  An unusually wide plateau in the quantized Hall resistance has been revealed
for a MQW heterostructure of wide p-GeSi / Ge / p-GeSi quantum wells with the
Fermi energy comparable to the well bottom bending amplitude. This plateau
exists in one of two metastable states of the sample, for which a symmetric
quasi-double-quantum-well system is formed inside the Ge layer, and corresponds
to the filling factor nu = 1 for each of two sublayers in the Ge layer. The
plateau exists not only within a magnetic field range related to the
quantum-Hall liquid, but extends beyond it into a so-called quantized Hall
insulator phase. For the other metastable state only a weak plateau is observed
in the Hall resistivity, corresponding to nu = 1 per Ge layer as a whole.
According to the existing theories, the extra wide plateau may be indicative of
a kind of disorder in a conducting layer, characterized by a uniform
distribution of puddles in their carrier density and by their small average
size. We attribute the differences between these two states to the existence of
two metastable modes in the self consistent potential profile that settle
spontaneously in the multilayer system, which are characterized by different
distributions of holes in the quantum well cross-section.
