MBE-grown gate-controlled quantum-dot nanostructure and its current–voltage characteristics

Abstract

Single-electron transport properties, recently observed in MBE-grown gate-controlled quantum dots, are studied by a self-consistent approach to the Poisson–Schrödinger problem. The potential profile in the cylindrical device is found from the solution of the Poisson equation as a superposition of external voltages, Schottky barrier potential, double-barrier potential of AlGaAs/InGaAs layers, and potential of ionized donors in n-GaAs layers. A small perturbation of the cylindrical symmetry has been taken into account. It is shown that the distribution of the ionized donors is of crucial importance in determining the current–voltage characteristics of the device. For the few-electron quantum dots, we have calculated the positions of peaks of source-drain current I as functions of gate voltage Vg and source-drain voltage Vsd. We have quantitatively described the shell-filling effects and reproduced the characteristic structure of Coulomb diamonds, i.e. the diamond-shaped regions in Vg–Vsd plane corresponding to the Coulomb blockade (I=0). We have also performed calculations with an external magnetic field taken into account and obtained a very good quantitative agreement between the calculated and measured magnetic-field behavior of the source-drain current at fixed Vsd≈0 and varying Vg.