FQHE STATES OF HIGH-MOBILITY N-SI SI1-XGEX HETEROSTRUCTURES IN PULSEDMAGNETIC-FIELDS/

Low temperature (mK) magneto-transport measurements of high quality n- type modulation-doped Si/Si0.7Ge0.3 heterostructures have been extende d to high magnetic fields (50T) and low temperatures (40mK). For the h igh mobility electrons confined to 2D in the biaxially tensile straine d Si layer, a two-valley system, signatures of the fractional quantum Hall effect (FQHE) in the Landau level filling factor region v < 1 (on e valley occupied, lowest spin state) usually observed in GaAs are rep licated out to v = 2/5 at B similar to 48T. For 1 < v < 2 however, (bo th valleys occupied, lowest spin state), prominent FQHE states such as v = 5/3 are absent, similar to the case in double layer GaAs systems. Tilted field experiments demonstrate that the valley splitting depend s only on the normal field component.