Czochralski Silicon- a radiation hard

material?

Vertex 2005 November 7 – 11

Chuzenji Lake, Japan

Alison BatesThe University of Glasgow, UK.

2

• Main players:– Ljubljana, CERN, SMART, CNM, Helsinki,

BNL and Hamburg.

Cz Characterization – Overview

Non-irradiated diodes

Diodes

protons

Diodes

neutrons

Diodes

π, e, γ

Strip detector

Irradiated strip detector

Lab tests TCT DLTS, TSC,.. Test beams

VA and LHC

speed

LHC speed

Lab measurements study:CVIV

Annealing studies

TCT provides:Depletion voltage (QV)

CCESpace charge determination

Electric field profileTrapping times

Defect characterization:Specific defect level

concentrationsTest beams:

Towards detector grade components…

CCEResolution

S/N,…..

3

• A crystalline silicon growth method.

– The growth method used by the IC industry. – Recent developments (~3 years) has meant that the silicon is

now of sufficient purity to allow use for HEP detectors.

• Pull Si-crystal from a Si-melt while rotating.

• Cz Silicon has an intrinsically high level of oxygen.

• MCz is Cz silicon grown in the presence of an magnetic field.

• Cheap production.

• Common production technique.

Czochralski Growth

What is Czochralski Silicon?

• IRST (Italy), CNM (Spain), CiS (Germany), Helsinki Institute of Physics (Finland) and BNL (USA) have all successfully produced Cz detectors.

4

Float Zone silicon (FZ)-the usual growth method used to make HEP detectors

Single crystal silicon

Poly silicon

RF Heating coil

Float Zone Growth

• Start with a polysilicon rod inside a chamber either in a vacuum or an inert gas

• An RF heating coil melts ≈2 cm zone in the rod

• The RF coil moves through the rod, moving the molten silicon region with it

• This melting purifies the silicon rod

• Oxygen can be diffused into the silicon – called Diffusion Oxygenated Float Zone (DOFZ) (done at the wafer level)

5

• O in Diffusion Oxygenated FZ (DOFZ) ~ 1x1017 cm-3

• O in magnetic Cz (MCz) ~ 2-5 x1017 cm-3

Why should Cz be any better? - Oxygen is important

• DOFZ: Saturation of reverse annealing

(24 GeV/c p - only little effect after neutron irradiation observed !)

• DOFZ silicon has less variation in Vfd with radiation compared to FZ – more radiation hard

• Adding carbon to silicon decreases the radiation hardness

For hadron radiation only

0 1 2 3 4 524 GeV/c proton [1014 cm-2]

0

2

4

6

8

10

|Nef

f| [

1012

cm-3

]100

200

300

400

500

600

Vde

p [V

] (3

00 m

)

Carbon-enriched (P503)Standard (P51)

O-diffusion 24 hours (P52)O-diffusion 48 hours (P54)O-diffusion 72 hours (P56)

Carbonated

Standard

Oxygenated

6

• DOFZ: Saturation of reverse annealing

(24 GeV/c p - only little effect after neutron irradiation observed !)

0 2.1014 4.1014 6.1014 8.1014 1015

p [p/cm2]

0.0

0.5

1.0

1.5

2.0

NY [1

013/c

m3 ]

200

400

600

800

1000

Vde

p [V

] (2

80 m

)standard standard

DOFZ 24h/1150oCDOFZ 24h/1150oC

DOFZ 72h/1150oCDOFZ 72h/1150oC

20 GeV/c proton irradiation

[G.Lindstroem et al.]

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

0

2

4

6

8

10

N

eff [

1011

cm-3

]

NC

NC0

gC eq

NA NA NY

[M.Moll]

Reverse Annealing Component

Why should Cz be any better? - Oxygen is important

• O in Diffusion Oxygenated FZ (DOFZ) ~ 1x1017 cm-3

• O in magnetic Cz (MCz) ~ 2-5 x1017 cm-3

• DOFZ silicon has less variation in Vfd with radiation compared to FZ – more radiation hard

• Adding carbon to silicon decreases the radiation hardness

For hadron radiation only

7

Cz Characterization – leakage current

300μm thick 5x5 mm2 p+n silicon diodes (all 1 kΩcm) have been characterized before and after 24 GeV/c proton irradiation at the CERN PS.

