Bias spectroscopy and simultaneous single-electron transistor charge state detection of Si:P double dots

We report a detailed study of low-temperature (mK) transport properties of a silicon double-dot system fabricated by phosphorous ion implantation. The device under study consists of two phosphorous nanoscale islands doped to above the metal–insulator transition, separated from each other and the source and drain reservoirs by nominally undoped (intrinsic) silicon tunnel barriers. Metallic control gates, together with an Al–AlO_x single-electron transistor (SET), were positioned on the substrate surface, capacitively coupled to the buried dots. The individual double-dot charge states were probed using source–drain bias spectroscopy combined with non-invasive SET charge sensing. The system was measured in linear (source–drain DC bias V_SD = 0) and non-linear (V_SD ≠ 0) regimes, allowing calculations of the relevant capacitances. Simultaneous detection using both SET sensing and source–drain current measurements was demonstrated, providing a valuable combination for the analysis of the system. Evolution of the triple points with applied bias was observed using both charge and current sensing. Coulomb diamonds, showing the interplay between the Coulomb charging effects of the two dots, were measured using simultaneous detection and compared with numerical simulations.