1. CVD Diamond Sensors for the Very Forward Calorimeter of a Linear Collider Detector
K. Afanaciev,
D. Drachenberg,
E. Kouznetsova,
W. Lange,
W. Lohmann

2. LCal at TESLA Backgroung : Beamstrahlung -> Radiation hard sensor
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 ?

3. 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 nm Au
Area 10 X 10 mm
Picture showing the difference b/w growth and substrate

4. I(V) dependence – setup
Measurements were done with
Keithly 487 picoammeter
Extremely low currents
=> N2 atmosphere
EM shielding
Diamond
Keithley 487 HV N2
Average resistance ~( ) Ohm (ohmic behavior)
3 samples from different groups have “non-ohmic” behavior and lower resistance
(~1011 Ohm)
Usual I(V) curve
Non-ohmic curve

5. Charge Collection Distance (CCD)
Qmeas. = Qcreated x ccd / L
Qcreated(mm) = 36 e-h pairs
&
Gate PA
discr
delay
ADC
Sr90
PM1
PM2
diam.
Scint.
The samples haven’t been irradiated before these measurements
All data was taken 2 minutes after bias voltage applied

6. CCD measurements results
Sample#
R(average), Ohm
CCD, mu
(+500 V)
(+800 V)
(-500 V)
(-800 V) 11
4.60E+13 35 37 12
3.20E+14 43 27 30 13
8.88E+11 25 33 21
5.92E+14 24 17 22
7.39E+14 9
10 (700V) 23
3.93E+14 10 31
1.04E+11 28
33 (400V) 32
5.12E+13 50 57
4.63E+13 49 54 52 58 41
5.12E+11
45 (400 V) 48 42
4.35E+14
5.24E+13 60 65

7. 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)

8. CCD – irradiation studies – results
Group #2 (substrate side removed). HV = 200V
Group #3 (growth side polished). HV = 300V

9. CCD – irradiation studies – results
Group #1 (substrate side polished). HV = 300V
Group #2 (substrate side removed). HV = 200V

10. CCD – irradiation studies – results
Group #3 (growth side polished). HV = 300V
Group #4 (both sides polished). HV = 300V

11. Results and further studies
Raman spectroscopy + photoluminescence analysis
-> no nitrogen, no silicon
FAP 2_1
FAP 4_2
N (575)
N (637)
LO Phonon
Si (770)
Reference spectra

12. Removed substrate
Group#3 – removed substrate (300 mm -> 240 mm)

13. 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