The origin of twins in the growth of the (100) plane of a beta-Ga2O3 crystal using EFG

Twins are common defects in beta-Ga2O3 crystals that affect the development of large single crystal substrates. To investigate the generation and development of twins, we grew a (100) oriented beta-Ga2O3 crystal using edge-defined film-fed growth (EFG). We characterized the (010) sample containing twins by polarized light stress meter, chemical etching, laser scanning confocal microscopy (LSCM) and transmission electron microscopy (TEM). The polarized light stress meter clearly distinguishes areas containing twins from those without. After H3PO4 etching at 150 degrees C for 1 h, LSCM observations revealed etch pits with mirror symmetry across the (100) twin boundary, with an angle of approximately 77 degrees between the array of etch pits and the boundary. The twins originate at the boundary (102) along the [201] direction, which is nearly perpendicular to the (100) plane, and then grow in steps on the side near the interior of the crystal. The twin boundary on the side near the edge of the crystal first undergoes stepwise extension and then gradually bends and grows, eventually forming a (100) twin boundary on both sides. TEM observations reveal a different arrangement of atomic density on either side of the twin boundary possessing the [201] orientation component. Furthermore, both (102) and (100) are slip planes for the beta-Ga2O3 crystal, indicating that the generation of twins is closely related to the slip plane.