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Near-infrared (NIR) Single Photon Counting Detectors (SPADs)

Near-infrared (NIR) Single Photon Counting Detectors (SPADs). Chong Hu, Minggou Liu, Joe C. Campbell & Archie Holmes ECE Department University of Virginia. Outline. Introduction to Single Photon Counting Detectors (SPADs) Current States of near-infrared SPADs Summary and Future Goals.

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Near-infrared (NIR) Single Photon Counting Detectors (SPADs)

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  1. Near-infrared (NIR) Single Photon Counting Detectors (SPADs) Chong Hu, Minggou Liu, Joe C. Campbell & Archie Holmes ECE Department University of Virginia

  2. Outline • Introduction to Single Photon Counting Detectors (SPADs) • Current States of near-infrared SPADs • Summary and Future Goals

  3. 2000 V Mature Novel t Superconductors PMT APD • High gain • Low dark current • Low noise • Low quantum efficiency • Large, bulky • Expensive • High voltage • Fragile • Ambient light catastrophic • Hotspot Generation and Resistive Barrier • High efficiency • Low dark counts • No afterpulsing • T < 1K!! • Electron & Hole avalanche multiplication • Good efficiency • Acceptable dark counts • Afterpulsing

  4. Geiger mode - APD functions as a switch AnalogDigital Responsivity Single photon detection efficiency Dark current Probability of dark count Concept of excess noise does not apply! Geiger-mode operation Single photon input time APD output Discriminator level time time Digital comparator output time time Dark count – from dark current Photon absorbed but insufficient gain – missed count Successful single photon detection

  5. on avalanche on Linear Geiger mode mode Geiger Linear quench mode mode Current Current Current Current off off arm Vdc + DV V V br br Voltage Voltage

  6. Performance Parameters Single photon input • Photon detection efficiency (PDE) • The probability that a single incident photon initiates a current pulse that registers in a digital counter • Dark count Rate (DCR)/Probability (DCP) • The probability that a count is triggered by dark current instead of incident photons time APD output Discriminator level time time Digital comparator output time time Dark count – from dark current Photon absorbed but insufficient gain – missed count Successful single photon detection

  7. Photon Detection Efficiency hPDE = hexternal x hcollection x Pavalanche InGaAsP 1.06, 1.3 mm InGaAs 1.55 mm

  8. 40m-diameter In0.53Ga0.47As/InP • Dark current • 0.18nA at 95% of Vbr at 297K • 0.15pA at 95% of Vbr at 200K • Good enough?

  9. 1.06 μm SPADs: DCR vs. PDE • InGaAsP absorber lower generation-recombination dark current • DCR approaching Si SPAD DCR with greatly increased PDE • Si SPADs have PDE < 2% at 1.06 μm 105 273K – 295K 300K * 104 259 K 250 K Dark Count Rate (Hz) 103 237 K 80 μm dia. InGaAsP SPAD 1-ns gated operation 500 kHz repetition rate 0.1 photon/pulse AP probability < 10-4 per gate 102 101 0% 10% 20% 30% 40% 50% Photon Detection Efficiency

  10. Dark Count Probability versus Photon Detection Efficiency 268K 215K -2 10 InGaAs/InP, 300K 1550 nm (2007) -3 10 InGaAs/InP (2007) -4 10 Dark Count Probability -5 240K 10 200K -6 10 -7 10 0 5 10 15 20 25 30 35 40 45 50 Single Photon Detection Efficiency (%)

  11. on avalanche on Linear Geiger mode mode Geiger Linear quench mode mode Current Current Current Current off off arm Vdc + DV V V br br Voltage Voltage

  12. Quenching circuit Quench avalanche current Reset the device Passive Quenching Quenched by discharging capacitance Slow recharge Active Quenching Raise the anode voltage Quick recharge Gated Quenching Quenching Techniques Vq>VEX

  13. Initial avalanche Released carriers from traps Afterpulsing Number of trapped carriers Biasing scheme

  14. Reduction of Afterpulsing: Decreasing Charge Flow Passive quenching The total charges flowing through device: Q=(Cs+Cd)Vex Cd: device capacitance Cs: stray capacitance

