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A: Chromium compensated GaAs sensors have been characterized using the chargeintegrating readout chip JUNGFRAU. Due to its low noise performance and 75 × 75 µm 2 pixel size, JUNGFRAU enables a precise measurement of the charge (of either polarity) with a high spatial resolution.Several sensor parameters like dark current, noise and spectral performance as well as the charge transport properties of the electrons have been determined. The short lifetime of holes in GaAs:Cr gives rise to an effect where pixels adjacent to a pixel with a photon hit show a strong negative signal when being absorbed close to the readout electrode. This so-called 'crater effect' has been simulated and allows an estimation of the hole lifetime in GaAs:Cr.

Previous works onchromium compensated gallium arsenide (GaAs:Cr) have shown high efficiency, good spatial and energy resolution, which is obviously connected with the high quality of material itself. The purpose of this research was to aggravate the diffusion process by increasing the annealing temperature and to observe whether there will be any degradation of material characteristics. The investigation of three 3-inch GaAs:Cr wafers with different annealing temperature of chromium was carried out. Resistivity and mobility-lifetime measurements were made using pad sensors made of these wafers. The I-V curves were built to estimate the resistivity across the wafer. Furthermore charge collection efficiency (CCE) measurements were carried out in order to estimate the µ e τ e product of GaAs:Cr. The resistivity mapping has showed a variation of resistivity across the wafer in the range from 1.25 × 10 9 to 5.5 × 10 8 Ohm cm. Although the third wafer showed quite good uniformity, the resistance didn't reached values higher than 3.5 × 10 8 Ohm cm. In spite of harsh diffusion conditions all the materials showed quite good CCE (about 90%) and µ e τ e more than 5 × 10 −5 cm 2 /V. Also a strong dependency between the resistivity and mobility-lifetime product was found only for one wafer. So the uniformity of µ e τ e product across the wafer can be stated independently of resistivity. More detailed information and discussion of experimental results is presented in the article.

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Results of investigation of X-ray sensors on the basis of GaAs compensated with chromium (HR GaAs) are presented in this work. HR GaAs material is shown to have the following physical parameters: the resistivity about 1GOhm*cm, the nonequilibrium charge carrier lifetime – hundreds of nanoseconds. Prototypes of microstrip and array HR GaAs sensors have been manufactured and tested. It is demonstrated that the sensors provide spatial resolution according to the pixel pitch and allow obtaining high quality X-ray images.

Producing of large area matrix detectors based on semiconductor materials with high atomic number suitable for the registration of the synchrotron radiation of high intensity in the photon energy range 20-90 keV is a relevant technological challenge of our time. This will develop a fundamentally new experimental base of scientific research conducted at leading X-ray synchrotron centers with high luminosity beams. The paper analyzes the possibility of using 4 inch gallium arsenide wafers to create a high-resistive GaAs:Cr detector quality structures on their basis and detector arrays of large area.