Chris Maloney

1
Characterization of a Geiger-mode Avalanche
Photodiode

• Chris Maloney
• May 10, 2011

2
Project Objectives

• To extract key parameters that will allow for
  effective and efficient operation of a
  Geiger-mode avalanche photodiode array in a LIDAR
  imaging system

3
Project Goals

• Extract key parameters
• Breakdown voltage
• Diode ideality factor
• Series resistance
• Dark count rate
• Optimal bias for imaging
• Number of traps present
• Type of traps present

4
Applications

• Avalanche photodiodes (APDs) are used for light
  detection and ranging (LIDAR)

Color coded video of a Chevy van produced by
Lincoln Lab LIDAR system
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Applications

• Altimetry
• Measuring rainforest canopy
• Measuring polar icecaps
• Mapping celestial bodies
• Mapping ocean topography
• Autonomous Landing
• Unmanned aircrafts
• Landing on Mars
• Landing on an asteroid

(Image Credit MOLA Science Team and G. Shirah,
NASA GSFC Scientific Visualization Studio.)
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Background

• Lincoln Laboratory at MIT has fabricated a 32x32
  array of Geiger-mode APDs for LIDAR imaging
  applications

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Linear-mode vs. Geiger-mode

• APDs can be operated in linear-mode or
  Geiger-mode
• Geiger-mode provides much more sensitivity
• Linear-mode can produce intensity images

(Image Credit D.F Figer.)
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Project Flowchart
NO
YES
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System Design
CAD camera part
Fabricated camera
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Front View
Without the lens
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Readout board integrated with camera
View inside of camera
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Detector integrated with readout board
32x32 APD array
Readout board and detector are both from MITs
Lincoln Laboratories
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System Design
Complete LIDAR system
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Diode IV Testing

• Shielded Probe Station
• Agilent 4156B Parameter Analyzer
• Noise Floor 1 fA

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Measured Reverse Diode Current vs. Voltage
Breakdown Voltage 28 V
Dark Current 0.1 pA Dark Current Density 1
nA/cm2
All diodes across the wafer are uniform
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Measured Forward Diode Current vs. Voltage
Series resistance 2 kO
n 1.0
No R/G region
No R/G region implies number of traps are minimal
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Gate Width Definition

• The amount of time the detector is ready to
  detect a photon

h?
Gate Width
Timing Gate
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Measured Dark Count Rate vs. Gate Width
Dark count rate should be constant
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Dead Pixels
Upper right corner is unresponsive due to low
yielding bump-bonds
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Measured Dark Count Rate vs. Gate Width 9 by 8
array
Dark count rate is constant and no longer
decreasing
21
Measured Dark Count Rate vs. Bias
Add 5V to x-axis to account for cathode voltage
Breakdown voltage is higher than breakdown
extracted from IV curve
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Afterpulsing Theory

• Detector is armed and a laser pulse is detected
• Detector cannot detect photons for tdead
• Any carriers caught in traps will also discharge
• Detector is armed
• If tdead is shorter than the trap lifetime then
  the trap will discharge while the detector is
  armed and will result in a false event

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Afterpulsing Model
1
? dark count rate Rdark measured dark count
rate without afterpulsing Pa avalanche
probability Nft number of filled traps tdead
dead time ttrap trap lifetime
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Measured Afterpulsing

• No afterpulsing seen
• No traps
• or
• Trap lifetime
• gt500 µs

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Acknowledgements

• Rochester Imaging Detector Lab
• Dr. Don Figer
• John Frye
• Dr. Joong Lee
• Brandon Hanold
• Kim Kolb
• Microelectronic Engineering Department
• Dr. Rob Pearson
• Dr. Sean Rommel
• Dr. Karl Hirschman
• This work has been supported by NASA grant
  NNX08AO03G

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References

• 1 K.E. Jensen, Afterpulsing in Geiger-mode
  avalanche photodiodes for 1.06 µm wavelength
  Lincoln Laboratory, MIT 2006.
• 2 D. Neamen, An Introduction to Semiconductor
  Devices McGraw Hill 2006.
• 3 R.F. Pierret, Semiconductor Device
  Fundamentals Addison-Wesley Publishing Company,
  Inc. 1996.