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Gonzalo Troncoso Fernandez Badab

Hole quantum dots in strained Ge/SiGe quantum-well heterostructures

Published on 20 March 2023
Thesis presented March 20, 2023

Semiconductor's quantum dots has been a fruitful research field for the last 40 years. Artificial-made atoms open a large amount of possibilities. From orbital quantum effect down to spin-polarization studies have been carried on from groups all around the world. Di Vicenzo's publication in 1998 pointed out the possibility of encoding quantum computing information in the spin states of charges inside quantum dots. Since then, several demonstrations have shown that this possibility is a reality, even though there are still quite a few stones in the path. Out of the semiconductors used to fabricate quantum dots, Ge is a new candidate that shows strong potential. Among its intrinsic proprieties, we find low hyperfine interaction due to its p-type character of the valence band, strong spin-orbit coupling, which allows a full electrical driving of the spin states, enhanced g-factor and low effective masses. The purpose of this thesis is developing a resilient fabrication recipe to form quantum dots in Ge heterostructures. Several steps of plasma etching, dielectric deposition, gate lithographies and metal evaporation have been probed and optimized. After the recipe was obtained, we proceeded to a mesoscopic characterization of the heterostructure and the quantum devices. Hole-Field Effect Transistors (H-FET), Quantum Point Contacts (QPC), Single Quantum Dots (SQD) and Double Quantum Dots (DQD) are fabricated and tested in this thesis. We probed the viability of the recipe to hots SQD and DQD, and reached the state-of-the-art for the Ge heterostructures quantum device fabrication. This thesis is the foundation for the future research in spin-based devices in Ge heterostructures.

Silicon, germanium, quantum, holes, heterostructures