Self-organized Pairs of Ge Double Quantum Dots with Tunable Sizes and Spacings Enable Room-Temperature Operation of Qubit and Single-Electron Devices

We report the first-of-its-kind, paired Ge double quantum dots (DQDs) using spacer technology in combination with selective oxidation of Si_{0 85}Ge_{0 15} in a self-organization approach. Process-controlled tunability of the spherical Ge QD diameters (5-20nm) and inter-QD spacings as close as 12nm were achieved by thermal oxidation of poly-SiGe spacer islands at each sidewall corner of Si₃N₄/poly-Si ridges. Based on the capability of producing highly-symmetrical Ge DQDs in terms of QD sizes and the coupling barriers of thermal SiO₂/densified Si₃N₄ between the QDs and proximal electrodes, we demonstrated room-temperature operation of Ge qubit devices, within which one QD encodes charges and the other QD-single-electron transistor (SET) senses and read-out the qubit. Theoretical analysis on the size-tunable density of states for Ge QDs and the tunneling paths in DQDs were conducted. Our Ge DQD system enables a practically achievable building block for QD qubit devices on Si platform.