Diodes processed at the Helsinki Institute of Physics from FZ, DOFZ and MCz silicon manufactured at Okmetric Oyj.

Silicon type α [A/cm]

FZ 4.96 x 10-17

DOFZ 4.85 x 10-17

MCz 4.73 x 10-17

The leakage current of MCz silicon after proton irradiation follows the same behaviour as FZ and DOFZ silicon

1012 1013 1014 1015

eq [ cm-2 ]

10-4

10-3

10-2

10-1

Nor

mal

ised

Cur

rent

[A

/cm

3 ]

FZ (f2)DOFZ (W317)DOFZ (d1)MCZ (n320)

4 min at 80oC

[A.G.Bates and M.Moll, to be published in NIMA]

8

The gradient of the slope after the minimum is β, which is a measure of the radiation hardness

Cz Characterization – radiation hard?

β has been measured to be smaller for MCz than DOFZ, FZ silicon for 10MeV, 50 MeV and 24 GeV proton irradiations

(E. Tuovinen, 4th RD50 workshop, May 2004)

MCz is more radiation hard than DOFZ or FZ silicon (with charged irradiation)

The irradiation experiments which have been performed with Cz/MCz are;

• reactor neutrons• 23 GeV protons• 10, 20, 30 MeV protons• 190 MeV pions• 900 MeV electrons• Co60 gamma

STFZDOFZCz

9

• Illuminate front (p+) or rear (n+) side of detector with 660 nm photons– Light penetrates only a few m depth

• Ramo’s theorem dictates signal will be dominated by one type of charge carrier

• I(t)=q E((t)) (t)drift

– e.g. hole dominated current (hole injection) is produced by illuminating the rear (n+) side of detector

660 nm laser light

p+

n+

Hole movement

Electron collection

Electric Field

De

pth

Front

rear

Hole injection

Low field

High field

Cz Characterization – Transient Current Technique

t[ns]0 5 10 15 20 25 30 35 40

]I

[V/5

0

0

0.01

0.02

0.03

0.04

0.05

U=150V

U=310V

Time [ns]Need signal deconvoluted from electronic shaping

10

Cz Characterization – Transient Current Technique

When the detector has been irradiated the drifting charge, Qe,h(t), will be lost with an exponential time dependence due to trapping in the defects

To derive the electric field profile/SC sign you must take trapping effects into account

The effective trapping probability, 1/eff, is the probability that a carrier is lost due to trapping in the silicon.

))(

exp()()(,

,,

heeff

oohehe

tttQtQ

Injection timeInjection charge

heeff

oheohe

tttQtQ

,

exp,,

Measured charge from detector

Corrected charge

Trapping compensation

11

For V>Vfd, then:

constant Q collected if no trapping

try various eff values

correct eff value is when gradient of this line is zero

Ch

arg

e [

arb

.]

Sqrt V [Sqrt V]

Cz Characterization – Transient Current Technique Charge Correction Method (CCM)

0 5 10 15t [ns]

0.02

0.04

0.06

0.08

0.10I

[V/5

0]

5

10

15

Q(t

) [a

rb.u

nits

]

corrected signalmeasured signal

integrated signal Example of an electron injection signal collected before (dashed) and after (solid line) the correction for the trapped charge. Details:

15 kΩcm FZ 5.2x1013 24 GeV/c p/cm2 Vfd = 30 Vmeasured at 90 V.

CCM method resulted in eff,e = 37.8 ns.

heeff

oheohe

tttQtQ

,

exp,,

12

Type inversion in FZ siliconElectron injection

= 1.74x1013 24 GeV/c p = 3.61x1014 24 GeV/c p

Low fieldLow field

High fieldHigh field

Time [ns] Time [ns]

I [V

/50O

hms]

I [V

/50O

hms]

1013 5 1014 524 GeV/c protons [ cm-2 ]

50

100

150

200

250

Vfd

[V]

1

2

3

| Nef

f | [

1012

cm

-3 ]

