(Color online) (a) HRXRD (0002) 2θ/ω scans of the samples used in this work. (b) XRD ω-scan rocking curves of InAlN. (c)-(e) Reciprocal space maps around reciprocal lattice point of all the samples. The vertical lines as marked with R = 0 correspond to fully strained InAlN, and the lines marked with R = 1 to fully relaxed InAlN. It is clear that the InAlN layer in sample A is pseudomorphic to GaN, while those in samples B and C contain relaxed sub-layers, as shown by the arrows in (d) and (e).
Cross-sectional TEM images recorded in zone axis projection of all the samples. InAlN layer is uniform in sample A (a) and consist of two sub-layers in samples B and C (b) and (c).
Calculated h c for the InAlN grown on GaN by using MB and PB models with isotropic approximation, and the model developed by Holec et al. that takes into account hexagonal symmetry of wurtzite material (Ref. 17). These calculations indicate the high sensitivity of h c to In content or misfit strain within the framework of strain-driven degradation. For comparison, the experimental thicknesses over which InAlN starts to degrade are also plotted. It is clear that these models fail to describe the present degradation.
TEM image of sample B, clearly showing the connection between the degradation and the TDs propagating from the underlying GaN.
(Color) Schematic diagram of the growth evolution of InAlN on GaN. (a) At the early stage of the degradation with V-pits formed. (b) The median stage with sidewalls of adjacent V-pits converged. (c) The final stage with a structure of two sub-layers formed. The bold black lines correspond to the growth surface of InAlN, the red lines to the border between the two sub-layers in InAlN, the green lines to the interface between InAlN and GaN, and the blue lines to TDs.
Some of the structural parameters of the samples used in this paper, including the thickness of InAlN ( d ), the FWHMs of (0002) ω-scan rocking curves, and the In contents in the InAlN layer of sample A and the coherent sub-layers in samples B and C.
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