Impact of surface treatments on the transport properties of germanium 2DHGs

Abstract

Holes in planar germanium (Ge) heterostructures show promise for quantum applications, particularly in superconducting and spin qubits, due to strong spin-orbit interaction, low effective mass, and absence of valley degeneracies. However, charge traps cause issues such as gate hysteresis and charge noise. This study examines the effect of surface treatments on the accumulation behaviour and transport properties of Ge-based two dimensional hole gases (2DHGs). Oxygen plasma treatment reduces conduction in a setting without applied top-gate voltage and improves the mobility and lowers the percolation density, while hydrofluoric acid (HF) etching provides no benefit. The results suggest that interface traps from the partially oxidised silicon (Si) cap pin the Fermi level, and that oxygen plasma reduces the trap density by fully oxidising the Si cap. Therefore, optimising surface treatments is crucial for minimising the charge traps and thereby enhancing the device performance.

4 pages, 3 figures, additional supplementary information

References in corpus (9)

• The Observation of Percolation-Induced 2D Metal-Insulator Transition in a Si MOSFET
• Hard superconducting gap in germanium
• Annealing shallow Si/SiO${}_2$ interface traps in electron-beam irradiated high-mobility metal-oxide-silicon transistors
• Lightly-strained germanium quantum wells with hole mobility exceeding one million
• A gate tunable transmon qubit in planar Ge
• Impact of interface traps on charge noise, mobility and percolation density in Ge/SiGe heterostructures
• Wafer-scale low-disorder 2DEG in ${}^{28}$Si/SiGe without an epitaxial Si cap
• A backgate for enhanced tunability of holes in planar germanium
• Mitigating variability in epitaxial-heterostructure-based spin-qubit devices by optimizing gate layout