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 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 ?

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

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 ~(1013-1014) Ohm (ohmic behavior) 3 samples from different groups have “non-ohmic” behavior and lower resistance (~1011 Ohm) Usual I(V) curve Non-ohmic curve

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

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

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 FAP 2_1 FAP 4_2 N (575) N (637) LO Phonon Si (770) Reference spectra

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

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