Temperature dependence of the magnetoresistance minima in n-channel Si/Si1-xGex modulation-doped quantum well structures

Shubnikov-de Haas (SdH) measurements between 0.04 and 4.2K have been performed on two modulation-doped n-type Si/Si_0.7Ge_0.3 heterostructures, and the temperature dependence of the resistivity minima in the SdH oscillations at integer filling factor was analysed. Above IK, the resistivity is thermally activated, corresponding to ρ_xx ^min ∝ σ^min _xx ∝ exp(-E_a/2kT) where the activation energy, E_a , is expected to be close to the cyclotron energy; however, the values of E_a obtained from experiment are much lower than this. The difference has been attributed to the fact that the Landé g factor is larger than the bulk value of 2. The temperature dependence of the resistivity deviated from this activated behaviour below IK, as found in measurements on disordered system, and this is interpreted as being due to hopping conduction.