Suppression of charges within Al₂O₃ high-κ dielectric and reduction of interface traps at cryogenic temperature of Ge n-MOS capacitor fabricated by plasma postoxidation and forming gas annealing

Germanium-based quantum devices are considered as promising candidates for scalable quantum information processing due to strong intrinsic spin-orbit coupling and the capability for ultrafast all-electrical spin manipulation. In order to fabricate fault-tolerant quantum encoding devices, it is important to improve the cryogenic properties of germanium-based metal oxide semiconductor (Ge MOS) structure with thin gate dielectric layers as much as possible. Based on a thin Al 2 O 3 /GeO x dielectric stack, we investigate the effect of oxygen plasma postoxidation (PPO) power and hydrogen forming gas annealing (H 2 FGA) temperature on cryogenic properties of Ge MOS capacitors in depth. By systematically depicting the distribution of interface traps density (D it ) within the Ge bandgap, we found that the formation of GeO x reduces the energy state density of characteristic defects across the Ge bandgap, thereby leading to the reduction of D it . The contribution of FGA to the reduction of fixed charge within Al 2 O 3 dielectric is clarified, and the C-V hysteresis effect improvement is revealed from the perspective of suppressing the trap charge area density within Al 2 O 3 dielectric by integrating PPO and FGA process. Finally, the D it of the Ge n-MOS capacitor with Al 2 O 3 /GeO x dielectric stack is reduced to 5 × 10 11 cm -2 ·eV -1 (@Ei-0.2eV) at 15K. The area density of fixed charge and trap charge within Al 2 O 3 are reduced from 1.4 × 10 12 cm -2 to 7.2 × 10 11 cm -2 and from 1.28 × 10 12 cm -2 to 5.13 × 10 10 cm -2 , respectively. This provides a technical pathway for the development of germanium-based devices for quantum computation.