Direct observation of spinodal decomposition phenomena in InAlN alloys during in-situ STEM heating

The spinodal decomposition and thermal stability of thin In_0.72Al_0.28N layers and In_0.72Al_0.28N/AlN superlattices with AlN(0001) templates on Al₂O₃(0001) substrates was investigated by in-situ heating up to 900 °C. The thermally activated structural and chemical evolution was investigated in both plan-view and cross-sectional geometries by scanning transmission electron microscopy in combination with valence electron energy loss spectroscopy. The plan-view observations demonstrate evidence for spinodal decomposition of metastable In_0.72Al_0.28N after heating at 600 °C for 1 h. During heating compositional modulations in the range of 2-3 nm-size domains are formed, which coarsen with applied thermal budgets. Cross-sectional observations reveal that spinodal decomposition begin at interfaces and column boundaries, indicating that the spinodal decomposition has a surface-directed component.