Atomic Layer Deposition Integration of Amorphous Boron Nitride with 2D Semiconductors

2D transition metal dichalcogenides (TMDs) exhibit unique electronic and optical properties and are actively under investigation as transistor channel materials to combat the critical limit in continued transistor scaling. While 2D TMDs are hailed as having no out-of-plane bonding, these systems are rarely defect-free, and the atomic thickness leads to a high susceptibility to environmental factors that reduce layer stability and electronic performance. Encapsulation with insulators is an effective method to not only prevent 2D TMD oxidation and degradation in ambient environment, but also provide a suitable dielectric environment for enhancing 2D device performance. For instance, hexagonal boron nitride (hBN) at the interface between 2D TMD and the oxide substrate can improve the carrier mobility up to an order of magnitude due to dielectric screening from charged impurities and the suppression of surface optical phonon scattering, both of which are commonly present in conventional 3D oxide substrates. Motivated by the robust dielectric properties of BN, we explore atomic layer deposition (ALD) of ultrathin (2-10 nm) BN as a wafer-scale, non-water-based, low-temperature process for 2D TMD encapsulation. Two routes of ALD, plasma-enhanced (PE) and thermal (Th), are explored to understand the impact of ALD precursor and processing parameters on the resulting chemical, structural, and dielectric properties of BN. ThALD, utilizing sequential injections of NH₃ and BCl₃, results in fully amorphous BN (aBN), whereas the increased energy from N₂ plasma generation in PEALD yields nanocrystalline BN with higher surface roughness. Furthermore, using Mo-based TMDs as a test 2D TMD system, we find significant improvement in the thermal and chemical stability of aBN-capped 2D TMD after prolonged periods (> 1 month) of time in ambient air. Finally, we will discuss the impact of aBN encapsulation on the electronic and optical properties of a range of TMDs, with discussion of implications on using aBN as a robust dielectric for 2D-based electronics.