Germanium Quantum-Dot Single-Hole Transistors with Self-organized Tunnel Barriers and Self-aligned Electrodes Using Ingenious Sidewall Spacer and Oxidation Techniques

We report the formation of Ge quantum dots (QDs) with self-organized tunnel barriers and self-aligned electrodes, using a coordinated combination of lithographic patterning and self-assembled growth. The core experimental design is based on the thermal oxidation of poly-SiGe spacer islands located at the included-angle location of Si3N4/Si-trenches with specially designed fanout structures. By suitably adjusting the process times for conformal deposition, direct etch back and thermal oxidation of poly-SiGe, Ge QDs and their tunnel barriers with good tunability in sizes and widths were controllably achieved. Ge QDs are electrically addressable via self-aligned Si electrodes, offering an effective building block for the implementation of single-electron devices.