Low-Temperature Atomic Layer Deposition of Gallium Nitride Using Tris(dimethylamido)gallium with a Coherent Nucleation on GaN (0001)

The development of low-temperature, plasma-free deposition methods for producing high-quality gallium nitride (GaN) is essential for fabricating next-generation electronic and optoelectronic devices. This study presents a thermal atomic layer deposition (ALD) process using tris(dimethylamido)gallium (TDMAGa) and ammonia (NH3) to grow GaN thin films. The growth characteristics were investigated over a temperature range of 150–250 °C to establish the ALD process window, and detailed film characterization was performed within the optimized range of 175–225 °C. Density functional theory calculations confirm the viability of this low-temperature approach because the activation energy for the reaction of the TDMAGa dimer with NH3 (0.60 eV) is significantly lower than that of the conventional trimethylgallium monomer (1.37 eV). A self-limiting film growth was achieved at a process temperature of 200 °C, yielding a growth rate of approximately 1.3 Å/cycle and excellent step coverage on high-aspect-ratio structures. Transmission electron microscopy revealed the formation of an atomically coherent crystalline interface between the ALD film and the n-GaN (0001) substrate. The thickness of this coherent layer increased with deposition temperature, ranging from 1.3 nm at 175 °C to 2.1 nm at 225 °C. Although film density and crystallinity improved with temperature, the highest nitrogen incorporation within the investigated temperature range was achieved at 200 °C, yielding a nitrogen-deficient composition with a N/Ga ratio of 0.59 and minimal impurity levels. This work demonstrates viable thermal ALD chemistry for producing conformal GaN films with pristine interfacial properties, offering a promising solution for temperature-sensitive devices.