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The silicon-germanium solid solutions Si l_x-Ge x are of interest in connection with investigations of promising materials for semiconductor detectors (SCDs) of ionizing radiation [1]. The positive qualities of both silicon and germanium are combined in this material: silicon as the wider-gap and higher-temperature material and germanium as the more efficient material with a quite high cross section of interaction with ionizing radiation.In the present paper we present the results of an investigation of the effect of the germanium content in single crystals of the alloy Sit_x-Ge x on the electrophysical, radio-and spectrometric characteristics of lithium-drift detectors based on them. Ingots of p-type Si l_x-Gex single crystals with resistivity of 10-100 fFcm, 5-10 mm in diameter, and with (I 11) crystallographic orientation were obtained by the method of crucibleless zone melting in vacuum. Semiconductor detectors based on Si l_x-Gex are 0.5-1.5 mm thick and they have a sensitive area of 0.1-0.2 cm2; they have gold metallization on the entrance window and an aluminum contact on the backside [2].The degree of structural uniformity of the volume of the base semiconductor Sit_x-Ge x was investigated as a function of the germanium content by the phase-frequency method [3].The degree of uniformity of the surface and volume of p-i-n structures was determined by measuring the current, capacitance, noise, spectrometric (R-V t) and radiometric (N-V t) parameters of the characteristics of the SCDs and the C-V characteristics of test MIS structures with pyrolytic silicon dioxide SiO2p, synthesized by a low-temperature method in an ultrapure medium [4, 5]. The energy resolution (R-V t) and the counting rate (N#-Vt) for 3 particles from 2~ on the E 3 -I MeV line as a function of the external bias voltage was determined at 300 K by the method of [6]. Differential analysis of the characteristics, taking into account the C-V characteristics of the test MIS structures, made it possible to estimate not only the density of surface and volume electronic states, but also the contribution of surface and volume defects to the volume and surface generation and excess components of the reverse current, as well as to the components of the intrinsic noise and energy resolution of the SCDs [7, 8]. The contribution of the indicated parameters of the SCDs to the radiometric characteristics of Sil_x-Ge x p-i-n detectors was determined by establishing a correlation between the electric and spectro-and radiometric parameters, Figure 1 displays the counting rate N 3 for 3 particles versus V t of Si l_x-Ge x SCDs with different germanium content in the base semiconductor. A characteristic feature of the (N~-V t) characteristics is that the counting rate depends strongly on the germanium concentration in Sil_x-Ge x SCD with x = 0,1-2% of the atomic fraction and almost total absence with x = 2-6% of the atomic fraction. The maximum increase of a factor of 3-4 in the counting rate was observed when the germanium concentration was increased from 0.5 ...
Single-crystal solid solutions of Si t _xGex are of interest as a new material for producing lithium-drifted detectors for providing the possibility of raising the recording efficiency for a, 0, and 3' radiation [1]. It is well known that the detectivity of the material is proportional to Z 5/2 (the nuclear charge of the atoms) and to the degree of homogeneity of the semiconductor material. The temperature operating range of a detector is lowered with a reduction in the width of the forbidden band of the semiconductor used to make it. Well-known analogs operating at room temperature have been made using silicon with Z = 14. Germanium detectors, which possess a higher sensitivity (Z = 32), require cooling to liquid nitrogen temperature (around -200~ Detectors utilizing Sil_xGe x with a small germanium content on the one hand retain the temperature operating range of silicon analogs and on the other hand are more sensitive on account of the presence of germanium atoms located in the semiconductor lattice in a substitution position. However, a solid solution compensated with lithium (as a material suitable for making a p-i-n detector) should then possess a high degree of compensation and a long carrier lifetime. These quantities are determined both by the. homogeneity of composition and distribution of impurities in the original solid solution and by the technology of compensating the material with lithium.In order to make a high-efficiency detector utilizing this material one must provide a compensated high-resistance sensitive region, a -1 eV high potential barrier, low reverse currents in the structure, and consequently a minority carrier lifetime of shorter than 10 -6 s. We previously showed that detectors utilizing Si z_xGex have a 0-particle count rate which is a factor of three higher than that for their silicon analog [1].In the present work we investigate the barrier height and the current-voltage characteristics of p-i-n detectors utilizing single crystals of Si 1 _xGex solid solutions with gold and aluminum contacts, and the influence of the material on the electrophysical properties of a lithium-compensated/-region with an atomic germanium concentration in the alloy of up to 10%. Lithium was drifted into original p-type alloy samples of resistivity 50-100 from, obtained by electron-beam crucible-free zone melting in a vacuum, using a technology developed for p-Si at 60~ in a field of 10 4 V/cm, the thickness of the i region being 400-600/~m.As is well known, the photoelectric method is direct and one of the most accurate for determining the barrier height since one can fred the height El, of the energy barrier by extrapolating the linear dependence of the square root of the photoresponse onto the energy axis [2]. As can be seen from Fig. 1, El, is independent of the germanium content and is equal to 0.95-I eV. At the same time, it is well known that the maximum Au-p-Si barrier (and our material has similar properties to silicon) is 0.75 eV.The barrier height 'r in two limiting cases is as follows: if D...
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