Faceted inversion domain boundary in GaN films doped with Mg

Homoepitaxial GaN films, doped with Mg, were grown by rf-plasma molecular-beam epitaxy on Ga-polarity (0001) templates. Convergent-beam electron diffraction analysis establishes that the film polarity changes from [0001] to $\text{[0001\_]}$ when the Mg flux during growth is approximately 1 ML/s. Secondary ion mass spectrometry indicates a doping concentration of ${\text{∼10}}^{20} {\mathrm{cm}}^{\mathrm{-3}}$ in the film where the inversion occurs, and a reduced Mg incorporation in the $\text{[0001\_]}$ material. Transmission electron microscopy shows that the inversion domain boundary is faceted predominantly along the {0001} and $\text{{h,h,−2h,l}}$ planes, with $\mathrm{l/h}$ approximately equal to 3. Using first-principles total energy calculations, we show that the $\text{{h,h,−2h,l}}$ segments of the boundary are stabilized by the incorporation of Mg in threefold coordinated lattice sites.