Superconducting proximity effect in ultra-scaled pure Ge quantum dots.*

The diverse applications and rich physics of hybrid superconducting-semiconducting systems has attracted significant research interest in improving the quality of these devices. Significant focus has been made on hybrid systems using a combination of Ge and Si to form a high mobility hole gas. However, there has been little research on pure Ge systems.
Using a thermally induced exchange reaction between single-crystalline Ge nanowires and Al pads, we fabricate monolithic Al-Ge-Al nanowire heterostructures with ultra-scale Ge segments contacted by crystalline Al leads. This fabrication technique allows full electrostatic control of the Ge segment and thus the ability to overcome the Schottky barrier.
We will present the low temperature transport properties of Al-Ge-Al nanowire heterostructures with ultra-scaled Ge segments of 40 nm in length and 25 nm in dimater. Exploiting the large tunability and high quality Al contacts we will show that we can access a variety of quantum transport regimes in a single device: from a quantum dot with single hole filling up to proximity induced supercurrent inside the pure Ge segment.