Reduction of dislocations in α-Ga₂O₃ epilayers grown by halide vapor-phase epitaxy on a conical frustum-patterned...

The compound α-Ga₂O₃ is an ultra-wide-bandgap semiconductor and possesses outstanding properties such as a high breakdown voltage and symmetry compared with other phases. It has been studied for applications in high-performance power devices. However, it is difficult to obtain a high-quality thin films because α-Ga₂O₃ can only grow heteroepitaxially, which results in residual stress generation owing to lattice mismatch and thermal expansion between the substrate and α-Ga₂O₃. To overcome this, α-Ga₂O₃ was grown on a conical frustum-patterned sapphire substrate by halide vapor-phase epitaxy. The surface morphology was crack-free and flat. The α-Ga₂O₃ grown on a frustum-patterned substrate and a conventional sapphire substrate at 500°C exhibited full-width at half-maxima of 961 and 1539 arcsec, respectively, for 10-12 diffraction. For the former substrate, lateral growth on the pattern and threading dislocation bending towards the pattern suppressed the propagation of threading dislocations generated at the interface, which reduced the threading dislocation propagation to the surface by half compared with that on the latter conventional substrate. The results suggest that conical frustum-patterned sapphire substrates have the potential to produce high-quality α-Ga₂O₃ epilayers.