Low-Temperature Thermal Atomic Layer Deposition of Aluminum Nitride Thin Films for Passivation Layers in GaN-Based Light-Emitting Diodes

Aluminum nitride is a promising passivation material for GaN-based micro-light-emitting diode (micro-LED) devices. However, depositing high-quality thin films at low temperatures without plasma remains challenging because conventional methods often compromise film quality or substrate integrity. In this study, we investigated the growth and properties of aluminum nitride films by low-temperature thermal atomic layer deposition (ALD) using tris(dimethylamino)aluminum (TDMAA) and ammonia (NH3) at 200–350 °C. Density functional theory (DFT) calculations indicate that the TDMAA dimer has a lower activation energy than the trimethylaluminum (TMA) monomer when reacting with NH3, which enables film deposition at lower temperatures. In situ quartz crystal microbalance (QCM) analysis suggests that film growth proceeds via ligand exchange reactions, with four to five dimethylamine molecules being released from the TDMAA dimer during the first half-reaction. Self-limiting conformal growth was achieved up to 300 °C, with a growth rate of 1.87 Å/cycle at this temperature. ALD-grown aluminum nitride films exhibited excellent interfacial coherence with GaN substrates even at deposition temperatures as low as 225 °C. Near the substrate, the stoichiometric composition of AlN was observed, while at the film surface, nitrogen atoms were gradually replaced by oxygen upon exposure to air. Higher deposition temperatures reduced the oxygen content due to improved film density and crystallinity. This low-temperature thermal ALD process enables the fabrication of stoichiometric AlN films with excellent conformality and interfacial coherence with the GaN substrate. These nanoscale films, specifically produced by purely thermal ALD processes at 200 to 300 °C, are promising for passivation layers in GaN-based micro-LED devices, thereby enhancing their efficiency.