Abstract
The spinodal decomposition and thermal stability of thin In0.72Al0.28N layers and In0.72Al0.28N/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 In0.72Al0.28N 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.
Highlights
III-nitride semiconductors attract attention for applications in optoelectronic devices owing to a direct bandgap, tenable from 0.6 eV to 6.2 eV1
Upon spinodal decomposition the domains formed in the cross-section are of the order of 2–3 nm at 700 °C, and they coarsen with time and temperature. This is in agreement with plan-view single-layer results presented in Figs 1 and 2. These results prove that the onset of spinodal decomposition preferably occurs at interfaces and at column boundaries
The microstructure development of metastable single In0.72Al0.28N layers and In0.72Al0.28N/AlN superlattices was studied by means of in-situ scanning transmission electron microscope (STEM) heating in a temperature range from 600 °C to 900 °C
Summary
III-nitride semiconductors attract attention for applications in optoelectronic devices owing to a direct bandgap, tenable from 0.6 eV to 6.2 eV1. MSE owns the advantage of permitting growth of epitaxial InAlN films at temperatures far below thermal equilibrium. This allows to cover the whole InN-AlN compositional range, including compositions inside the miscibility gap, without the onset of phase separation[15,16]. The spinodal decomposition was followed during heating of as-grown In0.72Al0.28N solid solution layers and In0.72Al0.28N/AlN superlattices, where the composition of the alloy was targeted deep inside the miscibility gap. Both Al and In segregate in In0.72Al0.28N layers into compositionally separated nanometre-size domains. Additional heating coarsens the domain size with increasing compositional differences from the original layer
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