Microstructural properties of over-doped GaN-based diluted magnetic semiconductors grown by MOCVD

We have grown transition metal (Fe, Mn) doped GaN thin films on c-oriented sapphire by metal-organic chemical vapor deposition. By varying the flow of the metal precursor, a series of samples with different ion concentrations are synthesized. Microstructural properties are characterized by using a high-resolution transmission electron microscope. For Fe over-doped GaN samples, hexagonal Fe ₃N clusters are observed with Fe ₃N(0002) parallel to GaN (0002) while for Mn over-doped GaN, hexagonal Mn ₆N _2.58 phases are observed with Mn ₆N _2.58(0002) parallel to GaN(0002). In addition, with higher concentration ions doping into the lattice matrix, the partial lattice orientation is distorted, leading to the tilt of GaN(0002) planes. The magnetization of the Fe over-doped GaN sample is increased, which is ascribed to the participation of ferromagnetic iron and Fe ₃N. The Mn over-doped sample displays very weak ferromagnetic behavior, which probably originates from the Mn ₆N _2.58.