Gunnar Lindstroem University of Hamburg

Gunnar Lindstroem – University of Hamburg Warsaw University 19-Oct-05 1

Gunnar LindstroemGunnar LindstroemUniversity of HamburgUniversity of Hamburg

See also:

Michael Moll Radiation Tolerant Sensors for Pixel Detectors

- CERN-RD50 project -Pixel2005 Bonn September 05

http://www.cern.ch/rd50http://www.cern.ch/rd50

Radiation Tolerant Detectorsfor Future HEP Experiments

Results from theCERN-RD50 Collaboration


Outline

Silicon Detectors for Particle Tracking

Motivation for R&D, the Challenge for Radiation Tolerance

The RD50 Collaboration

Radiation Damage, Deterioration of Detector Properties

Approaches for Solutions, Material and Device Engineering

Summary and Outlook


LHCproperties

Proton-proton collider, 2 x 7 TeVLuminosity: 1034

Bunch crossing: every 25 nsec, Rate: 40 MHzevent rate: 109/sec (23 interactions per bunch crossing)

Annual operational period: 107 sec

Expected total op. period: 10 years

Experimental requests Detector properties

Reliable detection of mips S/N ≈ 10

High event rate time + position resolution:

high track accuracy ~10 ns and ~10 µm

Complex detector design low voltage operation in normal ambients

Intense radiation field Radiation tolerance up to during 10 years 1015 hadrons/cm²

Feasibility, e.g. large scale availability200 m² for CMS known technology, low cost

Silicon Detectors: Favorite Choice for Particle Tracking

! Silicon Detectors meet all Requirements !


LHC ATLAS Detector – a Future HEP Experiment

Overall length: 46m, diameter: 22m, total weight: 7000t, magnetic field: 2TATLAS collaboration: 1500 members

micro-strip detectorfor particle tracking

principle of a silicon detector: solid state ionization chamber


Growing demand for Si-detectors in tracking applications

Covered area in m²


Main motivations for R&D on Radiation Tolerant Detectors: Super - LHC

RD50

• LHC upgrade LHC (2007), L = 1034cm-2s-1

(r=4cm) ~ 3·1015cm-2

Super-LHC (2015 ?), L = 1035cm-2s-1

(r=4cm) ~ 1.6·1016cm-2

• LHC (Replacement of components) e.g. - LHCb Velo detectors (~2010) - ATLAS Pixel B-layer (~2012)

• Linear collider experiments (generic R&D)Deep understanding of radiation damage will be fruitful for linear collider experiments where high doses of e, will play a significant role.

10 years

500 fb-1

5 years

2500 fb-1

5

0 10 20 30 40 50 60r [cm]

1013

51014

51015

51016

eq [

cm-2

]

total fluence eqtotal fluence eq

neutrons eq

pions eq

other charged

SUPER - LHC (5 years, 2500 fb-1)

hadrons eqATLAS SCT - barrelATLAS Pixel

Pixel (?) Ministrip (?)Macropixel (?)

(microstrip detectors)

[M.Moll, simplified, scaled from ATLAS TDR]

Adopted from M. Moll,CERN, Bonn, Sep-05

CERN-RD48

CERN-RD50


The CERN RD50 Collaboration http://www.cern.ch/rd50

RD50

Collaboration formed in November 2001Experiment approved as RD50 by CERN in June 2002Main objective:

Presently 251 members from 51 institutes

Development of ultra-radiation hard semiconductor detectors for the luminosity upgrade of the LHC to 1035 cm-2s-1 (“Super-LHC”).

Challenges: - Radiation hardness up to 1016 cm-2 required - Fast signal collection (Going from 25 ns to 10 ns bunch crossing ?)

- Low mass (reducing multiple scattering close to interaction point)- Cost effectiveness (big surfaces have to be covered with detectors!)

