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Infrared Detectors for Astronomical Applications

Infrared Detectors for Astronomical Applications. Mark D rzymala Rafal P iersiak. Infrared Discovery. William Herschel - Astronomer Discovered Infrared Light in 1800. Infrared and the Human Eye. Human Eye can only detect 0.01% of light at 0.75 microns

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Infrared Detectors for Astronomical Applications

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  1. Infrared Detectors for Astronomical Applications Mark Drzymala Rafal Piersiak

  2. Infrared Discovery William Herschel - Astronomer Discovered Infrared Light in 1800

  3. Infrared and the Human Eye • Human Eye can only detect 0.01% of light at 0.75 microns • Infrared spectrum ranges from ~1 to ~1000 microns • Near Infrared • Mid Infrared • Far Infrared

  4. Infrared in Astronomy • Visible spectrum light obstructed by dust and gasses • Near infrared unobscured by dust and gasses, smaller stars visible • Far infrared emitted by dust • Colder than coldest arctic night • Most of the infrared spectrum absorbed by Earth’s atmosphere

  5. How is Infrared Detected • Photovoltaic Effect • Electrons in valence band absorb photon energy and jump to conduction band • Electrons flow from n-type to readout integrated circuit (ROIC) then back into p-type

  6. Detector Materials • Near Infrared (1-5um) • InSb (Indium Antimonide)  1-6.7um • HgCdTe (Mercury Cadmium Telluride)  0.8-25um • Mid Infrared (5-28um) • SiGa (Gallium-doped Silicon) • SiAs (Arsenic-doped Silicon) • Far Infrared (28 – 200um) • Bolometers – photons absorbed and thermalized, change in resistance measured

  7. Primary Characteristics • Low readout noise ≈ 12e- • Very high quantum efficiency ≈ 100% • Extremely low dark current ≈ 0.01e-/s

  8. Read Out Noise • The Design of a readout circuit is very involved! • Low read out noise requires: • Proper mating of the detector and the readout circuit. • Minimal power consumption (few mW’s) Ideal Detector • Readout noise ≈ 12e- Realistic Detector • Readout noise ≈ 15e- ↔ 30e-

  9. Quantum Efficiency • Low readout noise ≈ 12e- • Very high quantum efficiency ≈ 100% • Extremely low dark current ≈ 0.01e-/s Efficiency of converting incident photons into electrons. Ideal Detector • Quantum efficiency ≈ 100% Realistic Detector • Quantum efficiency = 50% - 70%

  10. Dark Current The relatively small electric current that flows through a photosensitive device when no photons are entering the device. Ideal Detector • Dark current ≈ 0.01e-/s Realistic Detector • Dark current ≈ 0.05e-/s

  11. Sensor Implementation 2048x2048 H2RG sensor array Mosaic of 35 H2RG 2048x2048 sensor arrays

  12. Current Research • Extrasolar Planets • Finding Invisible Galaxies • (Formed just after the Big Bang)

  13. Future Astronomical Detectors • High Background Conditions • Cooling to 200 – 230 Kelvin • Switch to InSb detectors (λ = 1 – 5 μm) • Much cheaper, better yield, 100% QE • nBnInAs detectors (λ= 1 – 3.8 μm) • Shows promise for low dark currents!

  14. IR Experiment Typical IR LED 940 - 950nm Cutoff Wavelength 1.11μm

  15. Thank You

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