Cliffs, N.J.: Prentice Hall, 2006. Online Resources. Image 3.4.

  4. Why are they useful? Current Dark n-type p-type Voltage Illuminated

  5. Theory Basis for our experiment

  6. Electron-hole pairs and Recombination

  7. Defects in solar cells

  8. Diffusion • τ is the effective lifetime: the average time before recombination. • L is the effective diffusion length: the average distance before recombination.

  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 Low Excitation High Excitation Note: Models are consistent at intermediate excitation.

  14. results Summary of our findings

  15. Data compilation Exponential Behavior Reciprocal Behavior ~1015 ~1016

  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.

  17. Model Results After Pulse Steady State 1x1016 Theoretical response traps available Carrier Density (cm-3) 1x1015 traps filled Experimental fit 1x1014 2 4 6 8 Time (10-8 s)

  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?)

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