Influencing the morphological stability of MOVPE-grown β-Ga 2 O 3 films by O 2 /Ga ratio

The morphology evolution of (100) beta- Ga 2 O 3 films grown by metalorganic vapor phase epitaxy (MOVPE) is studied by atomic force microscopy (AFM). In particular, when grown under a high O 2 /Ga ratio (O 2 /Ga = 1250) and above a thickness of 350 nm, these films exhibit striking morphological instabilities, including step meandering and bunching, which contribute significantly to surface roughening. Transmission electronic microscopy (TEM) measurements reveal a morphological transition on the growing surface with a coexistence of step-flow and step-bunching growth modes resulting from these instabilities. In contrast, growth conditions with low O 2 /Ga ratios (O 2 /Ga = 350) effectively suppress meandering and bunching instabilities, resulting in films with excellent electrical properties. These observations are rationalized through the Burton -Cabrera -Frank (BCF) theory and Bales-Zangwill (BZ) instability (Gibbs-Thompson effect and Mullins-Sekerka instability) , thus bridging theoretical models and the experimental results.