Anomalous electrical properties of Si/Si1 − x Ge x heterostructures with an electron transport channel in Si layers

Abstract

The electrical properties of elastically stressed FET-like Si/Si1 − xGex layered heterostructures (x < 0.2) with a modulated dopant concentration are studied. It is presumed that the amplitude of a narrow (∼6-nm-thick) potential well in the Si layer corresponds to the amplitude of a fluctuation potential giving rise to nanoscale inhomogeneities in the Si channel. The structures in question undergo a phase transition from the insulating to metallic behavior as the electron density in the Si channel is varied. In a magnetic field, the structures with metallic conductivity have negative magnetoresistance (NMR) for both the longitudinal and transverse directions of the applied magnetic field with respect to the transport current passing through the structure. Investigating the dependence of NMR on the magnetic field strength showed that the main contribution to NMR is due to weak localization. Peculiar properties are also found in electrical measurements of the diode characteristics of the structures in question. In particular, the capacitance-voltage characteristics of these structures show well-defined resonance features, possibly related to one-and quasi-zero-dimensional inclusions existing in addition to two-dimensional charge carriers in the inhomogeneous two-dimensional film.