2DEG IN STRAINED SI/SIGE HETEROSTRUCTURES

Low-temperature magnetotransport properties for the recent n-type modulation-doped Si/SiGe heterostructures are reported. The biaxially tensile-stressed (100)Si surface layers on stress-relieved SiGe substrates are shown to have all the well known MOSFET characteristics but with more than an order of magnitude higher mobility. The four-fold degeneracy of the ground subband can be completely resolved at a magnetic field as low as 2 T. FQHE at 2/3 and 4/3 are clearly discerned and the activation energy at the plateaus is about 1 K at 10 T. The ratios between scattering time and single-particle relaxation time are 4-10 for a great number of samples examined. Low-temperature mobility appears to be capped below 2 x 10(5) cm2 V-1 s-1 at present, as reported from several laboratories. Comparison of data and model calculations of Stem and Laux for the temperature-dependent mobility are made. Fixed charge and surface roughness appear to be the limiting parameters for the samples currently examined.