KEYWORDS: Sensors, Gallium arsenide, X-rays, Active sensors, Temperature metrology, Electric field sensors, Annealing, Electrons, X-ray imaging, X-ray technology
In this article the results of experimental investigations of resistivity, charge collection efficiency, mobility lifetime μ n·τn product and I-V curves dependencies on thermal treatment of Me-GaAs:Cr-Me X-ray sensors are presented. Experimental samples were the pad sensors with active area 0.1-0.25 cm2 and active layer thickness of 400-500 μm. The μ n·τn product was estimated using charge collection efficiency dependency on bias measured with the use of gammarays of 241Am source.
It was shown that thermal treatment in the temperature range of 200-500°C doesn’t lead to a sufficient degradation of sensor’s characteristics and can be used in array detectors processing.
In this work we present the results of experimental study of the current-voltage characteristics, the electric field distribution and the charge collection efficiency in X-ray sensors based on high resistivity, chromium compensated gallium arsenide (HR GaAs). The experimental samples were 0.1-0.25 cm2 pad sensors with the sensitive layer thickness in the range of 250-1000 μm. It has been shown that the current-voltage characteristics in the range 0.02 – 1 V are determined by the high-resistance sensor bulk. A physical model of the nonequilibrium charge carrier transport has been suggested to estimate the Schottky barrier height in the contact of “metal-semiconductor” and the sensor material resistivity. It has been established that the sensor resistivity reaches 1.5 GOhm⋅cm at room temperature, with the Schottky barrier height constituting 0.80 – 0.82 eV. The electric field distribution was investigated using the Pockels effect at a wavelength of 920 nm. It has been found experimentally that in HR GaAs sensors the electric field distribution is much more homogeneous compared to the sensors based on SI GaAs: EL2. It has been shown that the temporal fluctuations of the electric field are absent in HR GaAs sensors. Analysis of the charge collection efficiency as a function of bias has demonstrated, that in the HR GaAs material the values of the mobility-lifetime product of the nonequilibrium charge carriers are in the order of 10-4 cm2/V and 3⋅10-7 cm2/V for electrons and holes, respectively.
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