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Persistent URL http://purl.org/net/epubs/work/29597
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Record Id 29597
Title Semi Conductor Detectors for the Inner Tracker of the ATLAS Experiment at CERN
Abstract The ATLAS detector will be a general purpose proton-proton detector built for the Large Hadron Collider (LHC) experiment at CERN. The LHC will collide beams of protons at energies of 7 TeV and the aim will be to test our current understanding of the structure of matter. Of particular importance, however, is the ability of the experiment to achieve energies higher than anything reached previously and this will provide an insight into new physics and the possibility of new and as yet undiscovered particles. It is perhaps at this experiment that the discovery of the Higgs boson will occur, and the existence of supersymmetry will be established. The most challenging aspects of the LHC operation in terms of the ATLAS detector will be the intense radiation levels present throughout the detector. In the innermost region the flux of charged particles will be extreme, and will significantly degrade any detector system present. Research carried out for this thesis has focussed on the inner detector at ATLAS, and in particular the semiconductor tracker (SCT) which is essential in identifying charged tracks and vertex positions from interactions. In chapter 1 an introduction to the Standard Model of particle physics will be given, along with a discussion on the semiconductor concepts and operation. Chapter 2 will continue with details of semiconductor operation and the fabrication procedures necessary to produce pad and microstrip detectors. Initial designs for the ATLAS SCT incorporated detectors fabricated from GaA's, and these were to be situated in the region closest to the beam pipe. This material was believed to be extremely radiation hard and hence able to withstand the intense fluence levels reached over the ten year operating period. Research for this thesis therefore began by investigating the use of GaA's as particle detectors. A study was undertaken to investigate the correlation between the resistivity of GaA's detectors and the charge collection efficiency, and the results will be presented in chapter 4. All detectors were then irradiated in a pion beam to fluences of ~10 superscript 14 pi cm superscript -2, and their subsequent degradation in charge collection efficiency measured. Ultimately it became clear that GaA' s was not as radiation hard as expected and would not be suitable for use in ATLAS. The ATLAS SCT therefore now comprises of silicon detectors throughout. In chapter 5 results are presented on the irradiation of full sized silicon microstrip detectors, measuring ~64mm squared, to the estimated 10 year fluence level of 3x10 superscript 14 pcm superscript -2. Two designs have been proposed for the SCT, either n- or p-doped strips fabricated on n-bulk material and referred to as the n-in-n and p-in-n respectively. Details of the irradiation procedure will be given, where 28 detectors from a variety of manufacturers were irradiated. After irradiation a selection of detectors were annealed in order to simulate the effect of yearly warm-ups in the SCT. Both n-in-n and n-in-p detectors were annealed for 21 days at 25 degrees centigrade, which is equivalent to a ten year warm-up scenario. Detector characteristics such as leakage current and depletion voltage were monitored over the annealing period, and results will be presented and discussed in chapter 6. The performance of several of these detectors was then determined in the H8 test chips. Results are presented in chapter 7 where the efficiency and bias characteristics will be discussed. The aim throughout this thesis has been to ascertain the effects of ATLAS conditions on semiconductor detectors. In particular, the research on silicon detectors primarily aimed to investigate the optimum detector design for use within ATLAS and to determine whether the n-in-n or p-in-n design would be most suitable over the ten year operation. The final decision, and a discussion of all results, will be given in chapter 8.
Organisation CCLRC
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Language English (EN)
Type Details URI(s) Local file(s) Year
Thesis RAL Theses RAL-TH-1999-004. 1999. 1999