Theory for n‐Surface Charge Layers in Hg_1−xCd_xTe MIS Structures

Abstract

The energy gap of the Hg1−xCdxTe‐system can be controlled by the mole fraction x of Cd. This offers the possibility to use this material as a model system for systematic investigations especially in the narrow‐gap region (corresponding to 0.16 ≦ x ≦ 0.25). The electronic structure, subband occupations, subband energies, and cyclotron masses are calculated for the two‐dimensional electron gas in MIS structures with this material using an approximate self‐consistent method. Both, inversion and accumulation conditions are considered. Comparisons with existing limited theoretical results and with experimental ones a) show the accuracy of the method used and b) allow to interpret the detailed experimental results from Shubnikov‐de Haas and cyclotron measurements available now. Predictions are made on the composition dependence of the electronic structure especially for inversion conditions.

Magneto-conductance spectroscopy of a narrow-gap MIS device

“…N s = Q inv /q = (C ins /Aq) × V T , where Q inv denotes the area density of the surface inversion charge under the anodic oxide layer. The partial occupancies have been determined as 0.701, 0.222 and 0.077 of the total inversion layer carrier concentration N s and are in good agreement with the published theoretical [12,13] and experimental [9][10][11]19] values. The agreement confirms the reliability of our results.…”

“…Sweeping of V g at fixed B leads to a progressive change of not only the surface carrier concentration but consequently also of the surface electric potential well and quantized subband energies. According to theoretical [12,13] and experimental [9][10][11]19] investigations, the first excited subband is reached at the total surface carrier concentration N s ≈ 3.6 × 10 11 cm −2 , which corresponds to V g − V T = 4.6 V. The second one starts at N s ≈ 14.7 × 10 11 cm −2 which relates to V g − V T = 18.8 V. Consequently, only the first few peaks near the inversion threshold in figure 2 (between ≈ − 17 V and −12 V) represent the Landau levels in the lowest subband at 7.0 T, and within the other range of bias voltage two or three subbands are simultaneously populated. This leads to a change in periodicity of the sweep of V g and, together with the abovementioned influence on the inversion layer parameters, it complicates interpretation of the measured curves.…”

“…Extensive studies of the Shubnikov-de Haas effect in the inversion and accumulation layers on MCT were published in [10,11]. From both types of measurement, the partial occupancy of each subband in the inversion layer can be deduced as a function of V g and of the total surface carrier concentration N s , and compared with the theoretical calculations [12,13].…”

Exchange and spin-orbit effects in inversion layers on the gapless semimagnetic semiconductor HgMnTe

“…From this point on, we shall restrict our consideration to the semiclassical approximation just as in the quantization of the spectrum described by set (3) (it is clear that the use of the semiclassical approximation immediately in (1) results in the loss of spinor-like effects), so also in calculation of the surface potential V (z). The validity of such an approach in narrow-gap semiconductors has been argued and demonstrated by a comparison with numerical selfconsistent calculations in many papers [42][43][44] (see also [8] and references therein).…”