RD50: Development of Radiation Hard Semiconductor Devices for High Luminosity Colliders

Belarus (Minsk), Belgium (Louvain), Canada (Montreal), Czech Republic (Prague (3x)), Finland (Helsinki, Lappeenranta), Germany (Berlin, Dortmund, Erfurt, Freiburg, Hamburg, Karlsruhe), Israel (Tel Aviv), Italy

(Bari, Bologna, Florence, Padova, Perugia, Pisa, Trento, Turin), Lithuania (Vilnius), Norway (Oslo (2x)), Poland (Warsaw(2x)), Romania (Bucharest (2x)), Russia (Moscow), St.Petersburg), Slovenia (Ljubljana), Spain

(Barcelona, Valencia), Switzerland (CERN, PSI), Ukraine (Kiev), United Kingdom (Exeter, Glasgow, Lancaster, Liverpool, Sheffield, University of Surrey), USA (Fermilab, Purdue University,

Rochester University, SCIPP Santa Cruz, Syracuse University, BNL, University of New Mexico)



Scientific Organization of RD50

SpokespersonMara Bruzzi

INFN and University of Florence

Deputy-SpokespersonMichael Moll

CERN

Defect / Material Characterization

Bengt Svensson(Oslo University)

Defect Engineering

Eckhart Fretwurst(Hamburg University)

Macroscopic Effects

Jaakko Härkönen(Helsinki HIP)

New Structures

Mahfuzur Rahman (Glasgow University)

Full DetectorSystems

Gianluigi Casse (Liverpool University)

New Materials

Juozas V.Vaitkus(Vilnius University)

•Characterization: (pre/post irradiation) SIMS, IR, PL, Hall, TSC, DLTS, EPR,… - V2O, O-dimers,… - high res. CZ, … - clusters, .. •Theory:

Defect formation, defect annealing,energy states,…..

•DOFZ/Oxygenation•High resistivity CZ•Epitaxial Silicon•Dimerization•Other impurities

H, N, Ge, …•Thermal donors•Pre-irradiation treatments

• SiC• CdTe• other materials

•Test structure characterization

IV, CV, CCE•NIEL•Device modeling•Operational conditions

•3D detectors•Thin detectors•Cost effective solutions

•LHC-like tests•Links to HEP•Links to R&D of electronics•Comparison: pad-mini-full detectors

CERN contact: Michael Moll


Radiation Damage in Silicon Sensors Two general types of radiation damage in detector materials:

Bulk (Crystal) damage due to Non Ionizing Energy Loss (NIEL) - displacement damage, built up of crystal defects –

I. Change of effective doping concentration (higher depletion voltage, under- depletion) II. Increase of leakage current (increase of shot noise, thermal runaway)

III. Increase of charge carrier trapping (loss of charge)

Surface damage due to Ionizing Energy Loss (IEL) - accumulation of positive in the oxide (SiO2) and the Si/SiO2 interface – affects: interstrip capacitance (noise factor), breakdown behavior, …

Impact on detector performance and Charge Collection (depending on detector type and geometry and readout

electronics!)

Signal/noise ratio is the quantity to watch Sensors can fail from radiation damage !Adopted from M. Moll,CERN, Bonn, Sep-05


Non Ionizing Energy Loss NIEL: displacement damage

10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103 104

particle energy [MeV]

10-5

10-4

10-3

10-2

10-1

100

101

102

103

104

D(E

) / (9

5 M

eV m

b)

neutronsneutrons

pionspions

protonsprotons

electronselectrons

100 101 102 103 104

0.4

0.60.8

1

2

4

neutronsneutrons

pionspions

protonsprotons

Point defects + clusters

Dominated by clusters

Damage effects generally ~ NIEL, however differences between proton & neutron damage


Radiation Damage I. – Effective doping concentration

n+ p+ n+

10-1 100 101 102 103

eq [ 1012 cm-2 ]

1

510

50100

5001000

5000

Ude

p [V

] (d

= 3

00m

)

