Electron Concentration in the Near-Surface Graded-Gap Layer of MBE n-Hg1–xCdxTe (x = 0.22–0.40) Determined from the Capacitance Measurements of MIS-Structures

Abstract

Capacitance-voltage (C–V) characteristics of MIS structures based on the graded-gap n-Hg_1–xCd_xTe (x = 0.22–0.40) grown by molecular-beam epitaxy were experimentally studied in the temperature range of 9–77 K. The concentrations of majority charge carriers in the near-surface layer of the semiconductor are determined from the capacitance value at the minimum of the (C–V) characteristic due to the high-frequency behavior of the capacitance characteristics of the structures with graded-gap layers with respect to the recharge time of surface states. The electron concentration in the near-surface layer of the graded-gap n-Hg_1–xCd_xTe at x = 0.22–0.23 in the working layer, found from the value of the capacitance at the minimum, considerably exceeds the integral electron concentration determined by the Hall method. With an increase in the composition in the working layer to x = 0.30–0.40, the difference in the values of the electron concentrations decreases substantially for the near-surface layers with close compositions on the surface. The results obtained are explained by the appearance of additional native defects of donor type in the near-surface graded-gap layer, and this effect is most clearly manifested at large composition gradients in the graded-gap layer. The results of processing of experimental C–V characteristics are in qualitative agreement with the results of studying the electron concentration distribution over the film thickness performed by the Hall method.