d. renker, psi - vertex 2006 overview of developments of silicon photomultiplier detectors dieter...

D. Renker, PSI - Vertex 2006D. Renker, PSI - Vertex 2006

Overview of Developments of Overview of Developments of Silicon Photomultiplier DetectorsSilicon Photomultiplier Detectors

Dieter RenkerDieter Renker


Geiger-mode APDs are devices which Geiger-mode APDs are devices which are only usefull for the detection of are only usefull for the detection of photons.photons.

Outline:Outline:

From Photomultiplier Tubes (PMTs) to Geiger-From Photomultiplier Tubes (PMTs) to Geiger-mode Avalanche Photodiodes (G-APDs)mode Avalanche Photodiodes (G-APDs)

Properties and ProblemsProperties and Problems ProducersProducers Choice of ParamatersChoice of Paramaters ConclusionConclusion


From PMT to G-APDFrom PMT to G-APD

PMTPMTs have been developed during almost 100 years. The first photoelectric tube was s have been developed during almost 100 years. The first photoelectric tube was produced by Elster and Geiter 1913. RCA made PMTs a commercial product in 1936. produced by Elster and Geiter 1913. RCA made PMTs a commercial product in 1936. Single photons can be detected with PMTs.Single photons can be detected with PMTs.

The high price, the bulky shape and the sensitivity to magnetic fields of PMTs forced The high price, the bulky shape and the sensitivity to magnetic fields of PMTs forced the search for alternatives.the search for alternatives.

PIN photodiodesPIN photodiodes are very successful devices and are used in most big experiments are very successful devices and are used in most big experiments in high energy physics (CLEO, L3, BELLE, BABAR, GLAST) but due to the noise of in high energy physics (CLEO, L3, BELLE, BABAR, GLAST) but due to the noise of the neccessary amplifier the minimal detectable light pulses need to have several 100 the neccessary amplifier the minimal detectable light pulses need to have several 100 photons.photons.

Avalanche photodiodesAvalanche photodiodes have internal gain which improves the signal to noise ratio have internal gain which improves the signal to noise ratio but still some 20 photons are needed for a detectable signal. The excess noise, the but still some 20 photons are needed for a detectable signal. The excess noise, the fluctuations of the avalanche multiplication limits the useful range of gain. CMS is the fluctuations of the avalanche multiplication limits the useful range of gain. CMS is the first big experiment that uses APD’s.first big experiment that uses APD’s.

G-APDsG-APDs can detect single photons. They have been developed and described since can detect single photons. They have been developed and described since the beginning of this millennium.the beginning of this millennium.


From PMTs to G-APDsFrom PMTs to G-APDs

Single photons clearly can be detected Single photons clearly can be detected with G-APDs. The pulse height spectrum with G-APDs. The pulse height spectrum shows a resolution which is even better shows a resolution which is even better than what can be achieved with a hybrid than what can be achieved with a hybrid photomultiplier.photomultiplier.

NIM A 504 (2003) NIM A 504 (2003) 4848


Geiger-mode APDGeiger-mode APD

A normal large area APD could be A normal large area APD could be operated in Geiger mode but it would operated in Geiger mode but it would never recover after a breakdown never recover after a breakdown which was initiated by a photon or which was initiated by a photon or athermally generated free carrier.athermally generated free carrier.

Way out:Way out:

Subdivide the APD structure into Subdivide the APD structure into many cells and connect them all in many cells and connect them all in parallel via an individual limiting parallel via an individual limiting resistor. The G-APD is born.resistor. The G-APD is born.

The technology is simple. It is a The technology is simple. It is a standard MOS (Metal-Oxide-Silicon) standard MOS (Metal-Oxide-Silicon) process and promises to be cheap. process and promises to be cheap. An educated guess is a price of 1 $An educated guess is a price of 1 $ per mmper mm22..

NIM A 504 (2003) 48


DesignDesign

Several designs are possible. Several designs are possible. Most of the G-APDs are of the Most of the G-APDs are of the type shown on top.type shown on top.

The number of cells in the G-The number of cells in the G-APDs ranges from 100 APDs ranges from 100 cells/mmcells/mm22 to 10.000 cells/mm to 10.000 cells/mm22..

