Two-dimensional MnGaN Layer formed by Nitridation of Mn $\surd $3 $\times $ $\surd $3-R30 structure on Wurtzite GaN (000\underline {1})*

There has been much interest in dilute Mn-doped GaN as a spintronic material. Recently, it has become of interest to consider the possible advantages of delta-doped magnetic layers, rather than a bulk alloy. Here we investigate experimentally the growth of single Mn-containing layers on top of wurtzite GaN as well as the overgrowth of GaN onto the Mn-containing layer, using a combination of N-plasma molecular beam epitaxy and reflection high energy electron diffraction. Sub-monolayer Mn deposition on GaN(000\underline {1}) results in a novel $\surd $3 $\times \quad \surd $3-R30 structure [1]. Upon nitrogen plasma exposure, this periodicity is removed; whereas, Mn is found remaining on the surface as measured by Auger electron spectroscopy. Unexpectedly, and in dramatic comparison to tiny lattice constant changes seen for bulk films, we find a huge -3.3 percent surface lattice contraction in both [10\underline {1}0] and [11\underline {2}0] azimuthal directions. This suggests the possible formation of a Mn0.25Ga0.75N 2-D alloy. Furthermore, subsequent overgrowth of GaN layers does not show significant lattice constant change compared to the nitridation process, up to a thickness of 20 ML or more.\\[4pt] [1] Chinchore et al., Applied Physics Letters \textbf{93(18)}, 181908 (2008).