Phase separation and atomic ordering in InxAlyGa1−x−yN layers Original Research Article

We studied the occurrence of phase separation and atomic ordering in quaternary InxAlyGa1−x−yN layers by transmission electron microscopy. Three layers of different compositions were examined: one lattice-mismatched In0.10Al0.02Ga0.88N layer together with two lattice-matched In0.12Al0.29Ga0.59N and In0.06Al0.18Ga0.76N layers. The composition modulations were seen in all the layers. The wavelengths (λ) of composition modulations resulting from phase separation were calculated using selected-area electron diffraction patterns. The smaller λ (9 nm) in In0.10Al0.02Ga0.88N layer in comparison to that in In0.12Ga0.88N layer (λ = 20 nm) suggests that the driving force for phase separation in InxAlyGa1−x−yN layers is greater than that in InxGa1−xN layers with similar In contents. Energy dispersive spectroscopy line profiles across InxAlyGa1−x−yN/GaN interfaces revealed a gradual increase in Al and In incorporation. Additional (0 0 0 1) diffraction spots in an SADP taken on an image zone from the In0.06Al0.18Ga0.76N layer suggests that atomic ordering can occur in quaternary layers. Arguments are developed to rationalize these experimental observations.