The sketches are taken from The sketches are taken from Zair Sadygov‘s presentation in Zair Sadygov‘s presentation in Beaune 2005. Zair Sadygov, Beaune 2005. Zair Sadygov, JINR, Dubna and Victor Golovin, JINR, Dubna and Victor Golovin, CPTA, Moscow have been the CPTA, Moscow have been the key persons in the development key persons in the development of G-APDs.of G-APDs.


PMT like propertiesPMT like properties

G-APDs behave like PMTs and therefore some people call them Silicon G-APDs behave like PMTs and therefore some people call them Silicon Photomultiplier, SiPM.Photomultiplier, SiPM.

The gain is in the range of 10The gain is in the range of 1055 to 10 to 1077. Single photons produce a signal of . Single photons produce a signal of several millivolts on a 50 Ohm load. No or at most a simple amplifier is several millivolts on a 50 Ohm load. No or at most a simple amplifier is needed.needed.

Pickup noise is no more a concern (no shielding).Pickup noise is no more a concern (no shielding).

There is no nuclear counter effect – even a heavily ionizing particle There is no nuclear counter effect – even a heavily ionizing particle produces a signal which is not bigger than that of a photon.produces a signal which is not bigger than that of a photon.

Since there are no avalanche fluctuations (as we have in APDs and PMTs) Since there are no avalanche fluctuations (as we have in APDs and PMTs) the excess noise factor is very small, could eventually be one.the excess noise factor is very small, could eventually be one.

Grooms theorem (the resolution of an assembly of a scintillator and a Grooms theorem (the resolution of an assembly of a scintillator and a semiconductor photodetector is independent of the area of the detector) is semiconductor photodetector is independent of the area of the detector) is no more valid.no more valid.


Binary DeviceBinary Device

G-APDs produce a standard signal when G-APDs produce a standard signal when any of the cells goes to breakdown. The any of the cells goes to breakdown. The amplitude Aamplitude Aii is proportional to the is proportional to the capacitance of the cell times the capacitance of the cell times the overvoltage.overvoltage.

AAii ~ C ~ C • (V – V• (V – Vbb))

When many cells fire at the same time the When many cells fire at the same time the output is the sum of the standard pulsesoutput is the sum of the standard pulses

A = ∑ A = ∑ AAii

The summing makes the device analog The summing makes the device analog again.again.

Hamamatsu 1-53-1A-1, cell size 70 x 70 m


SaturationSaturation

The output signal is proportional to The output signal is proportional to the number of fired cells as long as the number of fired cells as long as the number of photons in a pulse the number of photons in a pulse (N(Nphotonphoton) times the photodetection ) times the photodetection efficiency PDE is significantly efficiency PDE is significantly smaller than the number of cells smaller than the number of cells NNtotaltotal..

2 or more photons in 1 cell look 2 or more photons in 1 cell look exactly like 1 single photon.exactly like 1 single photon.

When 50% of the cells fire the When 50% of the cells fire the deviation from linearity is 20%.deviation from linearity is 20%.

)1( total

photon

N

PDEN

totalfiredcells eNNA


Dark CountsDark Counts

A breakdown can be triggered by an incoming A breakdown can be triggered by an incoming photon or by any generation of free carriers. The photon or by any generation of free carriers. The latter produces dark counts with a rate of 100 latter produces dark counts with a rate of 100 kHz to several MHz per mmkHz to several MHz per mm22 at 25°C and with a at 25°C and with a treshold at half of the one photon amplitude.treshold at half of the one photon amplitude.

Thermally generated free carriers can be reduced Thermally generated free carriers can be reduced by cooling (factor 2 reduction of the dark counts by cooling (factor 2 reduction of the dark counts every 8°C) and by a smaller electric field (lower every 8°C) and by a smaller electric field (lower gain).gain).

Field-assisted generation (tunneling) can only be Field-assisted generation (tunneling) can only be reduced by a smaller electric field (lower gain).reduced by a smaller electric field (lower gain).

Reduce the number of generation-recombination Reduce the number of generation-recombination centers in the G-APD production process.centers in the G-APD production process.

