Weak localization and charge-carrier interaction effects in a two-dimensional hole gas in a germanium quantum well in a Si

No abstract

The resistance of a quasi-ballistic wire fabricated in a high-mobility n-type Si/SiGe heterostructure is studied as a function of magnetic field in the temperature range 0.1 K-4.2 K. The wire has a length of 10 µm and a nominal width of 400 nm. When the magnetic field is increased from 0 T to 10 T we observe weak localization, reproducible resistance fluctuations and Shubnikov-de Haas oscillations. The various effects are superimposed on a background resistance showing the influence of diffuse sidewall scattering. All these effects are separated and analysed to give a quantitative and consistent picture of the electron transport. The magnitude of the various measured transport parameters indicates that the electron transport is quasi-ballistic. Size effects due to the influence of the confining boundary potential are observed and accounted for in the theoretical descriptions.

Magnetoresistance fluctuations in short quasiballistic Si/SiGe wire segments have been investigated as a function of magnetic field and temperature. The segments are measured in a four-probe geometry and the voltage probe distances L are taken smaller or larger than the phase coherence length l ͑Ϸ1.5 m at T ϭ0.1 K͒ and the electron mean free path l e ͑Ϸ0.8 m͒. At magnetic fields smaller than Bϭ1 T, the amplitude ␦R and the correlation field B c of both the symmetric and antisymmetric part of the resistance fluctuations have been studied as a function of probe distance and temperature. It is found that, despite the quasiballistic character of electron transport in our samples, the behavior of the amplitude and correlation field with probe separation is in good qualitative agreement with expressions derived for the diffusive regime. The observed magnitude of B c , however, is much larger than expected for the diffusive transport regime. A better agreement for B c is obtained using an expression adapted for the quasiballistic regime. The temperature dependence of the correlation field cannot be explained by expressions appropriate for the diffusive or the quasiballistic transport regime.