Composition Inhomogeneity In Nonpolar (10(1)Over-Bar0) And Semipolar (20(2)Over-Bar1) Inain Layers Grown By Plasma-Assisted Molecular Beam Epitaxy

In this study, we report the indium incorporation efficiency and structural quality of nonpolar (10 (1) over bar0) and semipolar (20 (2) over bar1) InAIN layers grown by plasma-assisted molecular beam epitaxy. The indium content is found to depend on surface orientation, and it is 5.7% for the nonpolar m-plane, 16.2% for semipolar, and 17.4% for c-plane (0001); this results in the indium incorporation efficiency trend (10 (1) over bar0) << (20 (2) over bar1) < (0001). One-dimensional strain relaxation is observed for the m-plane InAIN layer, while the semipolar and c-plane InAIN layers are strained to GaN. The structural quality of the m-plane and semipolar InAIN layers is assessed by scanning transmission electron microscopy (STEM) with particular focus on the composition homogeneity. Nonpolar and semipolar InAIN cross sections observed by STEM along the [1<(2)over bar>10] direction exhibited a columnar structure along the growth direction. No composition modulation is visible along the [0001] and [(1) over bar 014] directions for the m-plane and semipolar InAIN layers, respectively. The low indium content of the m-plane InAIN layer is attributed to the strain-induced compositional pulling effect predicted theoretically for this surface orientation. This effect is believed to be also responsible for the increase of incorporation efficiency in the top part of the layer after its relaxation by cracking.