QUANTUM HALL-EFFECT IN GE1-XSIX (111)GE MQW SAMPLES OF NONSTANDARD 6-POINT CONTACT GEOMETRY/

We investigate the Quantum Hail Effect (QHE) in selectively boron-dope d GeSi/(111)Ge multi-quantum well (MQW) samples of non standard geomet ry with six-point contacts disconnected from the sample edges. The Hai l resistance shows a well-pronounced quantisation that is consistent w ith integral QHE (IQHE) value (h/ve(2)) at temperature T = 4.2K. When the temperature was lower than 2.5K, unusual peaks on the R(xy) platea ux were observed. We explain this behaviour by non-equilibrium populat ion. of Landau levels that results from the separation of current cont acts from the edge of the sample. (C) 1995 Academic Press Limited