Cryogenic interface-state filling and tunneling mechanisms in strained Ge/SiGe heterostructures

TL;DR

This study investigates cryogenic interface-state trapping and tunneling mechanisms in strained Ge/SiGe heterostructures, combining experimental measurements with modeling to understand transport processes and improve quantum device stability.

Contribution

It provides a detailed analysis of interface-state filling and tunneling mechanisms at cryogenic temperatures in strained Ge/SiGe heterostructures, refining existing models and offering device improvement guidelines.

Findings

Crossover from trap-assisted to Fowler-Nordheim tunneling under different biases

Quantified the gradual filling process of interface states at cryogenic temperatures

Provided guidelines for reducing trap densities to enhance device performance

Abstract

Traps at the semiconductor-oxide interface are considered as a major source of instability in strained Ge/SiGe quantum devices, yet the quantified study of their cryogenic behavior remains limited. In this work, we investigate interface-state trapping using Hall-bar field-effect transistors fabricated on strained Ge/SiGe heterostructures. Combining transport measurements with long-term stabilization and Schr\"odinger-Poisson modelling, we reconstruct the gradual filling process of interface states at cryogenic condition. Using the calculated valence band profiles, we further evaluate the tunneling current density between the quantum well and the semiconductor-oxide interface. Our calculation demonstrates that the total tunneling current is consistent with a crossover from trap-assisted-tunneling-dominated transport to Fowler-Nordheim-tunneling-dominated transport under different gate bias regimes. These results refine the conventional Fowler-Nordheim-based picture of interface trapping in strained Ge/SiGe heterostructures and provide guidelines for improving Ge-based quantum device performance by improving barrier crystalline qualities and reducing dislocation-related trap densities.