1. Characterization of a Geiger-mode Avalanche Photodiode a Rochester Institute of Technology, Department of Electrical and Microelectronic Engineering; b Rochester Imaging Detector Laboratory May 10, 2011 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. 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 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. Motivation 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. 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. 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. Array Tested 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. Array Tested 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. Camera Design  Requirements Light tight Allow for thermoelectric cooler Mountable lens for imaging Connector interface for existing hardware Probeable hardware without disassembly Camera Design  Requirements Light tight Allow for thermoelectric cooler Mountable lens for imaging Connector interface for existing hardware Probeable hardware without disassembly 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 seen. 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 seen. Results 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. 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. 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. 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. Fig. 1. Enhanced LIDAR image of Mars (Image Credit: MOLA Science Team and G. Shirah, NASA GSFC Scientific Visualization Studio). 1 10 100 M Breakdown0 Ordinary photodiode Linear-mode APD Geiger-mode APD Response to a photon M 1 ∞ I(t) Fig. 2. Comparison of photodiode operation (Image Credit: Dr. Don Figer). Fig. 3. Actual array of Geiger-mode APDs. Fig. 4. CAD camera design (left); actual fabricated camera (right). Afterpulse APD current APD bias Timing gate Laser-induced firing V arm t dead Fig. 5. Waveform demonstrating afterpulse test. λ(t dead ) – Dark count rate with respect to dead time R dark – Dark count rate measured without afterpulsing P a – Avalanche probability N ft – Number of filled traps τ trap – Trap lifetime t dead – Dead time Eq. 1. Dark count rate with respect to dead time. Ideality factor of n = 1.0 No recombination/generation region Series resistance ~2 kΩ Fig. 6. Measured forward diode characteristic. Breakdown voltage ~32 V Geiger-mode operation ≥ 32 V Fig. 7. Dark count rate vs. bias. Fig. 8. Theoretical afterpulsing. Fig. 9. Measured afterpulsing. 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 No afterpulsing is seen Fig. 10. Complete LIDAR system ready for imaging. Chris Maloney a Advisors: Dr. Don Figer b, Dr. Rob Pearson a, Dr. Sean Rommel a