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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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