Conductivity mechanisms in the ordered surface phases and two-dimensional monosilicides of Cr and Fe on Si(111)

In situ Hall measurements at elevated temperatures of chromium (Si(1 1 1)ro ot3 x root3/30 degrees -Cr) and iron (Si(1 1 1)2 x 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 e ffect of the silicon substrate to electrical parameters of ultrathin films at different temperatures was taken into account. It was shown that ultrath in film of the Si(1 1 1)root3 x root3/30 degrees -Cr surface phase displays p-type semiconductor properties with the activation energy of E-a=0.12eV, but ultrathin film of the Si(1 1 1)2 x 2-Fe surface phase displays metal pr operties with small hole concentration. It was shown that layer-by-layer in crease of Cr (Fe) thickness and concurrent annealing of the sample at 350 d egreesC 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 w ith holes as the majority carriers. (C) 2001 Elsevier Science B.V. All righ ts reserved.