Open question: Radiation hardnessOpen question: Radiation hardness


Dark CountsDark Counts

The dark count rate falls rapidly with increasing threshold:

Hamamatsu 01-100-2

0.001

0.01

0.1

1

10

100

1000

0 1 2 3 4 5 6 7 8

Threshold [Number of Photo-Electrons]

Dar

k C

ou

nts

[kH

z]


CrosstalkCrosstalk

HHot-Carrier Luminescence: ot-Carrier Luminescence:

101055 carriers in an avalanche carriers in an avalanche breakdown emit in average 3 breakdown emit in average 3 photons with an energy higher photons with an energy higher than 1.14 eV. (than 1.14 eV. (A. Lacaita et al, A. Lacaita et al, IEEE TED (1993))IEEE TED (1993))

When these photons travel to a When these photons travel to a neighbouring cell they can neighbouring cell they can trigger a breakdown there.trigger a breakdown there.

Optical crosstalk acts like Optical crosstalk acts like avalanche fluctuations in a avalanche fluctuations in a normal APD. It is a stochastic normal APD. It is a stochastic process. We get the excess process. We get the excess noise factor back.noise factor back.

Hamamatsu 1-53-1A-1, cell size 70 x 70 m


Photon Detection EfficiencyPhoton Detection Efficiency

The photon detection efficiency (PDE) is the product of quantum efficiency of the The photon detection efficiency (PDE) is the product of quantum efficiency of the active area (QE), a geometric factor (active area (QE), a geometric factor (, ratio of sensitiv to total area) and the , ratio of sensitiv to total area) and the probability that an incoming photon triggers a breakdown (Pprobability that an incoming photon triggers a breakdown (P triggertrigger))

PDE = QE PDE = QE · · · · PPtriggertrigger

QE is maximal 80 to 90% depending on the wavelength.QE is maximal 80 to 90% depending on the wavelength.

The QE peaks in a relative narrow range of wavelengths because the sensitive The QE peaks in a relative narrow range of wavelengths because the sensitive layer of silicon is very thin (in the case shown the player of silicon is very thin (in the case shown the p++ layer is 0.8 layer is 0.8 m thick)m thick)

Hamamatsu 0-50-2 (400 cells)

0102030405060708090

100

350 400 450 500 550 600 650 700 750 800

Wavelength [nm]

QE

[%]

Dash and Newman

0.01

0.1

1

10

100

300 400 500 600 700 800 900

wavelegth [nm]

ab

s.

len

gth

of

lig

ht

in S

i [m

icro

n]



W.G. Oldham et al., IEEE TED 19, No 9 (1972)

The triggering probability depends on the position where the primary electron-hole pair is generated.

And it depends on the overvoltage. High gain operation is favoured.

Electrons have in silicon a better chance to trigger a breakdown than holes. Therefore a conversion in the p+ layer has the highest probability.



The geometric factor The geometric factor needs to be optimized needs to be optimized depending on the application.depending on the application.

Since some space is needed between the cells for the Since some space is needed between the cells for the individual resistors and is needed to reduce the optical individual resistors and is needed to reduce the optical crosstalk the best filling can be achieved with a small crosstalk the best filling can be achieved with a small number of big cells.number of big cells.

In a camera for air Cherenkov telescopes the best In a camera for air Cherenkov telescopes the best possible PDE is wanted. Since the number of photons possible PDE is wanted. Since the number of photons is small big cells are suitable and a geometric factor of is small big cells are suitable and a geometric factor of 60% and more is possible.60% and more is possible.

LSO crystals for PET produce many photons and LSO crystals for PET produce many photons and 1000 or more can be collected at the endface of the 1000 or more can be collected at the endface of the crystals. In order to avoid a saturation effect the crystals. In order to avoid a saturation effect the number of cells needs to be big and the cells small. number of cells needs to be big and the cells small. The geometric factor will be in the range of 30 to 40%.The geometric factor will be in the range of 30 to 40%.

Microscopic view of a G-APD produced by Hamamatsu

Microscopic view of a G-APD produced by Z. Sadygov (JINR)


Recovery TimeRecovery Time

The time needed to recharge a cell The time needed to recharge a cell after a breakdown has been quenched after a breakdown has been quenched depends mostly on the cell size depends mostly on the cell size (capacity) and the individual resistor (capacity) and the individual resistor (RC).(RC).

