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

Abstract

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 selfassembled 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.

Few-photon Detection of Ge Quantum-dot Single-hole Transistors in Few-hole Regime under Visible Irradiation

“…Thanks to the advancements in CMOS fabrication technology, SHTs in the few-charge regime have been experimentally demonstrated using small Si 13 or Ge QDs [14][15][16][17][18] . Ge-QD SHTs are particularly attractive for SPDs.…”

“…This is because Ge QDs are more likely to have a pseudo-direct bandgap structure for better photon-charge conversion than Si QDs, due to a larger exciton Bohr radius (α B ) of 24 nm in Ge as compared to that (α B, Si = 4.9 nm) in Si. Our previous work has already reported experimental fabrication and steady-state transfer characteristics (I D -V G ) of Ge-QD SHTs, comprising a single Ge spherical-QD (20 nm in diameter) self-aligned with source/drain reservoirs via tunneling barriers of SiO 2 /Si 3 N 4 17 .…”