Molecular beam epitaxy of germanium quantum wells with low surface roughness

Silicon and germanium are promising material platforms to host quantum processors based on spin qubits. While chemical vapor deposition methods have dominated the past two decades, producing state-of-the-art heterostructures [1,2], this work marks a diversion from the norm. We present the crystal growth and characterization of germanium quantum wells on virtual substrates using solid-source molecular beam epitaxy. We pay additional attention to the wafer preparation by employing in-situ atomic hydrogen surface treatment to remove the native wafer oxide at significantly reduced temperatures. We achieve heterostructures free from crosshatch dislocations and low root-mean-square surface roughness below 1 nm. Comprehensive structural characterization by atomic force microscopy, X-ray diffraction, and transmission electron microscopy delve into the composition strain and interface roughness. Finally, we employ a high-throughput screening cryostat with a base temperature of 100 mK to explore the quality of the quantum wells.

[1] Appl. Phys. Lett. 123, 092101 (2023)

[2] Small Sci., 3: 2200094