Avalanche Photodiodes from the Start.

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Avalanche Photodiodes from the Start.

• R. Rusack
• The University of Minnesota

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Early History

• Avalanche Photodiodes were invented by R.
  McIntyre at RCA in Canada in the late sixties.
• First considered in HEP at an Isabel meeting.
• Considered at the SDC for the readout of the EM
  shower max detector.
• RCA (? GE ? EGG)
• API
• RMD

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How they work
Electrons generated by the incident light are
multiplied in the high field region at the
junction.
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Why CMS selected APDs
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Nuclear Counter Effect
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APDs with crystals
High side tail suppressed by APD.
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APDs in the CMS detector
PbWO4 crystal
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Light Output from PbWO4
Light out from Bogorodisk PbWO4 crystal.
Output is peaked at 420 nm. 50 photons/MeV from
the
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APDs for CMS

• Manufacturer
• Hamamatsu Photonics, Japan.
• Quantity
• Two APDs per crystal 124,000 APDs with spares.
• Accessibility during operation
• None.
• Radiation levels
• Maximum expected dose 200 kGy and 2 1013
  neutrons/cm2.
• Crystal Light Outout
• 50 photons/MeV on a 4.5 cm2 area.

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Basic APD Structure
Junction
Si2N4 AR coating
5 5 mm2 active area
Groove to minimize surface leakage current.
APD is grown epitaxially on an n wafer.
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APD properties
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APD parameters I
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APD parameters II
Excess Noise Factor v Gain
Capacitance v Bias
Quantum Efficiency
Response uniformity at 420 nm.
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Problems Solved

• Radiation Damage
• Neutron
• Ionizing radiation.
• API effect.
• Quantum efficiency drift.
• Change to epoxy
• Lifetime
• Failure due to poor surface connectivity.
• Electrical Characteristics.
• High Capacitance.

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Irradiation Tests.

• Irradiation with protons
• All irradiation so far has been with an 70 MeV
  protons beam at PSI Switzerland.
• 2 1013 neutrons/cm2 in 1 hour.
• Irradiation with gammas.
• All irradiation with 60C0 source.
• Irradiation with neutrons.
• Setting up a Californium source (252Cf) for
  irradiation at the University of Minnesota.
• 2 1013 neutrons/cm2 in 2 days.

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Device failure
Irradiation in a 70 MeV proton beam.
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Diagnosis
Breakdown at this point when irradiated. High
current at the SiO2-Al interface. Solution
increase spacing of Al deposit.
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Lessons

• To bring a new technology to reality requires
• Time 1987 to 1996.
• Early resources. TNLRC/SSC to show viability.
• To go from a possibility to an established
  technology takes
• Time 1996 to 2001.
• Resources 500k.
• A manufacturer who sees this technology as a
  future money earner and does not expect to
  recover all costs of development from the
  experiment.
• Expect the unexpected.