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.