  Molecular beam epitaxy is one of the highest quality growth methods, capable
of achieving theoretical material property limits and unprecedented device
performance. However, such ultimate quality usually comes at the cost of
painstaking optimization of synthesis conditions and slow experimental
iteration rates. Here we report on high-throughput molecular beam epitaxy with
rapid screening of synthesis conditions using a novel cyclical growth and
in-situ etch method. This novel approach leverages sub-oxide desorption present
during molecular beam epitaxy and as such should be broadly applicable to other
material systems. As a proof of concept, this method is applied to rapidly
investigate the growth space for the ternary alloy (InxGa1-x)2O3 on (010)
oriented beta-Ga2O3 substrates using in-situ reflection high energy electron
diffraction measurements. Two distinct growth regimes are identified and
analyzed using machine learning image recognition algorithms, the first
stabilizing a streaky 2x surface reconstruction typical of In-catalyzed
beta-Ga2O3 growth, and the second exhibiting a spotty/faceted pattern typical
of phase separation. Targeted growth of (InxGa1-x)2O3 is performed under
conditions near the boundary of the two regimes resulting in a 980 nm thick
epitaxial layer with In mole fraction up to 5.6%. The cyclical growth/etch
method retains the ~1 nm surface roughness of the single crystal substrate,
increases experimental throughput approximately 6x, and improves single crystal
substrate utilization by >40x. The high-throughput MBE method enables rapid
discovery of growth regimes for ultra-wide bandgap oxide alloys for power
conversion devices operating with high efficiency at high voltages and
temperatures, as well as optical devices such as ultraviolet photodetectors.
