DISAPPEARANCE OF THE BREAKDOWN OF QUANTUM HALL-EFFECTS IN SHORT DEVICES

Device-length dependence of the breakdown of the integer quantum Hall effects is studied by using devices with narrow constricted regions of different lengths L at T = 1.5-4.2 K and Landau-level filling factors of nu = 2, 4 and 6. Samples are fabricated from GaAs/AlGaAs heterostr uctures. Sharp increase in the diagonal resistance R(x) at a critical current disappears, and is replaced by a continuous and gradual increa se in short constricted regions of L < 30 mu m. The observed L-depende nce supports an avalanche-type carrier multiplication mechanism trigge red by electron-superheating.