10-1

100

101

102

103

| Nef

f | [

1011

cm

-3 ]

600 V

1014cm-2

type inversion

n-type "p-type"

[M.Moll: Data: R. Wunstorf, PhD thesis 1992, Uni Hamburg]

p+

Change of Depletion Voltage Vdep (Neff) …. with particle fluence:

“Type inversion”: Neff changes from positive to negative (Space Charge Sign Inversion)

Short term: “Beneficial annealing” Long term: “Reverse annealing” - time constant depends on temperature: ~ 500 years (-10°C) ~ 500 days ( 20°C) ~ 21 hours ( 60°C) - Consequence: Detectors must be cooled even when the experiment is not running!

…. with time (annealing):

NC

NC0

gC eq

NYNA

1 10 100 1000 10000annealing time at 60oC [min]

0

2

4

6

8

10

N

eff [

1011

cm-3

]

[M.Moll, PhD thesis 1999, Uni Hamburg]

before inversionafter inversion

„Hamburg model“


Radiation Damage II. – Leakage current

1011 1012 1013 1014 1015

eq [cm-2]10-6

10-5

10-4

10-3

10-2

10-1

I /

V

[A/c

m3 ]

n-type FZ - 7 to 25 Kcmn-type FZ - 7 Kcmn-type FZ - 4 Kcmn-type FZ - 3 Kcm

n-type FZ - 780 cmn-type FZ - 410 cmn-type FZ - 130 cmn-type FZ - 110 cmn-type CZ - 140 cm

p-type EPI - 2 and 4 Kcm

p-type EPI - 380 cm

[M.Moll PhD Thesis][M.Moll PhD Thesis]

1 10 100 1000 10000annealing time at 60oC [minutes]

0

1

2

3

4

5

6

(t)

[10-1

7 A/c

m]

1

2

3

4

5

6

oxygen enriched silicon [O] = 2.1017 cm-3

parameterisation for standard silicon [M.Moll PhD Thesis]

80 min 60C

…. with time (annealing):

Tk

EIB

g2exp

Damage parameter (slope in figure)

Leakage current per unit volume and particle fluence

is constant over several orders of fluenceand independent of impurity concentration in Si can be used for fluence measurement

Change of Leakage Current (after hadron irradiation) …. with particle fluence:

eqVI

α

Leakage current decreasing in time (depending on temperature) Strong temperature dependence:

Consequence: Cool detectors during operation! Example: I(-10°C) ~1/16 I(20°C)


Radiation Damage III. – Charge carrier trapping

Deterioration of Charge Collection Efficiency (CCE) by trapping

Trapping is characterized by an effective trapping time eff for electrons and holes:

tQtQ

heeffhehe

,,0,

1exp)( defects

heeff

N,

1

where:

0 2.1014 4.1014 6.1014 8.1014 1015

particle fluence - eq [cm-2]

0

0.1

0.2

0.3

0.4

0.5

Inve

rse

trapp

ing

time

1/

[ns-1

]

data for electronsdata for electronsdata for holesdata for holes

24 GeV/c proton irradiation24 GeV/c proton irradiation

[M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund][M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund]

….. and change with time (annealing):

5 101 5 102 5 103

annealing time at 60oC [min]

0.1

0.15

0.2

0.25

Inve

rse

trapp

ing

time

1/

[ns-1

]data for holesdata for holesdata for electronsdata for electrons

24 GeV/c proton irradiation24 GeV/c proton irradiationeq = 4.5.1014 cm-2 eq = 4.5.1014 cm-2

[M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund][M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund]

Increase of inverse trapping time (1/) with fluence



Impact on Detector: Decrease of CCE

Two basic mechanisms reduce collectable charge: - trapping of electrons and holes (depending on drift and shaping time !)

- under-depletion (depending on detector design and geometry !)

