CVD Diamond Sensors for the Very Forward Calorimeter of a

Linear Collider Detector

K. Afanaciev,D. Drachenberg,E. Kouznetsova, W. Lange,W. Lohmann

LCal at TESLA• Detection and measurement of

electrons and photons at small angles

• Fast beam diagnostic

• Shielding of the inner part of the detector

Backgroung : Beamstrahlung

Per bunch crossing :

• ~15000 e± hit the LCAL• ~20 TeV of deposited energy

Expected dose :• for “bad” regions :

up to 10 MGy/year

-> Radiation hard sensor-> diamond ?

Diamond samples

• Fraunhofer Institute (Freiburg) :

– CVD diamond 12 x 12 mm– 300 and 200 um thickness– Different surface treatment :

• #1 – substrate side polished; 300 um• #2 – substrate removed; 200 um• #3 – growth side polished; 300 um• #4 – both sides polished; 300 um

– Metallization:• 10 nm Ti + 400 nm Au• Area 10 X 10 mm

Picture showing the difference b/w growth and substrate

Average resistance ~(1013-1014) Ohm (ohmic behavior)

3 samples from different groups have “non-ohmic” behavior and lower resistance

(~1011 Ohm)

I(V) dependence – setup

• Extremely low currents

=> N2 atmosphere

EM shielding

Measurements were done with

Keithly 487 picoammeter

Usual I(V) curve

Dia

mo

nd

Ke

ith

ley

48

7

HV

N2

Non-ohmic curve

Charge Collection Distance (CCD)

Qmeas. = Qcreated x ccd / L

Qcreated(m) = 36 e-h pairsThe samples haven’t been irradiated

before these measurementsAll data was taken 2 minutes after bias

voltage applied

&

Gate

PA

discr

discr

delay

ADCSr90

PM1

PM2

diam.

Scint.

CCD measurements results

Sample# R(average), OhmCCD, u

(+500 V) (+800 V) (-500 V) (-800 V)

11 4.60E+13 35 37

12 3.20E+14 35 43 27 30

13 8.88E+11 25 33 21

21 5.92E+14 24 17

22 7.39E+14 9 11 9 10 (700V)

23 3.93E+14 9 12 10 13

31 1.04E+11 28 33 (400V)

32 5.12E+13 50 57 50

33 4.63E+13 49 54 52 58

41 5.12E+11 45 (400 V) 48

42 4.35E+14

43 5.24E+13 54 60 65

CCD – irradiation studies

The samples were irradiated with Sr-source with estimated dose-rate of about 0.45 Gray per hour

The total absorbed dose for all the samples was at least 5 Gy.

Bias field was set to 1 V/m

Irradiation was homogeneous over the sample area

Parameters monitored during the irradiation:

- Sr-spectrum peak position

- width of the peak (->noise)

- current in HV-circuit

- test pulse from a generator (-> electronics stability)

CCD – irradiation studies – results

Group #2 (substrate side removed). HV = 200V

Group #3 (growth side polished). HV = 300V

CCD – irradiation studies – results

Group #1 (substrate side polished). HV = 300V

Group #2 (substrate side removed). HV = 200V

CCD – irradiation studies – results

Group #3 (growth side polished). HV = 300V

Group #4 (both sides polished). HV = 300V

Results and further studies

Raman spectroscopy + photoluminescence analysis

-> no nitrogen, no silicon

Reference spectra

N (575)

N (637)LO

Pho

non

Si (770)

FAP 2_1

FAP 4_2

Removed substrate

Group#3 – removed substrate (300 m -> 240 m)

Results and further studies

Group#2 in general can work as a detector

Raman spectroscopy + photoluminescence analysis

-> no nitrogen, no silicon

Next steps:

- Influence of the substrate side on CCD and stability

- Homogeneity and linearity required for the application