Alkali-antimonide Photocathodes for Gas-Avalanche Photomultipliers

A. LyashenkoAlkali-antimonide PCs for GPMPC workshop, Chicago 09

Alkali-antimonide Photocathodes for Gas-Avalanche Photomultipliers

Recent review on GPMs: Chechik & Breskin NIM A595 (2008) 116Summary article visible-light GPM: Lyashenko et al. JINST 4 (2009) P07005

A. Lyashenko, R. Chechik and A. BreskinWeizmann Institute of Science, Rehovot, Israel


UV-exist:UV-exist:ALICE, HADES,COMPASS, J-LAB, PHENIX

Visible-in courseVisible-in courseMotivation: • large areas, flat geometry• operation in magnetic fields• sensitivity to single photons• visible spectral range• fast (ns range)• high localization accuracy (sub-mm range)

Gaseous Photo-Multipliers (GPM)Gaseous Photo-Multipliers (GPM)


Principles of GPM operation

Photoelectron emission fromphotocathode

Avalanche chargemultiplication in gas

Signal recording


• Alkali-antimonide pc production (QE 20-50% @ 350-400nm in vacuum for semi-transparent PC)• Hot Indium sealing to package @130-150ºC => critical for pc

Multi-chamber UHV setupMulti-chamber UHV setup


•PC substrate treatment in air •PC substrate treatment in vacuum (usually baking at 270-3000C )• Evaporation of alkali-metals

PC sensitivity Long term stability

PC fabrication process:


100 200 300 400 500 600 700 8000,1

1

10

100

Na-K-Sb:Cs (S-20)

Spec

tral R

espo

nsivi

ty [m

A/W

]

Wavelength [nm]

Cs3Sb (S-11)

Na2KSbRb2CsSb

K2Cs-Sb

Photocathodes: Cs3Sb

Activation steps:

1. Evaporation of Sb at 180-2000C onto a substrate until it looses ~20% of its transparency

2. Exposure to Cs at 150-1800C until the maximum of photocurrent is reached.

3. Post-treatment if needed (removing of excess of Cs by baking at ~2000C)

Activation time: 30-60 minPC characteristics (typical):

• Wavelength of max response: λmax=370-400nm• Luminous sensitivity: 100-120μA/lm• Responsivity at λmax : 65-75mA/W• QE at λmax: 20-25%• Dark emission current at 250C: ≤0.1fA/cm2

• Surface resistance at 250C: 3*107Ohm/square

Designation: S-11

Large area: YES

Burle


Photocathodes: K2CsSb

PC characteristics (typical): • Wavelength of max response: λmax=380-420nm• Luminous sensitivity: 70-100 μA/lm• Responsivity at λmax : 100mA/W• QE at λmax: >30%• Dark emission current at 250C: ≤0.01fA/cm2

• Surface resistance at 250C: 6*109Ohm/square Features: Very high surface resistance

Activation steps:One possibility:1. Evaporation of Sb at 180-2000C onto a

substrate until 20% of transparency is lost

2. Exposure to K at 160-2000C until the maximum of photocurrent is reached (formation of K3Sb PC).

3. Repetitive (yo-yo) exposure to Cs & Sb at 180-2250C until the maximum of photocurrent is reached.

Another possibility: So called co evaporation

Large area: YES, needs a conductive layer100 200 300 400 500 600 700 800

0,1

1

10

100

Na-K-Sb:Cs (S-20)

Spec

tral R

espo

nsivi

ty [m

A/W

]

Wavelength [nm]

Cs3Sb (S-11)

Na2KSbRb2CsSb

K2Cs-Sb

Burle


Photocathodes: Na2KSbActivation steps:1. Evaporation of Sb at 180-2000C on

substrate until it looses 20% of its transparency

2. Exposure to K at 160-2000C until maximum photocurrent reached (K3Sb).

3. Exposure to Na at ~2200C until the raise of PC current start slowing down*.

4. Alternating addition of Sb and K at ~160-1800C until maximum photocurrent reached.

* Simultaneous evaporation of K and Na is possiblePC characteristics (typical):

• Wavelength of max response: λmax=380-410nm• Luminous sensitivity: 65-80μA/lm• Responsivity at λmax : 64mA/W• QE at λmax: 19-21%• Dark emission current at 250C: ≤0.0001fA/cm2

• Surface resistance at 250C: 2*106Ohm/squareFeatures: Outstanding temperature stability (up to 2000C), lowest dark currentLarge area: YES, but production is rather complicated, QE< other Bi-alkali.

