Vertex 2001 Brunnen, Switzerland Phil Allport Gianluigi Casse Ashley Greenall Salva Marti i Garcia Charge Collection Efficiency Studies with Irradiated Silicon Detectors  Evaluation of trapping effects  The influence of ballistic deficit  Fits to the Charge Collection Efficiency  Discussion and Conclusions

Vertex 2001 Brunnen, Switzerland Evaluation of Trapping Effects  Radiation damage to silicon detectors increases reverse currents, creates interface trapped charge, introduces traps reducing charge collection efficiencies changes the effective doping concentrations  Studies of the latter effect have shown significant improvements under charged hadron irradiation when high concentrations of interstitial oxygen are introduced  However, unlike in the case of n-side read-out detectors, the charge collection efficiencies for p-side read-out detectors do not plateau with voltage until well above the depletion voltage  This is usually assigned to the effect of trapping

Vertex 2001 Brunnen, Switzerland Old ATLAS Irradiated n-in-n Results 2  p/cm 2

Vertex 2001 Brunnen, Switzerland Detectors Studied Studies carried out with SCT miniature (cm  cm) p-side read- out micro-strip detectors (processed as test structures on ATLAS prototype wafers) using wide bandwidth (Phillips 6954) current amplifier Comparisons with the large area devices using SCT-128 analogue read-out have demonstrated good agreement (G. Casse et al.)

Vertex 2001 Brunnen, Switzerland Evaluation of Trapping Effects  Capacitance – Voltage Derived Depletion Voltage 1.9  0.1  p/cm 2 Oxygenated Miniature Micro-strip Detector V FD = 100  7 V from fitting C(V)

Vertex 2001 Brunnen, Switzerland Evaluation of Trapping Effects  Corresponding Charge Collection Efficiency vs Voltage 100 V

Vertex 2001 Brunnen, Switzerland Evaluation of Trapping Effects  The effects of trapping can be parameterized in terms of effective trapping time (Kramberger et al.) or, equivalently, velocity dependent attenuation length (Marti i Garcia et al.)  In both cases, trapping is highest where the field is lowest  These parameterizations assume timescales such that the total untrapped charge is collected, integrating over transient effects.  No influence of ballistic deficit is included  Both analyses give values of  (averaged over e and h) that agree.  e,h   eq = 1/  eff e,h (trapping  flux)

Vertex 2001 Brunnen, Switzerland Influence of Ballistic Deficit Since at the LHC electronics response times are close to charge collection times, signal loss due to incomplete charge integration must also be considered, which will also depend on the field within the detector. Non-irradiated p-strip Detector

Vertex 2001 Brunnen, Switzerland Influence of Ballistic Deficit  Oxygenated and non- oxygenated detectors have been studied which were irradiated in the CERN-PS and annealed to the minimum of the N eff vs time annealing curve

Vertex 2001 Brunnen, Switzerland Influence of Ballistic Deficit Detector labelFluence [p cm -2 ]Oxygenation[~2·10 17 at. Cm -3 ] NINon-irradiatedNo SO11.9  0.1 ·10 14 Yes SN11.9  0.1 ·10 14 No SO22.9  0.2 ·10 14 Yes SN22.9  0.2 ·10 14 No SO35.1  0.4 ·10 14 Yes SN35.1  0.4 ·10 14 No Several miniature detectors have been studied after irradiation and annealing.

Vertex 2001 Brunnen, Switzerland Influence of Ballistic Deficit Miniature detectors irradiated to 1.9  p/cm 2 Non-OxygenatedOxygenated

Vertex 2001 Brunnen, Switzerland Influence of Ballistic Deficit Miniature detectors irradiated to 2.9  p/cm 2 Non-OxygenatedOxygenated

Vertex 2001 Brunnen, Switzerland Influence of Ballistic Deficit Miniature detectors irradiated to 5.1  p/cm 2 Non-OxygenatedOxygenated

Vertex 2001 Brunnen, Switzerland Non-Oxygenated Detectors: Relative Ballistic Deficit Oxygenated 5.1  p/cm  p/cm  p / cm 2 Non-irradiated

Vertex 2001 Brunnen, Switzerland Oxygenated Detectors: Relative Ballistic Deficit 5.1  p/cm  p/cm  p/cm 2

Vertex 2001 Brunnen, Switzerland Fits to the Charge Collection Efficiency The above results suggest that, particularly at high doses, the ballistic deficit is not a major factor for LHC speed operation In the following fits, sufficient integration time has anyway been allowed such that the only charge loss is due to trapping Free parameters: attenuation length, depletion voltage V FD total generated charge Q  p/cm 2

Vertex 2001 Brunnen, Switzerland Fits to the Charge Collection Efficiency 2.9  p/cm  p/cm 2

Vertex 2001 Brunnen, Switzerland Fits to the Charge Collection Efficiency Detector label Fluence [p cm -2 ] Oxygen enrichment V FD [V] (From C-V) V FD [V] (From CCE) [  m] NI Non irr. No49  250  2 SO1 1.9  0.1 · Yes100  790   15 SN1 1.9  0.1 · No150  8137   220 SO2 2.9  0.2 · Yes121    138 SN2 2.9  0.2 · No218    122 SO3 5.1  0.4 · Yes181    84 SN3 5.1  0.4 · No320    55

Vertex 2001 Brunnen, Switzerland Fits to the Charge Collection Efficiency The fitted values of V FD agree with each other and with oxygenated data from RD48 (CERN LHCC ) taking account of the proton damage factor The fitted values of Q 0 : 18.1  0.3, 18.2  0.3, 17.7  0.3, 18.1  0.6, 18.2  0.4 and 18.3  0.4 are all consistent and agree with the pre-irradiation value 17.9  0.3

Vertex 2001 Brunnen, Switzerland Fits to the Charge Collection Efficiency The dependence of Q/Q 0 and therefore on  leads to a value of  eff = 5.6  0.6  cm 2 /ns Assuming this value allows extrapolation of CCE to high 

Vertex 2001 Brunnen, Switzerland Discussion and Conclusions Because for p-strip read-out, the trapping significantly affects the CCE(V), the improvements in V FD due to oxygenation do not give correspondingly large effects in terms of CCE The trapping dependence on the field leads to CCE(V FD ) being higher for non-oxygenated than oxygenated detectors by ~5% Read-out from the high-field n-side gives less dependence on trapping leading to the CCE(V)   V behaviour below V FD This would imply that for high doses, n-side readout should benefit more from oxygenation of the substrate

Vertex 2001 Brunnen, Switzerland Discussion and Conclusions The LHC-b vertex detector is proposed to use oxygenated n-strip detectors for which the first prototypes have just been delivered to Liverpool and are currently being irradiated in the CERN PS

Vertex 2001 Brunnen, Switzerland Discussion and Conclusions LHC-b uses back-to-back thinned disks for r and  plus double-metal routing

Vertex 2001 Brunnen, Switzerland Discussion and Conclusions LHC-b and the pixel systems of ATLAS and CMS need to maximise their survival; n-side readout oxygenated detectors look to offer the best possibilities Super-LHC with factor of 10 increased luminosity could also need such technology

Vertex 2001 Brunnen, Switzerland Discussion and Conclusions Detectors produced with n-side read-out do suffer from the disadvantage of requiring potentially expensive double-sided processing Use of p-type substrates does provide a viable alternative where cost is of paramount importance Comparison of p-type and n-type detectors after 3  p/cm 2