Heterostructures consisting of alternating GaN/AlN epitaxial layers represent the building blocks of state-of-the-art devices employed for active cooling and energy-saving lightning. Insights into the heat conduction of these structures are essential in the perspective of improving the heat management for prospective applications. Here, the cross-plane (perpendicular to the sample's surface) thermal conductivity of GaN/AlN superlattices as a function of the layers' thickness is established by employing the 3ω-method. Moreover, the role of interdiffusion at the interfaces in the phonon scattering is taken into account in the modeling and data treatment. It is found that the cross-plane thermal conductivity of the epitaxial heterostructures can be driven to values as low as 5.9 W/(m·K) comparable with those reported for amorphous films, thus opening wide perspectives for optimized heat management in III-nitride-based epitaxial multilayers.

In the Fe-doped GaN phase-separated magnetic semiconductor Ga$$\delta $$ δ FeN, the presence of embedded $$\gamma '$$ γ ′ -$$\hbox {Ga}_y \hbox {Fe}_{4-y}$$ Ga y Fe 4 - y N nanocrystals determines the magnetic properties of the system. Here, through a combination of anomalous X-ray diffraction and diffraction anomalous fine structure, the local structure of Ga in self-assembled face-centered cubic (fcc) $$\gamma '$$ γ ′ -$$\hbox {Ga}_y \hbox {Fe}_{4-y}$$ Ga y Fe 4 - y N nanocrystals embedded in wurtzite GaN thin layers is investigated in order to shed light onto the correlation between fabrication parameters, local structural arrangement and overall magnetic properties of the material system. It is found, that by adjusting the growth parameters and thus, the crystallographic surroundings, the Ga atoms can be induced to incorporate into 3c positions at the faces of the fcc crystal lattice, reaching a maximum occupancy of 30%. The magnetic response of the embedded nanocrystals is ferromagnetic with Curie temperature increasing from 450 to 500 K with the Ga occupation. These results demonstrate the outstanding potential of the employed experimental protocol for unravelling the local structure of magnetic multi-phase systems, even when embedded in a matrix containing the same element under investigation.

In the Fe-doped GaN phase-separated magnetic semiconductor GaδFeN, the presence of embedded γ'-Ga y Fe 4−y N nanocrystals determines the magnetic properties of the system. Here, through a combination of anomalous x-ray diffraction and diffraction anomalous fine structure, the local structure of Ga in self-assembled face-centered cubic (fcc) γ'-Ga y Fe 4−y N nanocrystals embedded in wurtzite GaN thin layers is investigated in order to shed light onto the correlation between fabrication parameters, local structural arrangement and overall magnetic properties of the material system. It is found, that by adjusting the growth parameters and thus, the crystallographic surroundings, the Ga atoms can be induced to incorporate into 3c positions at the faces of the fcc crystal lattice, reaching a maximum occupancy of 30%. The magnetic response of the embedded nanocrystals is ferromagnetic with Curie temperature increasing from 450 K to 500 K with the Ga occupation. These results demonstrate the outstanding potential of the employed experimental protocol for unravelling the local structure of magnetic multi-phase systems, even when embedded in a matrix containing the same element under investigation.