Speaker
Description
Gallium arsenide is extensively studied for about seven decades as an excellent material for semiconductor lasers, LEDs, and microwave electronics. GaAs has noticeable advantages over silicon and Cd(Zn)Te for radiation detectors. Particularly GaAs has higher electron mobility compared to Si and Cd(Zn)Te; higher average atomic number compared to Si; and lower probability and energy of the fluorescence photons compared to the Cd(Zn)Te [1]. These advantages result in a fast charge collection, good absorption efficiency up to 50 keV and a better uniformity compared to Cd(Zn)Te. Applications for the GaAs are foreseen in medical, mammography, small animal imaging, electron microscopy, synchrotrons, XFELs and non-destructive testing of composite materials.
In frame of Eurostar GoNDT project [2], Advafab has developed radiation detectors by chromium compensation [3] of commercially available 3” n-type Liquid Encapsulated Czochralski (LEC) GaAs wafers. Wafers were annealed in quartz reactor; processed by polishing and CMP; and were patterned, metallized, and diced.
We have demonstrated a wafer-level processing of 500 um thick GaAs using sensor designs compatible with different type of readout ASICs. Individual diced sensors were flip chip bonded to Timepix1 [4], Timepix2 [5], Timepix3 [6], Medipix3 [7] and UFXC32k [8] ASICs. Assemblies were evaluated to study the optimal sensor design and bias voltage; uniformity; sensor stability; energy resolution; charge transport properties and high X-ray flux operation.
The presentation summarises the GaAs performance results received from the contributing authors. It presents analytical comparisons to the formerly commercially available GaAs sensor material in terms of uniformity, spectral resolution and high flux operation. The Advafab’s GaAs present a better uniformity and similar energy resolution.
The high photon flux operation has been evaluated using an industrial X-ray tube in an open beam. It has been shown that Advafab’s GaAs can tolerate and operate stably in X-ray beam fluxes up to 160 Mcnt/s/mm2 while the previously commercially available material could survive only up to 60 Mcnt/s/mm2 before the count rate starts to decline.
The presentation concludes that it is possible to manufacture radiation sensors of chromium-compensated GaAs for photon counting applications with high uniformity and a good energy resolution that can operate at high X-ray fluxes.
[1] A.Owens, A.Peacock, Compound semiconductor radiation detectors, Nucl. Instr. and Methods A 531 (2004) 18–37
[2] This project has received funding from the Eurostars-3 Programme with co-funding
from the European Union’s Horizon Europe research and innovation programme under grant agreement E!0543.
[3] M.C. Veale et. al., Chromium compensated gallium arsenide detectors for X-ray and γ-ray spectroscopic imaging, Nucl. Instr. and Methods A 752 (2014) 6–14
[4] X. Llopart et al., Nucl. Instr. and Methods A 581, (2007), 485-494.
[5] W. Wong et al., Radiat. Meas. 131 (2020) 106230.
[6] T Poikela et al., JINST 9 (2014) C05013.
[7] R. Ballariga et al., Nucl. Instr. and Methods A 633, (2011), 15-18.
[8] P. Grybos et al., IEEE Trans. Nucl. Sci., vol. 63, no. 2, (2016), 1155-1161