FZ (f2) - Vfd from CVFZ (f2) - Vfd from IV

13

TCT in MCzHole injection

• MCz silicon always has the high electric field on the structured side of the detector even after high fluences using standard p+-on-n MCz detectors

• Avoid the expensive double sided processing costs that arise from using n+-on-n silicon detectors

14

Alison BatesTime [ns]

I [V

/50O

hms]

Low field

High field NO TYPE INVERSION IN CZ SILICON UP TO 5x1014 p/cm2

Hole injection signal

1013 5 1014 524 GeV/c protons [ cm-2 ]

50

100

150

200

250

300

Vfd

[V]

1

2

3

4

| Nef

f | [

1012

cm

-3 ]

MCZ (n320) - Vfd from IVMCZ (n320) - Vfd from CV

5x1014 p/cm2

14

MCz @5x1014 p/cm2

Confirmed by Gregor Kramberger et. al

15

Effective doping concentration - FZ

0.0

0.0

0.0

0.0

0.0

0.1

0.1

0.1

0 20 40 60 80

Fluence (10^13 n/cm2)

Nef

f [1

0^12

cm

-3]

-0.5

-0.3

-0.1

0.1

0.3

0.5

0 20 40 60 80

Fluence (10^13 n/cm2)

Nef

f [1

0^12

cm

-3]

-0.5

-0.3

-0.1

0.1

0.3

0.5

0 20 40 60 80Fluence (10^13 n/cm2)

Nef

f [1

0^12

cm

-3]

Donor Removalbuild up of -ve SC|Neff|

Donor Removal

ND*exp(-cΦ)

Build up of negative space charge

Cluster and V20 responsible

Resultant Neff shape can be explained by the two processes

16

0.0

0.2

0.4

0.6

0.8

1.0

0 20 40 60 80

Fluence (10^13 n/cm2)

Nef

f [1

0^12

cm

-3]

-0.5

-0.3

-0.1

0.1

0.3

0.5

0 20 40 60 80Fluence (10^13 n/cm2)

Nef

f [1

0^12

cm

-3]

Donor Removalbuild up of -ve SC|Neff|build up of +ve SC

0.0

0.0

0.0

0.0

0.0

0.1

0.1

0.1

0 20 40 60 80

Fluence (10^13 n/cm2)

Nef

f [1

0^12

cm

-3]

-0.5

-0.3

-0.1

0.1

0.3

0.5

0 20 40 60 80

Fluence (10^13 n/cm2)

Nef

f [1

0^12

cm

-3]

Donor Removal

ND*exp(-cΦ)

Build up of negative space charge

Cluster and V20 responsible

Resultant Neff shape can be explained by the three processes

Build up of positive space charge

Due to radiation induced donors (linked to O2?)

MCz has higher Oxygen content than FZ

Effective doping concentration - Cz

17

• Trapping times

– Effective trap introduction rate, βe, for electrons agree within experimental errors for FZ, DOFZ and Cz silicon.

– Effective trap introduction rate, βh, for holes are 10-30% larger than βe for all of FZ, DOFZ and Cz.

Cz silicon has similar trapping to FZ and DOFZ silicon

Cz Characterization –trapping

eqheeff he

,

,

1

18

1 10 100 1000

-40

-20

0

20

40

60

80

100

120

140

p-type

T=80ºC

N

eff

(x

1E

11

cm-3

)

Time (min)

PN std irradiated 3E13 p/cm2 PN oxg irradiated 3E13 p/cm2 PN std irradiated 2E14 p/cm2 PN oxg irradiated 2E14 p/cm2 PN std irradiated 3E14 p/cm2 PN oxg irradiated 3E14 p/cm2 NP std. irradiated 3E14 p/cm2 MCZ irradiated 3E13 p/cm2 MCZ irradiated 2E14 p/cm2 MCZ irradiated 3E14 p/cm2

n-type

Annealing studies - MCz shows excellent annealing behaviour

Cz Characterization – annealing

G. Pellegrini et. al “Annealing Studies of magnetic Czochralski silicon radiation detectors” NIM A, article in press

Cz

FZ

DOFZ

19

• Test beam at the CERN SPS of a MCz detector* before and after irradiation– LHC speed electronics (40MHz)

(3 SCTA (analogue) chips)