Example: ATLAS microstrip detectors + fast electronics (25ns)

p-in-n : oxygenated versus standard FZ- beta source- 20% charge loss after 5x1014 p/cm2 (23 GeV)

n-in-n versus p-in-n - same material, ~ same fluence- over-depletion needed

0 1 2 3 4 5p [1014 cm-2]

0

20

40

60

80

100

Q/Q

0 [%

]

oxygenatedstandard

max collected charge (overdepletion)

collected at depletion voltage

M.Moll [Data: P.Allport et all, NIMA 501 (2003) 146]

0 100 200 300 400 500 600bias [volts]

0.20

0.40

0.60

0.80

1.00

CC

E (a

rb. u

nits

)n-in-n (7.1014 23 GeV p/cm2)

n-in-n

p-in-n (6.1014 23 GeV p/cm2)

p-in-n

Laser (1064nm) measurements

[M.Moll: Data: P.Allport et al. NIMA 513 (2003) 84]



Approaches for Radiation Hardening

Scientific strategies:

I. Material engineering

II. Device engineering

III. Change of detectoroperational conditions

CERN-RD39“Cryogenic Tracking Detectors”„Lazarus Effect“

Defect Engineering of SiliconUnderstanding radiation damage

Macroscopic effects and Microscopic defectsSimulation of defect properties & kineticsIrradiation with different particles & energies

Oxygen rich SiliconDOFZ, Cz, MCZ, EPI

Oxygen dimer & hydrogen enriched SiPre-irradiated SiInfluence of processing technology

New MaterialsSilicon Carbide (SiC), Gallium Nitride (GaN)Diamond: CERN RD42 CollaborationAmorphous silicon

Device Engineering (New Detector Designs)p-type silicon detectors (n-in-p)thin detectors3D and Semi 3D detectorsStripixelsCost effective detectorsSimulation of highly irradiated detectorsMonolithic devices



Different Sensor mMaterials

R&D on diamond detectors:RD42 – Collaboration

http://cern.ch/rd42/

Recent review: P.J.Sellin and J.Vaitkus on behalf of RD50 “New materials for radiation hard semiconductor detectors”, submitted to NIMA

Property Diamond GaN 4H SiC Si Eg [eV] 5.5 3.39 3.26 1.12 Ebreakdown [V/cm] 107 4·106 2.2·106 3·105 e [cm2/Vs] 1800 1000 800 1450 h [cm2/Vs] 1200 30 115 450 vsat [cm/s] 2.2·107 - 2·107 0.8·107 Z 6 31/7 14/6 14 r 5.7 9.6 9.7 11.9 e-h energy [eV] 13 8.9 7.6-8.4 3.6 Density [g/cm3] 3.515 6.15 3.22 2.33 Displacem. [eV] 43 15 25 13-20

Wide bandgap (3.3eV) lower leakage current

than siliconSignal:

Diamond 36 e/mSiC 51 e/mSi 89 e/m

more charge than diamond

Higher displacement threshold than silicon

radiation harder than silicon (?)

Example: is SiC an option?

Result for SiC: very low CCE even for very thin devices



Monocrystalline Material: Float Zone Silicon (FZ)Float Zone process

Using a single Si crystal seed, meltthe vertically oriented rod onto the seed using RF power and “pull” themonocrystalline ingot

Mono-crystalline Ingot

Wafer production Slicing, lapping, etching, polishing

Oxygen enrichment (DOFZ) Oxidation of wafer at high temperatures



Czochralski Silicon (Cz) & Epitaxial Silicon (EPI)

Czochralski silicon • Pull Si-crystal from a Si-melt contained in a silica crucible while rotating.

• Silica crucible is dissolving oxygen into the melt high concentration of O in CZ

• Material used by IC industry (cheap) • Recent developments (~2 years) made CZ

available in sufficiently high purity (resistivity) to allow for use as particle detector.

