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

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Presentation transcript:

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

INTRODUCTION PROPERTIES AND BEHAVIOR OF SEMICONDUCTORS.

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

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

THEORY BASIS FOR OUR EXPERIMENT

ELECTRON-HOLE PAIRS AND RECOMBINATION

DEFECTS IN SOLAR CELLS

DIFFUSION

OUR EXPERIMENT SET-UP AND PROCEDURE

EXPERIMENT 1: SET-UP

EXPERIMENT 1: ANALYSIS

EXPERIMENT 2: SET-UP Pulsed Laser

EXPERIMENT 2: ANALYSIS

RESULTS SUMMARY OF OUR FINDINGS

DATA COMPILATION ~10 15 Exponential BehaviorReciprocal Behavior ~10 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, p.20. Steady State (Exp.1) After Pulse (Exp. 2) G≠0G≠0G=0

MODEL RESULTS Time (10 -8 s) 1x x x10 15 Carrier Density (cm -3 ) Experimental fit Theoretical response x x x x x x x x x x10 16 Steady State After Pulse x x x x x x10 16 traps available traps filled

CONCLUSIONS REFLECTIONS AND DIRECTION OF FUTURE WORK

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?)