Structure and recombination properties of twin boundaries in $\kappa$-phase of gallium oxide

Recent studies of the structure of the metastable hexagonal $\varepsilon$-phase of gallium oxide have established that it consists of oriented nanodomains of the orthorhombic $\kappa$-phase. In this work we demonstrate that when the $\kappa$-phase of gallium oxide is produced by epitaxial growth on gallium nitride, its hexagonal-prismatic microcrystals consist of rotary domains with built-in extended antiphase boundaries. It was found that domain and antiphase boundaries are characterized by reduced luminescence intensity.