Admittance measurements in the temperature range (8−77) K for characterization of MIS structures based on MBE n-Hg0.78Cd0.22Te with and without graded-gap layers

Admittance of MIS structures based on MBE n-Hg1-xCdxTe (x=0.22-0.23) with Al2O3 as insulator is experimentally investigated for the cases of the presence and absence of near-surface graded-gap layers with high content of CdTe. It is shown that the structures with graded-gap layers are characterized by a significant hysteresis of electrical characteristics, a deep and broad dip in the low-frequency capacitance-voltage characteristic, and high values of the differential resistance of the space charge region in the strong inversion. It is found that already at 77 K, the capacitance-voltage characteristics of structures with graded-gap layers have a high-frequency behavior relative to the recharge time of surface states in the frequency range of (1-2000) kHz. At frequencies exceeding 200 kHz and a temperature of (9−15) K, the capacitance-voltage characteristics of the structures without graded-gap layers have a high-frequency behavior relative to the recharge time of surface states located near the Fermi energy for an intrinsic semiconductor. Peculiarities of determining the density of surface states and the electron concentration in MIS structures with and without graded-gap layers are studied.