The effective density of shallow interface States Nss was investigated in temperature range T = 77 300 K using the field effect method in short-channel (0.5 5 µm) Si-MNOS and GaAs FETs with high (more then 1012 cm-2) concentration of built-in charge at the under-gate insulator. A peak-shape pesuliarity of the Nss was found, which manofests itself more distintly if the T is lower, concentration of the built-in charge is higher, and the date length is shorter. The peak was observed at the channel conductance G q2/h ragardless of variation of these parameters as to variation of the under-gate insulator thickness and the channel length to width ratio. It means that the peak energy depth ( 40 120 meV) varies with the T proportionally to the last, that contradicts to understanding of the interface states caused by both the fluctuation potential (FP), and surface defects or traps. The results are interpreted in frames of the percolation theory applied to conductivity of strongly disordered systems. The Nss peculiarity is associated with transition from conductivity of the 2D effective solid taking place when the FP is strongly screened by surface electrons to the one over a quasi — 1D potential trough organized by local rigions with reduced surface potential taking place when the FP becomes strong.
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