Evaluating the local bandgap across InxGa1-xAs multiple quantum wells in a metamorphic laser via low-loss EELS

TL;DR

This study uses advanced microscopy and spectroscopy to map local bandgap, indium concentration, and strain in quantum wells of a metamorphic laser, revealing inhomogeneities that impact device performance.

Contribution

It provides a detailed correlation between local composition, strain, and bandgap in quantum wells, combining experimental and theoretical analysis to understand their interplay.

Findings

Significant inhomogeneities near interfaces in indium and strain distributions.

Variations in bandgap are mainly due to indium concentration, with strain having minor influence.

Local inhomogeneities may affect the collective emission and efficiency of the device.

Abstract

Using high resolution scanning transmission electron microscopy and low-loss electron energy loss spectroscopy, we correlate the local bandgap (Eg), indium concentration, and strain distribution across multiple InxGa1-xAs quantum wells (QWs), on a GaAs substrate, within a metamorphic laser structure. Our findings reveal significant inhomogeneities, particularly near the interfaces, for both the indium and strain distribution, and subtle variations in the Eg across individual QWs. The interplay between strain, composition, and Eg was further explored by density functional theory simulations, indicating that variations in the Eg are predominantly influenced by the indium concentration, with strain playing a minor role. The observed local inhomogeneities suggest that differences between individual QWs may affect the collective emission and performance of the final device. This study highlights the importance of spatially resolved analysis in understanding and optimising the electronic and optical properties for designing of next-generation metamorphic lasers with multiple QWs as the active region.