Lecture
Van Marum Colloquium: Epitaxial growth of Germanium Quantum wells for Spin Qubit applications
- Dr. Vladimir Calvi (QuTech)
- Date
- Wednesday 11 November 2026
- Time
- Location
-
Gorlaeus Building
Einsteinweg 55
2333 CC Leiden - Room
- BM.1.23
Abstract
Holes confined in germanium quantum wells have emerged as a leading platform for semiconductor spin qubits. They combine a light effective mass, strong spin-orbit interaction enabling all-electrical control, and compatibility with silicon foundry processes. At QuTech we grow Ge/SiGe heterostructures by reduced-pressure chemical vapour deposition, fabricate them into gated devices, and benchmark them through cryogenic magnetotransport and qubit measurements. The goal is to build a direct feedback loop between material growth and quantum device performance.
In this talk I will give an overview of how strain is used as a design parameter. Compressively strained Ge quantum wells grown on Ge wafers rather than Si wafers show reduced disorder: two-dimensional hole gases reach mobilities of several million cm2/Vs and percolation densities near 101⁰ cm⁻2. These are the conditions needed for low charge noise in multi-dot qubit arrays. Spin-qubit measurements in these wafers also identify hyperfine coupling to ⁷3Ge and 2⁹Si nuclear spins as a key coherence limit, which motivates isotopic purification. Lowering the strain changes the hole effective mass and how strongly heavy and light holes mix. At the other end of the range, a new lattice-matched platform uses unstrained Ge buried beneath a strained SiGe barrier. It avoids the defective relaxed SiGe buffer entirely and shows strong, density-tunable heavy-hole/light-hole mixing. I will discuss what each regime offers for fast, coherent spin qubits, also will show some glimps of how we operate bottom-to-top starting from growing heterostructure, fabbrication and consequent magnetotransport and qubit measurements.