Structure and Thermal Stability of ε/κ-Ga₂O₃ Films Deposited by Liquid-Injection MOCVD

Area of Science:

• Materials Science
• Crystal Growth
• Thin Film Deposition

Background:

• Gallium oxide (Ga2O3) is a promising ultrawide bandgap semiconductor.
• Controlling the crystal phase (e.g., ε, κ, β) is crucial for device performance.
• Epitaxial growth of metastable Ga2O3 phases presents challenges.

Purpose of the Study:

• To investigate the crystal structure and thermal stability of epitaxial ε/κ-Ga2O3 thin films.
• To develop methods for distinguishing between ε and κ-phases of Ga2O3.
• To assess the phase transformation behavior of Ga2O3 films under thermal stress.

Main Methods:

• Liquid-injection metal-organic chemical vapor deposition (LI-MOCVD) for film growth.
• X-ray diffraction (XRD) φ-scan and conventional transmission electron microscopy (TEM) for phase identification.
• In situ and ex situ XRD, and atomic force microscopy (AFM) for thermal stability analysis.

Main Results:

• Epitaxial Si-doped Ga2O3 films (~1 nm roughness) were grown on sapphire substrates at 600°C.
• XRD and TEM can distinguish ε and κ-phases, but only if the κ-phase is suppressed for unambiguous ε-phase identification.
• Films maintained crystal structure up to 1100°C (5 min) or 900°C (10 min) in vacuum.
• Prolonged annealing induced partial transformation to β-phase Ga2O3 and potential amorphization.

Conclusions:

• LI-MOCVD enables the growth of epitaxial ε/κ-Ga2O3 thin films with controlled phase.
• Reliable methods for phase discrimination using XRD and TEM were established.
• The studied Ga2O3 phases demonstrate significant thermal stability, but phase transformation occurs at elevated temperatures and prolonged durations.