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P-N Junction Effects and Other Detectors

P-N Junction Effects and Other Detectors. S W McKnight and C A DiMarzio. P-N Junction. -. +. E. electrons. “holes”. E f. N a =density of acceptors (m -3 ). N d =density of donors (m -3 ). x. P-N Junction. E. +. -. electrons. E f. “holes”. x. Depletion Region. Abrupt Junction.

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P-N Junction Effects and Other Detectors

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  1. P-N Junction Effects and Other Detectors S W McKnight and C A DiMarzio

  2. P-N Junction - + E electrons “holes” Ef Na=density of acceptors (m-3) Nd=density of donors (m-3) x

  3. P-N Junction E + - electrons Ef “holes” x Depletion Region

  4. Abrupt Junction ρ P-side N-side qNd -xop xon x -qNa Charge conservation → q Na xop = q Nd xon

  5. Electric Field Calculation Poisson’s Equation: 1D Junction:

  6. Abrupt Junction P-side N-side -xop xon x

  7. P-N Junction E Junction “built-in” voltage Vo Ec Ef Ev w -xpo xno 0 x

  8. Built-in Voltage and Electric Field

  9. Drift and Diffusion Currents Hole Drift Current: Hole Diffusion Current: Diffusion Constant:

  10. Built-in Voltage from Current Balance Equilibrium condition: Jp (drift) + Jp (diffusion) = 0

  11. Built-in Voltage from Current Balance Electric field and Voltage:

  12. Built-in Voltage from Current Balance Since: pp≈ Na; nn ≈ Nd

  13. Depletion Region Width

  14. Junction Capacitance 1. Reverse bias: Q = depletion charge (ionized donors and acceptors) 2. Forward bias: Q = diffusion charge storage

  15. Reverse Bias Junction Capacitance A=junction cross-section area

  16. Junction Capacitance

  17. Thermal Detectors Incident Radiation Absorbing film Temperature Sensitive Device Electric leads/ Heat sinks

  18. Thermal Detectors • Thermocouple/Thermopile Detectors • Semiconductor Bolometers • Golay Cells • Pyroelectric detectors

  19. Thermopile Detectors Incident Radiation Absorbing film Electric leads/ Heat sinks Bi Sb (Thermocouples in series)

  20. Golay Cell Deformable membrane Detector Incident radiation Gas Light Source Mirror Absorber

  21. Pyroelectric Detector P(T) = Polarization + - - + + - + - + - A

  22. Ferroelectric Materials P Pr Ea

  23. Ferroelectric Domains Poled P=Pr Unpoled P=0

  24. Temperature Dependence of Ferroelectric Effect Tc = Ferroelectric Curie Temperature

  25. Pyroelectric Detectors Pyroelectric coefficent: Pyroelectric detector current: Ad = detector area = temperature rate of change

  26. Pyroelectric Materials

  27. Pyroelectric Detectors • Room temperature operation • Good frequency response • Low sensitivity

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