Alloying-Induced Crystal-Phase Transition in InxGaySez Alloys Grown on C-Sapphire Substrates by Molecular Beam Epitaxy: Implication for Next-Generation Optoelectronics

Going beyond graphene and transition-metal dichalcogenides, group III–VI metal chalcogenides (GIIIMCs) with diverse crystallinities appear as new rising stars and have recently attracted numerous interesting physics for prospective optoelectronics, even though they face crucial challenges in their epitaxial technology. In this work, for the first time, large-compositional range In_xGa_ySe_z ternary alloys have been deposited on c-sapphire substrates by molecular beam epitaxy (MBE). We explored that MBE of In_xGa_ySe_z on c-sapphire substrates undergoes a two-dimensional (2D)-to-three-dimensional (3D) structural phase transition, resulting in mixed-dimensional alloy heterostructures of 2D hexagonal-In_xGa_ySe_z and 3D zinc-blende/wurtzite In_xGa_ySe_z. The 2D-to-3D transition supposedly originates from the indium segregation and depends strongly on the indium composition. We also found that modulating the growth parameters such as In/Ga ratio, deposition temperature, and deposition time could be an effective way to precisely control the 2D/3D crystal phases of the alloys. Overall, the results pave the way for phase/physical engineering of GIIIMC-based alloys through MBE and realizing mixed-dimensional alloy heterostructures for multifunctional applications.

In_xGa_ySe_z alloys were epitaxially grown on c-sapphire by MBE over a wide composition range. Structure characterizations revealed indium-induced 2D-to-3D phase transitions forming mixed-dimensional heterostructures, in which the phase can be tuned via indium content and growth conditions. This work demonstrates controllable phase engineering of III−VI alloys, opening opportunities for multifunctional mixed-dimensional semiconductor applications.