Two types of breakdown of quantum Hall effect depending on the electron density fluctuation

We investigate different types of the breakdown of the quantum Hall effect (QHE), which are characterized by the sample width dependence of the critical current for the breakdown. The distinction of two different types of breakdown is thought to be the properties of the two-dimensional electron gas (2DEG) wafers, but it is not related directly to the 2DEG mobility and electron density determined by Hall measurement at low magnetic field. We observe the switching between linear and sublinear dependence of the QHE breakdown by varying temperature, gate voltage, and by illumination condition. The type of QHE breakdown is determined by the extent of potential fluctuations in the 2DEG, which are characterized by the random potential from ionized donors and by screening effects, comparing with those resulting from the thermal broadening of the electron distribution. The result of magnetocapacitance between 2DEG and Schottky gate also suggests that the 2DEG homogeneity play an important role in the breakdown of the QHE. (C) 2002 Elsevier Science B.V. All rights reserved.