Characterisation of the performance of p-type Si detectors for hard X-ray spectroscopy

Abstract

High-density compound semiconductors with sufficiently-high photon attenuations, such as CdZnTe, are required for the detection of the high-energy X-rays (>20 keV), typical to applications of the HEXITEC ASIC. However, in low-energy applications (2–20 keV), the lower electron-hole-pair generation energy of Si offers the potential of improved spectroscopic resolution. Si-based pixelated X-ray sensors are typically based on n-type material where holes are the carrier that form the signal measured on the pixels. However, the incorporation of p-type dopants into the material enables these sensors to be operated effectively in electron readout. This is similar to CdZnTe sensors, where electrons are measured by the pixels. Critically, this allows a single electron-sensitive chip to be utilised for low- and high-energy measurements. Presented in this paper are the results of the spectroscopic characterisation of four p-type-Si sensors (two 300 μm and two 500 μm thick), manufactured by Micron Semiconductors Ltd., and flip-chip bonded to the HEXITEC ASIC. At 13.94 keV all tested devices displayed average FWHM of <540 eV and the average ASIC-limited FWHM of 489 ± 75 eV measured for a single 300 μm module represents the highest resolution measured with the HEXITEC ASIC. Results also show very low pixel-to-pixel variations in the measured FWHM demonstrating the excellent spatial uniformity of these devices, and a study into the temporal stability of a single detector over a ∼30 h period demonstrated negligible changes in spectroscopic performance.