The important problem of creators of photodiode matrix in base on Hg_1-xCd_xTe is a passivation of semiconductor surface . The passivation coating must have low density of surface states in boundary, low densities of fixed and moved charges in insulators also passivation coating must have a stable and homogeneity of properties of boundary and insulator. For passivation surface of Hg_1-xCd_xTe proposed use of various insulators: native oxide and sulphide, SiO₂, ZnS, CdTe.  In this work results of investigation capacitance-voltage characteristics MIS-structures in base on graded-band n(p)-Hg_1-xCd_xTe (x=0.22 and x=0.32-0.36) with grown in situ  CdTe are submitted. For improvement stable and electrical strength of insulator coating for several samples on top CdTe formed additional protective layers SiO₂-Si₃N₄ for x=0.22 and ZnTe for  x=0.32-0.36.

The methods of determination of main parameters of boundary and insulator from capacitance-voltage characteristics of MIS-structures in base on graded-band Hg_1-xCd_xTe are modified. It is shown that for correct calculation of ideal low-frequency capacity-voltsge characteristics necessary take account of presence of graded-band layers. For various samples the density of fixed and moved charges, density of surface states near middle of forbidden gap are calculated. For all investigated MIS-structures observed little moved charge (less than 10^-5-10^-6 Cl/m²). For structures with x=0.22 at used as passivation coating only CdTe the density of fixed charge vary from 4.4×10^-5 Cl/m² to1.83×10^-4 Cl/m². For structures with x=0.32-0.36 with single layer CdTe as passivation coating density of fixed charge total 1.9×10^-4 Cl/m²,  formed of additional layer ZnTe is not lead to increase of value of density of fixed charge. For structures with x=0.32-0.36 formation of ZnTe lead to increase of density of surface states near middle of forbidden gap from 8.7×10¹⁰ eV^-1cm^-2 to (4-5) ×10¹¹ eV^-1cm^-2.

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