Transition between different types of breakdown of the quantum Hall effect by illumination, temperature change and the application of gate voltage

We investigate the breakdown of the quantum Hall effect (QHE) and observe a remarkable change in dependence of the critical current for the breakdown in sample width. Both linear and sub-linear dependences of the critical current on sample width are obtained for the same sample, depending on temperature, way of illumination, and gate bias voltage. The experimental results of the breakdown of the QHE are explained by comparing electron density fluctuations, which are characterized by the random potential from the ionized donors and by screening effects, with the thermal broadening of the electron energy distribution. It is suggested that the electron density fluctuations play an important role in the breakdown of the QHE.