Epitaxial lateral overgrowth of <i>m</i> -plane α-Ga ₂ O ₃ by halide vapor phase epitaxy

We demonstrated the epitaxial lateral overgrowth of <i>m</i>-plane α-Ga₂O₃ using halide vapor phase epitaxy. An <i>m</i>-plane α-Ga₂O₃/sapphire template with a patterned SiO₂ mask was used as the substrate. The highest lateral growth rate for a radial spoke-wheel patterned mask was obtained when the spoke was perpendicular to the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced><mml:mrow><mml:mn>11</mml:mn> <mml:mover><mml:mn>2</mml:mn> <mml:mo>-</mml:mo></mml:mover> <mml:mn>3</mml:mn></mml:mrow> </mml:mfenced> </mml:math> direction. In this case, the lateral-to-vertical growth rate ratio (<i>L</i>/<i>V</i> ratio), with <i>L</i> defined as the rate of increase in the width of an elongated α-Ga₂O₃ island, was as large as 5.8. This ratio was greater than that reported for an <i>m</i>-direction stripe mask on <i>a</i>-plane α-Ga₂O₃ by a factor of 3.3 and that for an <i>a</i>-direction stripe mask on <i>c</i>- and <i>m</i>-plane α-Ga₂O₃ by a factor of 13. The epitaxial lateral overgrowth (ELO) of α-Ga₂O₃ on a stripe mask (window/mask widths of 2.5 μm/7.5 μm) perpendicular to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced><mml:mrow><mml:mn>11</mml:mn> <mml:mover><mml:mn>2</mml:mn> <mml:mo>-</mml:mo></mml:mover> <mml:mn>3</mml:mn></mml:mrow> </mml:mfenced> </mml:math> resulted in the selective nucleation of elongated α-Ga₂O₃ islands with a flat triangular cross-section on the window areas and their coalescence into a compact film. Transmission electron microscopy revealed that the dislocation density in the laterally grown area decreased drastically because the propagation of dislocations in the seed layer was effectively blocked by the mask. We believe these results greatly contribute to the realization of <i>m</i>-plane α-Ga₂O₃-based future power devices.