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

Bates, R.L. et al. (1999) Development of low-pressure vapour-phase epitaxial GaAs for medical imaging. In: 6th International Workshop on GaAs Detectors and Related Compounds, Pruhonice, Czech Republic, 22-26 Jun 1998, pp. 1-13. (doi: 10.1016/S0168-9002(99)00403-9)

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.

• Item Type: Conference Proceedings
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Mathieson, Dr Keith and Bates, Dr Richard and O'Shea, Professor Val and Watt, Dr John and Smith, Professor Kenway
• Authors: Bates, R.L., Manolopoulos, S., Mathieson, K., Meikle, A., O'Shea, V., Raine, C., Smith, K.M., Watt, J., Whitehill, C., Pospı́šil, S., Wilhelm, I., Doležal, Z., Juergensen, H., and Heuken, M.
• Subjects: Q Science > QC Physics
• College/School: College of Science and Engineering > School of Physics and Astronomy