– p+-on-n MCz material– Area read out = 6.1 x 1.92 cm– 380 m thick– 1150 cm (after processing)– 50 m pitch parallel strips– Vdep measured = 420 V (CV)

*Many thanks to the Helsinki Institute of Physics for

the MCz detector

Cz Characterization – test beam

NIM A 535 (2004) 428

20

MCz test beam results

S / N > 23.5 + 2.5

(380 m thick)

Depleted the detector (~550 V)

(CV measured Vdep ~ 420 V)

• 1.3 x 1014 24 GeV p/cm2 S/N = 15

• 4.3 x 1014 24 GeV p/cm2 S/N = 11 (under depleted)

• 7.0 x 1014 24 GeV p/cm2 S/N = 7

(under depleted)

Sig

nal

[A

DC

Co

un

ts]

Bias Voltage [V]]S

ign

al [

AD

C C

ou

nts

]Bias Voltage [V]]

Unirradiated Detector Irradiated Detector

21

• Czochralski silicon is a cheap and standard industrial method for growing high purity silicon.

• Cz silicon – shows increased radiation hardness when compared to FZ or

DOFZ with charged irradiation– does not type invert with charged particle radiation

(up to a 24 GeV/c proton fluence of 5.1014 p/cm2)

– has the same trapping behaviour as FZ and DOFZ– has small variation in Neff with annealing time

• Cz strip detector read out with LHC speed electronics shows promising results both before and after irradiation.

Cz Characterization – Conclusions

Is Czochralski silicon something to get excited about?

22

Back up slides

23

5 101 5 102 5 103

time [ min ]

20406080

100120140160180

Vfd

[V]

0.5

1.0

1.5

2.0

2.5

| Nef

f | [

1012

cm

-3 ]

DOFZ (d1) - Vfd from CVDOFZ (d1) - Vfd from IV

5 101 5 102 5 103

time [ min ]

50

100

150

200

Vfd

[V

]

0.5

1.0

1.5

2.0

2.5

| Nef

f | [

1012

cm

-3 ]

MCZ (n320) - Vfd from CVMCZ (n320) - Vfd from IV

The evolution of the depletion voltage as determined by CV and IV methods for MCz silicon.

The evolution of the depletion voltage as determined by CV and IV methods for DOFZ (d1) silicon

24

• IRST, CNM, CiS, HIP and BNL have successfully produced Cz detectors.

• Sumitomo is no longer accessible and Okmetric Oyj require large orders (>1000 wafers per order)

Cz Characterization – procurement

25

0 1x1014

2x1014

3x1014

4x1014

5x1014

6x1014

7x1014

8x1014

9x1014

1x1015

0

1x1012

2x1012

3x1012

4x1012

5x1012

6x1012

7x1012

8x1012

9x1012

0

100

200

300

400

500

Ne

ff(c

m-3

)

Proton fluence (cm-2)

PN std PN oxg MCZ N-N oxg. P-stop 1E13 N-P std P-stop 10E13

Fu

ll dep

letion

voltag

e (V)

Confirmation of MCz depletion voltage behaviour of MCz after 24 GeV/c proton irradiation by G. Pellegrini et. al “Annealing Studies of magnetic Czochralski silicon radiation detectors” NIM A, article in press.

MCz

FZ

DOFZSCSI?

SCSI

Cz Characterization – proton irradiation

26

Confirmation of MCz depletion voltage behaviour of MCz after 190 MeV/c pion irradiation by G. Lindstroem et. al 1st RD50 workshop, October 2002

MCz

DOFZ

FZ

Cz Characterization – pion irradiation

27

0

100

200

300

400

500

600

700

0.0 0.2 0.4 0.6 0.8 1.0

Fluence (1015 1 MeV equivalent neutrons/cm2)

Vde

p (V

)

The minimum of Vdep is reached at 1-1.5×1014 n/cm2. Vdep is 650 at 1015 n/cm2.

Measurements after irradiation and before annealing

Cz Characterization – neutron irradiation

28

Cz Characterization – leakage current

5x5 mm2 p+n silicon diodes have been characterized before and after 24 GeV/c proton irradiation at the CERN PS.

