Germanium electrostatic quantum dot with integrated charge detector in an MOS structure

We report the fabrication and characterization of an electrostatic quantum dot in pure Germanium with an integrated charge measurement transistor. The device uses the Al2O3/Germanium interface for the confinement of carriers in the Germanium and an hybrid design with an electron quantum dot and hole transistor for the charge detection. The hole transistor, using with NiGe source and drain contacts, despite the modest low temperature carrier mobility of 450 cm2/Vs, has shown a sensitivity to the dot electric potential sufficient to detect single charges tunneling in and out of the quantum dot. The device is realized with a two level gate stack, with the top level used to attract electrons and the lower one to define the electron confinement potential and accumulate the hole transistor. The possibility to improve the device operation using a Al2O3/SiGe/Ge multilayer for the confinement of electrons at a smoother interface is discussed.