Epitaxial silicon• Chemical-Vapor Deposition (CVD) of Silicon• CZ silicon substrate used in-diffusion of oxygen• growth rate about 1m/min• excellent homogeneity of resistivity• up to 150 m thick layers produced (thicker is possible)• price depending on thickness of epi-layer but not

extending ~ 3 x price of FZ wafer



Oxygen in FZ, Cz and EPI

0 10 20 30 40 50 60 70 80 90 100Depth [m]

51016

51017

51018

5

O-c

once

ntra

tion

[1/c

m3 ]

SIMS 25 m SIMS 25 m

25 m

u25

mu

SIMS 50 mSIMS 50 m

50 m

u50

mu

SIMS 75 mSIMS 75 m

75 m

u75

mu

simulation 25 msimulation 25 msimulation 50 msimulation 50 msimulation 75msimulation 75m

Cz and DOFZ silicon

0 50 100 150 200 250depth [m]

51016

51017

51018

5

O-c

once

ntra

tion

[cm

-3]

51016

51017

51018

5

Cz as grown

DOFZ 72h/1150oCDOFZ 48h/1150oCDOFZ 24h/1150oC [G.Lindstroem et al.] [G.Lindström et al.,10th European Symposium on

Semiconductor Detectors, 12-16 June 2005]

• DOFZ: inhomogeneous oxygen distribution• DOFZ: oxygen content increasing with time

at high temperature

EPIlayer CZ substrate

• CZ: high Oi (oxygen) and O2i (oxygen dimer) concentration (homogeneous)

• CZ: formation of Thermal Donors possible !

Epitaxial silicon

• EPI: Oi and O2i (?) diffusion from substrate into epi-layer during production

• EPI: in-homogeneous oxygen distribution


Change of Neff: FZ, DOFZ, Cz and MCz Silicon

24 GeV/c proton irradiation

• Standard FZ silicon• type inversion at ~ 21013 p/cm2

• strong Neff increase at high fluence

• Oxygenated FZ (DOFZ)• type inversion at ~ 21013 p/cm2

• reduced Neff increase at high fluence

0 2 4 6 8 10proton fluence [1014 cm-2]

0

200

400

600

800

Vde

p [V

]

0

2

4

6

8

10

12

Nef

f [10

12 c

m-3

]

CZ <100>, TD killedCZ <100>, TD killedMCZ <100>, HelsinkiMCZ <100>, HelsinkiSTFZ <111>STFZ <111>DOFZ <111>, 72 h 11500CDOFZ <111>, 72 h 11500C

• CZ silicon and MCZ silicon no type inversion in the overall fluence range (verified by TCT measurements)

(verified for CZ silicon by TCT measurements, preliminary result for MCZ silicon) donor generation overcompensates acceptor generation in high fluence range

• Common to all materials (after hadron irradiation): reverse current increase increase of trapping (electrons and holes) within ~ 20%



Change of Neff: EPI Silicon

No type inversion in the full range up to ~ 1016 p/cm2 and ~ 1016 n/cm2 (type inversion only observed during long term annealing)Proposed explanation: introduction of shallow donors bigger than generation of deep acceptors

Epitaxial silicon grown by ITMELayer thickness: 25, 50, 75 m; resistivity: ~ 50 cmOxygen: [O] 91016cm-3; Oxygen dimers (detected via IO2-defect formation)

0 2.1015 4.1015 6.1015 8.1015 1016

eq [cm-2]

0

5.1013

1014

Nef

f (t 0)

[cm

-3]

0

50

100

150

Vfd

(t0)

[V] n

orm

aliz

ed to

50 m

50 m50 m25 m25 m

Reactor neutronsReactor neutronsTa = 80oCTa = 80oC

0 2.1015 4.1015 6.1015 8.1015 1016

eq [cm-2]

0

1014

2.1014

Nef

f(t0)

[cm

-3]

25 m, 80 oC25 m, 80 oC50 m, 80 oC50 m, 80 oC75 m, 80 oC75 m, 80 oC

23 GeV protons23 GeV protons

320V (75m)

