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Single Photon Detectors By: Kobi Cohen Quantum Optics Seminar 25/11/09

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Single Photon Detectors. By: Kobi Cohen Quantum Optics Seminar 25/11/09. Outline. A brief review of semiconductors P-type, N-type Excitations Photodiode Avalanche photodiode Geiger Mode Silicon Photomultipliers (SiPM) Photomultiplier Superconducting Wire - PowerPoint PPT Presentation


  • Single Photon DetectorsBy: Kobi CohenQuantum Optics Seminar25/11/09

  • OutlineA brief review of semiconductorsP-type, N-typeExcitationsPhotodiodeAvalanche photodiodeGeiger ModeSilicon Photomultipliers (SiPM) PhotomultiplierSuperconducting WireCharacterization of single photon sourcesHBT ExperimentSecond order correlation function

  • Semiconductors

  • Semiconductorselectrons and holes: negative and positive charge carriesEnergy-momentum relation of free particles, with different effective mass

  • SemiconductorsThermal excitations make the electrons jump to higher energy levels, according to Fermi-Dirac distribution:

  • SemiconductorsExcitations can also occur by the absorption of a photon, which makes semiconductors suitable for light detection:

  • Intrinsic SemiconductorsCharge carriers concentration in a semiconductor without impurities:

  • N-type SemiconductorSome impurity atoms (donors) with more valence electrons are introduced into the crystal:

  • P-type SemiconductorSome impurity atoms (acceptors) with less valence electrons are introduced into the crystal:

  • The P-N JunctionElectrons and holes diffuse to area of lower concentrationElectric field is built up in the depletion layerDrift of minority carriersCapacitance

  • Biased P-N junctionWhen connected to a voltage source, the i-V curve of a P-N junction is given by:Well focus on reverse biasing:larger electric field in the junctionextended space charge region

  • The P-N photodiodeElectrons and holes generated in the depletion area due to photon absorption are drifted outwards by the electric field

  • The P-N photodiodeThe i-V curve in the reverse-biased P-N junction is changed by the photocurrentReverse biasing:Electric field in the junction increases quantum efficiencyLarger depletion layerBetter signal

  • The P-I-N junctionLarger depletion layer allows improved efficiencySmaller junction capacitance means fast response

  • Detectors: Quantum EfficiencyThe probability that a single photon incident on the detector generates a signalLosses: reflectionnature of absorption a fraction of the electron hole pairs recombine in the junction

  • Detectors: Quantum EfficiencyWavelength dependence of :

  • Summary: P-N photodiodeSimple and cheap solid state deviceNo internal gain, linear responseNoise (dark current) is at the level of several hundred electrons, and consequently the smallest detectable light needs to consist of even more photons

  • Avalanche photodiodeHigh reverse-bias voltage enhances the field in the depletion layerElectrons and holes excited by the photons are accelerated in the strong field generated by the reverse bias.Collisions causing impact-ionization of more electron-hole pairs, thus contributing to the gain of the junction.

  • Avalanche photodiodeP-N photodiodeAvalanche photodiode

  • Summary: APDHigh reverse-bias voltage, but below the breakdown voltage.High gain (~100), weak signal detection (~20 photons)Average photocurrent is proportional to the incident photon flux (linear mode)

  • Geiger modeIn the Geiger mode, the APD is biased above its breakdown voltage for operation in very high gain.Electrons and holes multiply by impact ionization faster than they can be collected, resulting in an exponential growth in the currentIndividual photon counting

  • Geiger mode quenchingShutting off an avalanche current is called quenchingPassive quenching (slower, ~10ns dead time)Active quenching (faster)

  • Summary: Geiger modeHigh detection efficiency (80%).Dark counts rate (at room temperature) below 1000/sec. Cooling reduces it exponentially.After-pulsing caused by carrier trapping and delayed release.Correction factor for intensity (due to dead time).

  • Silicon PhotomultipliersSiPM is an array of microcell avalanche photodiodes (~20um) operating in Geiger mode, made on a silicon substrate, with 500-5000 pixels/mm2. Total area 1x1mm2.The independently operating pixels are connected to the same readout line

  • SiPM: Examples

  • Summary: SiPMVery high gain (~106)Dark counts: 1MHz/mm2 (~20C) to 200Hz/mm2 (~100K)Correction factor (other than G-APD)

  • PhotomultiplierPhotoelectric effect causes photoelectron emission (external photoelectric effect)For metals the work function W ~ 2eV, useful for detection in the visible and UV. For semiconductors can be ~ 1eV, useful for IR detection

  • PhotomultiplierLight excites the electrons in the photocathode so that photoelectrons are emitted into the vacuum Photoelectrons are accelerated due to between the dynodes, causing secondary emission

  • Summary: PhotomultiplierFirst to be invented (1936)Single photon detectionSensitive to magnetic fieldsExpensive and complicated structure

  • A remark image intensifiersA microchannel plate is an array consists of millions of capillaries (~10 um diameter) in a glass plate (~1mm thickness).Both faces of the plate are coated by thin metal, and act as electrodes.The inner side of each tube is coated with electron-emissive material.

  • Superconducting nano-wireUltra thin, very narrow NbN strip, kept at 4.2K and current-biased close to the critical current.A photon-induced hotspot leads to the formation of a resistive barrier across the sensor, and results in a measurable voltage pulse.Healing time ~ 30ps

  • SSPD meander configurationMeander structure increases the active area and thus the quantum efficiency

  • End of 1st part !

  • Hanbury Brown-Twiss Experiment (1)Back in the 1950s, two astronomers wanted to measure the diameters of stars

  • Hanbury Brown-Twiss Experiment (2)

  • Hanbury Brown-Twiss Experiment (3)In their original experiments, HBT set =0 and varied d.As d increased, the spatial coherence of the light on the two detectors decreased, and eventually vanished for large values of d.

  • Coherence timeThe coherence time c is originated from atomic processesIntensity fluctuations of a beam of light are related to its coherence

  • Correlations (1)We shall assume from now on that we are testing the spatially-coherent light from a small area of the source.The second order correlation function of the light is defined by:(Why second order?)

  • Correlations (2)For much greater than the coherence time:

  • Correlations (3)On the other and, for much smaller than the coherence time, there will be correlations between the fluctuations at the two times. In particular, if =0 :

  • Correlations: exampleIf the spectral line is Doppler broadened with a Gaussian lineshape, the second order correlation functions is given by:

  • Summary: correlations in classical light

  • HBT experiments with photonsThe number of counts registered on a photon counting detector is proportional to the intensity

  • Photon bunching and antibunchingPerfectly coherent light has Poissonian photon statisticsBunched light consists of photons clumped together

  • Photon bunching and antibunchingIn antibunched light, photons come out with regular gaps between them

  • Experimental demonstration of photon antibunchingAntibunching effects are only observed if we look at light from a single atom

  • Experimental demonstration of photon antibunchingAntibunching has been observed from many other types of light emitters

  • BibliographyFundamentals of Photonics, Saleh & Teich, Wiley 1991Quantum Optics: An introduction, Mark Fox, Oxford University Press 2006Hamamatsu MMPC datasheet (online)PerkinElmer APCM datasheet (online)Goltsman G., SSPD, APL 79(6),2001, 705-707Hanbury Brown, R. , and Twiss, R. Q. , Nature, 177, 27 (1956)Hanbury Brown, R. , and Twiss, R. Q. , Nature, 178, 1046 (1956)