Magnetoresistance of Ge-Si Whiskers in the Vicinity to Metal– Insulator Transition

The magnetoresistance of GeхSi1-х (x = 0.002¸   0.11) whiskers with an acceptor concentration (Na = 3x1018¸   2.1019 cm-3) near the metal-insulator transition (MIT) was studied at low temperatures (4.2 - 77)K in magnetic fields up to 14 T. It is shown that at 4.2 K the magnetoresistance of the Ge-Si whiskers on thedielectric side of the MIT is quadratic, while the magnetoresistance of the crystals on the metal side of the MIThas an exponential dependence on the magnetic field. In the samples in the immediate vicinity to the MIT on thedielectric side, negative magnetoresistance was detected, whereas in metal samples with a high germaniumcontent (x = 11 at.%) an anomalous positive magnetoresistance occurs. The resulting anomalous dependences arerespectively explained by the conductivity with respect to the delocalized A+ states of the upper Hubbard bandand the increase in the electron-electron interaction in Ge-Si whiskers at increasing germanium content.