Direct growth and interface reactions of ferroelectric Hf0.5Zr0.5O2 films on MoS2

Abstract

The integration of ferroelectric HfO2 films into two-dimensional layered-material-based devices is expected to provide significant functionality for future electronics. In this study, Hf0.5Zr0.5O2 (HZO) films are directly grown on single-crystalline MoS2 flakes by atomic layer deposition (ALD) with varying deposition temperatures using H2O or O3 oxidants. According to density functional theory calculations and Raman measurements, O3-based ALD oxidizes the MoS2 surface at the atomic layer level, in contrast to the H2O-based ALD process, thus facilitating the conformal deposition of an HZO film (10 nm) without any surface treatment of MoS2 at an elevated ALD temperature of 260 °C. Annealing the O3-based HZO film with a Mo capping layer at 600 °C significantly improves the ferroelectric properties with a symmetrical hysteresis loop on MoS2. However, distinct S out-diffusion accompanied by Hf, Zr, and O diffusion toward the Mo capping layer occurs because of the thermal dissociation of MoS2 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.