Quantum interference in the n-channel of a Si:SiGe quantum well

We have grown n-channel Si:SiGe quantum wells using gas source molecular beam epitaxy. The two-dimensional electron gas confined in the strained Si quantum well is weakly disordered and displays quantum interference in the form of a pronounced, low-field negative magnetoresistance. By fitting the data to the standard theory of weak localization, in the temperature range 50 mK to 6 K, we have been able to extract the product N_v alpha and the electron phase coherence length L_phi. Our results give a value for the product N_v alpha in the range 0.6+or-0.12, which is close to that expected for strong intervalley scattering and is similar to values obtained in Si MOSFETs. We show a power law dependence of L_phi with temperature, i.e. L_phi varies as T^-p2/. For T>0.7 K the value of the exponent p/2=0.75 which suggests that the dominant dephasing mechanism is electron-phonon scattering as observed in Si MOSFETs. However, for lower temperatures the variation is less pronounced (p/2=0.15). The weaker temperature dependence may be a precursor to a saturation in the value of L_phi as has recently been observed by other groups.