100 200 300 400 500 600 700 8000,1

1

10

100

Na-K-Sb:Cs (S-20)

Spec

tral R

espo

nsivi

ty [m

A/W

]

Wavelength [nm]

Cs3Sb (S-11)

Na2KSbRb2CsSb

K2Cs-Sb

Burle


)()()()(

)()()()(

)()()(

PMTWdarkPDPD

darkPDtransPDtrans

darkPMTtransPMTtrans

darkPCPC QET

IIII

IIIIQE

PC characterization


0 10 20 30 40 50 600123456789

10

Num

ber o

f K2Cs

Sb P

Cs

QE at max

[%]

N=28Mean QE=28.3%

QE of alkali-antimonide photocathodes

200 300 400 500 60005

10152025303540

a)

QE

[%]

Wavelength [nm]

Cs3Sb

200 300 400 500 6000

5

10

15

20

25

30

QE

[%]

Wavelength [nm]

Na2KSb c)

300 400 500 6000

10

20

30

40

50

60

QE

[%]

Wavelength [nm]

K2CsSb PCs

QE~48%

RECENT PHOTOCATHODES


300 400 500 6000

10

20

30

40

50

700 Torr Ar/CH4 (95/5)

Edrift

~500 V/cm

Vacuum

QE

[%]

Wavelength [nm]

SbK2Cs

0.0

0.2

0.4

0.6

0.8

1.0

extr

0,0 0,5 1,0 1,5 2,0 2,50,0

0,2

0,4

0,6

0,8

1,0

312 nm 365 nm 405 nm 436 nm 546 nm

K-Cs-Sb 700 Torr Ar/CH4 (95/5)

Tran

smis

sion

Electric field [kV/cm]

Photoelectron extraction from bi-alkali PC into gas

Optimal field for GPMHigher transmission in other gases, e.g. CH4


PC is stable in gas in the large vacuum chamber

Expected even better stability for sealed devices

Long-term photocathode stability in gasLong-term photocathode stability in gas

0 10 20 300

5

10

15

20

file:

200

8-02

-04_

PC

_sta

bilit

y_G

AS

312nm 365nm 405nm 436nm 546nm

QE

[%]

Time [days]

Cs3Sb PC, initial vacuum QE~25%@ 365 nm700 Torr Ar/CH

4 (95/5)

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

file:

200

8-02

-04_

PC

_sta

bilit

y_G

AS

312nm 365nm 405nm 436nm 546nm

QE

[%]

Time [days]

K2CsSb PC initial vacuum QE~48%@365 nm700 Torr Ar/CH4 (95/5)


Secondary effects in visible-sensitive GPMs Secondary effects in visible-sensitive GPMs Gaseous Photo-Multiplier (GPM)

PChn

readout plane

+++ avalanche

photonsions

incident photon

+secondaryemission

secondaryemission

GAS

Main problem: Ions & photons secondary e emission ion/photon feedback pulses gain & performance limitations

Photon feedback is largely reduced

PC masked by electrode*GEM: Gas Electron Multiplier - Sauli, NIM A 386, (1997) 531.

