Electrically isolated SiGe quantum dots

A variation of electric force microscopy (EFM) is used to measure the electrical isolation of SiGe quantum dots (QDs). The SiGe QDs are grown on mesas of ultrathin silicon on insulator. Near the mesa edges, the thin silicon layer has been incorporated into the QDs, resulting in electrically isolated QDs. Away from the edges, the silicon layer is not incorporated and has a two-dimensional resistivity of less than 800 TΩ per sq, resulting in relatively short RC times for charge flow on the mesa. The EFM technique we use here is a powerful probe of samples and devices with floating-gate geometries.