Afterpulses can prolong the recovery Afterpulses can prolong the recovery time because the recharging starts time because the recharging starts anew. Can be reduced by low gain anew. Can be reduced by low gain operation.operation.

Some G-APDs need hundreds of microseconds after a breakdown until the Some G-APDs need hundreds of microseconds after a breakdown until the amplitude of a second signal reaches 95% of the first signal. Smallest values amplitude of a second signal reaches 95% of the first signal. Smallest values for G-APDs with small cells and small resistors. for G-APDs with small cells and small resistors.

Polysilicon resistors are used up to now which change their value with the Polysilicon resistors are used up to now which change their value with the temperature. Therefore there is a strong dependence of the recovery time on temperature. Therefore there is a strong dependence of the recovery time on the temperature. the temperature. Go to a metal alloy with high resistivity like FeCr. Go to a metal alloy with high resistivity like FeCr.


G-APDs: AfterpulsesG-APDs: Afterpulses

Carrier trapping and delayed release causes afterpulses during a period of Carrier trapping and delayed release causes afterpulses during a period of several microseconds.several microseconds.

From S. Cova et al., Evolution and Prospect of Single-Photon Avalanche Diodes and Quenching Circuits (NIST Workshop on Single Photon Detectors 2003)

Afterpulses with short delay Afterpulses with short delay contribute little because the contribute little because the cells are not fully recharged but cells are not fully recharged but have an effect on the recovery have an effect on the recovery time.time.

Low temperatures elongate the Low temperatures elongate the release (factor of 3 for 25°C).release (factor of 3 for 25°C).


TimingTiming

taken from physics/0606037

Contribution from the laser 37 ps

The active layers of silicon are very The active layers of silicon are very thin (2 to 4 thin (2 to 4 m), the avalanche m), the avalanche breakdown process is fast and the breakdown process is fast and the signal amplitude is big. We can signal amplitude is big. We can therefore expect very good timing therefore expect very good timing properties even for single photons.properties even for single photons.

Fluctuations in the avalanche are Fluctuations in the avalanche are mainly due to a lateral spreading by mainly due to a lateral spreading by diffusion and by the photons emitted in diffusion and by the photons emitted in the avalanche.the avalanche.

A. Lacaita et al., Apl. Phys. Letters 62 (1992) A. Lacaita et al., Apl. Phys. Letters 62 (1992) A. Lacaita et al., Apl. Phys. Letters 57 (1990)A. Lacaita et al., Apl. Phys. Letters 57 (1990)

High overvoltage (high gain) improves High overvoltage (high gain) improves the time resolution.the time resolution.


TimingTiming

Carriers created in field free regions Carriers created in field free regions have to travel by diffusion. It can take have to travel by diffusion. It can take several tens of nanoseconds until they several tens of nanoseconds until they reach a region with field and trigger a reach a region with field and trigger a breakdown.breakdown.

At low gain the lateral spreading of the At low gain the lateral spreading of the depleted volume can be uncomplete depleted volume can be uncomplete and can enhance the diffusion tail.and can enhance the diffusion tail.

Pictures from S. Cova et al., Evolution and Prospect of Single-Photon Avalanche Diodes and Quenching Circuits (NIST Workshop on Single Photon Detectors 2003)


Signal rise and decay timeSignal rise and decay time

Hor. Scale 2 ns/div, vert. Scale 10 mV/div

Rise time 0.6 ns

quenching resistor

diode

biasRC

t

breakdownbiasD

breakdownbiasR

biasRC

t

D

DDbias

DD

R

DRbias

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maximum signalat 0

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isequation diffential thisofSolution

Fall time depends on the cell size (capacity) and the serial resistor


Long Term StabilityLong Term Stability

The stability of the light yield of The stability of the light yield of G-APDs from V. Golovin was G-APDs from V. Golovin was tested by Y. Kudenko and co-tested by Y. Kudenko and co-workers (INR, Moscow) workers (INR, Moscow) including an accelerated aging including an accelerated aging with very promising results.with very promising results.


