J.Harkonen and Z.Li, LHCC open session, CERN, 24th November 2004. CERN RD39 Collaboration: Cryogenic...

J.Harkonen and Z.Li, LHCC open session, CERN, 24th November 2004.

CERN RD39 Collaboration: Cryogenic Tracking Detectors

RD39 Status Report 2004

Jaakko Härkönen Helsinki Institute of Physics, Finland

Zheng Li Brookhaven National Laboratory, USA



OUTLINE

•Trapping: A limiting factor for detector operation •RD39 Strategy for radiation hardness up to 1016

neq/cm2

•Charge Injected Detector CID•Experimental results•Cryogenic detector module activities•Summary•Workplan for 2005


CERN RD39 Collaboration: Cryogenic Tracking DetectorsTrapping: A limiting factor for detector

operation

tthNvt

1 The trapping time-constant

is not dependent on T

The thermal velocity vth saturates at 20 kV/cm E-field to 107cm/s1016 neq/cm2 irradiation produces NT3-5*1015 cm-3 with 10-

15cm2 Particle generated charge carrier drifts 20-30m before it gets trapped regardless whether the detector is fully depleted or not ! 1016 neq/cm2 radiation load: 80-90% of the volume of d=300m detector is dead space !



HOW A TRAP CAN BE NEUTRALIZED ?

By filling them with current/charge or light injection.

0

2

4

6

8

10

12

14

16

18

100 150 200 250 300

T(K)

Q (

arb

. un

its)

Qcol

Qpol

•p+np+ symmetric structure irradiated to 3.75·1015 cm–2

•Bias potential 300 V (Qcol) or 0 V (Qpol ; the electric field is induced by the polarization of the detector)

•The p+np+ detector with this fluence can be operated already at 100 V bias

•Standard p+nn+ detector would deplete fully only above 1 kV bias at this fluence

CID (Charge Injected Detector) irradiated with 3,8*1015 n/cm2



DETRAPPING

The detrapping time-constant depends exponentially on T

kTECth

td eNv /

1

If a trap is filled (electrically non-active) the detrapping time-constant is crucial

For A-center (O-V at Ec-0.18 eV with 10-15 cm2 )

T(K) 300 150 100 77 60 55 50 45 40

d 10ps

10ns

10s

6ms

12.3s

5min

3,6 h

15 days

13 years



RD39 Strategy for radiation hardness up to 1016 neq/cm2

The detector CCE can be considered to be a product of two factors:

tdrttGF ed

wCCECCECCE /

,

Depletion term

Trapping term

o Electric field manipulation to increase depletion depth w (original Lazarus effect) CCEGF ~ 1

o Freeze out trapping effect at T lower than LHe T CCEt ~ 1


P+ P+

Jp

Jp = epμE

divJ=0

divE=ptr

E(x=0) = 0 (SCLC mode)

E(x) ~ V √ X

J(V) = V2

E(x)

The key advantage: The shape of E(x) is not affected by Nmgl, and stable at any fluence

Current injected detector (principle of operation)

xd

+


E(x) E(x)E(x)E(x)

x x x x

Ohmic mode

p>>ptr

E(x) = V/d J ~ V

“Diode” mode

p>ptr

E(x) ~ E(0) + ax

DL saturation p >> ptr E(x) = ax

SCLC mode

Ndl>ptr

E(x) ~ SQR(x) J ~ V2

Evolution of E(x) in CID with the injected current


log J

log V

Ohmic, J ~ V

SCLC, J ~ V2

DL saturation

“Diode”

I-V characteristic of CID

Proof of CID concept: – observation of SCLC and DL saturation behavior

Problem: - optimal range of V for CID operation


CID I-V simulation

Sample parameters Physical constants Calculated valuesd [cm] 0.035 eps0[F/m] 8.85E-14 mu [cm2/V*s]

Uc[V] 0 eps 11.7 VsN0[cm-3] 0.00E+00 q[C] 1.60E-19 Vth*Nc 4.13E+26Operation parameters k[J/K] 1.38E-23 Vth*Nv 1.25E+26

Ub [V] 30 oe [cm 2̂/Vs] 2.08E+03 Nc[cm-3] 2.1741E+19Temperature 250 vse [cm/s] 1.12E+07 Nv[cm-3] 8.6963E+18

dX [cm] 1.00E-04 be[T] 7.82E-01 ni[T],cm-3 7.23E+07

injected current oh [cm 2̂/Vs] 8.17E+02

Egen, eV 0 vsh [cm/s] 8.14E+06 IntN(d) 0.00E+00

Sig(e), cm2 0.00E+00 bh[T] 9.87E-01 Vth(e),cm/s 1.90E+07

Sig(h), cm2 0.00E+00 Eg (eV0 1.12 Vth(h),cm/s 1.44E+07

M, cm-3 0.00E+00 Parameter Ef, eV 0.56Jn [A/cm2] 0.00E+00 Calculated Ef, eV 0.01 DL #

Jp [A/cm2] 1.00E+00 D/A, 0/1 0 1 0 1electrons holes electrons holes electrons holes electrons holes