Diodes processed at the Helsinki Institute of Physics from FZ, DOFZ and MCz silicon manufactured at Okmetric Oyj.

Crystal

orientation

ρ (kΩcm) Oxygenation Thickness (μm)

Initial

Vfd (V)

FZ <100> 1 - 295 ± 2 235 ± 15

DOFZ <100> 1 75h at 1100oC 295 ± 2 269 ± 7

MCz <100> 1 - 304 ± 2 309 ± 5

Diode0 2 4 6 8 10 12

De

ple

tion

Volt

ag

e [

V]

200

220

240

260

280

300

320

340

360

MCz (n320)

DOFZ (d1)

FZ (f2)

Depletion voltages for FZ, DOFZ and MCz diodes before irradiation

Single guard ring was always connected.

29

1013 5 1014 524 GeV/c protons [ cm-2 ]

50

100

150

200

250V

fd [V

]

1

2

3

| Nef

f | [

1012

cm

-3 ]

FZ (f2) - Vfd from CVFZ (f2) - Vfd from IV

Cz Characterization – proton irradiation

• Diodes measured after 24 GeV/c proton irradiation and 4mins/80oC annealing with IV and CV techniques. • Guard ring connected. • CV measurements made with 10kHz in parallel mode.

FZ silicon

SCSI

30

1013 5 1014 524 GeV/c protons [ cm-2 ]

50

100

150

200

250V

fd [V

]

1

2

3

| Nef

f | [

1012

cm

-3 ]

FZ (f2) - Vfd from CVFZ (f2) - Vfd from IV

• Diodes measured after 24 GeV/c proton irradiation and 4mins/80oC annealing with IV and CV techniques. • Guard ring connected. • CV measurements made with 10kHz in parallel mode.

MCz silicon

SCSI

1013 5 1014 524 GeV/c protons [ cm-2 ]

50

100

150

200

250

300V

fd [V

]

1

2

3

4

| Nef

f | [

1012

cm

-3 ]

MCZ (n320) - Vfd from IVMCZ (n320) - Vfd from CV

SCSI?

Cz Characterization – proton irradiation

31

TCT in MCz

14

Alison Bates

I [V

/50O

hms]

Low field

High field

Time [ns]

I [V

/50O

hms]

Low field

High field

14 Confirmed by Gregor Kramberger et. al

Hole injection signal

1013 5 1014 524 GeV/c protons [ cm-2 ]

50

100

150

200

250

300

Vfd

[V]

1

2

3

4

| Nef

f | [

1012

cm

-3 ]

MCZ (n320) - Vfd from IVMCZ (n320) - Vfd from CV

5x1014 p/cm2

NO TYPE INVERSION IN CZ SILICON UP TO 5x1014 p/cm2

• MCz silicon always has the high electric field on the structured side of the detector even after high fluences using standard p+-on-n MCz detectors

32

CERN TCT set-up(1)

• Easy detector mounting• Floating guard ring

• Front and back illumination possible

• Peltier cooled to ~-10oC• Temp. stability to +0.1oC• Flushed with N2 gas

• Red 660 nm laser diode• IR 1060 nm laser diode • Amount of charge deposited can be

tuned - laser diode output controlled by pulse generator signal

Cu/Be spring contact to front pad

Au PCB for ground plate

Laser fibre for illuminating the top of the detector

Water cooling and gas system

33

CERN TCT set-up(2)

Pulse duration min 1.5 ns FWHM

Rise time of signal 1.5 ns

Almost no detector shaping from electronics

• Custom written LabVIEW DAQ• ROOT analysis of data*

*Data analysis software courtesy from the wonderful Gregor Kramberger

34

Signal treatment

• Deconvolution of the true signal from the measured signal

Measured signal = detector signal transfer function

Transfer function:

I(t)=TCT/R x dUosc(t)/dt + Uosc(t)/R

R = 50 from input of preamp

TCT= RCd (Cd = detector capacitance)

Time [ns]

I [V

/50

]

35

Charge Correction Method

• The CCM assumes three conditions:– There exists one dominant trapping time– The detrapping effects are negligible in the readout

time– All the lost charge is due to trapping

• The method requires no knowledge of the electric field profile in the detector or any information about the charge carrier distributions. All plots presented in this paper have been deconvoluted from the electronic transfer function of the TCT readout circuit and corrected for the trapped charge.

