Chris Maloney May 10, 2011 Characterization of a Geiger-mode Avalanche Photodiode

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 June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney

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 June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney

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 June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney

5 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 June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney (Image Credit: MOLA Science Team and G. Shirah, NASA GSFC Scientific Visualization Studio.)

6 Background ♦ Lincoln Laboratory at MIT has fabricated a 32x32 array of Geiger- mode APDs for LIDAR imaging applications June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney

7 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 June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney M Breakdown0 Ordinary photodiode Linear- mode APD Geiger- mode APD Response to a photon M 1 ∞ I(t) (Image Credit: D.F Figer.)

8 Project Flowchart June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney Receive detector Design camera Fabricate camera Light tight? Measure diode IV curve Extract IV parameters Write IDL code for performance tests Measure dark count rate vs. gate width Measure dark count rate vs. bias Measure dark count rate vs. dead time Analyze data YES NO

9 System Design June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney CAD camera partFabricated camera

10 Front View June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney Without the lens

11 Readout board integrated with camera June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney View inside of camera

12 Detector integrated with readout board June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney Readout board and detector are both from MIT’s Lincoln Laboratories 32x32 APD array

13 System Design June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney Complete LIDAR system

14 Diode IV Testing June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney ♦ Shielded Probe Station ♦ Agilent 4156B Parameter Analyzer ♦ Noise Floor ~ 1 fA

15 Measured Reverse Diode Current vs. Voltage Breakdown Voltage = 28 V Dark Current = 0.1 pA Dark Current Density ~ 1 nA/cm 2 June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney All diodes across the wafer are uniform

16 Measured Forward Diode Current vs. Voltage n = 1.0 No R/G region Series resistance = 2 kΩ June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney No R/G region implies number of traps are minimal

17 Gate Width Definition ♦ The amount of time the detector is ready to detect a photon June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney hνhν Timing Gate Gate Width

18 Measured Dark Count Rate vs. Gate Width June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney Dark count rate should be constant

19 Dead Pixels June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney Upper right corner is unresponsive due to low yielding bump-bonds

20 Measured Dark Count Rate vs. Gate Width – 9 by 8 array June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney Dark count rate is constant and no longer decreasing

21 Measured Dark Count Rate vs. Bias June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney Breakdown voltage is higher than breakdown extracted from IV curve Add ~5V to x-axis to account for cathode voltage

22 Afterpulsing Theory ♦ Detector is armed and a laser pulse is detected ♦ Detector cannot detect photons for t dead ♦ Any carriers caught in traps will also discharge ♦ Detector is armed ♦ If t dead is shorter than the trap lifetime then the trap will discharge while the detector is armed and will result in a false event June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney Afterpulse APD current APD bias Timing gate Laser-induced firing V arm t dead

23 Afterpulsing Model June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney λ – dark count rate R dark – measured dark count rate without afterpulsing P a – avalanche probability N ft – number of filled traps t dead – dead time τ trap – trap lifetime [1]

24 Measured Afterpulsing June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney ♦ No afterpulsing seen No traps or Trap lifetime >500 μs

25 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 June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney

26 References [1] K.E. Jensen, “Afterpulsing in Geiger-mode avalanche photodiodes for 1.06 μm wavelength” Lincoln Laboratory, MIT [2] D. Neamen, “An Introduction to Semiconductor Devices” McGraw Hill [3] R.F. Pierret, “Semiconductor Device Fundamentals” Addison-Wesley Publishing Company, Inc June 21, 2015 Characterization of a Geiger-Mode APD C. Maloney