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

2. P-N Junction EfEf electrons “holes” E x +- N a =density of acceptors (m -3 ) N d =density of donors (m -3 )

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

4. Abrupt Junction x ρ -qN a qN d P-sideN-side -x op x on Charge conservation → q N a x op = q N d x on

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

6. Abrupt Junction x P-sideN-side -x op x on

7. P-N Junction EfEf E x EvEv EcEc Junction “built-in” voltage VoVo -x po x no 0 w

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 Jp (drift) + Jp (diffusion) = 0 Equilibrium condition:

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

12. Built-in Voltage from Current Balance Since: p p ≈ N a ; n n ≈ N d

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 Absorbing film Temperature Sensitive Device Electric leads/ Heat sinks Incident Radiation

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

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

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

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

22. Ferroelectric Materials P EaEa PrPr

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

24. Temperature Dependence of Ferroelectric Effect T c = Ferroelectric Curie Temperature

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

26. Pyroelectric Materials MaterialPyroelectric Coefficient BaTiO 3 2 x 10 -8 C cm -2 K -1 Triglycine Sulfate (TGS)2-3.5 x 10 -8 LiNbO 3 4 x 10 -9 LiTaO 3 6 x 10 -9 SrBaNbO 3 1 x 10 -7

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