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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The investigation results of GaAs:Cr X-ray sensor noise characteristics are presented. Measured samples were 3*3 mm 2 and thickness in the range of 300-500 µm. It is shown that the proposed method can be used to reveal the nature of dominant noise and calculate the energy resolution of structures. This technique allows estimation of the optimal operating voltage of GaAs:Cr sensors and characterization of detector material.

A: Currently, semiconductors with high atomic number Z arouse strong interest in construction of X-ray sensors. One of the most prospective materials are presented by elements from the group A III B V . Gallium arsenide compensated with chromium (HR-GaAs:Cr) is one of these materials and exhibits unique characteristics. The sensors based on HR-GaAs:Cr demonstrate high absorption efficiency. The response of HR-GaAs:Cr sensors to subnanosecond X-and β-ray pulses of 28 ÷ 52 keV from an accelerator of runaway electrons are described in this research. The samples have symmetric metal-semiconductor-metal structure. The active area of the samples was 0.09 cm 2 and the thickness of sensitive layer was 145 ÷ 500 µm. Experimental characteristics of pulses were compared with theoretical estimations. An optimal thickness of sensitive layer of HR-GaAs:Cr sensors was determined, which allowed us to obtain the minimal possible value of output pulse duration ≈ 1 ns.

Cr sensors noise characteristics were investigated by means of amplitude spectrum analysis. Noise characteristics of HR-GaAs:Cr sensors with different metal contacts were investigated at different shaping times. Using IR laser the electron-hole pairs were generated in the sensors in order to simulate X-ray radiation and study energy resolution of the sensor. Additionally, the nature of dominant noise, optimal shaping time and extreme energy resolution were determined. Finally, the most preferable metal contacts were selected for the HR-GaAs:Cr sensors, which allow to decrease a noise level.