ELECTRON-TRANSPORT IN THE SI(111)-CR(ROOT-3X-ROOT-3)R30-DEGREES-ALPHA-SI SURFACE PHASE AND IN EPITAXIAL-FILMS OF CRSI, CRSI2 ON SI(111)

We present the results of measuring the temperature dependence (1.2 K less-than-or-equal-to T less-than-or-equal-to 300 K) of the sheet resi stance and the magnetoresistance tensor components for the Si(111)-Cr( square-root 3 X square-root 3)R30-degrees surface phase and Cr-Si epit axial films coated with an amorphous Si film (20 angstrom). The format ion of surface structures at metal deposition was investigated by LEED and transmission electron microdiffraction. The electrical conductivi ty of the Si-Cr surface phase was found to obey the sigma(square) = aT 0.4 law with R(square) greater-than-or-equal-to 100 kohm at T less-tha n-or-equal-to 50 K, which cannot be explained by either a metal-insula tor transition, or hopping conductivity models. The Cr-Si ultrathin ep itaxial films show a metallic behavior with R(square) = 0.37 and 2.2 k ohm for the CrSi and CrSi 2 films, respectively, with very high sheet hole concentration (3 X 10(15) cm-2) and low carrier mobility (mu less -than-or-equal-to 7 cm2/V.s). The sigma(square)(T) dependence for the CrSi2 films is in agreement with the In T law corresponding to localiz ation and electron-electron interaction models of 2D metallic conducto rs.