Coulomb Blockade Spectroscopy of Holes in Ge/SiGe with a Charge Sensor

Hole spins in Ge are currently being broadly investigated for spin qubit applications. We investigate the low-energy states of the first few holes confined in a quantum dot (QD) within a strained Ge/SiGe quantum well using Coulomb blockade spectroscopy. Here, the shape of the confinement potential is expected to significantly influence the shell filling and related quantum properties of the hole spins. Therefore, we use surrounding gate electrodes to electrostatically shape the QD's lateral confinement potential. We analyze the addition energy spectrum as a function of magnetic field and hole number using a charge sensor. Comparison with a Fock-Darwin model reveals the shell filling that is tuned by confinement asymmetry. Furthermore, sweeping the magnetic field orientation both in- and out-of-plane allows us to map the g-tensor anisotropy (at B ≈ 1 T). We discuss these results in the context of multi-hole interactions and variations in confinement shape. Finally, we also present recent results on the impact of optical illumination on threshold voltages and quantum confinement shape due to the screening effects of interface traps.