EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Due to their direct bandgap, GeSn and SiGeSn alloys have aroused great interest for photonic applications [1]. To understand and control the emission properties of GeSn heterostructure based devices developed at CEA (Fig. 1a), the chemical composition at nanometer scale must be accurately determined. One particular challenge is to accurately quantify the composition of 20 nm thick confinement barriers based on a SiGeSn ternary alloy, as the bandgap drastically depends on the Si content [2] and thus modify the emission properties of the device (Fig. 1b). Advanced EDX method is therefore necessary to detect and quantify slight variations of composition in SiGeSn barriers at nanoscale (Fig. 1c). Our presentation will cover all the critical aspects that must be included in such highly accurate quantification such as the thin lamella preparation, the zeta-factor calibration or the X-ray absorption.
Our quantification is validated on the bottom barrier layer by combining XRD and XRF measurements. We will also reveal a slight Si depletion in the SiGeSn top layer that, coupled with crystal deformation analysis, helps to understand the impact of substrate on growth of epilayers. These results are therefore a precious tool to predict and precisely tune the composition of the confinement barriers, and so to enhance emission properties of this device.

Reference:

[1] Chrétien, J. et al. GeSn Lasers Covering a Wide Wavelength Range Thanks to Uniaxial Tensile Strain. ACS Photonics 6, 2462–2469 (2019).

[2] Stange, D. et al. Short-wave infrared LEDs from GeSn/SiGeSn multiple quantum wells. Optica 4, 185 (2017).

This work was performed on the PlatForm for NanoCharacterisation (PFNC) and was supported by the “Recherche Technologique de Base” Program of the French Ministry of Research.