Performance of bulk semi-insulating GaAs-based sensor and its comparison to Si-based sensor for Timepix radiation camera

Abstract

A: Nowadays, pixelated detectors based on Timepix readout chip play important role in various fields of science and research like particle physics, advanced spectrometry and especially X-ray imaging for medical and material purposes. Present work is focused on the evaluation of the 350 µm thick prototype (semi-insulating) SI GaAs sensor performance and its comparison to 300 µm thick Si sensor that was chosen as a reference. Both sensors consist of 256 × 256 pixels matrix with pixel pitch of 55 µm. We performed flat field illumination to test the pixel homogeneity and found out that the response of GaAs sensor is less homogeneous in terms of number of counts across the sensor compared to Si sensor. The imaging performance was tested using two samples of different absorption strength, specifically one less-absorbing sample and one more-absorbing sample. We found out that our fabricated SI GaAs sensor shows better imaging performance than Si sensor in case of imaging more-absorbing sample and vice versa. This is due to different prevalent detection efficiency regions. The spatial resolution was determined to be 8.73 lp/mm and 8.25 lp/mm for GaAs and Si sensor, respectively. Also, spectrometric measurements were carried out and results show that Si sensor has about 2 times higher energy resolution in comparison with SI GaAs sensor. K: X-ray detectors; Inspection with x-rays; X-ray radiography and digital radiography (DR)

Spreading of an active region of semi-insulating GaAs detectors after radiation degradation

“…In [20] we evaluated the resistivity and electron mobility of SI GaAs material for irradiation doses up to 104 kGy using galvanomagnetic measurements. The resistivity initially decreased slightly with dose from a value of 1.9×10 7 Ωcm to 1.8×10 7 Ωcm at 24 kGy and then began a monotonic increase to a level of 2.5×10 7 Ωcm at a dose of 104 kGy.…”

“…The top side was covered by a circular Schottky contact of 1 mm diameter made of Ti/Pt/Au multilayer with a total thickness of 135 nm and the bottom side by a 170 nm thick whole-area Ni/AuGe/Au multilayer as it is depicted in figure 1. The resistivity of utilized VGF (Vertical Gradient Freeze) SI GaAs substrate was 2×10 7 Ωcm and its Hall mobility was 7219 cm 2 /Vs at room temperature.…”

“…On the other hand, the charge mobility of GaAs, 8000 cm 2 V −1 s −1 (electrons) and 400 cm 2 V −1 s −1 (holes) at RT, dominates over silicon, and undoped SI GaAs detectors achieve one of the best reaction rates among semiconductor detectors. Both bulk SI GaAs materials, the undoped [3,7,8] and the Cr-dopped [9][10][11] were utilized as sensors for multi-pixel single-photon counting Timepix [12] detectors suitable for application in radiation imaging.…”

Study of the contrast resolution of Timepix detector with a semi-insulating GaAs sensor

“…Parameters of the detector were published in detail in our previous work [18]. The SI GaAs Timepix detector showed a very good spectrometric performance that was tested using a monoenergetic radiation of 59.5 keV from 241 Am and 24.1 keV and 27.3 keV Kα and Kβ photons from indium fluorescence [19]. The imaging quality of the detector was very high and comparable to that of silicon Timepix detectors.…”

“…Figure 1 shows a distribution of the pixel counts of one taken image of an SI GaAs Timepix camera for a uniform illumination from an X-ray tube. The typical background image was shown in our previous works in which we used the same pixel detector [18,19]. We used the counting mode of the imaging Timepix detector for the measurement.…”