OBSERVATION OF 77 K COULOMB STAIRCASES IN GAAS ALGAAS HETEROSTRUCTURES IMPLANTED BY A FOCUSED ION-BEAM/

We report evidence of single electron tunneling at 77 K in GaAs/AlGaAs heterostructures implanted with a single line scan of a focused ion b eam (FIB). We observe clear staircases in the current-voltage characte ristics when the current is measured across the implanted area. These staircases exist in all the fabricated devices but show variations in step width and step height. The observed staircases most likely origin ate from single electron tunneling through a specific Coulomb island i n the random distribution of potential fluctuations which results from implantation damage. Analysis of the observed step widths results in an estimate of the spatial extent of the island which is consistent wi th the correlation length of the potential fluctuations estimated from the defect density. (C) 1995 Academic Press Limited