Reducing the β-Ga₂O₃ Epitaxy Temperature to 240 °C via Atomic Layer Plasma Processing

In this work, we report on low-temperature as-grown single-phase epitaxial beta-gallium oxide (β-Ga2O3) films on c-plane sapphire at the substrate temperature of 240 °C using plasma-enhanced atomic layer deposition (PEALD). The films were deposited using triethylgallium (TEG) and Ar/O2 plasma as the metal precursor and oxygen co-reactant, respectively. Growth experiments were performed with an rf-power level of 50 W. Additionally, each unit ALD cycle was followed by in situ Ar-plasma annealing treatment, which consisted of Ar-plasma exposure for 20 s at 250 W rf power. X-ray diffraction (XRD) of the sample on sapphire revealed epitaxial Ga2O3 film signature with the monoclinic β-phase. On the other hand, GIXRD of the samples grown on Si and glass displayed polycrystalline β-Ga2O3 films. High-resolution transmission electron microscopy (HR-TEM) confirmed the epitaxial relationship of the Ga2O3 layers grown on sapphire substrates. X-ray photoelectron spectroscopy (XPS) shed light on the chemical bonding states of pure β-Ga2O3 layers outlining the Ga–O bonding states. STEM-EDX measurements confirmed the pristine nature of the β-Ga2O3 film with carbon atomic composition falling below the tool’s detection levels.