Phase separation and atomic ordering in InxAlyGa1−x−yN layers

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 〈11¯00〉 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.