MAGNETOTRANSPORT IN ULTRATHIN ERAS EPITAXIAL LAYERS BURIED IN GAAS

Magneto-transport measurements have been performed on epitaxial layers of ErAs buried inside insulating GaAs with thicknesses from 15 nm (bulk like) to 0.7 nm (quantum confined). Magneto-transport in bulk like layers is consistent with a low density semi-metal. Scattering of the carriers from the 4f spins causes a spin disorder anomaly at the antiferromagnetic/paramagnetic phase boundary at low temperatures and magnetic fields. The simplest models of size quantization of semi-metals predict that the thinnest layers, 0.7 nm, should be semiconducting with an energy gap of the order of 1 eV. This is not observed. Instead these sub-nanometer thick films show a large negative magneto-resistance suggestive of bound magnetic polarons which are destroyed in modest magnetic fields. © 1990.