  15. Passive Quenching with Active Reset (PQAR)

  16. Vb 10-4 10-5 10-6 34s 15s Dark count probability (/ns) PQAR at 230K 70 Vex=2.6V 60 Vex=2.0V 50 Vex=1.6V Hold-off = 15s 40 Measured counts x 1000 (/s) 30 20 10 0 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 CW laser power (fW) Voltage on device Compare with gated mode results NEP ~ 10-16 W/Hz1/2

  17. Gated Quenching of a SPAD AC pulse Excess bias width (V ) ex Total bias V on APD br V dc Time Laser pulse Time Avalanche pulse Time Avalanche pulse photon Missed Avalanche pulse (false negative) due to incident photon due to dark carriers (false positive) ß Photon Detection Efficiency Dark Count Rate

  18. Rs=50Ω Amplifier Counter A Cac Cag 10MΩ Vgate Vbias Gated-PQAR • Compared to PQAR • Suppressed dark counts by gated bias • Reduced complexity • Array operation: recharge together, quench separately The transistor can be HBT monolithically integrated on the SPAD, and the its gate/base input can be shared over the whole array.

  19. Gated Quenching and Gated PQAR 10 8 6 4 Dark Count Rate (kHz) 220K 200K 180K 2 220K 200K gated-quenching 180K gated-PQAR 1 0 5 10 15 20 25 30 35 Photon Detection Efficiency (%)

  20. Gated Quenching and Gated PQAR 220K, Vex = 5.6% -3 10 200K, Vex = 6.0% 180K, Vex = 6.2% 220K, Vex = 5.6% 200K, Vex = 6.0% 180K, Vex = 6.2% Dark Count Probability gated-quenching -4 10 gated-PQAR -5 10 0.01 0.1 1 10 Repetition Rate (MHz)

  21. Conclusions • Performance of Geiger-mode APDs is improving rapidly • Acceptable detection efficiencies and dark count probability levels • Getting a better control over the afterpulsing problem

  22. Future Goals • Move closer to quantum limited detection • Dark Current  0 • Quantum Efficiency  100% • Read Noise  0 • Move to longer wavelengths • Do photon number resolving

  23. High QE Structure

  24. Type-II Quantum Wells (QWs) Formed between materials with staggered band line-ups • Electrons and holes are confined in adjoining layers • Spatially indirect absorption and emission • Smaller effective bandgap for long-wavelength operation E GaAs0.5Sb0.5 0.79eV ΔEc=0.236eV CB 0.49eV ≈ 2.5 μm VB Ga0.47In0.53As 0.77eV ΔEv=0.247eV x

  25. Where we are now (pin devices) Rogalski, A., Progress in Quant. Elec., 27(2-3), pp 59 (2003) -2 V bias (200K) -2 V bias (RT)

  26. Gated-PQAR for Synchronized Detection Gated Quench • Compared to gated quench • Comparable circuit complexity • Wider AC pulses: easier to generate and synchronize • Uniform output pulse shape, good for photon-number-resolution with multiplexing photon photon photon AC output Gated-PQAR photon photon photon Vbias Transistor on: low resistance for fast reset Vgate Transistor off: high resistance for fast passive quench Vdiode output

  27. Questions??

  28. InP AlInAs Decreasing thickness: m m m 0.2 m, 0.5 m, 1.0 m Simulated Breakdown Probabilities J. P. R. David, University of Sheffield

  29. 20 x 20 Array – 98% yield • 4 x 4 Subarray – uniform single-photon • response

  30. Afterpulsing Probability vs. Total Charge AC pulse Delay 1ms Period Laser pulse

  31. Total Charge Flow

  32. “Effective Excess Noise Factor”

  33. Pixel Level Monolithic Integration of Active Switching Elements • Reduced parasitics • Faster quenching • Reduced afterpulsing • Increased transmission and sampling rates • Packaging advantages W R R =50 =50 s s Counter Counter Active switching element V V bias bias

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