Speaker
Description
GaAs was extensively studied for the last 70 years, but still remains the material of choice only in
certain areas (like production of commercial semiconductor lasers). Noticeable advantages of GaAs over Si
for radiation detector manufacturing, such as higher electron mobility (8000 vs 1400 cm2/(V·s)), higher
average atomic number (31.5 vs 14) and wider bandgap (1.43 vs 1.12 eV) [1] result in better charge
collection, higher radiation absorption efficiency, superior radiation hardness and lower noise. Silicon is
preferable in this area mainly due to low cost and well-established technology for electronic device
production. However, with the last developments in vertical gradient freeze (VGF) growth of bulk GaAs
crystals, this material came very close to silicon in terms production feasibility. High-quality 4” and 6“
wafers of semi-insulating GaAs material available on market make possible adaptation of Si processing
technology for large-scale production of GaAs hybrid radiation detectors.
As part of the European H2020 funded X-MINE [2] project Advacam has studied possibilities to produce
radiation detectors using VGF semi-insulating GaAs material available in the market. We used 3”, 4” and 6”
<100> VGF GaAs wafers with resistivity in range of 1-7*108 Ohm-cm with thickness of 575-625 um. We
have demonstrated a wafer-level processing of the wafers using sensor designs compatible with Timepix
readout ASIC [3]. Figure 1 (left) shows a 3” and 4” GaAs wafers
The presentation summarises the GaAs wafer-level processing and micro packaging. Comparison of the
electrical, X-ray imaging and spectroscopic performance of the GaAs sensors manufactured from different
sizes of semi-insulating wafers will be given. The presented properties include leakage current, measured
point-spread-function, material homogeneity, stability and energy resolution. We have concluded that the
electron collection modality is superior over the hole collection and that the VGF GaAs shows imaging
quality comparably to silicon but worse energy resolution.
REFERENCES
[1] 1. A.Owens, A.Peacock, Compound semiconductor radiation detectors, Nuclear Instruments and Methods in
Physics Research A 531 (2004) 18–37
[2] This project has received funding from the European Union’s Horizon 2020 research and innovation programme
under grant agreement No 730270.
[3] X. Llopart et al., Nucl. Instrum. Meth. A, Vol. 581, p. 485-494, (2007).
