621.315The dependence of active and reactive components of the admittance of MIS structures based on heteroepitaxial Hg 0.78 Cd 0.22 Te produced by molecular-beam epitaxy as a function of bias voltage is experimentally studied in the frequency range 1 kHz -1 МHz. The resistance of the epitaxial-film volume is shown to significantly affect the measured admittance in the case where the electron concentration in HgCdTe is up to 5⋅10 14 cm -3 , and this is manifested in a number of features of the capacity-voltage characteristics. The resistance of the epitaxial-film volume is found for the samples with different initial conductivity and for the samples with graded-band subsurface layers. The techniques are proposed that make it possible to avoid the influence of volume resistance on the admittance of MIS structures on the basis of heteroepitaxial HgCdTe.

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Influence of the CdTe content in a near-surface graded-gap layer on the admittance of MIS-structures fabricated on the basis of heteroepitaxial Hg1−xCdxTe (x = 0.22–0.23 and 0.31–0.32) films grown by molecular beam epitaxy was investigated in a wide temperature range. It is shown that a temperature drop from 77 K to 8 K results in a decrease of hysteresis of the capacitance-voltage (C-V) characteristics and a decrease of frequencies which corresponds to a high-frequency behaviour of C-V characteristics of MIS-structures based on n-HgCdTe (x = 0.22–0.23) with and without graded-gap layersand also for MIS-structures based on n-HgCdTe (x = 0.31–0.32). Temperature dependences of the resistance of the epitaxial film bulk and differential resistance of the space-charge region (SCR) in strong inversion mode were studied. The experimental results can be explained by the fact that for MIS-structures based on n-HgCdTe (x = 0.22–0.23) with the graded-gap layers and for MIS-structures based on n-HgCdTe (x = 0.31–0.32), the differential resistance of SCR is limited by Shockley-Read generation at 25–77 K. Differential resistance of SCR for MIS-structures based on n-HgCdTe (x = 0.22–0.23) without the graded-gap layers is limited by tunnelling through deep levels at 8–77 K.

621.315The effect of graded-band-gap layers on the differential resistance of space-charge region in MIS structures based on MBE HgCdTe (x = 0.225) is examined. It is shown that the effect of resistance of the epitaxial-film bulk on the measured capacitance and resistance should be taken into account for correct determination of space-charge region parameters. The presence of near-surface layers with increased Cd contents results in an increase in the resistance of the space-charge region in strong inversion. The product of semiconductor resistance by area as high as 15 Ω⋅cm 2 is obtained despite suppression of tunnel generation-recombination through deep levels in MIS structures with graded-band-gap layers. This might be due to background photogeneration and diffusion of minority charge carriers. The mechanisms for limitation of the differential resistance of space-charge region at different temperatures are discussed for n-HgCdTe (x = 0.225 and 0.292) and p-HgCdTe (x = 0.225). IN RODUCTIONMolecular-beam epitaxy (MBE) of Hg 1-x Cd x Te allows growing hetero-epitaxial structures with the specified indepth distribution of composition, which in turn makes it possible to further optimize the characteristics of infrared detectors. Near-surface layers with enhanced content of Cd decrease the effect of surface recombination on the chargecarrier lifetime in the epitaxial film bulk [1]. Examination of electrical characteristics of MIS structures based on graded-band-gap MBE HgCdTe is necessary for evaluation of the quality of passivating coatings as well as for development of monolithic IR detector arrays. The conventional methods for studying electrical characteristics of MIS structures are designed for semiconductors uniform in depth and cannot be applied to characterization of MIS structures based on graded-band-gap semiconductors in the same form. When examining the properties of MIS structures based on graded-band-gap MBE HgCdTe, one should take into account the resistance of epitaxial film bulk [2] and near-surface graded-band-gap layers [3]. The conductance of MIS structures in strong inversion provides information on the differential resistance of space-charge region (SCR) which determines the rate of recombination of minority carriers in the SCR. The product of the SCR differential resistance and the area (R SCR A d ) is the most important characteristic of MIS photodiodes [4,5] as well as photodiodes where the p-n transition is generated by doping [6,7]. Thus, in [4], for bulk HgCdTe of composition 0.22 the maximum value of those cited in literature R SCR A d = 120 Ω⋅cm 2 at 77 K is listed, whereas in [8], for epitaxial HgCdTe with composition 0.223 without a near-surface graded-band-gap layer, the values

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