Atomic layer deposition of Al₂O₃ on MoS₂, WS₂, WSe₂, and h-BN: surface coverage and adsorption energy

Uniform deposition of high-k dielectrics on two-dimensional (2D) crystals is highly desirable for their use in future nano-electronic devices. Here, the surface coverage of the Al₂O₃ films grown by atomic layer deposition (ALD) was investigated on mechanically-exfoliated MoS₂, WS₂, WSe₂, and h-BN flakes for exploring the deposition kinetics of the Al₂O₃ films on the 2D crystals. The film coverage followed a decreasing order of WSe₂ > WS₂ > MoS₂ > h-BN, which was mainly determined by the ALD temperature and adsorption energy (E_ads) of the ALD precursor (trimethyl-aluminum) during the initial ALD cycles. The obtained |E_ads| values of the precursor on the 2D crystals corresponded well to a van der Waals physisorption energy of 0.05-0.26 eV. Furthermore, the magnitude of the extracted E_ads values showed a strong dependence on the induced dipole polarizability of the 2D crystals. The obtained results demonstrate that the surface coverage of the ALD high-k dielectrics can be modulated by choosing the types of the 2D substrates, and could provide a pathway for the integration of high-k dielectrics in 2D crystal-based nano-electronic devices.