Et=Edl-Ev 1.117 0.6 0.48 0.64 0.55 0.57

E(x) calculation sig/e[cm2] 1.00E-15 1.00E-17 1.00E-15 5.00E-15

Iterations 2 Imin, A/cm2 1.00E-12 sig/h[cm2] 1.00E-15 1.00E-15 1.00E-15 5.00E-15

Kdesipaiton 0.8 points 50 Ndl[cm-3] 0.00E+00 0.00E+00 2.80E+12 0.00E+00

Imax, A/cm2 1.00E+00 Sig*Vth 1.90E-08 1.44E-08 1.90E-10 1.44E-08 1.90E-08 1.44E-08 9.49E-08 7.19E-08

detrap.prob. 3.59E+11 3.97E-12 1.39E-01 1.03E-01 5.31E-02 2.69E+01 6.82E+00 5.23E+00

Row X E0(x) E1(x) n(x) p(x) Ff(x) Neff(x) Ff(x) Neff(x) Ff(x) Neff(x) Ff(x) Neff(x)

# cm V/cm v/cm cm-3 cm-3

I-V calculationMACRO

shallow donors deep acceptor deepdonor shallow acceptors

0.0E+0

5.0E+3

1.0E+4

1.5E+4

2.0E+4

2.5E+4

3.0E+4

0 0.01 0.02 0.03 0.04 0.05

E(x)

0.0E+005.0E+121.0E+131.5E+132.0E+132.5E+133.0E+13

0.00 0.02 0.04 0.06

Neff

1.E+001.E+021.E+041.E+061.E+081.E+101.E+121.E+14

0.00 0.02 0.04 0.06

n(x)p(x)

start

CID I-V simulation software


A12, Cz(PTI), P+- N - N+, Fn=1015cm-2

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1 10 100 1000

Bias, V

Cu

rren

t, A

/cm

2

180k

200k

220k

250k

Fit 180K

Fit 200K

Fit 220K

Fit 250K

CID I-V characteristics


CID I-V characteristics

1,E-10

1,E-09

1,E-08

1,E-07

1,E-06

1,E-05

1,E-04

1,E-03

1,E-02

1 10 100 1000 10000

Voltage (V)

Cu

rre

nt d

en

city

(A

/cm

2)

5e14 cm-2

1e15 cm-2

3e15 cm-2

Fit

Fit

Fit

Fit, 1e16 cm-2

Experimental and simulated IV’s of CIDs @ 220K

Decreasing I with fluence !!


Fn=1015cm -2, T=220K

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1 10 100 1000

Bias, V

Cu

rre

nt,

μA

/cm

2

Wacker FZ, BNL

Wacker FZ, HIP

Cz HIP

Wacker FZ, PTI

Cz, PTI

Reproducibility of CID technology(detector dark current)

J=V2/d3


0

100

200

300

400

500

600

700

800

900

1000

0.0E+00 5.0E+14 1.0E+15 1.5E+15 2.0E+15 2.5E+15 3.0E+15 3.5E+15

Fluence, n/cm2

Th

res

ho

ld v

olt

ag

e,

V

FZ, Wacker, BNL

FZ, Wacker, HIP

ZC, HIP

FZ, Wacker, PTI

CZ, PTI

Reproducibility of CID technology(threshold voltage)

Vthr= Ntr·d2

Vthr~ Φ·d2


CCE measurements

Injection mode

Standard mode


• Silicon P+ - n – N+ and P+ - n – P+ structures heavily irradiated by neutrons operate in SCLC mode with hole injection

• The I-V threshold voltage and the dark current are in the range of hundreds volts, which fits to the detector application requirements

• CID I-Vs are stable under irradiation

• Technology of CIDs is developed with pre-irradiation by neutrons

• No effect for the detector performance by:– type of Si – technology

• The developed software for CIDs engineering allows proper simulation of I-Vs with two key physical parameters:

– Deep trap activation energy of 0.48eV from the valence band– Deep trap concentration proportional to fluence

Conclusions



CHARGE INJECTION SUMMARY

If a trap level is filled (say, by current or charge injection) and then frozen (very long detrapping time) at cryogenic temperatures, this trap level will no longer be able to trap free carriers again, and it becomes electrically inactive.

In this case, the CCE can be improved as well to a value close to 1

CCE can be increased close to 1 by manipulating the electric field in the detector via current and/or charge injection at temperatures from 130 K to 150 K.

Feasible solution for very high luminosity colliders ?



LOW TEMPERATURE SUMMARY

Readout electronics becomes faster and has lower noise

No leakage current >> low electrical power from HV supply

Low depletion voltage (original Lazarus effect)

CCE increase without reduction of detector thickness (increase of charge collection depth)



RD39 RESOURCES

*Device processing: Brookhaven National Laboratory BNL (USA), Ioffe PTI

(Russia), Helsinki Institute of Physics HIP (Finland).

*Irradiations: protons (Accelerator Laboratory,Univ. of Jyvaskyla,Univ. of

Karlsruhe) neutron (Jozef Stefan Institute JSI, Ljubljana) 60Co (Brookhaven National Laboratory)

*Characterizations:CCE JSI, FCT Algarve University, Faro, Portugal DLTS Univ. of Florence, PTI TCT BNL, PTI

CV/IV Practically all member institutes



RD39 WORKPLAN FOR 2005

Device Physics and Basic Research • Optimization of Deep Level (DL) spectra by CID pre-irradiation and intentional contamination. • CCE measurements on CID pre-irradiated by protons and neutrons• Strip detectors based on CID approach (strips). •Completetion of LH TCT setup construction at CERN cryolab.

1. Testing of new etching techniques of edgeless detectors. 2. Improving the cryomodule operation below 200K3. Module construction of CID strip detectors.

Cryomodules

J.Harkonen and Z.Li, LHCC open session, CERN, 24th November 2004. CERN RD39 Collaboration: Cryogenic...

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