105V (25m)

230V (50m)

G.Lindström et al.,10th European Symposium on Semiconductor Detectors, 12-16 June 2005


Epitaxial Silicon - Annealing

0 20 40 60 80 100proton fluence [1014 cm-2]

0

50

100

150

200

250

Vde

p [V

]

0.20.40.60.81.01.21.4

|Nef

f| [1

014 c

m-3

]

EPI (ITME), 50mEPI (ITME), 50mFZ (MPI), 50mFZ (MPI), 50m

Ta=80oCTa=80oCta=8 minta=8 min

100 101 102 103 104 105

annealing time [min]

0

50

100

150

Vfd

[V]

EPI (ITME), 9.6.1014 p/cm2EPI (ITME), 9.6.1014 p/cm2

FZ (MPI), 1.7.1015 p/cm2FZ (MPI), 1.7.1015 p/cm2

Ta=80oCTa=80oC

[E.Fretwurst et al., Hamburg][E.Fretwurst et al., Hamburg]

• 50 m thick silicon detectors:- Epitaxial silicon (cm on CZ substrate, ITME & CiS) - Thin FZ silicon (4Kcm, MPI Munich, wafer bonding technique)

• Thin FZ silicon: Type inverted, increase of depletion voltage with time• Epitaxial silicon: No type inversion, decrease of depletion voltage with time

No need for low temperature during maintenance of SLHC detectors!



Damage Projection – SLHC

- 50 m EPI silicon: a solution for pixels ?-G.Lindström et al.,10th European Symposium on Semiconductor

Detectors, 12-16 June 2005 (Damage projection: M.Moll)

Detector withcooling when not

operated

0 365 730 1095 1460 1825time [days]

0

100

200

300

400

500

600

Vfd

[V]

50 m cold50 m cold50 m warm50 m warm25 m cold25 m cold25 m warm25 m warm

S-LHC scenarioS-LHC scenario

Detector withoutcooling when not

operated

Radiation level (4cm): eqeq(year) = 3.5 (year) = 3.5 10 101515 cm cm-2 -2

SLHC-scenario: 1 year = 1 year = 100 days beam (-7100 days beam (-7C)C) 30 days maintenance (20 30 days maintenance (20C)C)

235 days no beam (-7235 days no beam (-7C or 20C or 20C)C)


Signal from irradiated EPI

Epitaxial silicon: CCE measured with beta particles (90Sr)25ns shaping timeproton and neutron irradiations of 50 m and 75 m epi layers

CCE (50 m) eq= 8x1015 n/cm-2,

2300 electrons

CCE (75 m) = 2x1015 n/cm-2,4500 electrons

CCE (50 m): 1x1016cm-2 (24GeV/c protons) 2400 electrons

[G.Kramberger et al.,RESMDD - October 2004]Adopted from M. Moll,CERN, Bonn, Sep-05


Microscopic defects

Damage to the silicon crystal: Displacement of lattice atoms

I

I

V

V

Distribution of vacancies created by a 50 keV Si-ion

in silicon (typical recoil energy for 1 MeV neutrons):

Schematic[Van Lint 1980]

Simulation[M.Huhtinen 2001]

Vacancy + Interstitial

“point defects”, mobile in silicon,can react with impurities (O,C,..)

V

Iparticle SiS EK>25 eV

EK > 5 keVpoint defects and defect clusters

Defects can be electrically active (levels in the band gap) - capture and release electrons and holes from conduction and valence band can be charged - can be generation/recombination centers - can be trapping centers



Characterization of microscopic defects - gamma and proton irradiated silicon detectors -

2003: Major breakthrough on g-irradiated samplesFor the first time macroscopic changes of the depletion voltage and leakage current can be explained by electrical properties of measured defects !

