Spatially resolved investigation of strain and composition variations in (In,Ga)N/GaN epilayers

TL;DR

This study uses spatially resolved x-ray diffraction and cathodoluminescence to analyze strain and composition variations in (In,Ga)N/GaN epilayers, revealing strain relaxation and compositional pulling effects.

Contribution

It provides detailed spatial mapping of strain and indium distribution, highlighting the correlation between strain relaxation and compositional variations in the epilayers.

Findings

Strain relaxation occurs with increasing indium content toward the surface.

Lateral indium distribution variations increase with strain relaxation.

Distinct regions of strained, unstrained, and relaxed layers are identified.

Abstract

The strain state and composition of a 400 nm thick (In,Ga)N layer grown by metal-organic chemical vapor deposition on a GaN template are investigated by spatially integrated x-ray diffraction and cathodoluminescence (CL) spectroscopy as well as by spatially resolved CL and energy dispersive x-ray analysis. The CL investigations confirm a process of strain relaxation accompanied by an increasing indium content toward the surface of the (In,Ga)N layer, which is known as the compositional pulling effect. Moreover, we identify the strained bottom, unstrained top, and gradually relaxed intermediate region of the (In,Ga)N layer. In addition to an increase of the indium content along the growth direction, the strain relaxation leads to an enhancement of the lateral variations of the indium distribution toward the surface.