Direct growth and interface reactions of ferroelectric Hf 0.5 Zr 0.5 O 2 films on MoS 2

The integration of ferroelectric HfO 2 films into two-dimensional layered-material-based devices is expected to provide significant functionality for future electronics. In this study, Hf 0.5 Zr 0.5 O 2 (HZO) films are directly grown on single-crystalline MoS 2 flakes by atomic layer deposition (ALD) with varying deposition temperatures using H 2 O or O 3 oxidants. According to density functional theory calculations and Raman measurements, O 3 -based ALD oxidizes the MoS 2 surface at the atomic layer level, in contrast to the H 2 O-based ALD process, thus facilitating the conformal deposition of an HZO film (10 nm) without any surface treatment of MoS 2 at an elevated ALD temperature of 260 °C. Annealing the O 3 -based HZO film with a Mo capping layer at 600 °C significantly improves the ferroelectric properties with a symmetrical hysteresis loop on MoS 2. However, distinct S out-diffusion accompanied by Hf, Zr, and O diffusion toward the Mo capping layer occurs because of the thermal dissociation of MoS 2 at an additional atomic layer level, thereby leading to the subsequent reduction of weak HZO bonds by the released S atoms along the grain boundaries.