GEM*

70μm50μm

GEM+

++

DV

1e in

>1000e out

Ehole

Edrift

Eind


IBF: Ion Back-Flow Fraction

Major efforts to limit ion backflow1 .GATING operation in “gated-mode” deadtime,

trigger2 .NEW e- - - - MULTIPLIERS operation in continuous mode

)cascaded-GEM, MICROMEGAS…&: OTHERS(

Challenge: BLOCK IONS WITHOUT AFFECTING ELECTRON COLLECTION

IBF: The average fraction of avalanche-generated ions back-flowing to the photocathode


Visible-sensitive GPM: Ion-feedback developmentVisible-sensitive GPM: Ion-feedback development

Visible-sensitive gas photomultiplier review: M. Balcerzyk et al., IEEE Trans. Nucl. Sci. Vol. 50 no. 4 (2003) 847

1 GIBFeff stable operation of visible sensitive GPMif

200 220 240 260 280 300 320 340100

101

102

103

104

700 Torr Ar/CH4 (95/5)

Edrift

=0.5kV/cm

Tota

l gai

n

VGEM

[V]

K-Cs-Sb QE=22%@375nm

CsI

K-Cs-Sb

K-Cs-Sb, Na-K-Sb, Cs-Sb : Current deviates from

exponential Max Gain ~ few 100, IBF~10%

G~105, γ+eff - ?, IBF - ?


Calculation of ion induced secondary emission probability from bi-alkali PCs γ+eff=γ+·εextr

Auger neutralization + Backscattering

PC K-Cs-Sb Na-K-Sbγ+

eff 0.027 0.029

PC

GAS

3 4 5 6 7 8 9 100,0

0,1

0,2

0,3

0,4

0,5

K-Cs-Sb

CH4+

N 0(Ek) [

elec

trons

per

ion

per e

V]

Ek [eV]

Na-K-Sb

4 6 8 10 12 14 16 18 200,0

0,1

0,2

0,3

0,4

0,5

0,6

+ [el

ectro

ns p

er io

n]E'

i [eV]

K-Cs-Sb PC

A.Lyashenko et al., J. Appl. Phys. (2009) accepted, arXiv:0904.4881

Most gases


Measurements of γ+eff=γ+·εextr

PC K-Cs-Sb Na-K-Sbγ+

eff (experiment) 0.03±0.01 0.02±0.006

200 220 240 260 280 300 320 340100

101

102

103

104

700 Torr Ar/CH4 (95/5)

Edrift

=0.5kV/cm

Tota

l gai

n

VGEM

[V]

K-Cs-Sb QE=22%@375nm

CsI

K-Cs-Sb

effmeas IBFGGG

1


Effective IISEE from K-Cs-Sb and Na-K-Sb PCs

PC K-Cs-Sb Na-K-SbIon CH4

+ CH4+

γ+eff (exp) 0.03±0.01 0.02±0.006

γ+eff(theory) ~0.03 ~0. 03

PC

extreff

Ar/CH4 (95/5), γeff+ ~0.03, Gain ~ 105 => IBF < 3.3*10-4

1 GIBFeff stable operation of visible sensitive GPMif


The Microhole & Strip plate (MHSP)Two multiplication stages on a single, double-sided, foil

R&D: Weizmann/Coimbra

30mm

100mm

100mm

70mm

140mm

210mm

Veloso et al. Rev. Sci. Inst. A 71 (2000) 237.

7 times lower IBF than with cascaded GEMs

Strips: multiply charges


Reverse-biased MHSP (R-MHSP) conceptReverse-biased MHSP (R-MHSP) concept

410V 70VAC

+++++ions

electrons Flipped-R-MHSPR-MHSP

Can trap its own ions

Ions are trapped by negatively biased cathode strips

Lyashenko et al., JINST (2006) 1 P10004 Lyashenko et al., JINST (2007) 2 P08004

Roth, NIM A535 (2004) 330Breskin et al. NIM A553 (2005) 46Veloso et al. NIM A548 (2005) 375

Can trap only ions from successive stages

Strips: collect ions


103 104 105 2x10510-4

10-3

10-2

F-R-MHSP/GEM/MHSP R-MHSP/GEM/MHSP

Edrift

=0.5kV/cm

Ar/CH4 (95/5), 760 Torr

IBF

Total gain

Lyashenko et al., JINST (2007) 2 P08004

IBF measured with 100% e-collection efficiency

IBF=3*10-4 @ Gain=105 is 100 times lower than with 3GEMs

1st R-MHSP or F-R-MHSP: ion defocusing (no gain!)Mid GEMs: gainLast MHSP: extra gain & ion blocking

