Morphological Evolution of Atomic Layer Deposited Hafnium Oxide on Aligned Carbon Nanotube Arrays

Microscopic study of the nucleation and growth of atomic layer deposition (ALD) dielectrics onto carbon nanotubes (CNTs) is an essential while challenging task toward high-performance devices. Here, we capture the morphological evolution and growth behaviors of ALD-HfO₂ onto SiO₂/Si-supported aligned CNT arrays (A-CNTs) under three ALD recipes via cross-sectional high-resolution scanning transmission electron microscopy. The HfO₂ in ALD I (200 °C) preferentially nucleates on the SiO₂ substrate in heterogeneous growth mode, resulting in films with considerable pinholes, while ALD II (90 °C) and III (90 °C and extra H₂O presoak) exhibit homogeneous growth with nucleation on both SiO₂ and CNTs, yielding uniform films. Arrangement defects in A-CNTs exacerbate nonuniformity of HfO₂ and tube-tube separation plays deterministic roles affecting the HfO₂-CNT interfacial morphology. Electrical measurements from A-CNTs metaloxide-semiconductor devices validate these findings. Our investigation contributes valuable insights for optimizing ALD processes for enhanced dielectric integration on A-CNTs in next-generation electronics.