Influence of the Compositional Grading on Concentration of Majority Charge Carriers in Near-Surface Layers of n(p)-HgCdTe Grown by Molecular Beam Epitaxy

Abstract

The capacitive characteristics of metal–insulator-semiconductor (MIS) structures based on the compositionally graded Hg1−xCdxTe created by molecular beam epitaxy have been experimentally investigated in a wide temperature range (8–77 K). A program has been developed for numerical simulation of ideal capacitance–voltage (C–V) characteristics in the low-frequency and high-frequency approximations. The concentrations of the majority carriers in the near-surface semiconductor layer are determined from the values of the capacitances in the minima of low-frequency C–V curves. For MIS structures based on p-Hg1−xCdxTe, the effect of the presence of the compositionally graded layer on the hole concentration in the near-surface semiconductor layer, determined from capacitive measurements, has not been established. Perhaps this is due to the fact that the concentration of holes in the near-surface layer largely depends on the type of dielectric coating and the regimes of its application. For MIS structures based on n-Hg1−xCd x Te (x = 0.22–0.23) without a graded-gap layer, the electron concentration determined by the proposed method is close to the average concentration determined by the Hall measurements. The electron concentration in the near-surface semiconductor layer of the compositionally graded n-Hg1−xCd x Te (x = 0.22–0.23) found from the minimum capacitance value is much higher than the average electron concentration determined by the Hall measurements. The results are qualitatively explained by the creation of additional intrinsic donor-type defects in the near-surface compositionally graded layer of n-Hg1−xCd x Te.