The experimental temperature dependence (4.2–300 K) of the conductance of mesoscopic quasi-2D electronic systems under conditions of the insulator-metal percolation transition are discussed for the case of metal-nitride-oxide-semiconductor silicon transistor structures with an inversion n channel and an extremely high (≥1013 cm−2) built-in charge density (source of electrostatic fluctuation potential). Saddle domains of the fluctuation potential are analyzed within the framework of the Landauer-Buttiker formalism. These domains, being point quantum contacts between wells in the chaotic potential distribution, determine both the nature of electron transport and the conditions of the insulator-metal transitions. The results of analyzing the dependence of the conductivity on temperature and field (on the gate voltage) are shown to be consistent. The shape of the effective potential barrier for the electron tunneling transport across the saddle domains is reconstructed.

Special features of the percolation transition in quasi-two-dimensional (quasi-2D) electron systems (metal-nitride-oxide-semiconductor structures with n-type inversion channels) with a strong fluctuation potential (FP) and a gate length smaller than the correlation radius of a percolation cluster (in which case the structure conductance is controlled by isolated saddle-point regions of the FP) are considered. Experimentally measured dependences of the conductance on the field-electrode potential and the temperature are analyzed in the context of the Landauer-Büttiker formalism. Energy parameters of the FP saddle-point regions and effective density of electron states (N SS ∝ m/πℏ2) near the percolation level are determined from the experimental data. Consistency between the experimental results and the proposed statistical model of the formation of FP saddle-point regions in quasi-2D systems is demonstrated. It is shown that saddles transform into potential troughs extended in the direction of the percolation route as the percolation trough is approached.

The effective density of shallow interface states Nss is investigated in the temperature range T=77–300 K using the field-effect method in short-channel (0.5–5 µm) Si-MNOS and GaAs-based FET’s with high (greater than 1012 cm−2) concentrations of built-in charge in the subgate insulator. A peculiarity of the density of electronic states Nss was found having the form of a peak, which manifests itself more distinctly at lower temperatures, higher concentrations of built-in charge, and shorter gates. The peak was observed at the same values of the channel conductance G∼q2/h, regardless of variations in the above-enumerated parameters, the thickness of the sub-gate insulator, and the channel-length-to-width ratio. This means that the energy depth of the peak (∼40–120 meV) varies in proportion to T, which contradicts the current understanding of the interface states caused by both the fluctuation potential (FP) and surface defects or traps. The results are interpreted within the framework of percolation theory applied to the conductivity of strongly disordered systems. The Nss peculiarity is associated with a transition from the conductivity of a two-dimensional effective solid, which occurs when the fluctuation potential is strongly screened by surface electrons, to conductivity via a quasi-one-dimensional potential trough organized by local regions with reduced surface potential under conditions of a strong fluctuation potential.

A threshold vanishing of the Hall emf with decreasing gate voltage is observed at ≈ 77 K in semiconductor systems which are disordered as a result of a high built-in charge density near the plane of the 2D-electron channel. The effect is observed at a channel conductivity σ ≈ e 2 / h and is due to a transition to nondegenerate-electron transport via a 2D percolation cluster having a quasi-1D character of the conduction. We have established that the conductance of “short” structures, having a length of the order of the correlation length of a percolation cluster, equals ≈ e 2 / h per electron and is determined by isolated percolation paths having a lowered percolation threshold. These phenomena are a general property of disordered 2D systems.