Atomic scale indium distribution in a GaN/In0.43Ga0.57N/Al0.1Ga0.9N quantum well structure

Quantitative high resolution electron microscopy (HRTEM) is used to map the indium distribution in a GaN/In0.43Ga0.57N/Al0.1Ga0.9N quantum well at the atomic scale. Samples with atomically flat surfaces were prepared for microscopy by anisotropic chemical etching. The developed preparation procedure minimizes a possible confusion of thickness variations with local compositional fluctuations in the lattice images. An irregular distribution of indium is observed that is attributed to the formation of clusters with estimated diameters of 1-2 nm. The indium concentration gradient across GaN/In0.43Ga0.57N interfaces is measured to extend typically over a distance of 1nm. It is more than twice as large across the In0.43Ga0.57N/Al0.1Ga0.9N interface. Indium segregation into the Al0.1Ga0.9N layer during crystal growth is likely to cause this unusual large width of the In0.43Ga0.57N/Al0.1Ga0.9N interfaces. This introduces an asymmetric In distribution across the quantum well with respect to the growth direction.