High In-content InGaN layers synthesized by plasma-assisted molecular-beam epitaxy: growth conditions, strain relaxation and In incorporation kinetics

摘要

We report the interplay between In incorporation and strain relaxationkinetics in high-In-content InxGa1-xN (x = 0.3) layers grown by plasma-assistedmolecular-beam epitaxy. For In mole fractions x = 0.13-0.48, best structuraland morphological quality is obtained under In excess conditions, at Inaccumulation limit, and at a growth temperature where InGaN decomposition isactive. Under such conditions, in situ and ex situ analysis of the evolution ofthe crystalline structure with the growth thickness points to an onset ofmisfit relaxation after the growth of 40 nm, and a gradual relaxation duringmore than 200 nm which results in an inhomogeneous strain distribution alongthe growth axis. This process is associated with a compositional pullingeffect, i.e. indium incorporation is partially inhibited in presence ofcompressive strain, resulting in a compositional gradient with increasing Inmole fraction towards the surface.