MANIFESTATION OF PERCOLATION CONDUCTIVITY OF SHORT-CHANNEL FIELD-EFFECT TRANSISTORS IN THE SPECTRUM OF SHALLOW INTERFACE STATES

The effective density of shallow interface states N-SS,, is investigat ed in the temperature range T=77-300 K using the field-effect method i n short-channel (0.5-5 mu m) Si-MNOS and GaAs-based FET's with high (g reater than 10(12) cm(-2)) concentrations of built-in charge in the su b-gate insulator. A peculiarity of the density of electronic states N- SS,, was found having the form of a peak, which manifests itself more distinctly at lower temperatures, higher concentrations of built-in ch arge, and shorter gates. The peak was observed at the same values of t he channel conductance G similar to q(2)/h, regardless of variations i n the above-enumerated parameters, the thickness of the sub-gate insul ator, and the channel-length-to-width ratio. This means that the energ y depth of the peak (similar to 40-120 meV) varies in proportion to T, which contradicts the current understanding of the interface states c aused by both the fluctuation potential (FP) and surface defects or tr aps. The results are interpreted within the framework of percolation t heory applied to the conductivity of strongly disordered systems. The N-SS,, peculiarity is associated with a transition from the conductivi ty of a two-dimensional effective solid, which occurs when the fluctua tion potential is strongly screened by surface electrons, to conductiv ity via a quasi-one-dimensional potential trough organized by local re gions with reduced surface potential under conditions of a strong fluc tuation: potential. (C) 1997 American Institute of Physics. [S1063-782 6(97)01212-X].