Development of low-pressure vapour-phase epitaxial GaAs for medical imaging

RL Bates, S Manolopoulos, K Mathieson, A Meikle, V O'Shea, C Raine, KM Smith, J Watt, C Whitehill, S Pospisil, I Wilhelm, Z Dolezal, H Juergensen, M Heuken

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11 Citations (Scopus)

Abstract

A summary is given of progress accomplished with the development of low-pressure vapour-phase epitaxial GaAs as a material for X-ray detectors. As the III–V concentration ratio is altered from Ga-rich to As-rich, the material is shown to improve from p-type, to n-type with compensation via deep levels, to n-type with a doping density of 1.7×1014 atoms cm−3. The measured barrier height is 0.8 V, as expected for the Ti contact used. Overdepletion was obtained before breakdown, enabling a layer thickness of m to be deduced for the final sample. For the later samples, charge collection for 60 keV Am-241 gammas was bias independent at a value of 100±8%. Spectra were also obtained from Sr-90 electrons. The most probable value of the charge collected as a function of the bias reached a plateau and from this value a depletion width of m was found for the final sample, equal to the epitaxial layer thickness. Results from detailed alpha and low-energy proton spectroscopy are shown for diodes fabricated from this material. A charge collection efficiency of 100% was obtained when the diode could be depleted sufficiently. The concept of a charge collection depth was introduced, since a significant amount of charge was collected without bias. The minimum depth of such a region was shown to be m at 0 V reverse bias, far greater than the m predicted for the depletion depth. Charge coupling between the guard ring and the pad was observed and successfully modelled.
Original languageEnglish
Pages (from-to)1-13
Number of pages13
JournalNuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Volume434
Issue number1
DOIs
Publication statusPublished - 11 Sep 1999

Keywords

  • epitaxial GaAs
  • medical imaging
  • vapour-phase epitaxial GaAs

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