Characterization of InGaN quantum wells with gross fluctuations in width

摘要

Gross well-width fluctuations are observed in InGaN quantum wells (QWs), and have been linked to an overall three-dimensional morphology consisting of a network of interlinking InGaN strips. While these networks may be clearly observed in atomic force microscopy of appropriate uncapped epilayers, the surface morphology of capped (QW) samples reveals little or nothing of the subsurface structure of the InGaN. Hence transmission electron microscopy (TEM) must be used to determine the variations in QW thickness and composition. The network structure may be observed in either bright-field TEM or scanning transmission electron microscope high angle annular dark field images in plan-view studies of single QWs. It is suggested that multi-QWs could be imaged in cross section and the anisotropy of the network structure used as a potential signature of the three-dimensional morphology. The anisotropic nature of the network structure correlates well with the alignment of step edges in the GaN pseudosubstrates, and it is suggested that the network structure forms via the decomposition of In-rich regions arising at or near step edges.