  Ga2O3 is a wide-band-gap semiconductor of great interest for applications in
electronics and optoelectronics. Two-dimensional (2D) Ga2O3 synthesized from
top-down or bottom-up processes can reveal brand new heterogeneous structures
and promising applications. In this paper, we study phase transitions among
three low-energy stable Ga2O3 monolayer configurations using density functional
theory and a newly developed machine-learning Gaussian approximation potential,
together with solid-state nudged elastic band calculations. Kinetic minimum
energy paths involving direct atomic jump as well as concerted layer motion are
investigated. The low phase transition barriers indicate feasible tunability of
the phase transition and orientation via strain engineering and external
electric fields. Large-scale calculations using the newly trained
machine-learning potential on the thermally activated single-atom jumps reveal
the clear nucleation and growth processes of different domains. The results
provide useful insights to future experimental synthesis and characterization
of 2D Ga2O3 monolayers.
