Conductivity mechanisms in the ordered surface phases and two-dimensional monosilicides of Cr and Fe on Si(1 1 1)

In situ Hall measurements at elevated temperatures of chromium (Si(1 1 1)√3×√3/30°-Cr) and iron (Si(1 1 1)2×2-Fe) surface phases and ultrathin Cr and Fe monosilicide films are presented. Within the framework of the two-layer model of conductors connected in parallel, the shunting effect of the silicon substrate to electrical parameters of ultrathin films at different temperatures was taken into account. It was shown that ultrathin film of the Si(1 1 1)√3×√3/30°-Cr surface phase displays p-type semiconductor properties with the activation energy of Ea=0.12 eV, but ultrathin film of the Si(1 1 1)2×2-Fe surface phase displays metal properties with small hole concentration. It was shown that layer-by-layer increase of Cr (Fe) thickness and concurrent annealing of the sample at 350°C results in the growth of epitaxial CrSi(1 1 1) (FeSi(1 1 1)) on Si(1 1 1), which at thickness of 1.5–2.4 nm displays metal-type conductivity with holes as the majority carriers.