2004: Big step in understanding the improved radiation tolerance of oxygen enriched and epitaxial silicon after proton irradiation

[APL, 82, 2169, March 2003]

[I.Pintilie, RESMDD, Oct.2004]

Levels responsible for depletion voltage changes after proton irradiation:

Almost independent of oxygen content:• Donor removal •“Cluster damage” negative charge

Influenced by initial oxygen content:• I–defect: deep acceptor level at EC-0.54eV (good candidate for the V2O defect) negative charge Influenced by initial oxygen dimer content (?):• BD-defect: bistable shallow thermal donor (formed via oxygen dimers O2i) positive charge

See further: I. Pintilie et al, NIM A 556 (2005) 56 + NIM A, in press


Device Engineering: p-in-n versus n-in-n


p-on-n silicon, under-depleted:

• Charge spread – degraded resolution

• Charge loss – reduced CCE

p+on-n

n-on-n silicon, under-depleted:

•Limited loss in CCE

•Less degradation with under-depletion

•Collect electrons (fast)

n+on-nn-type silicon after type inversion:


n-in-p microstrip detectors

• Miniature n-in-p microstrip detectors (280mm) • Detectors read-out with LHC speed (40MHz) chip (SCT128A) • Material: standard p-type and oxygenated (DOFZ) p-type• Irradiation:

G. Casse et al., NIMA 535 (2004) 362

CCE ~ 60% after 3 1015 p cm-2 at 900V( standard p-type)

0 2.1015 4.1015 6.1015 8.1015 1016

fluence [cm-2]

0

5

10

15

20

25

CCE

(103 e

lect

rons

)

24 GeV/c proton irradiation24 GeV/c proton irradiation

[Data: G.Casse et al., Liverpool, February 2004][Data: G.Casse et al., Liverpool, February 2004]

CCE ~ 30% after 7.5 1015 p cm-2 900V (oxygenated p-type)

n-in-p: - no type inversion, high electric field stays on segmented side - collection of electrons

At the highest fluence Q~6500e at Vbias=900V

eq = 4.6 1015 cm-2



Does thickness pay? Low fluence eq ≤ 1014 cm-2:negligible trapping of charge carriers, signal for mip (minimum ionizing particle) proportinal to detector thickness: S ~ d

Trapping material independent, strong increase with fluence (see above)

Large fluence eq ≥ 5·1015 cm-2:signal height dominated by charge trapping, collection distance deff ≤ 100 msignal for mip: S ~ deff

10 years at LHC

5 y S-LHCEquiv. Fluence in 1015 cm-2

Signal vs. Φeq for 600V Signal vs. bias for Φeq = 1016 cm-2

! After Φeq = 1016 cm-2 S(mip) = about 2000-2500 e regardless of material and thickness !

T. Lari, Milano


Summary At fluences up to 1015cm-2 (Outer layers of a SLHC detector) the change of depletion

voltage and the large area to be covered by detectors is the major problem. CZ silicon detectors could be a cost-effective radiation hard solution

(no type inversion, use p-in-n technology) p-type silicon microstrip detectors show very encouraging results:

CCE 6500 e; eq=

41015 cm-2, 300m, collection of electrons, no reverse annealing observed in CCE measurement!

At the fluence of 1016cm-2 (Innermost layer of a SLHC detector) the active thickness of any silicon material is significantly reduced due to trapping. The promising new options are: ⁃Thin/EPI detectors : drawback: radiation hard electronics for low signals needed e.g. 2300e at eq 8x1015cm-2, 50m EPI, …. thicker layers will be tested in 2005/2006 ⁃ 3D detectors : drawback: technology has to be optimized ….. steady progress within RD50

New Materials like SiC and GaN (not shown) have been characterized . ⁃ CCE tests show that these materials are not radiation harder than silicon

Adopted from M. Moll,CERN, Bonn, Sep-05Further information: http://cern.ch/rd50/

Gunnar Lindstroem University of Hamburg

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