Voltage-Tunable Quantum-Dot Array by Patterned Ge-Nanowire-Based Metal-Oxide-Semiconductor Devices

We report the fabrication of an array of highly scaled Ge-nanowire-based (radius similar to 25 nm) vertical metal-oxide-semiconductor devices that can operate as voltage-tunable quantum dots (VTQDs) at room temperature. The electrons in such nanowires experience geometrical confinement in the radial direction, whereas they can be confined axially by tuning the applied bias to manipulate the quantum states. Such three-dimensional confinement of electrons is confirmed from the steplike responses in the roomtemperature capacitance-voltage (C-V) characteristics at relatively low frequency (200 kHz). Each step is observed to encompass convolution of the quantized states occupying about six electronic charges. Such ultrasmall capacitance (similar to aF) is measured by exploring a technique that utilizes the method of removing frequency dispersion. Details of such carrier confinement are analyzed in the current work by theoretically modeling the device's transport properties based on the nonequilibrium Green function formalism.