SINGLE-ELECTRON TUNNELING AND COULOMB CHARGING EFFECTS IN ULTRASMALL DOUBLE-BARRIER HETEROSTRUCTURES

An extensive study of charge transport through submicron-diameter doub le barrier heterostructure diodes is reported. The occupation of the q uantum well with single electrons, starting from zero, is observed in the form of sharp steps in the current-voltage characteristics. The ma gnitude of the current steps can be controlled by changing the barrier thicknesses and thus their transparency for tunneling electrons. The plateau width of the current steps is related to the energies of the e lectron states in the quantum well that are affected by the lateral qu antum confinement, and by Coulomb charging effects. Diameter dependent studies of the tunneling current suggest that the lateral quantum con finement can result from the surface depletion potential, potential fl uctuations, or single impurities. High magnetic field studies confirm this conclusion. The contribution of the Coulomb charging energy is in vestigated by using an asymmetric double barrier profile. It is shown that tunneling through submicron-diameter double barrier heterostructu res provides valuable insight into the electronic properties of quantu m boxes containing a few electrons.