Characterization of a Geiger-mode Avalanche
Photodiode
Chris
May 10, 2011
a
Maloney
aRochester
Advisors: Dr. Don
b
Figer ,
Dr. Rob
a
Pearson ,
Institute of Technology, Department of Electrical and Microelectronic Engineering; bRochester Imaging Detector Laboratory
Results
Array Tested
Objective
The objective of this project was to extract key parameters that will
allow for effective and efficient operation of a Geiger-mode
avalanche photodiode (APD) array in a light detection and ranging
(LIDAR) imaging system.
Motivation
A 32x32 array of 100 µm
silicon Geiger-mode APDs was
designed and fabricated at MIT’s
Lincoln Laboratories. The
Rochester Imaging Detector Lab
(RIDL) was given the responsibility
to test and characterize the array.
LIDAR imaging systems can be used for a variety of applications.
The most common is altimetry. Measuring the altitude of an object
can be useful for observing celestial bodies, polar ice caps or ocean
levels. In addition, this imaging system can be implemented in
autonomous landing systems.
Fig. 3. Actual array of Geiger-mode APDs.
Fig. 6. Measured forward diode characteristic.
•Ideality factor of n = 1.0
•No recombination/generation region
•Series resistance ~2 kΩ
Fig. 4. CAD camera design (left); actual fabricated camera (right).
Requirements
• Light tight
• Allow for thermoelectric cooler
• Mountable lens for imaging
• Connector interface for existing hardware
• Probeable hardware without disassembly
Fig. 1. Enhanced LIDAR image of Mars (Image Credit:
MOLA Science Team and G. Shirah, NASA GSFC
Scientific Visualization Studio).
Geiger-mode Operation
APDs can be operated in linear-mode or Geiger-mode. Geiger-mode
operation means the diode is biased at or just above the breakdown
voltage of the device. This ensures single-photon sensitivity of the
device.
M
Linear-mode
APD
Geiger-mode
APD
100
Afterpulsing
Afterpulsing occurs when an event is seen during a timing gate, and
the dead time before the next timing gate is not long enough to
account for the discharge of trapped charge. A false event will be
Laser-induced
seen.
Afterpulse
APD current
APD bias
10
Fig. 7. Dark count rate vs. bias.
•Breakdown voltage ~32 V
•Geiger-mode operation ≥ 32 V
Camera Design
Fig. 8. Theoretical afterpulsing.
Ordinary
photodiode
Dr. Sean
a
Rommel
firing
Varm
Timing gate
•Short trap lifetimes show a steep peak
•Long life times exhibit a shallow peak
•Deep level traps have long lifetimes and
have a minimal effect on afterpulsing
Fig. 9. Measured afterpulsing.
•No afterpulsing is seen
Fig. 10. Complete LIDAR system ready for imaging.
Conclusions
It was expected to see the results that were measured in the
afterpulsing experiment. From the forward diode characteristic, no
recombination/generation region was seen, implying that there are a
minimal amount of traps in the device. Either there are no traps in
the device or the lifetime makes the peak too shallow to see or so
steep that it occurs before the shortest dead time. RIDL now has the
means to test for afterpulsing in devices that MIT will be sending
them in the coming months.
tdead
1
Fig. 5. Waveform demonstrating afterpulse test.
0
Response to
I(t)
a photon
Breakdown
1
M
Fig. 2. Comparison of photodiode operation
(Image Credit: Dr. Don Figer).
∞
λ(tdead) – Dark count rate with respect to dead time
Rdark – Dark count rate measured without afterpulsing
Pa – Avalanche probability
 t dead 
N ft

exp 
Nft – Number of filled traps  (tdead )  Rdark  Pa
  
 trap
trap 

τtrap – Trap lifetime
Eq. 1. Dark count rate with respect to dead time.
tdead – Dead time
Acknowledgements
I would like to thank Dr. Figer, John Frye, Dr. Rommel, Dr. Pearson
and Dr. Hirschman for their help during this project. This work has
been supported by NASA grant NNX08AO03G.