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

TL;DR

This study investigates how indium incorporation and strain relaxation interact during the growth of high-In-content InGaN layers via plasma-assisted molecular-beam epitaxy, revealing inhomogeneous strain and compositional gradients.

Contribution

It provides new insights into the growth conditions, strain relaxation mechanisms, and indium incorporation kinetics in high-In-content InGaN layers.

Findings

Misfit relaxation begins after 40 nm of growth

Strain relaxation occurs gradually over 200 nm

Incorporation is inhibited by compressive strain, causing compositional gradients

Abstract

We report the interplay between In incorporation and strain relaxation kinetics in high-In-content InxGa1-xN (x = 0.3) layers grown by plasma-assisted molecular-beam epitaxy. For In mole fractions x = 0.13-0.48, best structural and morphological quality is obtained under In excess conditions, at In accumulation limit, and at a growth temperature where InGaN decomposition is active. Under such conditions, in situ and ex situ analysis of the evolution of the crystalline structure with the growth thickness points to an onset of misfit relaxation after the growth of 40 nm, and a gradual relaxation during more than 200 nm which results in an inhomogeneous strain distribution along the growth axis. This process is associated with a compositional pulling effect, i.e. indium incorporation is partially inhibited in presence of compressive strain, resulting in a compositional gradient with increasing In mole fraction towards the surface.