36

parameter summary

e h

[10-16 cm2/ns] [10-16 cm2/ns]

FZ (f2) 5.59 + 0.29 7.16 + 0.32

DOFZ (d1) 5.73 + 0.29 6.88 + 0.34

MCz (n320) 5.81 + 0.32 7.78 + 0.39

DOFZ (W317) 5.48 + 0.22 6.02 + 0.29

Dortmund [2]DOFZ

5.08 + 0.16 4.90 + 0.16

Ljubljana [3]DOFZ and FZ

5.34 + 0.19 7.08 + 0.18

Lancaster/Hamburg [4] FZ 5.32 + 0.30 6.81 + 0.29

Hamburg [5]FZ, DOFZ and Cz

5.07 + 0.16 6.20 + 0.54

Table 4. Comparison of βe and βh determined after 24 GeV/c proton irradiation. The top 4 rows are the values found in this work while the last four rows show data previously obtained by other groups. All values

have been scaled to 5oC, for the temperature dependence of β (see section 4.5).

37

What’s the limitations with FZ detectors

• p+n detectors deplete from the front segmented side before irradiation

• p+n FZ detectors type invert at a certain radiation level and then deplete from the back side of the detector

• The Vfd is increasing every day hence at some point the detector will be operated under-depletion, in which case:

– Charge spread – degraded resolution– Charge loss – reduced CCE

p+n detector before type inversion and under-depleted.

38

What’s the limitations with FZ detectors

• p+n detectors deplete from the front segmented side before irradiation

• p+n FZ detectors type invert at a certain radiation level and then deplete from the back side of the detector

• The Vfd is increasing every day hence at some point the detector will be operated under-depletion, in which case:

– Charge spread – degraded resolution– Charge loss – reduced CCE

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 600 V

1014cm-21014cm-2

"p - type""p - type"

type inversiontype inversion

n - typen - type

[Data from R. Wunstorf 92]

39

n-on-n silicon, under-depleted:

•Limited loss in CCE

•Less degradation with under-depletion

Depletion fraction

reso

luti

on

n+on-n

Charge spread for p+on-n Si

For LHCb n+on-n detectors are the technology choice

40

Macroscopic changes

Shockley-Read-Hall statistics Shockley-Read-Hall statistics (standard theory) (standard theory)

  

Trapping (e and h) CCE

shallow defects do not contribute at room

temperature due to fast detrapping

charged defects

Neff , Vdep

e.g. donors in upper and acceptors in lower half of band

gap

generation leakage current

Levels close to midgap

most effective

Increased NoiseReduced SignalEffects the operating voltage

e

e

41

Depletion voltage in FZ silicon

• Neff – Effective doping concentration

• Neff positive – n-type silicon (e.g. Phosphorus doped – donor)

• Neff negative – p-type silicon (e.g. Boron doped – acceptor)

• Donor removal and acceptor generation

– type inversion: n p– depletion width grows from n+

contact

2d

VN dep

eff

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 600 V

1014cm-21014cm-2

"p - type""p - type"

type inversiontype inversion

n - typen - type

[Data from R. Wunstorf 92]

cNN effeff exp0Neff(0) is the effective doping concentration before irradiation = 0.025cm-1 measured after beneficial anneal

before inversion

after inversion

n+ p+ n+

42

• Defects located close to the middle of the bandgap can generate current.

• Damage parameter (slope)

independent of eq and impurities

used for fluence calibration

Reverse current and Carrier Trapping

eqV

I

.

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

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

p-type EPI - 2 and 4 Kcmp-type EPI - 2 and 4 Kcm

p-type EPI - 380 cmp-type EPI - 380 cm

kT

ETTI g

2exp2

T dependence

• Defects can trap the charge carriers

• CCE = Charge Collection Efficiency

• CCE is reduced by radiation induced traps

• Problems arise if the de-trapping time becomes less than 25ns for the LHC

• t is the carrier transient time (e or h), β is a constant.

eqtrapping

tt

CCE

exp)exp(

Material independent