Electron Tunneling in Stepped Nanostructured Barrier

P.G. Datskos and T. Thundat

Department of Physics and Astronomy, University of Tennessee
and Oak Ridge National Laboratory

D. M. Nicholson, G. Muralidharan, and S. Rajic

Oak Ridge National Laboratory

T. M. Daniels_Race and H. Li

Department of Electrical and Computer Engineering, Duke University

We fabricated "stepped" quantum barriers based on GaAs heterostructures grown with a molecular beam epitaxy (MBE) technique. These stepped barriers consist of layers of quantum wells that act as adjacent multiple electron barriers. Electron transport through such barriers is dependent on the applied electric field and on temporary electron states (induced by the external electric field). At low electric fields, stepped double barriers allow only thermally activated electron transport. However, as the electric field is increased resonant energy levels develop that are confined between the stepped barriers. Electron tunneling current flows at specific values of electric field that energetically match these resonances with the occupied part of the conduction band; this leads to an observed negative differential resistance. Calculations of ballistic electron transport can aid in determining structures that will have high ｳpeak-to-valleyｲ ratios in the transmitted electron current. We performed calculations of current_voltage characteristics (CVC) for a number of many stepped quantum barrier geometries. We also measured electron tunneling current through stepped barriers as a function of voltage. We will present our results and compare our calculations with the experimental results for MBE grown GaAs based structures.