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Reciprocal capacitance transients? Tim Gfroerer and Peter Simov Davidson College, Davidson, NC with Mark Wanlass National Renewable Energy Lab, CO ~ Supported by the American Chemical Society – Petroleum Research Fund ~. Quick Outline. Review diode capacitance and the DLTS experiment

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Quick Outline

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  1. Reciprocal capacitance transients?Tim Gfroerer and Peter SimovDavidson College, Davidson, NCwith Mark WanlassNational Renewable Energy Lab, CO~ Supported by the American Chemical Society – Petroleum Research Fund ~

  2. Quick Outline • Review diode capacitance and the DLTS experiment • Our measurements and an unusual result • A possible explanation and a nice way to test it …

  3. - - - - - - - - - - + + + + + + + + + + + + + + + + + + + + + + + + + + + + With Bias - - + + Bias-Dependent Depletion P+ N Depletion Layer

  4. Diode Capacitance d1 No bias Vbuilt-in C = DQ/DV ~ eA/d ENERGY d2 Vbuilt-in+Vapplied Reverse bias Reverse bias increases the separation between the layers where free charge is added or taken away.

  5. - - - - - - - - - - - - + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Depletion Layer With Bias Temporary Reduced Bias Depletion Layer With Bias Temporary Reduced Bias Depletion Layer With Bias - - + + Defect characterization via DLTS P+ N

  6. Typical DLTS Measurements

  7. Computer with LabVIEW (5) Digital Scope(Tektronix) (1) Capacitance meter (Boonton) (2) (4) Oxford 77K Temp Controller (3) Pulse Generator Agilent Cryostat with sample Peter Simov (Davidson ’08) DLTS Experiment

  8. Device Structure and Band Diagram {

  9. Exponential transient analysis

  10. Reciprocal Analysis

  11. Conclusions • Capacitance transients are non-exponential and rates are incompatible with conventional thermal activation analysis • The reciprocal of the capacitance varies linearly with time, and the slope yields a single thermal activation energy of 0.38eV. Future Work • Thermally-activated reciprocal behavior is a characteristic of hopping transport. • Test dependence on transport distance by varying magnitude of bias pulse.

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