[en] The problem of charge separation in a GaAs detector has been solved by means of mathematical modeling. Dynamics of the process for a three-dimensional detector is described in this work in detail. It is shown that in case of interaction with alpha particles, the plasma time can reach several nanoseconds in a strong electric field. In a weak electric field the plasma time exceeds the charge carrier lifetime. The time of separation of charge carriers created by a gamma photon in a strong electric field is 100 ps. The results of calculation are confirmed by experimental data

[en] A mathematical modeling of processes of charge division and collection in GaAs detectors has been carried out. The charge carriers behavior has been described by the system of continuity equations and Poisson's equation. We studied a case when semi-insulating (SI) GaAs contains deep centers of only one type with the abrupt cross-section dependence on field. A concentration of empty traps was taken at a level of 10¹⁵-10¹⁶ cm^-3. All the parameters of deep centers correspond to the EL2 center which is dominant in SI GaAs. Interaction with γ-rays and electrons were simulated by electron-hole packets of corresponding dimensions. It was shown that dynamics of charge division in the case of trapping and without trapping is determined by three factors: (1) the electric field strength value in the region of electron-hole pairs creation; (2) a concentration of non-equilibrium charge carriers in that region (i.e. the ionizing radiation type); (3) the region dimensions

[en] An analysis of the performance of X-ray pixel detectors based on SI-GaAs doped with Cr has been carried out. An analytic form for electron and hole currents of a pixel has been obtained. The detector based on our material has high charge-collection efficiency only when the pixel contacts are anodes in contrast to LEC SI-GaAs. The mean charge collected on pixel contact is calculated for radiation energies of 30 and 60 keV (charge is averaged over all monoenergetic photons irradiating the detector cell)

[en] An analysis of the performance of X-ray pixel detectors based on semi-insulating GaAs doped with Cr has been carried out. An analytic form for electron and hole currents has been obtained. The detector based on our material has high charge collection efficiency only when positive potential is applied to pixels, in contrast to semi-insulating materials (LEC SI-GaAs). A mean charge of a pixel contact is calculated for photon energy of 30 and 60 keV. The maximum mean charge is 3000e for the detector thickness of 300 μm and photon energy of 30 keV and 2300e for the detector thickness of 600-800 μm and photon energy of 60 keV

[en] X-ray detectors for use with a scanning radiographic device have been developed based on the technique of compensated semi-insulating GaAs. The main detector feature is a linear current-voltage characteristic due to the use of Ohmic contacts. The detector consists of two identical detectors connected to power supplies with different polarities in order to minimize the detector leakage current. Testing of the detectors has been carried out at the Budker Institute of Nuclear Physics. The detector was used with the digital X-ray apparatus 'LDRD SIBERIA-N'. The detector parameters have been studied, looking at the dependence with radiation dose, with the applied bias voltage and with the gamma photon energy, using photons in the range of 60-120 keV. Images of a test-object were obtained with a resolution of 1.4 line pairs per mm for a detector with 400 μm pitch and 2.8 line pairs per mm for a detector with 200 μm pitch

[en] Results of the measurements of the working parameters of GaAs detector samples are presented, which may be used as the basis for the construction of X-ray imaging medical systems. To estimate the influence of heat dissipation from the GaAs detectors themselves and from their associated read-out electronics, an investigation of the temperature dependence of their working parameters has been carried out

[en] The growth of GaAs epitaxial structures for X- and γ-ray detectors and the device characteristics have been investigated. Conditions of reproducible LPE growth of GaAs layers more than 100 μm thick on substrates of 40 μm diameter have been established. Complex doping with tin and deep Cr-acceptor have been studied for the liquid-phase epitaxial growth in a wide temperature range. A method has been developed for GaAs:Sn,Cr layer growth with the resistivity in the range (10⁷-10⁹)Ω cm and with thickness up to 550 μm. Detector p-i-n structures have been fabricated on the base of high-resistivity GaAs layers. The electric field distribution and current flow mechanisms in the diodes have been studied. Diodes have been fabricated with a dark current density of 1x10^-7A/cm² at a reverse bias voltage of 100 V. Alpha particle and γ-ray spectra of the detectors have been measured. An X-ray image has been obtained with a strip detector based on LPE layers

[en] The results of the measurements working parameters of GaAs detector samples as the basis for the design of the X-ray sensitive detectors are presented. To select the optimal operating conditions for GaAs detectors the study of the temperature dependence of their working parameters has been done

[en] The growth and characteristics of the detector p-i-n-structures fabricated by means of the epitaxial methods are discussed. High-resistivity i-layers containing chromium as a compensated impurity have been grown on the n-GaAs substrates by the liquid-phase epitaxy method. The layer thicknesses are (150-250) μm, their resistivities lie in the interval ρ=(5x10⁶-2.5x10⁸) ohm cm. The thin Zn-doped p-layer has been grown upon the i-layer by the vapour-phase epitaxy method. The electric field profiles in the p-i-n-diodes have been measured. The reverse current-voltage characteristics of the diodes have been analysed. The sensitivity of the structures to β- and γ- radiations has been investigated

[en] GaAs coordinate detectors for X-ray systems of scanning type have been developed. Two modifications of the detectors have been constructed for ionizing radiation detection in parallel and perpendicular to the electric field direction in the detector bulk. The detectors have 64 active regions with 100 μm pitch. In order to reach the minimum value of coupling capacitance and resistance coupling between active regions, the latter is separated by narrow gaps on unit cells. The gaps are made by means of reactive ion etching. The detectors are fabricated on the base of vapor-phase epitaxial material 40-45 μm in thickness with free carriers concentration of p₀=10¹² cm^-3. Input capacitance of a detector cell is 0.25 pF, dark current is 30-50 pA per cell. The detectors have almost 100% charge collection efficiency for all types of ionizing radiation. High resolution of the detector allows to detect structures of a spectrum from the ²⁴¹Am source in the energy range of 14-17 keV