Strategy for reliable strain measurement in InAs/GaAs materials from high-resolution Z-contrast STEM images

Maryam Vatanparast,Per Erik Vullum,Jian-Min Zuo,Magnus Nord,Randi Holmestad,Turid W Reenaas

doi:10.1088/1742-6596/902/1/012021

Abstract

Geometric phase analysis (GPA), a fast and simple Fourier space method for strain analysis, can give useful information on accumulated strain and defect propagation in multiple layers of semiconductors, including quantum dot materials. In this work, GPA has been applied to high resolution Z-contrast scanning transmission electron microscopy (STEM) images. Strain maps determined from different g vectors of these images are compared to each other, in order to analyze and assess the GPA technique in terms of accuracy. The SmartAlign tool has been used to improve the STEM image quality getting more reliable results. Strain maps from template matching as a real space approach are compared with strain maps from GPA, and it is discussed that a real space analysis is a better approach than GPA for aberration corrected STEM images.

Highlights

Geometric phase analysis (GPA) is a novel and widely applied technique that can be used for quantitative measurements of lattice strains in both high-resolution transmission electron microscopy (HRTEM) and atomic resolution high angular annular dark field (HAADF) scanning transmission electron microscopy (STEM) images
Much of the noise and horizontal, artificial strain lines seen in the strain map from a single STEM image acquired with the pixel time of 38.8 s are removed in the strain map of the HAADF-STEM image after applying SmartAlign with 90̊ rotation between every image in the stack that is shown in Fig.1 (b)
While the approach used by GPA is advantageous for the analysis of HRTEM images of limited spatial resolution, ideally, the analysis of aberration corrected STEM images should take the advantages of all frequencies, and this can be achieved using real space based methods based on atomic peak finding or template matching (TeMA) [5, 6]

Summary

Introduction

GPA is a novel and widely applied technique that can be used for quantitative measurements of lattice strains in both high-resolution transmission electron microscopy (HRTEM) and atomic resolution high angular annular dark field (HAADF) STEM images. 2. Experimental Details In the present work, the GPA technique is applied to experimental HRSTEM images of InAs/GaAs quantum dot (QD) based intermediate band solar cell (IBSC) materials.

Results

Conclusion