Filling factor dependence of electron effective mass in Si/SiGe quantum wells at high magnetic field

Far-infrared cyclotron resonance of a two-dimensional electron gas in strai ned Si/SiGe single quantum wells was studied at low temperatures (1.5-25 K) in high magnetic fields up to 40 T. We found a remarkable Landau-level fil ling factor (v) dependence of the effective mass with prominent peaks at ar ound v = 1 and 2. The carrier scattering time deduced from the line-width w as found to oscillate also as a function of v. The result is explained by s creening of impurity potentials that depends on the filling of the Landau l evels. (C) 2001 Elsevier Science B.V. All rights reserved.