1. Design, Development, and Testing of a Transient Capacitance Spectroscopy System Presented by: Kiril Simov Special thanks to: Dr. Tim Gfroerer Department of Physics, Davidson College Project supported by the American Chemical Society - Petroleum Research Fund

2. Pioneers in Measurements of Depth *picture taken from Serway, Raymond A., Beichner, Robert J. and Jewett, John W. Physics for Scientists and Engineers 5th Edition, Saunders College Publishing: Orlandon, FL, 2000 Motivation: Measuring the Depth of Defect –Related Traps in Semiconductors

3. Formation of Depletion Layer (Step 1) + + + ++ + + + + + + + + + - + + + + + + + + + + + + + + + + -- - -- - - - -

4. Formation of Depletion Layer (Step 2) + + + ++ + + + + + + + + + - + + + + + + + ++ + + + + + + - - - - - - - - - Depletion Layer

5. Depletion Layer + Bias + + + ++ + + + + + + + + + - + + + + + + + ++ + + + + + + - - - - - - - - - Depletion Layer Bias Depletion Layer

6. Depletion Layer + Bias in Equilibrium + + + ++ + + + + + + + + + - + + + + + + + ++ + + + + + + - - - - - - - - - Depletion Layer Bias Depletion Layer

7. Energy diagram in the depletion region No bias With bias Energy

8. Carrier Trapping Conductance Band Valence Band Defect Level Trap depth Energy -

9. Carrier Escape kT Low Temperature kT slow fast High Temperature - -

10. What do we measure? Low Temp High Temp time Change in Capacitance

11. Instrument Control Loop Computer w/ LabVIEW Temperature Controller Circuit + Cap. Meter Oscilloscope 1.Set temperature T 2.Wait for T to stabilize 3.Send bias pulse 4.Measure capacitance C 5.Obtain C vs. time graph from scope 6.Next T Cryostat and SAMPLE 1&2 3 4 5

12. LabVIEW Control Panel

13. LabVIEW Diagram

14. Data Analysis Panel

15. Conclusions and Future Work We have developed a versatile Transient Capacitance Spectroscopy (TCS) system using LabVIEW Accurate TCS spectra have been obtained using test diodes We will use the system next summer to characterize new devices in collaboration with the National Renewable Energy Laboratory