Germanium Spherical Quantum-Dot Single-Hole Transistors With Self-Organized Tunnel Barriers and Self-Aligned Electrodes

We report the fabrication and electrical characterization of single-hole transistors (SHTs), in which a Ge spherical quantum dot (QD) weakly couples to self-aligned electrodes via self-organized tunnel barriers of Si3N4. A combination of lithographic patterning, sidewall spacers, and self-assembled growth was used for fabrication. The core experimental approach is based on the selective oxidation of poly-SiGe spacer islands located at the specially designed included-angle locations of Si3N4/Si-trenches. By adjusting processing times for conformal deposition, etch back and thermal oxidation, good tunability in the Ge QD size and its tunnel-barrier widths were controllably achieved. Each Ge QD is electrically addressable via self-aligned Si gate and reservoirs, thus offering an effective building block for implementing single-charge devices.

Automated summary

We present the fabrication and electrical characterization of single-hole transistors (SHTs) utilizing a Ge spherical quantum dot (QD) weakly coupled to self-aligned electrodes via self-organized tunnel barriers of Si3N4. The fabrication process involves lithographic patterning, sidewall spacers, and self-assembled growth. By selectively oxidizing poly-SiGe spacer islands located at specific included-angle locations of Si3N4/Si trenches, controllable tunability of Ge QD size and tunnel-barrier widths is achieved. Each Ge QD can be electrically accessed through self-aligned Si gate and reservoirs, making it a promising building block for single-charge devices.