Tilted Domain and Indium Content of InGaN Layer on $m$-Plane GaN Substrate Grown by Metalorganic Vapor Phase Epitaxy

The accurate alloy composition of a nonpolar InGaN grown on $m$-plane GaN is estimated from X-ray reciprocal-space maps (RSMs) of ($20\bar{2}1$) and ($21\bar{3}0$) diffractions. In this estimation, the anisotropic residual strain in $m$-plane is carefully considered. In order to avoide the error which may be generated by the anisotropic strain and tilted domains in the film of InGaN, the lattice constants along $m$-, $a$-, and $c$-directions are determined using a pair of two RSMs normalized to the unit reciprocal vector along $m$-direction. The indium content of InGaN is derived from RSMs data using Poisson effect and Vegard's law. Based on this method, the incorporation of indium into InGaN is investigated. This incorporation is found to be promoted with the increase in the substrate miscut angle and the growth rate. From the precise analysis of RSMs, some of the InGaN domains on $m$-plane GaN substrates are found to be tilted toward $\pm a$-direction despite of the substrate miscut toward $c$-direction.