BEST ION BLOCKING:BEST ION BLOCKING:““COMPOSITE” CASCADED MULTIPLIERSCOMPOSITE” CASCADED MULTIPLIERS::

IBF=3*10-

4


• 20% QE drop @ 2 μC/mm2 ion charge on photocathode: • only ~ 4 x faster drop compared to thin ST CsI (~8 μC/mm2)

K-Sb-Cs PC ageing in avalanche modeK-Sb-Cs PC ageing in avalanche mode

Real conditions: gain=105; IBF=3*10-4. •20% QE drop 46 years @ 5kHz/mm2 ph. same conditions with a MWPC (IBF~0.5) 3000 times shorter lifetime: ~5 days!

A. Breskin al. NIM A553 (2005) 46

0 2 4 6 8 10 12 14 160,0

0,2

0,4

0,6

0,8

1,0

1,2

CsI(300A) QE~7%(180nm) 50Torr, CH

4, G~103

K-Cs-Sb

PC1 QE~17% (375nm), 100Torr, G~103

PC2 QE~25% (375nm), 100Torr, G~20 PC3 QE~11% (375nm), 700Torr, G~103

Ar/CH4 (95:5)

0408

16_S

b-K-

Cs_P

Cage

ing

Rela

tive

PC c

urre

nt

PC accumulated charge [mC/mm2]


Sealed detectorTest detector setup

Visible-sensitive GPMVisible-sensitive GPMUHV compatible materials

Bi-alkaliphotocathode

cascadedmultiplier

GEM/MHSP

M. Balcerzyk et al., IEEE Trans. Nucl. Sci. Vol. 50 no. 4 (2003) 847


200 220 240 260 280 300100

101

102

103

104

105

106

107

K-Cs-Sb CsI (exp. fit)

Double-GEM

Edrift=0.5 kV/cm, QE~27%@375nm700 Torr Ar/CH4 (95/5)

K-Cs-Sb CsI (exp. fit)

F-R-MHSP/GEM/MHSP

Tota

l gai

nV

AC_MHSP, DV

GEM [V]

Continuous operation of F-R-MHSP/GEM/MHSPContinuous operation of F-R-MHSP/GEM/MHSP with K-Cs-Sb photocathodewith K-Cs-Sb photocathode

Gain ~105 at full photoelectron collection efficiencyFirst evidence of continuous high gain operation of visible-sensitive

GPM

K-Cs-Sb

CsI

Lyashenko et al., JINST (2009) 4 P07005


Short-term GPM stabilityShort-term GPM stability

Rate: 12kHz/mm2 photonsGain: 105

Total anode charge ~125μC

300 400 500 60005

10152025303540

fresh PC in vacuum in gas after 14 hours @ gain 105

file: 2

008-

05-2

5_FR

GM

_KCs

Sb_l

ong_

term

_sta

b

700 Torr Ar/CH4 (95/5)

QE

[%]

Wavelength [nm]

K2CsSb


Visible-sensitive GPM featuresVisible-sensitive GPM features

Single photon sensitivityNo ion-feedback

Fast ns pulses

19 ns0 100 200 300 400 500

100

101

102

103

104

105

Gain ~ 105

Gain ~ 2*105

Gain ~ 3*105

700 Torr Ar/CH4 (95/5)

K-Cs-Sb (QE~26%@375nm)F-R-MHSP/GEM/MHSP

Coun

ts

Channel

100 photoelectrons


SummarySummary

Alkali-antimonide PCs for GPMsHigh (>40%) QE values reached Stability in gas verifiedProbability of IISEE evaluated Required IBF estimated

MHSP/GEM-based CASCADED MULTIPLIERS• 100 times lower IBF than with cascaded GEMs with full efficiency for collecting primary electrons!• Gain ~105 reached with visible-sensitive K-Cs-Sb PC• Demonstrated stable GPM operation at a gain 105

• Atmospheric pressure operation Many potential applications in large-area photon detectors: Particle Physics, Medical Imaging, Astroparticle, Military, Bio

First evidence of high-gain continuous operation of visible-sensitive GPM

Documents

Alkali-antimonide Photocathodes for Gas-Avalanche Photomultipliers