Performance of epitaxial and HPSI 4H-SiC detectors for plasma X-ray imaging systems

The room temperature X-ray spectral response of Schottky barrier diodes (SBDs) and bulk detectors on n-type epitaxial 4H-SiC and high-purity semi-insulating (HPSI) 4H-SiC substrates is investigated in the energy range of 30-40 keV for fusion plasma X-ray imaging systems (XIS). The different noise components (in terms of FWHM-equivalent noise energy) of the detector energy resolution are also analyzed. An energy resolution of 3.5 keV FWHM (for ¹⁵²Eu X-rays), ∼ 90% charge collection efficiency (CCE) at -100 V are obtained with the SBD detectors. The intrinsic detection efficiency of the SBD detectors at 32 keV and 40 keV is found to be 0.42%, and 0.23%, respectively. In SBD detectors, the X-ray produced signal strength is unchanged with time, therefore the polarization phenomenon is not observed. An energy resolution of 11.2 keV FWHM is noted from the ¹³⁷Cs X-ray spectral response of the bulk detectors. It is found that the X-ray produced signal decreases with time after the bias voltage was applied to the bulk detectors because of the polarization effect; thus CCE and detection efficiency decreases with time. The CCE attained with the bulk detectors at -500 V is not more than 30%. The identified intrinsic efficiency of the bulk detectors is lower than the SBD detectors. Furthermore, to study the reliability the 4H-SiC detectors in a fusion-reactor like environment, 14.1 MeV and 4.5 MeV neutron irradiation effects on the X-ray spectral response of the detectors are analyzed up to a fluence 10¹¹ n/cm². Based on the present results, the possible application of the 4H-SiC detectors in the fusion XIS is discussed.