1 / 30

Types of Semiconductor Detectors

Types of Semiconductor Detectors. S W McKnight and C A DiMarzio. Outline. Bolometers Photoconductive detectors Photovoltaic detectors. Bolometers. Incident Radiation. Absorbing film. Semiconductor Bolometer. Electric leads/ Heat sinks. Cryogenically cooled ~ 4.2 K.

pisces
Download Presentation

Types of Semiconductor Detectors

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Types of Semiconductor Detectors S W McKnight and C A DiMarzio

  2. Outline • Bolometers • Photoconductive detectors • Photovoltaic detectors

  3. Bolometers Incident Radiation Absorbing film Semiconductor Bolometer Electric leads/ Heat sinks Cryogenically cooled ~ 4.2 K

  4. Semiconductor Bolometer E k Ef Eb Impurity level Binding Energy (Eb) ~ 50 meV

  5. Effect of ΔT on Si Bolometer Conductivity Ambient temperature = 4.2K → kT=0.362 meV Temperature = 4.3K → kT=0.371 meV

  6. Photoconductive Detectors E k Eg

  7. Conductivity Conductivity: σ = n e μ e=electron charge (1.6x10-19 C) =Electron scattering time (average time between scattering events) Mobility:

  8. Photoconductivity Dark current: σd = no e μn + po e μp Photocurrent: σph = Δn e μn + Δp e μp Δn =Δp = photo-induced carrier density (m-3) = Nphη / V Nph = incident photon flux (s-1) η = quantum efficiency = carrier recombination time V = sample volume

  9. Photoconductivity Recombination in n-type material: Steady-state solution: Quantum efficiency: η = (1-R) Pe-h Pe-h = probability of absorption creating electron-hole pair

  10. Photoconductors

  11. HgxCd1-xTe Band Gap Eg=-0.302+1.93x+ 5.35x10-4 T(1-2x) -0.810x2 + 0.823x3 Eg= -0.26eV Eg= 1.6eV HgTe “Zero-gap” (inverted bands) CdTe

  12. Photovoltaic Detectors • P-N junction detector • Incident light creates voltage • Same mechanism as solar cell

  13. P-N Junction E Donor Levels Ef electrons Eg “holes” Ef Acceptor Levels x Doped Semiconductor (p-type) Doped Semiconductor (n-type)

  14. P-N Junction - + E electrons “holes” Ef x

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

  16. P-N Junction E Ec electrons Ef “holes” Ev - + x Depletion Region

  17. P-N Junction Currents Jdiffusion E Jdrift Ec Junction “built-in” voltage Vo Ef Ev - + x Depletion Region

  18. P-N Junction Currents N-doped material: n≈Nd (# of donors)

  19. P-N Junction Currents (No Bias Voltage) Jdrift = A np = -Jo Jdiffusion = B e-Vo/kT JTotal = -Jo + B e-Vo/kT = 0 (equilibrium) → B= Jo e+Vo/kT

  20. Biased P-N Junction Jdiffusion E Jdrift Ec Vo-Va Va Ef Ev Depletion Region Va x

  21. P-N Junction Currents (Bias Voltage=Va) Jdrift = A np = Jo Jdiffusion = B e-(Vo-Va)/kT JTotal = -Jo + B e-(Vo-Va)/kT B= Jo e+Vo/kT → JTotal = Jo (eVa/kT -1 )

  22. 0.09 0.08 0.07 0.06 0.05 Junction Current (Amps) 0.04 0.03 0.02 0.01 0 -0.01 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 V (volts) a P-N Junction Current IJunction Io=A Jo = 0.005 A - + VJunction

  23. Photovoltaic Detection Jdiffusion E Jdrift Ec Junction “built-in” voltage Vo Ef Ev - + Depletion Region x

  24. Photovoltaic Detection • Absorption in depletion region creates electrons/hole pairs • Built in electric field accelerates electrons and holes toward neutral region • Photocurrent adds Iph= ηe Nph to drift current

  25. P-N Junction Photocurrent 0.06 Io=A Jo = 0.005 A 0.04 Iph=A Jph = 0.02 A Junction Current (Amps) 0.02 0 -0.02 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 V (volts) a

  26. Photovoltaic Sensing Circuit + Vph -

  27. Photoconductive Sensing Circuit Iph - + Vd

  28. Photoconductive Detection E Jdrift Ec Vo+ Vd Ev Ef - + Depletion Region x

  29. Avalanche Photodetection E Jdrift Ec Vo+ Vd Ev Ef Depletion Region x

  30. Avalanche Photodiode • Large reverse bias on junction • Photoelectrons create electron/hole pairs in depletion region • Electron and holes can create more electron/hole pairs • Device has gain (like PMT)

More Related