Simulation and optimization of spin-orbit quantum dot circuit with integrated quantum point contact read-out

We use computer simulation to study a novel laterally coupled quantum dot (LCQD) circuit with integrated quantum point contact (QPC) for charge read-out. The prototype of the device is shown (Elzerman at al., 2003) with the SEM view of the top gate patterns in the xy direction. The two circles indicate the location of the two dots. The simulated layer structure in the z direction is shown. In order to obtain the electron density inside the LCQD, we solve self-consistently 3D Poisson and Kohn-Sham equations within the local spin density approximation (LSDA), while outside the LCQD, we use the Thomas-Fermi approximation to compute the charge densities. The above differential equations are discretized on a nonuniform 3D mesh using realistic doping profiles and boundary conditions (Matagne and Leburton, 2002). Electronic states and eigenenergy spectra reflecting the particular LCQD confinement are obtained as a function of the external gate biases. The conditions for charging the dots with successive electrons, as a function of the applied gate biases, are determined by the Slater´s rule, by which we derive the stability diagram for the system in the few-electron regime (Zhang et al., 2004). We investigate the detector sensitivity of different QPC gate geometries to the first electron charging in the quantum dot. For this purpose, we obtain the variation of the potential energy saddle point in the constriction at the first electron charging as a function of different QPC gate biases. We then use the Buttiker formula (Buttiker, 1990) to compute the relative change of the conductance (/spl Delta/G/G) over the specified QPC gate bias range. Our results indicate that constrictions with dented designs give more sensitive detectors than conventional QPC geometries.