Impact of surface passivation on the electrical stability of strained germanium devices

Strained germanium hole spin qubits are promising for quantum computing, but the devices hosting these qubits face challenges from high interface trap density, which originates from the naturally oxidized surface of the wafer. These traps can degrade the device stability and cause an excessively high threshold voltage. Surface passivation is regarded as an effective method to mitigate these impacts. In this study, we perform low-thermal-budget chemical passivation using the nitric acid oxidation of silicon method on the surface of strained germanium devices and investigate the impact of passivation on the device stability. The results demonstrate that surface passivation effectively reduces the interface defect density. This not only improves the stability of the device’s threshold voltage but also enhances its long-term static stability. Furthermore, we construct a band diagram of hole surface tunneling at the static operating point to gain a deeper understanding of the physical mechanism through which passivation affects the device stability. This study provides valuable insights for future optimization of strained Ge-based quantum devices and advances our understanding of how interface states affect device stability.