Hopping conductivity and coulomb correlations in 2D arrays of Ge/Si quantum dots

摘要

The temperature and magnetic-field dependences of the conductivity associated with hopping transport of holes over a 2D array of Ge/Si(001) quantum dots with various filling factors are studied experimentally. A transition from the Efros-Shklovskii law for the temperature dependence of hopping conductivity to the Arrhenius law with an activation energy equal to 1.0-1.2 meV is observed upon a decrease in temperature. The activation energy for the low-temperature conductivity increases with the magnetic field and attains saturation in fields exceeding 4 T. It is found that the magnetoresistance in layers of quantum dots is essentially anisotropic: the conductivity decreases in an increasing magnetic field oriented perpendicularly to a quantum dot layer and increases in a magnetic field whose vector lies in the plane of the sample. The absolute values of magnetoresistance for transverse and longitudinal field orientations differ by two orders of magnitude. The experimental results are interpreted using the model of many-particle correlations of holes localized in quantum dots, which lead to the formation of electron polarons in a 2D disordered system. © 2005 Pleiades Publishing, Inc.