More PropertiesMore Properties

There are more features which are not mentioned yet:There are more features which are not mentioned yet:

G-APDs work at low bias voltage (~50 V),G-APDs work at low bias voltage (~50 V), have low power consumption (< 50 have low power consumption (< 50 W/mmW/mm22),), are insensitive to magnetic fields up to 15 T,are insensitive to magnetic fields up to 15 T, are compact, rugged and show no aging,are compact, rugged and show no aging, tolerate accidental illumination,tolerate accidental illumination, cheap because they are produced in a standard MOS process (10 to cheap because they are produced in a standard MOS process (10 to

100 $/cm100 $/cm22))


Where to go shopingWhere to go shoping

There is competition. Currently there are 6 producers: There is competition. Currently there are 6 producers:

Center of Perspective Technology and Apparatus (CPTA), Moscow, Center of Perspective Technology and Apparatus (CPTA), Moscow, RussiaRussia

MePhi/Pulsar Enterprise, Moscow, RussiaMePhi/Pulsar Enterprise, Moscow, Russia SensL, Blackrock, Ireland SensL, Blackrock, Ireland JINR/Micron Enterprise, Dubna and Zelenograd, RussiaJINR/Micron Enterprise, Dubna and Zelenograd, Russia Hamamatsu, Hamamatsu City, JapanHamamatsu, Hamamatsu City, Japan Radiation Monitor Devices (RMD), Boston, USARadiation Monitor Devices (RMD), Boston, USA

and developments in several institutes:and developments in several institutes:

Max-Planck Semiconductor Lab, MunichMax-Planck Semiconductor Lab, Munich Center for Scientific and Technological Research of TrentoCenter for Scientific and Technological Research of Trento


G-APD from Hamamatsu PhotonicsG-APD from Hamamatsu Photonics

Catalog item beginning 2007


Choice of ParamatersChoice of Paramaters

Many different designs are possible:Many different designs are possible:

Semiconductor material – PDE, wavelength Semiconductor material – PDE, wavelength p-silicon on a n-substrate – highest detection efficiency for blue lightp-silicon on a n-substrate – highest detection efficiency for blue light n-silicon on a p-substrate – highest detection efficiency for green lightn-silicon on a p-substrate – highest detection efficiency for green light Thickness of the layers – range of wavelength, crosstalkThickness of the layers – range of wavelength, crosstalk Doping concentrations – operating voltage and its rangeDoping concentrations – operating voltage and its range Impurities and crystal defects – dark counts, afterpulsesImpurities and crystal defects – dark counts, afterpulses Area of the cells – gain, geometric factor, dynamic range, recovery timeArea of the cells – gain, geometric factor, dynamic range, recovery time Value of the resistors – recovery time, count rate/cellValue of the resistors – recovery time, count rate/cell Type of resistors – temperature dependenceType of resistors – temperature dependence Optical cell isolation (groove) – crosstalkOptical cell isolation (groove) – crosstalk


Medical Application (PET)Medical Application (PET)


Fiber readoutFiber readoutScintillating tiles and wavelength shifting fibers:

Start for the cosmic calibration of Alice TOF detectors uses G-APDs from CPTA.

MiniCal for a calorimeter in the ILC. Used are G-APDs from MePhi/Pulsar.


ConclusionsConclusions

G-APDs are the best choice for the detection of light when G-APDs are the best choice for the detection of light when there is a magnetic field and/or when space and power there is a magnetic field and/or when space and power consumption are limited. consumption are limited.

Due to the standard MOS production process G-APDs will be Due to the standard MOS production process G-APDs will be cheap.cheap.

Most of the devices are still small (1x1 mmMost of the devices are still small (1x1 mm22) but areas of ) but areas of 5x5 mm5x5 mm2 2 are available and 10x10 mmare available and 10x10 mm22 is planed. Also is planed. Also available is a monolithic array of 4 diodes with 1.8x1.8 available is a monolithic array of 4 diodes with 1.8x1.8 mmmm22 each and small interspace. each and small interspace.

The development started some 10 years ago but still there The development started some 10 years ago but still there is a broad room for improvements. Many parameters can be is a broad room for improvements. Many parameters can be adjusted to optimise the devices.adjusted to optimise the devices.

d. renker, psi - vertex 2006 overview of developments of silicon photomultiplier detectors dieter...

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