Low-temperature high-quality epitaxial AlN films deposited by plasma-enhanced atomic layer deposition

This work demonstrates low-temperature epitaxial growth of aluminum nitride (AlN) films by plasma-enhanced atomic layer deposition (PEALD). AlN, an ultra-wide bandgap semiconductor with broad applications in optoelectronics and high-power electronics, was deposited on gallium nitride (GaN) templates (GaN-on-sapphire). Single-crystal quality films were obtained at a remarkably low temperature of 300 °C while avoiding additional in situ energetic plasma exposures or ex situ annealing steps, which can damage the film. High crystalline quality is indicated by narrow x-ray diffraction rocking curves of 288 arc sec (0.08°) and 497 arc sec (0.138°) for 10 and 70 nm films, respectively. Continuous high-quality epitaxial growth was maintained across the full film thickness, even at 70 nm, as confirmed by high-resolution transmission electron microscopy and selected area electron diffraction. Atomic force microscopy revealed smooth surface morphologies with an average roughness below 1 nm. The demonstrated epitaxial quality over the 10–70 nm thickness range, achieved at only 300 °C by a PEALD process, enables opportunities for III-nitride integration into thermally sensitive processes (e.g., silicon technology) and into GaN-based devices.