Spontaneous Ordering in Bulk GaN:Mg Samples

Transmission electron microscopy evidence of spontaneous ordering in Mg-doped, bulk GaN crystals grown by a high pressure, high temperature process is reported for the first time. The ordering consists of Mg-rich planar defects formed on basal planes separated by 10 nm and occurs only for growth with $(000\overline{1})$ N polarity. The ordering leads to the formation of satellite diffraction spots dividing the (0001) reciprocal lattice distance into 20 parts. This ``microsuperlattice'' can be described as polytypoids comprised of planar defects with some characteristics of inversion domain boundaries.