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

Research output: Contribution to journalArticle

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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

Fingerprint

Medical imaging
Vapor pressure
low pressure
vapor phases
Diodes
depletion
diodes
Epitaxial layers
Protons
proton energy
Doping (additives)
Spectroscopy
Detectors
electric contacts
X rays
plateaus
Atoms
Electrons
breakdown
rings

Keywords

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

Cite this

Bates, RL ; Manolopoulos, S ; Mathieson, K ; Meikle, A ; O'Shea, V ; Raine, C ; Smith, KM ; Watt, J ; Whitehill, C ; Pospisil, S ; Wilhelm, I ; Dolezal, Z ; Juergensen, H ; Heuken, M. / Development of low-pressure vapour-phase epitaxial GaAs for medical imaging. In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 1999 ; Vol. 434, No. 1. pp. 1-13.
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Bates, RL, Manolopoulos, S, Mathieson, K, Meikle, A, O'Shea, V, Raine, C, Smith, KM, Watt, J, Whitehill, C, Pospisil, S, Wilhelm, I, Dolezal, Z, Juergensen, H & Heuken, M 1999, 'Development of low-pressure vapour-phase epitaxial GaAs for medical imaging', Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, vol. 434, no. 1, pp. 1-13. https://doi.org/10.1016/S0168-9002(99)00403-9

Development of low-pressure vapour-phase epitaxial GaAs for medical imaging. / Bates, RL; Manolopoulos, S; Mathieson, K; Meikle, A; O'Shea, V; Raine, C; Smith, KM; Watt, J; Whitehill, C; Pospisil, S; Wilhelm, I; Dolezal, Z; Juergensen, H; Heuken, M.

In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 434, No. 1, 11.09.1999, p. 1-13.

Research output: Contribution to journalArticle

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T1 - Development of low-pressure vapour-phase epitaxial GaAs for medical imaging

AU - Bates, RL

AU - Manolopoulos, S

AU - Mathieson, K

AU - Meikle, A

AU - O'Shea, V

AU - Raine, C

AU - Smith, KM

AU - Watt, J

AU - Whitehill, C

AU - Pospisil, S

AU - Wilhelm, I

AU - Dolezal, Z

AU - Juergensen, H

AU - Heuken, M

N1 - 6th International Workshop on Gallium Arsenide and Related Compounds, PRAGUE, CZECH REPUBLIC, JUN 22-26, 1998

PY - 1999/9/11

Y1 - 1999/9/11

N2 - 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.

AB - 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.

KW - epitaxial GaAs

KW - medical imaging

KW - vapour-phase epitaxial GaAs

U2 - 10.1016/S0168-9002(99)00403-9

DO - 10.1016/S0168-9002(99)00403-9

M3 - Article

VL - 434

SP - 1

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JO - Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

JF - Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

SN - 0168-9002

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