Browsing by Author "Chen, Ching-Lun"

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Self-organized Pairs of Ge Double Quantum Dots with Tunable Sizes and Spacings Enable Room-Temperature Operation of Qubit and Single-Electron Devices
(2019-01-01)
Peng, Kang-Ping
;
Chen, Ching-Lun
;
Tang, Ying-Tsan
;
Kuo, David
;
George, Thomas
We report the first-of-its-kind, paired Ge double quantum dots (DQDs) using spacer technology in combination with selective oxidation of Si0 85Ge0 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.
Tunable diameter and spacing of double Ge quantum dots using highly-controllable spacers and selective oxidation of SiGe
(2019-08-05)
Huang, Tsung-Lin
;
Peng, Kang-Ping
;
Chen, Ching-Lun
;
Lin, Horng-Chih
;
George, Tom
We report the novel tunability of the diameters and spacings of paired Ge double quantum dots (DQDs) using nano-spacer technology in combination with selective oxidation of Si0.85Ge0.15 at high temperature. Pairs of spherical-shaped Ge QDs were formed by the selective oxidation of poly-SiGe spacer islands at each sidewall corner of the nano-patterned Si3N4/poly-Si ridges. The diameters of the Ge spherical QDs are essentially determined by geometrical conditions (height, width, and length) of the nano-patterned spacer islands of poly-SiGe, which are tunable by adjusting the process times of deposition and etch back for poly-SiGe spacer layers in combination with the exposure dose of electron-beam lithography. Most importantly, the separations between the Ge DQDs are controllable by adjusting the widths of the poly-Si/Si3N4 ridges and the thermal oxidation times. Our self-organization and self-alignment approach achieved high symmetry within the Ge DQDs in terms of the individual QD diameters as well as the coupling barriers between the QDs and external electrodes in close proximity.